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PubMed1998

Differential projections of ciliated and microvillous olfactory receptor cells in the catfish, Ictalurus punctatus.

The primary olfactory projections of channel catfish Ictalurus punctatus have been examined with postmortem tracing by using either 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate or 1,1-dilinoleyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI). Following DiI deposition into small areas in different parts of the posterior olfactory bulb, olfactory sensory neurons always were labeled throughout the olfactory epithelium. No obvious topographical mapping exists between the epithelium and olfactory bulb. The different dye placements, however, did result in labeling of different morphologies of receptor cells, depending on the site of injection. Retrogradely labeled neurons in the olfactory epithelium were classified into three types on the basis of their height: tall, intermediate, and short. Tall olfactory sensory neurons had perikarya at the bottom one-fourth of the epithelium, extended slender dendrites to the epithelial surface, and possessed numerous cilia on the apical dendritic tips. These tall olfactory sensory neurons were labeled predominantly following DiI applications to the ventral part of the posterior olfactory bulb. In contrast, the short olfactory sensory neurons had perikarya situated within the superficial half of the epithelium and with short apical dendrites bearing microvilli. These short olfactory sensory neurons projected predominantly to the dorsal, posterior olfactory bulb. Thus, short microvillous receptor cells and tall ciliated receptor cells connect to different parts of the olfactory bulb, although the receptor cells are intermingled within the olfactory epithelium. Because different parts of the olfactory bulb are thought to respond preferentially to different classes of odorants, these results suggest that receptor cell morphology may be related to odorant quality detection. In addition, to compare this study with previous in vivo studies, Fluoro-Gold was injected in vivo into either the olfactory bulb or intraperitoneally. These in vivo studies show that so-called "type II ciliar receptor cells" of the nonsensory epithelium are labeled nonselectively by blood-borne substances, but they are not labeled by postmortem injections of DiI anywhere in the olfactory bulb.

Animals↗
PubMed1998

Cells of origin of the trigeminohypothalamic tract in the rat.

Recent studies have demonstrated that a large number of spinal cord neurons convey somatosensory and visceral nociceptive information directly from cervical, lumbar, and sacral spinal cord segments to the hypothalamus. Because sensory information from head and orofacial structures is processed by all subnuclei of the trigeminal brainstem nuclear complex (TBNC) we hypothesized that all of them contain neurons that project directly to the hypothalamus. In the present study, we used the retrograde tracer Fluoro-Gold to examine this hypothesis. Fluoro-Gold injections that filled most of the hypothalamus on one side labeled approximately 1,000 neurons (best case = 1,048, mean = 718 +/- 240) bilaterally (70% contralateral) within all trigeminal subnuclei and C1-2. Of these neurons, 86% were distributed caudal to the obex (22% in C2, 22% in C1, 23% in subnucleus caudalis, and 18% in the transition zone between subnuclei caudalis and interpolaris), and 14% rostral to the obex (6% in subnucleus interpolaris, 4% in subnucleus oralis, and 4% in subnucleus principalis). Caudal to the obex, most labeled neurons were found in laminae I-II and V and the paratrigeminal nucleus, and fewer neurons in laminae III-IV and X. The distribution of retrogradely labeled neurons in TBNC gray matter areas that receive monosynaptic input from trigeminal primary afferent fibers innervating extracranial orofacial structures (such as the cornea, nose, tongue, teeth, lips, vibrissae, and skin) and intracranial structures (such as the meninges and cerebral blood vessels) suggests that sensory and nociceptive information originating in these tissues could be transferred to the hypothalamus directly by this pathway.

Animals↗
PubMed1999

Brainstem neurons with descending projections to the spinal cord of two elasmobranch fishes: thornback guitarfish, Platyrhinoidis triseriata, and horn shark, Heterodontus francisci.

We studied two cartilaginous fishes and described their brainstem supraspinal projections because most nuclei in the reticular formation can be identified that way. A retrogradely transported tracer, horseradish peroxidase or Fluoro-Gold, was injected into the spinal cord of Platyrhinoidis triseriata (thornback guitarfish) or Heterodontus fransisci (horn shark). We described labeled reticular cells by their position, morpohology, somatic orientation, dendritic processes, and laterality of spinal projections. Nineteen reticular nuclei have spinal projections: reticularis (r.) dorsalis, r. ventralis pars alpha and beta, r. gigantocellularis, r. magnocellularis, r. parvocellularis, r. paragigantocellularis lateralis and dorsalis, r. pontis caudalis pars alpha and beta, r. pontis oralis pars medialis and lateralis, r. subcuneiformis, r. peduncularis pars compacta, r. subcoeruleus pars alpha, raphe obscurus, raphe pallidus, raphe magnus, and locus coeruleus. Twenty nonreticular nuclei have spinal projections: descending trigeminal, retroambiguus, solitarius, posterior octaval, descending octaval, magnocellular octaval, ruber, Edinger-Westphal, nucleus of the medial longitudinal fasciculus, interstitial nucleus of Cajal, latral mesencephalic complex, periventricularis pretectalis pars dorsalis, central pretectal, ventromedial thalamic, posterior central thalamic, posterior dorsal thalamic, the posterior tuberculum, and nuclei B, F, and J. The large number of distinct reticular nuclei with spinal projections corroborates the hypothesis that the reticular formation of elasmobranches is complexly organized into many of the same nuclei that are found in frogs, reptiles, birds, and mammals.

Animals↗
PubMed1999

DNA plasmid that codes for human Bcl-2 gene preserves axotomized Clarke's nucleus neurons and reduces atrophy after spinal cord hemisection in adult rats.

Spinal cord injury in adult mammals causes atrophy or death of some axotomized neurons. The product of the antiapoptotic gene Bcl-2 prevents neuron death in vivo. We delivered Bcl-2 by intraspinal injection of a DNA plasmid encoding this gene to determine if axotomized neurons destined to undergo retrograde death could be rescued. Axons of the right side Clarke's Nucleus (CN) were cut unilaterally in adult Sprague-Dawley rats by T8 hemisection, leaving the contralateral (left) CN as an intact control. Two months postoperatively, there was approximately 35% loss of total CN neurons in the right L1 segment. Only 15% of large CN neurons (>400 microm2), whose axons project to the cerebellum, survived--indicating atrophy and/or death of 85% of these cells. We injected a DNA plasmid encoding the human Bcl-2 gene and the bacterial reporter gene LacZ, which was complexed with cationic lipids, into the right side of segment T8 of the normal spinal cord, or just caudal to the hemisection site. The reporter gene was expressed in the perikarya of right CN neurons at L1 for up to 7 days, but not 14 days. Two months following T8 hemisection and Bcl-2/LacZ DNA injection, there was no significant loss of CN neurons ipsilateral to the lesion. Surprisingly, 61% of large neurons survived, indicating partial protection from atrophy. In contrast, a DNA plasmid that codes for the LacZ reporter gene, but not Bcl-2, did not prevent CN neuron death or atrophy. Administration of the Bcl-2 gene in adult rats and its expression in these CNS neurons prevents retrograde cell death, and also minimizes atrophy. These results may serve as the basis for developing novel gene therapy strategies for patients with spinal cord injury.

Animals↗
PubMed1999

Mu- and delta-opioid receptor mRNAs are expressed in spinally projecting serotonergic and nonserotonergic neurons of the rostral ventromedial medulla.

The rostral ventromedial medulla (RVM) is an important mediator of the supraspinal component of opioid antinociception. Previous studies have suggested that activation of the cloned mu- and delta-opioid receptors (MOR1 and DOR1 respectively) in the RVM produces the antinociception mediated by spinally projecting neurons. In the present study, we investigated the expression of mRNA encoding either MOR1 or DOR1 in the RVM of rats. In addition, we examined quantitatively the expression of MOR1 and DOR1 mRNAs in spinally projecting RVM neurons including serotonergic (5HT) cells by using in situ hybridization, immunocytochemistry, retrograde tract-tracing, and the physical disector. Brainstem neurons were labeled in 14 male Sprague-Dawley rats by applying Fluoro-Gold (FG) topically to the dorsal surface of the lumbosacral spinal cord. Five-micrometer-thick cryostat sections were cut and in situ hybridization was performed by using full-length cRNA probes labeled with 35S-UTP. We found that 43% of RVM projection neurons expressed MOR1 mRNA and 83% of RVM projection neurons expressed DOR1 mRNA. Of 192 retrogradely labeled cells in the RVM, 51 cells (27%) were immunoreactive for 5HT. Of this population, half appeared to be labeled for the mRNA encoding MOR1 and over three-fourths appeared to be labeled for the mRNA encoding DOR1. Thus, we conclude that bulbospinal neurons express MOR1 and DOR1; moreover, MOR1 and DOR1 are expressed by significant proportions of 5HT neurons projecting to or through the dorsal spinal cord.

Animals↗
PubMed1999

Colocalization of androgen receptors and mating-induced FOS immunoreactivity in neurons that project to the central tegmental field in male rats.

Bilateral lesions of the central tegmental field (CTF) in male rats virtually eliminate mating behavior. This study examined if mating-induced Fos expression (a measure of neuronal activation) and androgen receptors (AR) are colocalized in brain and spinal cord neurons which project to the CTF. Animals received unilateral injections of the retrograde tracer Fluorogold (FG) in the lateral part of the CTF (CTFl), and 10 days later were killed after ejaculating with females. Brains and spinal cords were examined for FG transport, AR-immunoreactivity (AR-ir), and Fos-immunoreactivity (Fos-ir). AR-ir and Fos-ir were visualized with fluorescence microscopy using cyanine-conjugated and fluorescein-conjugated secondary antibodies. The CTFl received projections from AR-containing neurons in forebrain structures (bed nucleus of stria terminalis, medial preoptic area, lateral and ventromedial hypothalamus), in the central amygdala and various mid- and hindbrain structures (dorsolateral tegmentum, superior and inferior colliculi, pedunculopontine nucleus), and in the lumbosacral spinal cord (lamina X). Some of the AR-containing neurons in bed nucleus of stria terminalis and in the dorsal part of the medial preoptic area with projections to the CTFl were activated by mating. Most AR-containing neurons in spinal lamina X with projections to the CTFl were also activated by mating. Information from spinal cord and pontine nuclei and from outputs descending from the forebrain may be relayed in the CTFl. Thus, as part of a network of hormone-sensitive neurons linking brain and spinal cord mechanisms for mating, the CTFl could participate in the integration of visceral and somatic information relevant for sexual behavior.

Animals↗
PubMed1999

Distribution of bulbospinal gamma-aminobutyric acid-synthesizing neurons of the ventral respiratory group of the rat.

Spinal respiratory motoneuron activity is controlled primarily by excitatory and inhibitory neurons in the medulla oblongata. To identify bulbospinal inhibitory neurons, immunohistochemistry for glutamic acid decarboxylase (GAD) was combined with retrograde labeling of projections to the C(4) ventral horn with Fluoro-Gold. GAD-immunoreactive bulbospinal neurons were located in the ventrolateral portion of the intermediate reticular nucleus, the ventral portion of the medial reticular nuclei, and the raphe and spinal vestibular nuclei. Small numbers of bulbospinal ventral respiratory group neurons were GAD immunoreactive. These neurons were distributed throughout the rostral ventral respiratory group and the Bötzinger complex. Surprisingly, low numbers of Bötzinger neurons, a population thought to be exclusively inhibitory, were GAD immunoreactive. These results suggest that the rostral ventral respiratory group and the Bötzinger complex both contain heterogeneous bulbospinal neuron populations, only some of which have gamma-aminobutyric acid (GABA)-mediated inhibitory control over phrenic motoneurons. Furthermore, the ventral respiratory group contained many GABAergic neurons that lacked bulbospinal projections.

Animals↗
PubMed1999

Topographic organization of serotonergic dorsal raphe neurons projecting to the superior colliculus in the Mongolian gerbil (Meriones unguiculatus).

Recent evidence suggests that the dorsal raphe nucleus (DRN) of the brainstem is a collection of neuronal clusters having different neurochemical characteristics and efferent projection patterns. To gain further insight into the neuroanatomic organization of the DRN, neuronal populations projecting to the superior colliculus (SC) were mapped in a highly visual rodent, the Mongolian gerbil (Meriones unguiculatus). Retrograde tracers Fluoro-Gold (FG) or cholera toxin subunit-B (CTB) were injected into the superficial layers of the SC, and serotonin (5-hydroxytryptamine, 5-HT) -positive cells were identified by using immunocytochemistry in the FG-injected animals. Based on its projections to the SC, the DRN was divided into five rostrocaudal levels. In the rostral and middle levels of the DRN, virtually all FG-filled cells occurred in the lateral DRN, and 36-55% of 5-HT-immunoreactive (5-HT-ir) cells were also double-labeled with FG. Caudally, FG-filled cells occurred in the lateral, ventromedial, and interfascicular DRN; and 44, 12, and 31% of 5-HT-ir cells, respectively, were also FG-filled. The dorsomedial DRN contained only a small proportion of FG-filled cells at its most caudal level and was completely devoid of FG-filled cells more rostrally. The CTB-injected animals showed a similar distribution of retrogradely labeled cells in the DRN. Topographically, the dorsal tegmental nucleus and the laterodorsal tegmental nucleus appeared to be closely associated with 5-HT-ir cells in the caudal DRN. These results suggest that the lateral DRN and the ventromedial/interfascicular DRN may be anatomically, morphologically, and neurochemically unique subdivisions of the gerbil DRN.

Animals↗
PubMed2000

Dopaminergic innervation of the subthalamic nucleus in the normal state, in MPTP-treated monkeys, and in Parkinson's disease patients.

The existence of a dopaminergic innervation of the subthalamic nucleus (STN) has been demonstrated in rats but has remained controversial in primates. The aim of the present study was first to demonstrate the existence of a dopaminergic innervation of the STN in monkeys using tracing methods and then to quantify the loss of dopaminergic fibers in the parkinsonian state in monkeys and humans. Following injection of Fluoro-Gold into the STN of a vervet monkey (Cercopithecus aethiops), retrogradely labeled neurons were found to be scattered in all dopaminergic areas of the mesencephalon. Injection of biotin dextran amine into dopaminergic areas A8 and A9 of two monkeys resulted in anterogradely labeled axons located throughout the whole extent of the STN. Labeled axons that also expressed tyrosine hydroxylase (TH) were reconstructed from serial sections. Some terminal axonal arborizations had profuse branching and occupied much of the STN, and others were restricted to small portions of the nucleus. In TH-immunoreactive sections, numerous sparse, fine, and varicose TH-positive fibers were observed in the STN of normal monkeys and humans. Quantification of these TH-positive fibers revealed a 51% loss of TH-positive fibers in MPTP-intoxicated monkeys and a 65% loss in Parkinson's disease patients compared with their respective controls. These findings demonstrate the existence of a dopaminergic innervation of the STN in primates. The loss of dopaminergic innervation in MPTP-intoxicated monkeys and in Parkinson's disease patients may directly affect the activity of STN neurons and could participate in the hyperactivity of the structure.

Aged↗
PubMed2000

The normal distribution and projections of constitutive NADPH-d/NOS neurons in the brainstem vestibular complex of the rat.

The vestibular system is a highly conserved sensory system in vertebrates that is largely responsible for maintenance of one's orientation in space, posture, and balance and for visual fixation of objects during motion. In light of the considerable literature indicating an involvement of nitric oxide (NO) in sensory systems, it is important to determine whether NO is associated with vestibular pathways. To study the relationship of NO to vestibular pathways, we first examined the normal distribution of constitutive NADPH-diaphorase (NADPH-d), a marker for nitric oxide synthase (NOS), in the vestibular complex (VC) and then examined its association with selected vestibular projection neurons. Survey of the four major vestibular nuclei revealed that only the medial vestibular nucleus contained significant numbers of perikarya stained for NADPH-d/NOS. By contrast, all the vestibular nuclei contained a network of fine processes that stained positive for NADPH-d, although the density of this network varied among the individual nuclei. To determine whether NADPH-d/NOS neurons project to vestibular efferent targets, injections of the retrograde tracer Fluoro-Gold were made into known targets of second-order vestibular neurons. Vestibular neurons containing constitutive NADPH-d/NOS were found to project predominantly to the oculomotor nucleus. A small number of neurons also participate in vestibulothalamic and intrinsic vestibular connections. These results indicate that NADPH-d/NOS neurons are prevalent in the MVN and that a subpopulation of these neurons project to the oculomotor complex. Nitric oxide is probably released locally from axons located throughout the vestibular complex but may play a particularly important role in vestibulo-ocular pathways.

Animals↗
PubMed1990

Three-dimensional computer-aided analysis of the intraganglionic topography of primary muscle afferent neurons in the rat.

A microcomputer system was used to reconstruct, in the L5 dorsal root ganglion (DRG) of the rat, the three-dimensional arrangement of primary neurons which had been labelled by application of horseradish peroxidase (HRP) and fluoro-gold (FG) to various muscle nerves of the leg. Analysis of the data and animation of the reconstructed images with commercially available software were instrumental in identifying the preferential intraganglionic locations of the neurons innervating muscles such as the soleus (SOL), the gastrocnemius lateralis (GL), and medialis (GM), or parts of the GM. These locations appeared to be somewhat related to the position of the muscles in the posterior compartment of the leg. Additionally, the study provided quantitative estimates of muscle afferent neuronal populations, allowed a comparison of the labelling performances of HRP and FG, and finally indicated that few DRG neurons project to two different muscles.

Animals↗
PubMed1991

Spatial segregation between populations of ponto-cerebellar neurons: statistical analysis of multivariate spatial interactions.

This study applies terms and methods for describing spatial interactions between multivariate spatial point patterns, which are, to our knowledge, new in neurobiology. We consider two categories of points, type 1 and 2, distributed within a certain reference volume (such as a nucleus of the brainstem or a cortical area). The points may, for example, represent different categories of labelled cells or axonal fields of termination. We say that there is spatial neutrality between points of type 1 and 2 if the types are signed by random labelling. If a mechanism drives the two point categories together, we say that the point patterns are positively associated. Conversely, if a mechanism drives type 1 and 2 points apart, we say that they are segregated. By comparing two cumulative distribution functions of distances between points, we can distinguish neutrality, positive association, and segregation. One function, H12(t), is the cumulative distribution function of the distance t between a pair of randomly selected points of type 1 and 2. The other, H00(t), is the corresponding function for a pair of points randomly selected without reference to type. Plots of the estimated difference between these two functions give an indication of positive association, neutrality, or segregation. A statistical test, based on simulations of random (neutral) distributions, can be used to see whether deviations from neutrality are significant. We apply the analysis described above to a major pathway of the brain, namely the ponto-cerebellar projection. Different types of cells in the pontine nuclei are retrogradely labelled with the fluorescent tracers Rhodamine-B-isothiocyanate, Fluoro-Gold, and Fast Blue. The tracers are injected in adjacent or more distant folia of the cerebellar paraflocculus. The location of the somata of labelled cells are recorded and the total distribution reconstructed in three dimensions and displayed on a dynamic graphics workstation. We ask whether different units (folia) in the paraflocculus receive information from the same population, from two different positively associated populations, or from segregated cell populations. We find a statistically significant tendency for cell populations projecting to adjacent folia to be positively associated, although there are few cells containing multiple labels. Populations of neurons projecting to folia wider apart are significantly segregated. From inspections of the reconstructions, using real-time rotations, we find that the swarms of labelled neurons tend to accumulate in shells or lamellae in the pons. Within the lamellae, the cells are aggregated in clusters and bands with empty holes (containing unlabelled ponto-cerebellar cell bodies, presumably projecting to other cerebellar targets) in between.(ABSTRACT TRUNCATED AT 400 WORDS)

Amidines↗
PubMed2002

Projections of the posterodorsal preoptic nucleus and the lateral part of the posterodorsal medial amygdala in male gerbils, with emphasis on cells activated with ejaculation.

The posterodorsal preoptic nucleus (PdPN) and the lateral part of the posterodorsal medial amygdala (MeApd) express Fos with ejaculation in male gerbils. Ejaculation-activated cells participate in the PdPN and MeApd projections to each other and to the sexually dimorphic preoptic area (SDA), but those projections involve less than 20% of the activated PdPN cells and less than 50% of the activated MeApd cells. To identify other potential targets of ejaculation-activated cells, we traced PdPN and lateral MeApd outputs using biotinylated dextran amine. The principal part of the bed nucleus of the stria terminalis (BSTpr) and the anteroventral periventricular nucleus (AVPv) were labeled from both sites and were injected with Fluoro-Gold to determine whether PdPN and lateral MeApd cells that express Fos with ejaculation would be retrogradely labeled. Fluoro-Gold was also applied to the dorsomedial hypothalamus (DMH) and retrorubral field (RRF) because such injections label PdPN cells in rats. The PdPN-DMH projection is minimal in gerbils, involving few, if any, ejaculation-related cells. Ejaculation-activated PdPN cells project to the AVPv (43%), dorsal BSTpr (30%), and RRF (12%). Those in the lateral MeApd project to the dorsal BSTpr (43%) and AVPv (18%). When these percentages are combined with those for ejaculation-activated cells involved in the PdPN and lateral MeApd projections to each other and to the medial SDA, the totals reach 100%. Thus, every PdPN and MeApd cell activated with ejaculation may participate in one of these projections. Similar projections may contribute to the similar behavioral effects of the PdPN and MeApd.

Afferent Pathways↗
PubMed2002

Neonatal development of projections to the basolateral amygdala from prefrontal and thalamic structures in rat.

Recently an animal model for neurodevelopmental disorders has been developed. In this model the effects of an early neonatal [postnatal day 7 (Pd7)] basolateral amygdala lesion are compared with the effects of a lesion later in life (Pd21). Early amygdala damage results in enduring behavioral disturbances that become more manifest after puberty. These disturbances were not present in animals lesioned at Pd21. Accordingly it was postulated that the early damage may affect the neuroanatomical and neurochemical organization and functioning of other brain structures. To obtain information on the innervation of the amygdala during normal development, we used the retrograde tracer fluoro-gold. From neonatal day 7 onward (studied until Pd19), retrogradely labeled cells were present in the caudal and rostral thalamus, the substantia innominata, and the prefrontal but not the caudal cortex. Development of the topography of the projecting cells differed substantially for the thalamic regions and substantia innominata vs. the cortical regions. In thalamic regions and substantia innominata, no changes were observed during the studied period (Pd7-Pd9). In the prefrontal cortex, the number of labeled cells increased (from Pd7 to Pd13), the topography of the location of the cells changed from unilateral to bilaminar (from Pd9 to Pd13), and the number of subareas in which the cells were present increased (from Pd7 to Pd13). In the caudal cortex, relatively few cells were present up to Pd15. From Pd17 onward, a bilaminar topography of the location of the cells was observed. These data provide information on the circuitry that may be involved in the aberrant neurodevelopment of neonatally amygdala-lesioned rats, which has been proposed as an animal model for neurodevelopmental psychopathological disorders.

Aging↗
PubMed2002

Characterization of the optic nerve and retinal ganglion cell layer in the dysmyelinated adult Long Evans Shaker rat: evidence for axonal sprouting.

Myelin in the central nervous system (CNS) is hypothesized to help guide the growth of developing axons by inhibiting sprouting of aberrant neurites. Previous studies using animal models lacking CNS myelin have reported that increasing capacity for sprouting axons is negatively correlated with the degree of myelination. In the present study, we investigated the optic nerves of the recently identified Long Evans Shaker (LES) rat with prolonged dysmyelination of adult axons to determine whether the lack of myelin basic protein (MBP) in adult LES rats could manifest as increases in the population of CNS axons. We observed numerous small, unmyelinated axon profiles (<0.3 microm in diameter) clustered in bundles alongside normal caliber axons in dysmyelinated LES rats but not in normal myelinated Long Evans (LE) rats. These putative axon profiles resembled sprouting axons previously described in the CNS. Moreover, the high number of small putative axon profiles could not be accounted for by any significant increases in the number of ganglion cells and displaced amacrine cells in the ganglion cell layer when compared with normal rats as evaluated by using a variety of techniques. This finding suggests that the observed clusters of putative axon profiles were not due to developmental abnormalities in the retina but to the lack of myelin in the optic nerves of LES rats. The adult LES rat, therefore, may serve as a useful model to study the role of myelin in regulating axon development or axon regeneration after CNS injury in the adult mammalian system.

Animals↗
PubMed2002

Origin of the dopaminergic innervation of the central extended amygdala and accumbens shell: a combined retrograde tracing and immunohistochemical study in the rat.

The origin of the dopaminergic innervation of the central extended amygdala (EAc; i.e., the lateral bed nucleus of the stria terminalis [BSTl]-central amygdaloid nucleus [Ce] continuum) and accumbens shell (AcSh) was studied in the rat by combining retrograde transport of Fluoro-Gold (FG) with tyrosine hydroxylase (TH) immunofluorescence. Perikaryal profiles (PP) immunoreactive to FG and to both FG and TH were counted in A8-A14 dopaminergic districts. Our results suggest that dopaminergic inputs to the EAc and AcSh arise from the ventral tegmental area-A10, substantia nigra, pars compacta-A9, and retrorubral nucleus-A8 groups as well as from the dorsal raphe nucleus and periaqueductal gray substance, housing the dorsocaudal part of A10 group (A10dc). Quantitative estimates reveal that the A10dc group contains approximately half of the total number of FG/TH double-labeled PP projecting to Ce and BSTl. By using an anti-dopamine serum, DR/PAG projections to Ce were confirmed to be in part dopaminergic. In contrast, modest numbers of FG/TH double-labeled PP were seen in the A10dc group after injections in the sublenticular extended amygdala, interstitial nucleus of the posterior limb of the anterior commissure or AcSh. Ventral mesencephalic projections to the EAc display a crude mediolateral topographic organization, whereas those to the AcSh are topographically organized along a mediolateral and an inverted dorsoventral dimension. The diencephalic dopaminergic groups do not innervate the EAc or AcSh, except for the periventricular gray-A11 which sends light dopaminergic projections to Ce and BSTl. Overall, the present results provide additional details on the organization of the mesolimbic dopaminergic system that critically controls behavioral responsiveness to salient environmental stimuli.

Afferent Pathways↗
PubMed2002

Endomorphin-1 and -2 immunoreactive cells in the hypothalamus are labeled by fluoro-gold injections to the ventral tegmental area.

Endomorphin-1 and -2 (EM1, EM2) are endogenous opioids with high affinity and selectivity for the mu-opioid receptor. Cells expressing EM-like immunoreactivity (EM-LI) are present in the hypothalamus, and fibers containing EM-LI project to many brain regions, including the ventral tegmental area (VTA). The VTA is one of the most sensitive brain regions for the rewarding and locomotor effects of opioids. It contains mu-opioid receptors, which are thought to mediate gamma-aminobutyric acid-dependent disinhibition of dopamine transmission to the nucleus accumbens. We investigated whether hypothalamic EM-LI cells project to the VTA, where they could play a natural role in this circuitry. The retrograde tracer Fluoro-Gold (FG) was microinjected into the anterior or posterior VTA in rats. Nine days later, colchicine was injected, and 24 hours later, the animals were perfused and processed for fluorescence immunocytochemistry. Numerous FG-labeled cells were detected in the hypothalamus. Both EM1-LI and EM2-LI cells were present in the periventricular nucleus, between the dorsomedial and ventromedial hypothalamus and between the ventromedial and arcuate nuclei. Subpopulations of EM1-LI and EM2-LI cells were labeled by FG. Injections of FG to the anterior and posterior VTA were both effective in producing double-labeled cells, and an anterior-posterior topographical organization between the VTA and hypothalamus was observed. The results support the idea that some endomorphin-containing neurons in the hypothalamus project to the VTA, where they may modulate reward and locomotor circuitry.

Animals↗