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PubMed1996

Ascending and descending projections from the rostral nucleus of the solitary tract originate from separate neuronal populations.

Anterograde studies have shown that neurons within the rostral (gustatory) nucleus of the solitary tract project to the parabrachial nucleus, as well as to sites within the medulla including the reticular formation and caudal nucleus of the solitary tract. In order to determine the degree to which the same neurons contribute to both projections, injections of retrograde tracers were made simultaneously into both the parabrachial nuclei and medullary reticular formation of the rat. Only a small proportion of neurons were double labeled. Consistent with studies in hamster, labeled neurons projecting to the parabrachial nuclei in rat consisted of both stellate and elongate neurons, concentrated within the central subdivision of the rostral nucleus of the solitary tract. Injections into the medullary reticular formation also labeled both stellate and elongate neurons but these were concentrated in the ventral subdivision of the nucleus. The results of the present study demonstrate that different populations of neurons in the nucleus of the solitary tract contribute to ascending and descending pathways. This suggest a possible functional specialization within the nucleus of the solitary tract for those neurons whose output eventually reaches the forebrain compared to those neurons with local connections.

Afferent Pathways↗
PubMed1999

Combinatorial expression of cadherins in the tectum and the sorting of neurites in the tectofugal pathways of the chicken embryo.

The expression of four cadherins (N-cadherin, R-cadherin, cadherin-6B and cadherin-7) was mapped in the developing tectal system of the chicken embryo from four to 19 days of incubation. Each of the cadherins is expressed in a restricted fashion in specific tectal layers, with partial overlap between the cadherins. In some layers, subpopulations of neurons differentially express the cadherins, e.g., in the stratum griseum centrale. Double labeling demonstrates that many of the projection neurons in this layer co-express at least two cadherins. Fibers of the efferent (tectofugal) pathways originating in these neurons also differentially express the cadherins, most prominently at around 1 1 days of incubation. While the different subpopulations of cadherin-expressing projection neurons are dispersed and mixed within the tectum, their neurites sort out and fasciculate according to which cadherin they express, as they collect in the major output of the tectum, the brachium colliculi superioris. From here, cadherin-expressing fascicles follow separate paths to their respective target areas, some of which also express the respective cadherins, in a matching fashion. We propose that the preferentially homophilic binding of cadherins provides a potential adhesive basis for the sorting and selective fasciculation of specific subpopulations of neurites, similar to the well-established sorting and aggregation of cells expressing cadherins. The combinatorial expression of cadherins by the tectal projection neurons may contribute to the complexity and specificity of functional connections in this system.

Animals↗
PubMedDate not supplied

Pathways from auditory cortex to the cochlear nucleus in guinea pigs.

The inferior colliculus (IC) and superior olivary complex (SOC) are important sources of descending pathways to the cochlear nucleus. The IC and SOC are also targets of direct projections from the auditory cortex but it is not known if cortical axons contact the cells that project to the cochlear nucleus. Multi-labeling techniques were used to address this question in guinea pigs. A fluorescent anterograde tracer was injected into temporal cortex to label corticofugal axons. Different fluorescent tracers were injected into one or both cochlear nuclei to label olivary and collicular cells. The brain was subsequently processed for fluorescence microscopy and the IC and SOC were examined for apparent contacts between cortical axons and retrogradely labeled cells. The results suggest that cortical axons contact cochlear nucleus-projecting cells in both IC and SOC. In both regions, contacts were more numerous on the side ipsilateral to the injected cortex. In the IC, the contacted cells projected ipsilaterally or contralaterally to the CN. In the SOC, the contacted cells projected ipsilaterally, contralaterally or bilaterally to the CN. We conclude that auditory cortex is in a position to modulate descending pathways from both the IC and SOC to the cochlear nucleus.

Animals↗
PubMed1985

The efferent vestibular neurons in the toad (Bufo bufo L.): their location and morphology. A horseradish peroxidase study.

Retrogradely labeled neurons are observed in the central nervous system of the toad after peripheral application of peroxidase to the anterior and posterior stumps of the VIIIth nerve. These efferent vestibular neurons are localized in the brainstem only ipsilaterally to the treated nerve; they are restricted within a region close to the motor nucleus of the VIIth nerve, outside the vestibular nuclear complex, and are predominantly localized to the borders between the gray and white matter in an arrangement that seems to surround the motor nucleus of the VIIth nerve. No evidence was found for the existence of labeled Purkinje cells in the cerebellar cortex and therefore of a cerebellolabyrinthine pathway. The efferent vestibular neurons are medium-sized cells with two prominent dendrites, often oriented in a mediolateral direction. A comparative analysis between these neurons and the contiguous motoneurons of the VIIth nerve permitted differentiation of the two groups of neurons as to: distribution in a mediolateral direction, distribution in depth from the brainstem surface, longitudinal extension in the caudorostral direction and morphologic characteristics and dendritic arrangement of the neurons.

Animals↗
PubMed1982

Halothane and the carotid sinus reflex: evidence for multiple sites of action.

Baroreceptor reflexes have been found to be attenuated during halothane anesthesia in humans and experimental animals. The baroreceptor reflex arc is comprised for a number of components, including receptors, afferent and efferent nerve pathways, central integratory centers, peripheral ganglia, and effector organs, at which halothane might exert an inhibitory effect. This study was performed to determine the effect of halothane at each component in order to identify the site or sites of baroreflex attenuation due to halothane. The baroreflex effects on heart rate initiated by carotid sinus pressure changes were examined in conscious and anesthetized (0.0%, 0.75%, and 1.5% halothane in 50% N2O and O2, pls 25 mg/kg thiopental) dogs. In addition, carotid sinus afferent activity, cardiac sympathetic efferent activity and heart responses to direct sympathetic and parasympathetic efferent stimulation were examined in anesthetized dogs. Preganglionic and postganglionic sympathetic nerve activities were recorded simultaneously during baroreceptor activation to determine ganglionic effects of halothane. All levels of anesthesia significantly (P less than 0.05) attenuated reflex changes in heart rate produced by the pressure changes compared to conscious dogs. Significant decreases in cardiac sympathetic efferent activity were produced at 1.5% halothane (P less than 0.05). The depression in postganglionic activity was significantly greater than that or preganglionic activity, indicating a ganglionic-blocking effect by halothane. Cardiac chronotropic changes produced by direct efferent stimulation of sympathetic and vagal fibers were attenuated significantly by halothane (P less than 0.05). On the other hand, baroreceptor afferent activity was increased at 1.5% halothane. This sensitization of baroreceptors appeared to contribute to decreased levels of sympathetic tone, leading to blunted reflex changes in nerve activity. Therefore, halothane was found to have multiple sites of action, leading to depression of the baroreflex.

Animals↗
PubMed1977

Ventral root mapping of cardiac nerves in the canine using evoked potentials.

The sympathetic efferent contribution of left ventral roots T2, T3, and T4 to some cardiac nerves was studied using evoked potentials in mongrel dogs anesthetized with sodium pentobarbital. Electrical stimulation of the ventral roots while recording evoked potentials from the sympathetic chain, anterior ansa subclavia, posterior ansa, ventrolateral cervical cardiac nerve, ventromedial cervical cardiac nerve, and the vagosympathetic trunk demonstrated that A-, B-, and C-type fibers exist in these efferent neural pathways. The range of conduction velocities observed was 0.7-104 m/s. T2 contributed the largest number of A-type fibers, and T2 and T3 contributed C-type fibers equally, while T4 had the least number of fibers coursing through the cardiac nerves.

Animals↗
PubMed2001

Excitatory stimulation of neurons in the arcuate nucleus inhibits gastric acid secretion via vagal pathways in anesthetized rats.

It is well established that autonomic control of gastrointestinal function is modulated by central autonomic neurotransmission. In this context it has been shown that gastrointestinal motility and secretion can be modulated by exogenous neuropeptides microinjected into the paraventricular nucleus of the hypothalamus (PVN). Furthermore, there is considerable evidence suggesting that neurons projecting from the arcuate nucleus (Arc) to the PVN may be the source of endogenous neuropeptide release in the PVN. This poses the question whether stimulation of neurons in the arcuate nucleus, e.g. by an excitatory amino acid, alters gastrointestinal function. In the present study, we investigated the effect of an excitatory amino acid, kainate, microinjected into the arcuate nucleus on gastric acid secretion in urethane-anesthetized rats. Kainate (140 pmol/rat) bilaterally microinjected into the Arc induced an significant inhibition of pentagastrin (PG) stimulated (16 mg/kg per h) gastric acid secretion throughout an observation period of 120 min after microinjection. Microinjection of kainate into hypothalamic areas outside the arcuate nucleus did not modify gastric secretion. Bilateral cervical vagotomy blocked the effect of kainate injected into the Arc on PG-stimulated gastric acid secretion. These data show that gastric secretory function can be modulated by stimulation of neuronal activity in the Arc via efferent vagal pathways. The results suggest that the arcuate nucleus is a forebrain area involved in the CNS regulation of gastrointestinal function.

Anesthetics, Intravenous↗
PubMed1987

Recording of single unit potentials in human spinal nerve roots: a new diagnostic tool.

Single unit potentials can be recorded directly with wire electrodes during an operation in man. Since averaging is not necessary this recording method is a fast neuromonitoring tool. Using 2 pairs of platinum electrodes it was possible to record extracellular single unit potentials at 2 sites in nerve root filaments in the spinal canal and to determine conduction velocities. Afferent and efferent single unit potentials could be distinguished from each other by a reversed conduction time and a reversed potential change making a differentiation between dorsal and ventral root parts possible. An activity increase due to touching the skin could be recorded. Therefore dermatomes of nerve root filaments and root filaments of dermatomes can be identified during the operation.

Action Potentials↗
PubMed2006

Development of the deep cerebellar nuclei: transcription factors and cell migration from the rhombic lip.

The deep cerebellar nuclei (DCN) are the main output centers of the cerebellum, but little is known about their development. Using transcription factors as cell type-specific markers, we found that DCN neurons in mice are produced in the rhombic lip and migrate rostrally in a subpial stream to the nuclear transitory zone (NTZ). The rhombic lip-derived cells express transcription factors Pax6, Tbr2, and Tbr1 sequentially as they enter the NTZ. A subset of rhombic lip-derived cells also express reelin, a key regulator of Purkinje cell migrations. In organotypic slice cultures, the rhombic lip was necessary and sufficient to produce cells that migrate in the subpial stream, enter the NTZ, and express Pax6, Tbr2, Tbr1, and reelin. In later stages of development, the subpial stream is replaced by the external granular layer, and the NTZ organizes into distinct DCN nuclei. Tbr1 expression persists to adulthood in a subset of medial DCN projection neurons. In reeler mutant mice, which have a severe cerebellar malformation, rhombic lip-derived cells migrated to the NTZ, despite reelin deficiency. Studies in Tbr1 mutant mice suggested that Tbr1 plays a role in DCN morphogenesis but is not required for reelin expression, glutamatergic differentiation, or the initial formation of efferent axon pathways. Our findings reveal underlying similarities in the transcriptional programs for glutamatergic neuron production in the DCN and the cerebral cortex, and they support a model of cerebellar neurogenesis in which glutamatergic and GABAergic neurons are produced from separate progenitor compartments.

Animals↗
PubMed1980

Afferent and efferent nerve endings of the outer hair cells in the rabbit.

The afferent and efferent nerve endings of the outer hair cells of the rabbit were investigated electron-microscopically. The afferent nerve ending was 1.4 X 2.0 microns in size and contained small vesicles, spherical mitochondria, and occasionally multivesicular bodies. The partially thick and dense membranes on either side of the synaptic cleft were observed and this region of the synaptic cleft was high in electron density. This area was considered to be an active zone of the afferent nerve ending. The efferent nerve ending was 4.0 X 6.0 microns in size and contained many synaptic vesicles, many oblong mitochondria, and multivesicular bodies. Synaptic vesicles were concentrated at some sites opposite the synaptic cleft. This area was thought to be an active zone where vesicles discharge their contents into the synaptic cleft. Furthermore, in some places of the synaptic cleft there were gaps (0.16 X 0.68 microns) which contained small vesicles. The gaps in the synaptic cleft have been briefly discussed.

Animals↗
PubMed1997

[Intubation of afferent lacrimal ducts--a review of techniques].

The authors present a review of various techniques of long-term intubation of efferent lacrimal pathways by a silicone fibre. They use an original way of intubation and intubate the insertion probes of the intubation set from the lower nasal outlet by means of a titanium loop under direct optic control by means of an endoscope. The use of the endoscope makes it possible to reduce the number of complications and iatrogenic damage of the mucosa and it enhances the effectiveness of the procedure. The authors prefer the use of special intubations sets; for young children intubation sets made from soft metal are preferable. At present all their demands are met by the intubation set they developed in collaboration with the Technical University, Prague. During the period between April 1994 and August 1996 the authors used the described technique for bicanalicular intubation of the efferent lacrimal pathways in 127 children and in adult patients 6x. In 86 instances they used an intubation set of Geuder Co., 44 times their own intubation set.

Adult↗
PubMed1997

Assessment of the penile vascular system with color-coded duplex sonography and pharmacocavernosometry and -graphy in impotent men.

OBJECTIVE: To examine the extent to which color-coded duplex sonography permits complete clarification of vessel-dependent erectile dysfunction (ED). MATERIAL AND METHODS: A total of 215 patients with ED were examined. All patients underwent pharmacocolor-coded duplex sonography (PHCCDS; 20 micrograms of prostaglandin E1, PGE1, intracavernosally) as well as pharmacocavernosometry and -graphy (PHCM and PHCG; 20 micrograms of PGE1 intracavernosally). The penile vessels were visualized, i.e. the dorsal arteries, the cavernosal arteries, and the anastomoses between them, as well as the venous pathways. Peak flow and end-diastolic flow in all arteries and, when present, anastomoses were determined after stimulation. Induction flow to achieve maximal tumescence/rigidity as well as maintenance flow were determined during PHCM. Finally, for the morphological visualization of the cavenous body and possible venous insufficiencies, a radiography in 2 planes was produced with infusion of a water-soluble contrast medium. RESULTS: In 145 patients with a grade 0-III tumescence after stimulation with 20 micrograms of PGE1, PHCCDS revealed an end-diastolic flow of > 5 cm/s, with a peak flow velocity > 25 cm/s in the 2 cavernosal and 2 dorsal arteries. The deep dorsal vein of the penis was visualized in 110 of these 145 patients with a blood flow > 5 cm/s, and in 35 cases with a blood flow < 5 cm/s. Venous drainage to the corpus spongiosum was visualized in 80 patients with a blood flow > 10 cm/s. All patients had a pathologically increased induction (normal value < 100 ml/min) and maintenance venous flow (normal value < 10 ml/min) in the PHCM as well as venous drainage in the PHCG. Sixty patients with a tumescence grade of IV-V (rigidity) had a peak flow velocity clearly > 25 cm/s, an end-diastolic flow < 5 cm/s in the 2 cavernosal and 2 dorsal arteries in the PHCCDS, as well as induction values < 100 ml/min and maintenance flow values < 10 ml/min in the PHCM, without visible insufficient efferent venous pathways on the PHCG. In 29 patients (13.5%) hemodynamically active anastomoses perforating the tunica albuginea could be detected. Ten patients with a tumescence grade of III had a peak flow velocity < 25 cm/s and an end-diastolic flow < 5 cm/s without venous leakage in PHCM and PHCG. CONCLUSION: PHCCDS allows for the assessment of arterial flow disorder as well as of venous leakage in ED. PHCM and PHCG should only be carried out in patients in whom surgical or radiological interventional procedures at the efferent venous pathways are planned.

Alprostadil↗
PubMed1987

FMRF-amide-like immunoreactive efferent fibers and FMRF-amide suppression of pacemaker neurons in eyes of Bulla.

The eyes of certain marine gastropods including Aplysia and Bulla, contain circadian pacemakers, which produce a circadian rhythm of autogenous compound action potential (CAP) activity. The CAPs are generated by the synchronous spike discharge of a distinctive population of retinal pacemaker neurons whose axons convey the CAP activity to the CNS. When CAP activity is recorded from a preparation with eyes attached to the CNS, the CAP activity is modulated by efferent activity. In this study we have identified FMRF-amide-like immunoreactive efferent axons in the optic nerves of Bulla. These axons arborize in the basal retinal neuropil adjacent to the pacemaker neurons and are in a position to make synaptic contacts with their dendrites. Similar immunoreactive fibers are not observed in Aplysia eyes. Exogenous FMRF-amide at micromolar concentrations suppresses ongoing CAP activity in isolated eyes but does not suppress the ERG or phase shift the circadian rhythm of CAP activity. Intracellular recordings from the retinal pacemaker neurons reveal that FMRF-amide hyperpolarizes the membrane potential, suppresses spike discharge, and decreases the input resistance, suggesting that a K conductance is increased. Electrical stimulation of the region of the cerebral ganglion that contains FMRF-amide immunoreactive neurons suppresses ongoing CAP activity. All these results are consistent with the idea that the FMRF-amide immunoreactive central neurons and their axons provide a pathway for efferent modulation of the CAP rhythm generated by the retinal pacemaker neurons.

Animals↗
PubMedDate not supplied

Human root and cord potentials evoked by Achilles tendon tap.

Lumbosacral root potentials and sacral spinal cord segmental responses were recorded epidurally in 24 normal adult subjects by tapping the Achilles Tendon with the electronic hammer (mechanical). The averaged responses were also recorded from the same epidural levels after the electrical stimulation of the Posterior Tibial nerve at the popliteal fossa (electrical). While the dorsal and reflexively evoked ventral root responses were easily obtained by the electrical stimulation; by the mechanical stimulation only a late and small ventral root response with two negative deflections could be evoked at the L4-5 or L5-S1 I.V. (intervertebral) epidural levels. The ventral root responses elicited by mechanical stimulation appeared 4.0 msec later than those elicited by the electrical stimulation. This time interval was exactly the same when the latencies of the Soleus reflexes to both stimuli were compared that for the Achilles tendon reflex being 4.0 msec delayed. When the sums of their afferent and the efferent conduction times (to and from Th12-L1 I.V. levels) were extracted from the total conduction times of the Soleus H and Achilles tendon reflex obtained by the EMG recordings, the sacral cord conduction delay was found 1.8 msec for the H-Reflex and 4.1 msec for the Achilles tendon reflex. It was suggested that the twice longer time delay along the sacral cord to Achilles tendon tap might be due to the oligosynaptic linkage of the Achilles tendon reflex or it may result from highly dispersed afferent volley producing a slowly rising wave or excitation that takes longer to reach threshold for the soleus motoneurone discharges.

Achilles Tendon↗
PubMed1999

Reflex effects from leptin sensors in the white adipose tissue of the epididymis to the efferent activity of the sympathetic and vagus nerve in the rat.

Efferent nerve signals were recorded from the central cut end of the small nerve filament dissected from the sympathetic nerve innervating the white adipose tissue (WAT) of epididymis, inter scapular brown adipose tissue (BAT), pancreas, liver, adrenal medulla, and vagus nerve innnervating the pancreas and liver. Injection of leptin (2 ng, 0.2 ml) into the white adipose tissue of the either side of the epididymis evoked reflex activation of the sympathetic nerve activity and suppression in vagus nerve activity. These observations suggest that leptin sensors in the white adipose tissue of the epididymis play a role in reflex regulation of metabolic functions of the body through the modulatory change in sympathetic and vagal outflow.

Adipose Tissue↗
PubMed1988

The efferent projections of the rat lateral habenular nucleus revealed by the PHA-L anterograde tracing method.

The efferent connections of the rat lateral habenular nucleus (LHb) were demonstrated using anterograde transport of the lectin Phaseolus vulgaris leucoagglutinin (PHA-L). Following PHA-L injections into the LHb, neuronal somata located in the lateral two thirds of the LHb were labeled with PHA-L. Individual axonal fibers and terminal specializations were clearly visible. This permitted detailed mapping of both efferent fiber pathways and terminal distributions. Previous reports on fiber pathways were substantially confirmed and several new findings were revealed. (1) Major rostrally oriented fibers enter the medial forebrain bundle via 3 routes which initially branch from the fasciculus retroflexus: the mediodorsal thalamic nucleus and ventromedial thalamic nucleus; the zona incerta and fields of Forel; and the ventral tegmental area of Tsai. (2) A major decussation to the contralateral thalamic nuclei occurs in the central medial thalamic nucleus. (3) Caudally directed fibers follow two courses: one to the deep mesencephalic nucleus, central grey, dorsal raphe nucleus and the deep layers of the superior colliculus; and the other to the median raphe nucleus, oral pontine reticular formation and raphe pontis nucleus. The present results offer more detailed information concerning the dorsal diencephalic system.

Animals↗
PubMed1996

Connections of the torus semicircularis and oliva superior in the frog, Rana esculenta: a Phaseolus vulgaris leucoagglutinin labeling study.

The afferent and efferent connections of the frog principal nucleus (TP) of torus semicircularis (TOS) and superior olive (SO) were examined by employing the anterograde and retrograde transport patterns of Phaseolus vulgaris leucoagglutinin (PHA-L). After injecting the tracer into these nuclei it was found that the TP projected to the ipsilateral posterior and central thalamic nuclei, all subdivisions of the bilateral TDS and the ipsilateral nucleus isthmi (NI). In the rhombencephalon the projection was restricted mainly to the contralateral SO and the cochlear nucleus (CN). Retrogradely labeled cells were found in most of the areas that contained anterogradely labeled terminals. The termination areas of the SO fibers were similar to the projections of fibers of TP origin in the diencephalic and in the mesencephalic auditory centers. A strong projection was followed into the contralateral SO; the CNs received fibers at both sides. Caudally to the SO the reticular formation, the spinal nucleus of the trigeminal nerve, the solitary nucleus and the dorsal column nuclei were supplied by the fibers of the SO origin. Retrogradely labeled cells were found in the TOS, tegmental nuclei, solitary nucleus, dorsal column nuclei and in the spinal nucleus of the trigeminal nerve. Our results indicate that the frog auditory pathway is more complex at the level of the secondary and tertiary fiber projections than has been previously recognized.

Afferent Pathways↗
PubMed2006

The articulo-cardiac sympathetic reflex in spinalized, anesthetized rats.

Somatic afferent regulation of heart rate by noxious knee joint stimulation has been proven in anesthetized cats to be a reflex response whose reflex center is in the brain and whose efferent arc is a cardiac sympathetic nerve. In the present study we examined whether articular stimulation could influence heart rate by this efferent sympathetic pathway in spinalized rats. In central nervous system (CNS)-intact rats, noxious articular movement of either the knee or elbow joint resulted in an increase in cardiac sympathetic nerve activity and heart rate. However, although in acutely spinalized rats a noxious movement of the elbow joint resulted in a significant increase in cardiac sympathetic nerve activity and heart rate, a noxious movement of the knee joint had no such effect and resulted in only a marginal increase in heart rate. Because this marginal increase was abolished by adrenalectomy suggests that it was due to the release of adrenal catecholamines. In conclusion, the spinal cord appears to be capable of mediating, by way of cardiac sympathetic nerves, the propriospinally induced reflex increase in heart rate that follows noxious stimulation of the elbow joint, but not the knee joint.

Adrenalectomy↗