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PubMed2006

Organization and origin of the connection from the inferior to the superior colliculi in the rat.

The inferior colliculus (IC) is the main ascending auditory relay station prior to the superior colliculus (SC). The morphology and origin of the connection from inferior to superior colliculus (I-SC) was analyzed both by anterograde and retrograde tracing. Irrespective of the subregion of the IC in which they originate, the terminal fields of these connections formed two main tiers in the SC. While the dorsal one primarily involved the stratum opticum and the stratum griseum intermediale, the ventral one innervated the deep strata, although some fibers did connect these tiers. While the dorsal tier occupied almost the whole extension of the SC, the ventral one was mostly confined to its caudomedial quadrant. The fiber density in these tiers decreased gradually in a rostral gradient and the terminal fields became denser as the anterograde tracer at the injection site was distributed more externally in the cortex of the IC. Retrograde tracing confirmed this result, although it did not reveal any topographic ordering for the I-SC pathway. Most presynaptic boutons of the I-SC terminal field were located either inside or close to the patches of acetylcholinesterase activity. Together with previous anatomical and physiological studies, our results indicate that the I-SC connection relays behaviorally relevant information for sensory-motor processing. Our observation that this pathway terminates in regions of the superior colliculus, where neurons involved in fear-like responses are located, reinforce previous suggestions of a role for the IC in generating motor stereotypes that occur during audiogenic seizures.

Acetylcholinesterase↗
PubMed2007

Connections of functional areas in the mustached bat's auditory cortex with the auditory thalamus.

The auditory thalamus is the major target of the inferior colliculus and connects in turn with the auditory cortex. In the mustached bat, biosonar information is represented according to frequency in the central nucleus of the inferior colliculus (ICc) but according to response type in the cortex. In addition, the cortex has multiple areas with neurons of similar response type compared to the single tonotopic representation in the ICc. To investigate whether these transformations occur at the level of the thalamus, we injected anatomical tracers into physiologically defined locations in the mustached bat's auditory cortex. Injections in areas used for target ranging labeled contiguous regions of the auditory thalamus rather than separate patches corresponding to regions that respond to the different harmonic frequencies used for ranging. Injections in the two largest ranging areas produced labeling in separate locations. These results indicate that the thalamus is organized according to response type rather than frequency and that multiple mappings of response types exist. Injections in areas used for target detection labeled thalamic regions that were largely separate from those that interconnect with ranging areas. However, injections in an area used for determining target velocity overlapped with the areas connected to ranging areas and areas involved in target detection. Thus, separation by functional type and multiplication of areas with similar response type occurs by the thalamic level, but connections with the cortex segregate the functional types more completely than occurs in the thalamus.

Acoustic Stimulation↗
PubMed1988

Neural control of leg movements in a metamorphic insect: persistence of larval leg motor neurons to innervate the adult legs of Manduca sexta.

During metamorphosis of the hawkmoth Manduca sexta, the larval thoracic legs along with their associated sensory organs and muscles degenerate and new adult legs develop. The larval legs are small and relatively simple structures capable of lateral extension and medial flexion allowing them to grasp the substrate as the caterpillar crawls along. By contrast, the adult legs are used for walking with an alternating gait. They are much larger than the larval legs and articulate such that they are capable of movement in several directions. This change in form and function is accompanied by a reorganization of the neural circuits controlling leg movements. In a previous report (Kent and Levine: J. Comp. Neurol. 271:559-576, '88) we described motor neurons innervating the larval prothoracic legs, and here we describe motor neurons innervating the prothoracic legs of the adult. Using a combination of cobalt staining methods and the persistent fluorescent dye Fluoro-Gold, we have found that some, if not all, larval leg motor neurons are retained and innervate the new adult leg muscles. Moreover, we have been able to discover the fate of individual larval leg motor neurons by marking a single larval neuron with Fluoro-Gold and using a second fluorescent dye to double label the same neuron in the adult. Our results suggest that specific larval leg motor neurons innervate corresponding muscles in the adult stage, although their apparent function is significantly different. In addition, the motor neurons undergo significant remodeling of their dendritic branching patterns during metamorphosis, alterations which doubtless contribute to their new roles in adult behavior.

Animals↗
PubMed1988

Projections of submucosal neurons to the myenteric plexus of the guinea pig intestine: in vitro tracing of microcircuits by retrograde and anterograde transport.

The enteric nervous system (ENS) can mediate reflex activity without input from the brain or spinal cord. The ENS thus contains intrinsic primary afferent neurons that link mucosal sensory receptors with motor neurons in the myenteric plexus. The intrinsic primary afferent neurons of the gut have not yet been identified. Although the submucosal plexus is known to innervate the mucosa, where enteric sensory receptors are located, no submucosal to myenteric projections have previously been found. In order to determine whether such projections exist, the submucosal plexus was examined following the microinjection of a retrograde tracer (Fluoro-Gold or 4-acetoamido, 4'-isothiocyanostilbene-2,2'-disulphonic acid [SITS]) into single myenteric ganglia. In addition, the myenteric plexus was studied following the iontophoretic injection of an anterograde tracer (Phaseolus vulgaris leucoagglutinin; [PHA-L]) into single submucosal ganglia. Ganglia were visualized by use of differential interference contrast optics and were injected from the beveled tip of a glass micropipette; 2.5-3.0 hours were allotted for retrograde and 20-24 hours (under culture conditions) for anterograde transport. In the myenteric plexus, a small number of the neurons of each injected ganglion were fluorescent and additional neurons in distant myenteric ganglia (predominantly orad) were also retrogradely labeled. About five to six submucosal neurons deep to but not directly underneath the injected myenteric ganglion were labeled by Fluoro-Gold or SITS and only rarely was there more than one labeled neuron in a submucosal ganglion. When control injections of Fluoro-Gold were placed into the muscle instead of a ganglion, some myenteric neurons near the injection site became labeled indicating an innervation of the circular muscle by myenteric neurons; however, there was no labeling of neurons in the submucosal plexus. Similarly, if connections between the myenteric and submucosal plexuses were severed before injecting Fluoro-Gold, no submucosal neurons were labeled. Following injection of PHA-L into a single submucosal ganglion, small-diameter axons were labeled in approximately 2 myenteric ganglia as well as in several distant submucosal ganglia (mainly anal and circumferential to the injection site). Additional labeled fibers traveled with blood vessels or surrounded mucosal crypts. It is concluded that submucosal neurons project to the myenteric plexus as well as to the mucosa and to one another. These observations are consistent with the hypothesis that at least some intrinsic enteric primary afferent neurons reside in the submucosal plexus.

4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfo↗
PubMed1989

Identification of vagal efferent fibers and putative target neurons in the enteric nervous system of the rat.

The stomach and small intestine receive an efferent innervation from the dorsal motor nucleus of the vagus (DMX). The current experiments were undertaken as a partial test of the hypothesis that the CNS innervates only a small number of command neurons in a restricted number of enteric ganglia. The anterograde tracer Phaseolus vulgaris leucoagglutinin (PHA-L) was injected into the DMX by iontophoresis, and 10-21 days later PHA-L was visualized in the bowel by immunofluorescence. Varicose vagal efferent fibers, labeled by PHA-L, were found in the myenteric plexus as far distally as the ileo-colic junction. PHA-L-labeled varicose axons were rare in comparison to nonlabeled fibers, entered a minority of myenteric ganglia, and contacted a small proportion of the neurons. Ganglia thus innervated by vagal efferent fibers were more numerous in the stomach than in the small intestine. Within the stomach, these ganglia were common in the antrum than in the corpus and none were found in the wall of the rumen. Innervated ganglia in the small intestine became progressively more sparse distally. No PHA-L-labeled axons were observed in the submucosal plexus, thus raising the possibility that vagal modulation of secretomotor responses involves an intermediate synapse in the myenteric plexus. Nonvaricose bundles of PHA-L-labeled fibers were also observed. These bundles appeared to utilize the connectives of the myenteric plexus as a pathway within which to descend within the bowel. Vagal efferent bundles were found to pass through the pyloric sphincter to enter the small intestine from the stomach; thus vagal fibers can reach the distal intestine by an intraenteric route that is not lesioned by crushing mesenteric nerves. The existence of this pathway affects the interpretation of experiments seeking to utilize such lesions to distinguish intrinsic from extrinsic neurites. Possible target neurons of the vagal efferent innervation were identified by simultaneously demonstrating the immunoreactivities of 5-hydroxytryptamine (5-HT), vasoactive intestinal polypeptide (VIP), enkephalin (ENK), galanin (GAL), and tyrosine hydroxylase (TH) along with that of PHA-L. Vagal terminals in the myenteric plexus appeared selectively to contact 5-HT- and, to a significantly lesser extent, VIP-, but not ENK- or GAL-immunoreactive neurons. Apparent vagal innervation of 5-HT-immunoreactive neurons was significantly more common in the duodenum, where a majority of the 5-HT-immunoreactive cells were encircled by varicose PHA-L-labeled axons, than in the stomach.(ABSTRACT TRUNCATED AT 400 WORDS)

Efferent Pathways↗
PubMed1989

Diverse afferents converge on the nucleus paragigantocellularis in the rat ventrolateral medulla: retrograde and anterograde tracing studies.

The nucleus paragigantocellularis in the ventrolateral medulla has been implicated in cardiovascular, pain, and analgesic functions; and it has also been found to be a major afferent to the pontine nucleus locus coeruleus. In the present study, afferents to the nucleus paragigantocellularis were identified in the rat by means of the retrograde tracers wheat germ agglutinin-conjugated horseradish peroxidase or Fluoro-Gold. Projections to the nucleus paragigantocellularis arise from a wide variety of nuclei with autonomic, visceral, and sensory-related functions. Major afferents with consistent and robust retrograde labeling include most laminae of the spinal cord, the caudal lateral medulla, the contralateral paragigantocellularis, the nucleus of the solitary tract, the A1 area, the lateral parabrachialis, the Kölliker-Fuse nucleus, the periaqueductal gray, and a preoculomotor nucleus in the ventral central gray, the supraoculomotor nucleus. Other notable afferents, seen only after large caudal injections into the nucleus paragigantocellularis, include the lateral hypothalamus, the paraventricular nucleus of the hypothalamus, and the medial prefrontal cortex. Minor afferents include the gigantocellular nucleus, the area postrema, the caudal raphe groups, the inferior colliculus, the A5 area, and the locus coeruleus. The projection from the supraoculomotor nucleus, not previously reported as an afferent to the ventrolateral medulla, was confirmed with anterograde tracing by means of Phaseolus vulgaris-leucoagglutinin. Iontophoretic deposits of Phaseolus vulgaris-leucoagglutinin into the nucleus of the solitary tract (commissuralis level) or into the periaqueductal gray also yielded terminal fiber labeling in the nucleus paragigantocellularis. Fibers from the supraoculomotor nucleus and the nucleus of the solitary tract were densest in the lateral aspect of the nucleus paragigantocellularis (corresponding to the rostroventrolateral reticular nucleus), while fibers from the periaqueductal gray were more medially located. Previous studies have defined inputs to the rostral ventrolateral medulla from the cochlear nucleus as well as from the colliculi. In the present study, deposits of wheat germ agglutinin-conjugated horseradish peroxidase or Phaseolus vulgaris-leucoagglutinin into the cochlear nucleus or the superior colliculus yielded only sparse anterograde labeling in the nucleus paragigantocellularis, but heavily labeled adjacent areas. The inferior collicular injections yielded strong but restricted anterograde labeling in the rostromedial paragigantocellularis, medial to the facial nucleus. These results indicate that the paragigantocellularis area receives inputs from diverse brain structures. Neurons in the nucleus paragigantocellularis afferent to the locus coeruleus, being distributed throughout this region, may provide a channel where several types of information are integrated and transmitted to the extensive locus coeruleus noradrenergic efferent network...

Afferent Pathways↗
PubMed1990

Topography in the phrenic motoneuron nucleus demonstrated by retrograde multiple-labelling techniques.

A combination of retrograde tracing methods was employed to distinguish populations of motoneurons supplying different motor unit territories in the feline diaphragm. The compatibility of the tracers--horseradish peroxidase, fast or true blue, diamidino yellow, and fluorogold--was first assessed by applying the different tracers concurrently to separate cut branches of hindlimb and neck muscle nerves. On the basis of these initial observations fast blue, fluorogold, and horseradish peroxidase were chosen to compare the distribution of motoneurons whose axons ran in different primary branches of the phrenic nerve. Motoneurons with different target territories were extensively intermixed throughout most of the phrenic motor nucleus. However, motoneurons innervating the sternal and medial costal part of the diaphragm were distributed more densely in the rostral part of the phrenic motor pool, whereas motoneurons serving the lateral costal part were concentrated more caudally. Crural motoneurons were intermingled with costal motoneurons in the middle and caudal portions of the nucleus. Motoneurons within the phrenic nucleus are distributed in clusters. Such clusters commonly contained motoneurons labelled from two or more primary branches. Thus, the highly ordered topography of muscle units in the diaphragm is not mirrored by the intraspinal distribution of phrenic motoneurons.

Amidines↗
PubMed1990

Immunohistochemical subpopulations of retinopetal neurons in the nucleus olfactoretinalis in a teleost, the whitespotted greenling (Hexagrammos stelleri).

Two subpopulations of retinopetal neurons in the nucleus olfactoretinalis (NOR) were revealed by means of general histological, tract tracing, and immunohistochemical methods in a marine teleost, the whitespotted greenling (Hexagrammos stelleri). Two types of cells in the NOR (M cell, L cell) were morphologically distinguishable from one another. The cell bodies of M cells were medium-size and fusiform, while those of L cells were large and ellipsoidal or irregular. M cells were located at the ventralmost region of the junction between the olfactory bulb and telencephalon, while L cells were scattered more rostrally along the ventromedial surface of the olfactory bulb. Following applications of HRP or Fluoro-Gold to the optic nerve, almost all M cells and about half of the L cells were labeled in the contralateral NOR. L cells showed strong immunoreactivities to gonadotropin releasing hormone (GnRH) and Phe-Met-Arg-Phe-NH2 (FMRFamide), whereas M cells showed only weak GnRH-immunoreactivity and no FMRFamide-immunoreactivity. Axons of L cells were detected in the optic nerve by means of GnRH- and FMRFamide-immunohistochemistry. The axons were concentrated in the myelinated edge (the oldest area) of the "ribbon" optic nerve. GnRH- and FMRFamide-immunoreactive fibers constituted a plexus at the junction between the inner nuclear layer and inner plexiform layer. The existence of two structurally separate classes of NOR cells suggests two functionally separate channels from the NOR to the retina.

Animals↗
PubMed1990

Connections of the subthalamic nucleus with ventral striatopallidal parts of the basal ganglia in the rat.

The present study was undertaken to establish the precise anatomical relationship of the subthalamic nucleus (STh) with limbic lobe-afferented parts of the basal ganglia in the rat. The anterograde tracer Phaseolus vulgaris-leucoagglutinin (PHA-L), injected in the STh, the globus pallidus, the ventral pallidum, the ventral striatum, and the parafascicular thalamic nucleus, and the retrograde tracers Fluoro-Gold (FG) and cholera toxin B (CTb), injected in the globus pallidus, the ventral pallidum, the ventral striatum, and the ventral mesencephalon, were used for this purpose. The results of these tracing experiments confirm the general notion of reciprocal connections between the STh and pallidal areas. Thus the dorsomedial part of the STh is connected with the subcommisural ventral pallidum, whereas a more ventral and lateral part of the medial STh is related to the medial globus pallidus. The lateral hypothalamic area, directly adjacent to the STh, containing neurons with a morphology quite similar to those in the STh, projects to parts of the ventral pallidum related to the olfactory tubercle. The reciprocal projection from this pallidal area to subthalamic regions appears to be very sparse. The medial STh sends strong projections to the medial part of the entopeduncular nucleus and the adjacent lateral hypothalamic area. Sparser projections from the medial STh reach the rostral and medial part of the caudate-putamen and the nucleus accumbens. The nucleus accumbens sends a very sparse projection back to the medial STh. The projections of the medial STh to the ventral mesencephalon appear also to be topographically organized. The lateral hypothalamus and a few cells in the most medial part of the STh project to the ventral tegmental area, whereas progressively more lateral parts of the ventral mesencephalon, in particular the substantia nigra, receive input from successively more lateral and caudal parts of the STh. In addition, a number of STh fibers reach the midbrain extrapyramidal area. The lateral part of the parafascicular thalamic nucleus projects to the lateral part of the STh, whereas parafascicular neurons medial to the fasciculus retroflexus project to the dorsomedial portion of the STh. The medial part of the STh and the adjacent lateral hypothalamus are intimately connected with limbic parts of the basal ganglia in a way similar and parallel to the connections of the lateral STh with motor-related parts of the basal ganglia. These findings suggest a role for the STh in nonmotor functions of the basal ganglia.

Animals↗
PubMed1990

Dendritic bundling in layer I of granular retrosplenial cortex: intracellular labeling and selectivity of innervation.

The extrinsic projections to and from the retrosplenial cortex have been studied in detail, but the intrinsic circuitry within this region has been characterized less completely. To further define the internal connections, small injections of the retrograde, fluorescent tracer Fluorogold were made into the retrosplenial cortex of the rat. These injections label neurons in layers II-V of the contralateral homotopic cortex. In layers III-V, the labeled neurons are present over an area much larger than the injection site, but in layer II neurons are labeled in a very precise homotopic pattern. Following these injections, only the neurons in layer II display heavily labeled apical dendrites, and these labeled dendrites form tight bundles in layer Ic and Ib of the cortex and spread out in layer Ia. An examination of Golgi-stained material demonstrates that most of the neurons in layer II are small pyramidal cells with 2-3 small basal dendrites and a single, large apical dendrite that arborizes extensively in layer Ia. To verify the structure of the layer II neurons, they were intracellularly filled with Lucifer yellow. Examination of these labeled cells confirms the observations from the Golgi-stained material and demonstrates that many apical dendrites of the layer II cells angle acutely, apparently to join a bundle and/or avoid an interbundle space. Tract tracing experiments demonstrate that the anteroventral nucleus of the thalamus appears to project selectively to the region containing the dendritic bundles, whereas intracortical projections appear to terminate in layers Ib and Ic in the 30-200 microns spaces between the bundles. Furthermore, the areas containing the bundles display dense AChE staining, but the interbundle spaces are almost free of AChE staining. These findings demonstrate a form of dendritic bundling that is input and output specific and may play an important role in the regulation of thalamic inputs to the cingulate cortex.

Animals↗
PubMed1990

Projections to the pontine nuclei from choline acetyltransferase-like immunoreactive neurons in the brainstem of the cat.

By use of retrograde transport of horseradish peroxidase-wheat germ agglutinin (HRP-WGA) in combination with monoclonal antibodies against choline acetyltransferase (ChAT), we show that putative cholinergic inputs to the feline pontine nuclei originate from cells in the dorsolateral pontine tegmentum. These cells form a loosely arranged continuum that nevertheless may be subdivided into two groups on the basis of differences in cell morphology. One group consists of double-labeled cells in the periventricular gray substance medial to, and partly merging with, the nucleus locus coeruleus. The other group consists of double-labeled cells surrounding the brachium conjunctivum. In two cats with tracer injections in the pontine nuclei, 81% and 84%, respectively, of the retrogradely labeled cells in the dorsolateral pontine tegmentum are ChAT-like immunoreactive (ChAT-LI). In the same experiments, many ChAT-LI cells, but no retrogradely labeled cells, are seen in the basal telencephalon. The pontine nuclei contain a plexus of thin ChAT-LI fibers with varicosities resembling en passant as well as terminal boutons. These ChAT-LI fibers appear to branch extensively and cover all parts of the pontine nuclei. Following injections of rhodamine-B-isothiocyanate (RITC) in the thalamus and Fluoro-Gold in the pontine nuclei and surrounding regions in the same animal, all retrogradely labeled cells in the dorsolateral pontine tegmentum are labeled with both tracers, whereas most cells in the paramedian pontine reticular formation are labeled either with RITC or Fluoro-Gold. Thus it appears that all cells in the dorsolateral pontine tegmentum that project to the pontine nuclei also project to the thalamus. In analogy with findings by others in the dorsal lateral geniculate nucleus, we suggest that the putative cholinergic projections to the pontine nuclei may serve to modulate transmission of cerebellar afferent information in accordance with the behavioral state of the animal.

Animals↗
PubMed1990

Supraspinal projections to the ventromedial lumbar spinal cord in adult male rats.

In the present study, the fluorescent tract tracing compound Fluorogold was used to study the afferents of the SNB (spinal nucleus of the bulbocavernosus), which is found in the ventromedial spinal grey and innervates penile muscles of the male rat. Fluorogold was iontophoretically injected into the SNB, which was located by recording antidromic activation of the motoneurons after stimulating the bulbocavernosus muscle. Retrogradely labeled cells were found in laminae I, V-IX, and area X of the lumbar spinal cord, suggesting segmental input to the SNB. Supraspinally, the greatest number of labeled cells were in the medulla oblongata, particularly in the lateral vestibular nucleus, gigantocellular reticular nucleus, and ventral and alpha divisions of the gigantocellular reticular nucleus. Labeled cells were also observed in the medullary raphe nuclei, the ventral medullary nucleus, and the spinal vestibular nucleus. In the pons, labeled cells were observed in the nucleus locus coeruleus, nucleus subcoeruleus, and caudal pontine reticular nucleus. No labeled cells were present in the cerebellum, rostral pons, mesencephalon, and cerebral cortex. The most rostral occurrence of labeled cells was in the medial parvicellular division of the hypothalamic paraventricular nucleus. These potential afferents to the SNB identified in male rats imply that the inputs to motoneurons that innervate sex-specific muscles involved in male reproductive behavior may be similar to the inputs to lumbar motoneurons described in the female rat that innervate muscles involved in female sexual behavior.

Animals↗
PubMed1990

Simultaneous labeling of vagal innervation of the gut and afferent projections from the visceral forebrain with dil injected into the dorsal vagal complex in the rat.

The vagal innervation of the different layers of the rat gastrointestinal wall was identified with the fluorescent carbocyanine dye Dil, injected into the dorsal motor nucleus of the vagus (dmnX). Multiple, bilateral injections were used to label all dmnX preganglionic motoneurons, and as a consequence, most of the vagal primary afferents that terminate in the adjacent nucleus of the solitary tract (nts) were also retrogradely and transganglionically labeled. With Fluorogold used to label the enteric nervous system completely and specifically, the Dil-labeled vagal profiles could be visualized and quantified in their anatomical relation to the neurons of the myenteric and submucous ganglia. In the myenteric plexus, vagal fibers and terminals were found throughout the gastrointestinal tract as far caudal as the descending colon, but there was a general decreasing proximodistal gradient in the density of vagal innervation. All parts of the gastric myenteric plexus (fundus, corpus, antrum), as well as the proximal duodenum, were extremely densely innervated, with vagal fibers and terminals in virtually every ganglion and connective. Further caudally, both the percentage of innervated myenteric ganglia and the average density of label within the ganglia rapidly decreased, with the exception of the cecum and proximal colon, where up to 65% of the ganglia were innervated. In the gastric and duodenal submucosa very few and in the mucosa no vagal fibers and terminals were found. With both normal epifluorescence and laser scanning confocal microscopy, highly varicose or beaded terminal structures of various size and geometry could be identified. The Dil injections, which impregnated the dmnX as well as the adjacent nts, resulted in retrograde and anterograde labeling of all the previously reported forebrain connections with the dorsal vagal complex. We conclude that the myenteric plexus is the primary target of vagal innervation throughout the gastrointestinal tract, and that its innervation is more complete than previously assumed. In contrast, vagal afferent (and efferent) innervation of mucosa and submucosa seems conspicuously sparse or absent. Furthermore, the use of more focal injections of Dil offers the prospect to simultaneously identify specific subsets of vagal preganglionics and their central nervous inputs.

Animals↗
PubMed1991

The cells of origin of the spinohypothalamic tract in cats.

Various cutaneous and visceral stimuli alter the discharge rates of neurons in the hypothalamus. Changes in the activity of hypothalamic neurons are thought to play important roles in eliciting neuroendocrine, autonomic, and affective responses to somatosensory and visceral stimuli. Information from peripheral structures has been considered generally to reach the hypothalamus via multisynaptic ascending pathways. Recently, a direct projection from the spinal cord to the hypothalamus was demonstrated in rats. The goal of this study was to determine whether a similar projection exists in cats. Either wheat germ agglutinin conjugated to horseradish peroxidase, a mixture of this tracer and the B subunit of cholera toxin conjugated to horseradish peroxidase, or fast blue was injected into the hypothalamus of cats. Injections were centered in the hypothalamus in seven cats and did not spread to the thalamus, zona incerta or midbrain. After these injections, retrogradely labeled neurons were observed bilaterally in each of the 17 spinal segments that were examined. A total of approximately 400-500 labeled neurons was observed in alternate sections through these segments in the most effective cases. Roughly 70% of the labeled neurons were located contralaterally. Labeled neurons were found predominantly in the deep dorsal horn, the intermediate zone/ventral horn and in the area surrounding the central canal. A few were also noted in the superficial dorsal horn. The first and second sacral segments contained the largest numbers of retrogradely labeled neurons in the spinal cord. The number of spinohypothalamic tract neurons observed in this study in cats was roughly an order of magnitude smaller than that previously reported for rats. This finding suggested either that the spinohypothalamic tract is relatively small in cats or that our tracing techniques did not label many spinohypothalamic tract neurons in cats. To test the sensitivity of one of our tracing techniques, control injections of wheat germ agglutinin conjugated to horseradish peroxidase that filled the ventrobasal thalamus were made in two cats. In both cases, thousands of spinal cord neurons were labeled. In summary, our results indicate that a spinohypothalamic tract exists in cats. However, our findings also suggest that the total number of spinohypothalamic tract neurons in cats may be an order of magnitude smaller than it is in rats.

Animals↗
PubMed1991

Distribution of motoneurons supplying cat sartorius and tensor fasciae latae, demonstrated by retrograde multiple-labelling methods.

Sartorius (SART) and tensor fasciae latae (TFL) in the cat hindlimb are functionally heterogeneous muscles with regions that differ in their skeletal actions and electromyographic recruitment during normal activity. The topographical organization of motoneurons supplying different regions of SART or TFL has been investigated by exposing cut nerve branches supplying different peripheral territories to a combination of retrograde tracers, including Fast Blue (FB), Fluorogold (FG), and horseradish peroxidase (HRP). Motoneurons supplying medial, central, and anterior regions of SART were intermixed extensively throughout a single columnar nucleus located in the ventrolateral part of segments L4 and L5. With this column, motoneurons supplying medial SART tended to lie more rostrally than those supplying anterior regions, but the gradient was modest and showed some cat-to-cat variation. Two major branches entered anterior SART at different proximodistal levels. When these two branches were exposed to different tracers, most motoneurons contained a single tracer; only a few double-labelled cells were apparent. The labelling suggests that anterior SART may contain two separate, in-series divisions of motor units. In TFL, motoneurons supplying nerve branches to posterior, central, and anterior parts of the muscle were intermingled indiscriminately in a single ventrolateral cell column in L6 and rostral L7. These results suggest that topographical organization in lumbar motor nuclei does not always reflect the highly ordered biomechanical and functional specialization evident in the peripheral organization of the muscles themselves.

Amidines↗
PubMed1991

Detection and characterization of a sensory microganglion associated with the spinal accessory nerve: a scanning laser confocal microscopic study of the neurons and their processes.

The spinal accessory nerve has been generally thought to be a cranial nerve with purely motor function, innervating the trapezius and sternocleidomastoid muscles. The present study identified clusters of sensory neurons consistently associated with this cranial nerve in adult rats. Either a single microganglion or several dispersed microganglia were found that adhered to the spinal root of the nerve, to small vessels, or were free within the subarachnoid space. The neurons of the ganglion had axons that joined the spinal root of the nerve proximal to its exit from the skull. Additional branches appeared to have an intracranial distribution within the arachnoid of the brainstem and along its vessels. Several findings suggest that the function of the ganglion is sensory and not autonomic. First, the architectural features of neurons within the ganglion (including their size, pseudounipolar morphology, and the lack of synaptic contacts) are similar to those of neurons in other sensory ganglia. Second, substance P and calcitonin gene-related peptide coexist within neurons of the microganglion, whereas markers for the major transmitters found in autonomic ganglia in rats are absent. Third, the expression of peptides in neurons of the ganglion was sensitive to neonatal capsaicin treatment. Finally, neurons within the ganglion were filled with a retrogradely transported dye after injection of the dye into the cervical spinal cord. Although the function of the ganglion is not known, its features are consistent with a role in nociception from the muscles of the spinal accessory complex, and it may be involved in headaches that have an occipital distribution.

Accessory Nerve↗
PubMed1991

Cortical connections of the caudal subdivision of the dorsolateral area (V4) in monkeys.

Evidence suggests that all primates have rostral and caudal subdivisions in the region of visual cortex identified as the dorsolateral area (DL) or V4. However, the connections of DL/V4 have not been examined in terms of these subdivisions. To determine the cortical connections of the caudal subdivision of DL (DLC) in squirrel monkeys, injections of the neuroanatomical tracers wheat germ agglutinin conjugated to horseradish peroxidase, Diamidino Yellow, and Fluoro-Gold were made in cortex rostral to V II. To aid in delineating the borders of DLC, cortex was also evaluated architectonically. Based on similar patterns of connections, DLC extends from dorsolateral to ventrolateral cortex. DLC receives strong, feedforward input from V II and projects in a feedforward fashion to the rostral subdivision of DL (DLR) and caudal inferior temporal (IT) cortex, including a separate location in the inferior temporal sulcus. DLC has weaker connections with V I, the middle temporal area (MT), cortex rostral to MT in the location of the fundal superior temporal area (FST), cortex dorsal to DLC, ventral cortex rostral to V II, and cortex in the frontal lobe, lateral to the inferior arcuate sulcus. Only lateral DLC has connections with V I, and only dorsolateral DLC has connections with cortex dorsal to DLC. The topographic organization of DLC was inferred from its connections with V II. Thus, dorsolateral DLC represents the lower field, lateral DLC represents central vision, and ventrolateral DLC represents the upper field. Limited observations were made on DLR. Confirming earlier observations (Cusick and Kaas: Visual Neurosci. 1:211, 1988), DLR is paler than DLC myeloarchitectonically. DLR receives only sparse feedforward input from V II, but stronger input from DLC. DLR has strong connections with cortex just rostral to dorsal V II, ventral posterior parietal cortex in the sylvian fissure, MT, the medial superior temporal area, FST, and the inferior temporal sulcus. DLR also shares connections with IT cortex. Thus, while both DLC and DLR are involved in the pathway relaying visual information to IT cortex, an area specialized for object vision, DLR also projects densely to areas such as MT involved in the pathway relaying to posterior parietal cortex, a region specialized for spatial localization and motion perception.

Amidines↗
PubMed1991

Cortical connections of dorsal cortex rostral to V II in squirrel monkeys.

A region of dorsal cortex along the rostral border of V II has been described as comprising a visual area or areas separate from more lateral cortex in both New and Old World primates. To evaluate these possibilities in squirrel monkeys, we studied patterns of cortical connections by injecting Fast Blue, Fluoro-Gold, horseradish peroxidase, and wheat germ agglutinin conjugated to horseradish peroxidase into the dorsal region and related results to distinctions in myeloarchitecture. Our major conclusions are as follows. 1) The dorsal region (D) has distinctly different connections from the area found laterally, the caudal subdivision of the dorsolateral area (DLC). These include major connections with the rostral subdivision of the dorsolateral area (DLR), ventral posterior parietal cortex in the Sylvian fissure, the middle temporal area (MT), the medial superior temporal area (MST), ventral cortex just rostral to V II, and cortex in the inferior temporal sulcus. Weaker connections are with V I, V II, DLC, the fundal superior temporal area (FST), and the frontal lobe. In contrast, DLC has strong connections with V II and inferior temporal (IT) cortex, weaker connections with DLR, and lacks connections with ventral posterior parietal cortex (Steele et al: J Comp Neurol 306:495-520, 1991). 2) Caudal and rostral aspects of dorsal cortex differ in the magnitude of connections with V I, V II, DLR, and FST. These differences are consistent with the previous proposal that at least two visual areas, caudal and rostral, occupy the dorsal region in squirrel monkeys (Krubitzer and Kaas: Visual Neurosci 5:165, 1990), but they could also reflect regional differences in the connections of a single visual area. 3) The dorsal region is more densely myelinated than surrounding cortex; however, rostral aspects of dorsal cortex are less myelinated than caudal aspects, again suggesting the existence of at least two areas. 4) The distinctiveness of connections between dorsal cortex and rostral as compared to caudal dorsolateral cortex provides further evidence for dividing the region of DL into two visual areas, DLC and DLR (Cusick and Kaas: Visual Neurosci 1:211, 1988; Steele et al: J Comp Neurol 306:495-520, 1991).

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