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PubMed1990

Correlated onset and patterning of proopiomelanocortin gene expression in embryonic Xenopus brain and pituitary.

To identify cellular interactions that underlie the spatially appropriate transcription of neural genes, we characterized the embryonic development of proopiomelanocortin (POMC) gene expression in Xenopus laevis using in situ hybridization histochemistry. This has led to the establishment of a unique model system for studying how a neuropeptide gene program in four distinct cell groups is set up in pituitary and forebrain. The embryonic onset and patterning of POMC expression was found to be spatially and temporally correlated inside and outside the brain. The first POMC cells in the pituitary primordium and diencephalon were juxtaposed near the infundibulum at stage 29/30, indicating they undergo molecular differentiation much earlier than previously reported for this system. By stage 31/32, many more POMC cells appeared in the morphologically undifferentiated pituitary primordium and brain. In fact, these cells were seen throughout the presumptive anterior and intermediate lobes of the pituitary and posterior diencephalon at the same time that the pituitary primordium is translocating ventral to diencephalon. By stage 39/40, coordinated morphogenesis produced the adult pattern of POMC cells localized in distinct anterior and intermediate pituitary lobes and two diencephalic nuclei. We propose in light of these findings that embryonic cells in the pituitary primordium and brain are simultaneously induced to transcribe the POMC gene, possibly as a result of reciprocal brain-pituitary interactions.

Animals↗
PubMed1989

[Effect of TRH and histidyl-proline diketopiperazine (cyclo(His-Pro] on catecholamine secretion].

The effects of TRH and its metabolite, histidyl-proline diketopiperazine (cyclo(His-Pro] on catecholamine metabolism in the central nervous system, peripheral tissues and plasma were examined in adult and young Wistar rats aged 3 weeks. The intravenous administration of 50 micrograms of TRH produced an increase in plasma epinephrine, cerebral dopamine and a reciprocal decrease in norepinephrine and dopamine in diencephalon and midbrain. In contrast, 50 micrograms of cyclo(His-Pro) induced a rise in plasma dopamine and a decrease of dopamine in cerebellum, pons and medulla oblongata. After intraperitoneal injection of 3 mg of alpha-methyl-p-tyrosine, which blocked re-uptake of catecholamines in synapses, intrathecal administration of 30 ng TRH accelerated 2 times metabolic turnover of norepinephrine and dopamine in cerebral hemisphere, diencephalon and midbrain as well as norepinephrine turnover in cerebellum, pons, medulla oblongata, heart and brown adipose tissue. Consecutive intrathecal administration of TRH for 6 days enhanced cerebral catecholamine content. These results indicate that (1) TRH accelerates metabolic rate of catecholamine in the central nervous system as well as peripheral tissues, and (2) TRH acts on both noradrenergic and dopaminergic neurons in cerebral hemisphere, diencephalon and midbrain, whereas cyclo(His-Pro) acts mainly on dopaminergic neurons in cerebellum, pons and medulla oblongata.

Animals↗
PubMed1984

Influence of liver injury on the catecholamine metabolism in rat brain.

The present study investigated the brain catecholamine metabolism of rats with liver injury induced either by malnutrition or with CCl4. In the malnutrition group, the plasma tyrosine concentration was low, while it showed a tendency to be high in the cerebral cortex. Dopamine concentrations were low in both the cerebral cortex and diencephalon. Norepinephrine concentrations were low in the cerebral cortex, striatum and diencephalon. Tyrosine hydroxylase activity was elevated while monoamine oxidase activity was decreased in the striatum. In the CCl4 group, tyrosine concentrations in the plasma and cerebral cortex did not change. The dopamine concentration in the cerebral cortex increased five days after, and the norepinephrine concentration in the diencephalon increased 24 h after the last administration of CCl4. These data suggest that catecholaminergic neurons in the brain may be substantially affected by liver injury. It may be considered that malnutrition disturbs brain development, particularly in young rats.

Animals↗
PubMed1992

Binding capacities and affinities at mu-, delta- and kappa-opioid sites in membrane suspensions from guinea-pig brain regions.

Binding capacities and affinities (KD) of ligands at mu-, delta- and kappa-opioid binding sites were determined by selective labelling techniques together with analysis of saturation curves in seven regions of the guinea-pig brain. The kappa-sites predominated over the other sites in most regions and were 90% of the total in the cerebellum; binding capacities at kappa-sites were highest in the cortex, intermediate in the cerebellum, striatum and mesencephalon and lowest in the diencephalon, hippocampus and pons-medulla. At the mu-sites, binding capacities were highest in the diencephalon and mesencephalon, with intermediate levels in the pons-medulla, cortex and striatum, and low levels in the hippocampus and cerebellum. The highest binding capacity at the delta-sites was in the striatum, intermediate in the cortex, diencephalon and hippocampus, low in the mesencephalon and pons-medulla and not detectable in the cerebellum. No regional differences in binding affinities were found at mu-, delta- and kappa-sites with [3H]-[D-Ala2,MePhe4,Gly-ol5]enkephalin (KD = 1.10-2,61 nM), [3H]-[D-Ala2,D-Leu5]enkephalin (KD = 0.81-1.94 nM) and [3H]-(-)-bremazocine (KD = 0.083-0.185 nM). Thus in guinea-pig brain there are regional differences in opioid binding capacity and in the distribution of mu-, delta- and kappa-sites, but not in binding affinities.

Animals↗
PubMed2001

Pax-6 regulates expression of SFRP-2 and Wnt-7b in the developing CNS.

Wnt signaling regulates a wide range of developmental processes such as proliferation, cell migration, axon guidance, and cell fate determination. In this report, we studied the expression of secreted frizzled related protein-2 (SFRP-2), which codes for a putative Wnt inhibitor, in the developing nervous system. SFRP-2 is expressed in several discrete neuroepithelial domains, including the diencephalon, the insertion of the eminentia thalami into the caudal telencephalon, and the pallial-subpallial boundary (PSB). We also noted that Wnt-7b expression was similar to SFRP-2 expression. Because many of these structures are disrupted in Pax-6 mutant mice, we examined SFRP-2 and Wnt-7b expression in the forebrains of Pax-6 Sey/Sey mice. We found that Pax-6 mutants lack SFRP-2 expression in the PSB and diencephalon. Interestingly, Pax-6 mutants also lack Wnt-7b expression in the PSB, but Wnt-7b expression in the diencephalon is preserved. Furthermore, in the spinal cord of Pax-6 mutants, SFRP-2 and Wnt-7b expression was greatly reduced. Our results suggest that by virtue of its apposition to Wnt-7b expression, SFRP-2 may modulate its function, particularly at boundaries such as the PSB, and that changes in Wnt signaling contribute to the phenotype of Pax-6 mutants.

Animals↗
PubMed1991

The early development of the frog retinotectal projection.

The guidance of retinal ganglion cell axons has been investigated in embryos of the frog Xenopus. During the initial development of the brain a series of axon tracts are laid down forming a basic 'scaffold' or framework. Retinal axons grow through one of these tracts, the tract of the post-optic commissure (tPOC). This is the only tract that extends through the rostral part of the brain at these early stages of development. The origin and development of the tPOC has been studied using antibodies which label neurons at their earliest stages of differentiation. The first sign of the tPOC is a chain of neurons which differentiate simultaneously in the caudolateral part of the diencephalon. Axons from these neurons grow the short distance between adjacent cells interlinking the chain to form a descending tract. A series of other axon projections are then added to the tPOC, each of which is segregated into a particular subregion of the tract. Retinal axons are added to the tract approximately 18 h after its formation. They grow in the sub-pial part of the tract and always occupy the rostral-most edge. Retinal axons follow the tract to the region of the developing tectum where they leave, turn dorsally, and terminate. The reliance of retinal axons on this pre-existing pathway has been demonstrated by experimentally altering the course of the tPOC during its early development. The caudo-lateral wall of the diencephalon has been rotated through 90 degrees at a stage just before the tPOC neurons differentiate. Confirmation of the predicted alteration in the course of the tPOC has been made using immunocytochemistry. In such manipulated brains, retinal axons maintain their strong affinity for the rostral edge of the tPOC, following its altered course through the diencephalon.

Animals↗
PubMedDate not supplied

[Effect of low-frequency whole-body vertical vibration on the serotoninergic system of the brain and spinal cord].

Rat experiments were performed to study variations in serotonin (5-HT) and its metabolite (5-hydroxy indole acetic acid) in different CNS compartments. Control animals were exposed to an acute vibration stress (10 Hz, 1 mm, 2 m/sec2, 15 min) and experimental animals to a prolonged (52-54 days) vibration test. Acute vibration led to 5-HT activation which was most significant in the hippocampus, diencephalon, cerebellum and in the sacrolumbar cord. Prolonged vibration caused an increase of 5-HT in the parietal cortex and its enhanced utilization in the striatum, diencephalon, pons and in the sacrolumbar cord. As compared to the controls, vibration produced a smaller accumulation of 5-HT in the hippocampus and a larger accumulation in the cerebellum, diencephalon, medulla oblongata and spinal cord. The paper discusses the role of regional changes in 5-HT metabolism and reactivity of serotoninergic structures in the mechanism of vibration-related somatosensory disorders.

Animals↗
PubMed1987

Origin of the adenohypophyseal vessels in the rat.

The origin of the portal vessels and the adjacent structures are described in rat embryos (gestational Days 11, 12 and 13) injected with India ink via the umbilical veins. Without the interposition of mesoderm Rathke's pouch comes into contact with the prosencephalic vesicle and its diverticulum, the processus infundibularis. Developmental changes in the shape of the prosencephalic vesicle influence the formation of Rathke's pouch. Before separation of the latter from the diencephalon and the processus infundibularis (Day 12), branches start growing around Rathke's pouch from the capillary network covering the prospective hypothalamus, and these vessels may be now considered as the forerunners of the primary portal vessels. After the separation of the anterior wall of Rathke's pouch from the diencephalon (Day 13) the primary portal veins are present and the hypothalamo-adenohypophyseal portal circulation is ready to function. The hypothalamic plexus is supplied by the primitive maxillary artery and by some small branches of the internal carotid arteries. The venous outflow leads into the intercavernous sinus and into the primitive maxillary veins. No arterial vessels in the primitive pharyngeal wall could be observed before the appearance of the primary portal vessels. The present observations clearly demonstrate that the adenohypophyseal vessels are derived only from the vascular network of the diencephalon, without contribution from the pharyngeal vessels, and that the portal vascular bed develops as a single entity.

Animals↗
PubMed1993

Experimental studies on central benzodiazepine receptors in the brains of hepatic encephalopathy rats.

With radioligand binding assay, we studied the central benzodiazepine receptors (CBR) in the different regions of brain including the telencephalon, diencephalon, brain stem and cerebellum in a rat model of hepatic encephalopathy (HE) induced by partial hepatectomy following carbon tetrachloride (CC1(4)) intoxication and in the controls. Affinities (Kd) and densities (Bmax) of [3H]-flunitrazepine binding to crude synaptic membranes in the telencephalon of HE rats were obviously increased as compared with those of the controls. It was only in the diencephalon, the brain stem and the cerebellum of HE rats that increased Bmax values were observed, while the Kd values remained unchanged. The results support the recent suggestion that the alterations of CBR play a significant role in the pathogenesis of HE. Among the ranges of the alterations of CBR in the HE rats, the telencephalon ranked first, the brain stem second, the cerebellum third, and the diencephalon last.

Animals↗
PubMed1996

The effect of methamphetamine on histamine level and histidine decarboxylase activity in the rat brain.

To examine biochemical changes in the brain histamine (HA) neuron system after acute and chronic administrations of methamphetamine (MAP), HA levels and histidine decarboxylase (HDC) activities in the rat cortex, striatum, diencephalon, midbrain, pons-medulla and cerebellum were measured. In the cortex and striatum, acute administration of MAP (1 and 3 mg/kg) increased HA levels 1 h later. Acute administration of MAP (10 mg/kg) and chronic administration of MAP (3 mg/kg) for 21 days also increased HA levels and HDC activities in the cortex and striatum I h after the last injection. In the diencephalon, acute administration of MAP (3 and 10 mg/kg) and chronic administration of MAP (3 mg/kg) decreased HA level 1 h after the last injection, but chronic administration of MAP (3 mg/kg) increased HDC activity 1 h after the last injection. There were no significant changes in HA levels and HDC activities in other regions after acute and chronic administrations of MAP. These findings suggest that MAP may activate the brain HA neuron system, although MAP acts more strongly on the cortex and striatum than on the diencephalon.

Animals↗
PubMed1996

Axonal projection patterns of neurons in the secondary gustatory nucleus of channel catfish.

The second gustatory nucleus of teleost fishes receives ascending fibers from the primary gustatory center in the medulla and sends efferent fibers to several nuclei in the inferior lobe of the diencephalon. Similar to the corresponding parabrachial nucleus in birds and mammals, the secondary gustatory nucleus of catfish consists of several cytoarchitectonically distinct subnuclei which receive input from different portions of the primary gustatory nuclei. However, it is unclear how the subnuclear organization relates to the processing of gustatory information in the hindbrain and the subsequent transmission of that information to the forebrain. To determine whether cells within different subnuclei of the secondary gustatory nucleus of channel catfish project to different diencephalic targets, single cells were intracellularly labeled with biocytin. Three subnuclei have been identified in the secondary gustatory nucleus: a medial subnucleus spanning most of the rostrocaudal extent of the nucleus, a central subnucleus and a dorsal subnucleus, the latter two located in the rostrolateral portion of the complex. Cells throughout the secondary gustatory nucleus typically possessed similar collateral projections to several nuclei in the inferior lobe, although four of the six cells filled in the medial subnucleus projected only to nucleus centralis. The only apparent subnucleus-specific projection pattern involved cells at the rostral edge of the secondary gustatory nucleus and in the secondary visceral nucleus. Axons of these cells terminated only in restricted portions of nucleus lobobulbaris. These results suggest that efferents from different subnuclei of the secondary gustatory nucleus of catfish, like those of the parabrachial nucleus of birds and mammals, do not possess simple, topographical projections to target nuclei in the diencephalon.

Animals↗
PubMed2000

Expression of chondroitin sulfate proteoglycans in the chiasm of mouse embryos.

Chondroitin sulfate (CS) proteoglycans have been implicated as molecules that are involved in axon guidance in the developing neural pathways. The spatiotemporal expression of CS was investigated in the developing retinofugal pathway in mouse embryos by using the CS-56 antibody. Immunoreactive CS was detected in inner regions of the retina as early as embryonic day 11 (E11). Its expression in subsequent stages of development followed a centrifugal, receding gradient that appeared to correlate with the sequence of axogenesis in the retina. In the chiasm, immunoreactive CS was expressed at E12, before the arrival of retinal axons. When the retinal axons navigated in the chiasm at E13-E14, immunoreactive CS remained at a low level in the optic fiber layer of the chiasm but was observed prominently in the caudal parts of the ventral diencephalon. This pattern followed closely the array of stage-specific-embryonic-antigen-1-positive neurons in the ventral diencephalon, with a V-shaped configuration that bordered the posterior boundary of the retinal axons, and a rostral raphe extension that ran across the decussating axons in the chiasm. Thus, the CS epitope is implicated in patterning the course of early retinal axons and in regulating axon divergence in the chiasm. At the lateral region of the chiasm, where the retinal axons cross the midline and approach the optic tract, a CS-immunopositive region coincided with the region in which active sorting of dorsal retinal axons from ventral retinal axons occurs. Moreover, at the threshold of the optic tract, the immunoreactive CS was restricted only to the deep part of the optic fiber layer, suggesting an inhibitory role of the CS epitope in repelling newly arrived axons to superficial regions of the optic tract during the development of chronotopic order at this part of the retinofugal pathway.

Animals↗
PubMed1996

Sites of origin and patterns of migration of vasotocin/mesotocin neurons in developing brain of the chick.

Vasotocin/mesotocin (VT/MT) producing neurons are known to migrate extensively during development of the hypothalamus. Birthdating studies as well as immunohistochemical studies suggested the possibility that VT/MT producing neurons originate from specific sites of the neural tube. Furthermore, a relationship between the site of origin and the eventual fate of VT/MT cells has been suggested. This study proposes to identify the sites of origin of VT/MT cells and to establish whether magnocellular and parvocellular VT/MT, and neuromodulatory and neurosecretory VT/MT arise from common or different areas of the developing neural tube. To do so, the embryological distribution of VT/MT producing neurons of the chick was studied with immunohistochemistry. Analysis of the youngest brains in which VT/MT cells could be detected (embryonic day 7.25, E7.25) suggested the presence of two separate sites of origin. The first site was located in the hypothalamic anlage, next to the third ventricle, and the second in the mesencephalon, next to the fourth ventricle. Three-dimensional reconstructions of the location of VT/MT cells throughout development substantiated the hypothesis that diencephalic VT/MT cells originate from the first site while mesencephalic ones originate from the second site. Mesencephalic VT/MT producing cells were confined to the nucleus of Edinger-Westphal and were only detectable during a brief period in development (E7.25-E10). Diencephalic VT/MT producing neurons were noted to form two main paths from their sites of origin to the rostral diencephalon. Quantitative analysis confirmed this caudal to rostral displacement. Magnocellular and parvocellular VT/MT+ cells were intermingled at the diencephalic site of origin as well as in the migratory paths. Neuromodulatory and neurosecretory VT/MT cells of the diencephalon appeared to be derived from a common diencephalic site of origin. These studies support the hypothesis that while specific groups of progenitors may be important in allowing their offspring to produce VT/MT, they do not appear to influence the morphological attributes (magnocellular vs. parvocellular), nuclear locations, or functional characteristics of these cells.

Animals↗
PubMed2002

Distribution of tyrosine hydroxylase (TH) and dopamine beta-hydroxylase (DBH) immunoreactivity in the central nervous system of two chondrostean fishes (Acipenser baeri and Huso huso).

To obtain a better understanding of the evolution of the brain catecholaminergic systems of fishes, we have examined the distribution of catecholamine-synthesizing enzymes in two species of sturgeon (Acipenser baeri and Huso huso) using antibodies against tyrosine hydroxylase (TH) and dopamine-beta -hydroxylase (DBH; only analyzed in Acipenser). Both sturgeons showed TH-immunoreactive (THir) neurons widely distributed in most regions of the brain, the highest number of THir cells being located in the forebrain (olfactory bulb, preoptic area, and posterior tuberculum). THir cells were also seen in other forebrain areas (retrobulbar area, dorsal and ventral telencephalic areas, hypothalamus, ventral thalamus, pretectal area) and in the brainstem (locus coeruleus, viscerosensory area, caudal reticular formation, and area postrema). Immunoreactive fibers and varicosities showed a wide distribution, being particularly abundant in the diencephalon and mesencephalon. DBH-immunoreactive (DBHir) cells were observed in the anterior tuberal nucleus, where these cells were TH-negative, and in the locus coeruleus and the caudal rhombencephalon (vagal reticular formation), where the DBHir cells were also THir. DBHir fibers were scarce in the telencephalon and very abundant in the diencephalon, mesencephalon, and rhombencephalon. The comparative analysis of the catecholaminergic systems of chondrosteans and those observed in other groups of fishes and tetrapods indicate a similar organization of many nuclei, as well as characteristics that are probably primitive, such as the presence of a large number of forebrain catecholaminergic groups.

Animals↗
PubMed2006

Comparative study of the sources of neuronal projections to the site of gonadotrophin-releasing hormone perikarya and to the anteroventral periventricular nucleus in female rats.

The rat ovulatory cycle is dependent on the preoptic region encompassing the gonadotrophin-releasing hormone (GnRH) perikarya and the anteroventral periventricular nucleus (AVPV). Retrograde tract tracing was used to identify and compare the sources of inputs to these sites in female rats. Within the telencephalon and diencephalon, the incidence of retrograde labelling from both sites was moderate to abundant in the ventral lateral septum, posteromedial bed nucleus of the stria terminalis, amygdalohippocampal area and the periventricular, medial preoptic, anterodorsal preoptic, dorsomedial suprachiasmatic, arcuate, and posterior ventrolateral ventromedial hypothalamic nuclei. In these regions, the incidence of retrograde labelling was either greater from the AVPV than from the GnRH perikarya site or similar from both sites. In the medial amygdaloid, parastrial, striohypothalamic, and ventral premammillary nuclei, the retrograde labelling from the AVPV greatly exceeded the sparse incidence from the GnRH perikarya site. In contrast, retrograde labelling from the GnRH perikarya site predominated in the median preoptic, lateroanterior and dorsomedial hypothalamic nuclei, subparaventricular zone, and retrochiasmatic area; it was abundant in the AVPV. Caudal to the diencephalon, retrograde labelling from either site was sparse, except in the lateral parabrachial nucleus, which displayed a particularly high incidence from the GnRH perikarya site. Other mesencephalic regions labelled from either site included the periaqueductal gray and dorsal and median raphe nuclei. The most caudal labelling was found in the ventrolateral medulla and region of the solitary tract nucleus; this was almost exclusively from the GnRH perikarya site. These findings further elucidate the neuroanatomical connections underlying the control of the ovulatory cycle.

Animals↗
PubMed1975

The connections and laminar organization ofthe optic tectum in a reptile (lguana iguana).

The goals of this study were: (1) to describe the total pattern of projections from the optic tectum of Iguana iguana and Pseudemys scripta; and (2) to describe the contributions of particular lamina of the Iguana's optic tectum to this total pattern. Lesions were made in the optic tectum of the Iguana which damaged either all or only certain tectal laminae and, for comparison with the Iguana, lesions in the turtle's optic tectum were made which involved all laminae. The anterograde degeneration resulting from these lesions was stained with the Fink-Heimer ('67) method. The total pattern of projections from the optic tectum in the Iguana and the turtle is similar to that reported for representatives of other vertebrate classes. That is, the optic tectum gives rise to ipsilateral ascending projections to pretectal nuclei, to nucleus rotundus and to nucleus geniculatus lateralis pars ventralis of the diencephalon and, in addition, to a contralateral ascending pathway which courses via the supraoptic decussation to the contralateral diencephalon. Tectotectal connections and several descending pathways were also recognized in each species. The descending pathways include ipsilateral tectobulbar and tecto-isthmi pathways and a contralateral predorsal bundle. Lesions which damaged only certain tectal laminae in the Iguana revealed a laminar organization of the efferent projections. A lesion restricted to the superficial retinal-recipient layers, stratum griseum et album superficiale, resulted in degeneration in only nucleus isthmi pars magnocellularis and nucleus geniculatus lateralis pars ventralis. A lesion which involved both the retinal-recipient layers and stratum griseum centrale resulted in degeneration in only one additional structure, nucleus rotundus. A small lesion involving the deep periventricular layers as well as the superficial layers produced degeneration in the predorsal bundle and the ipsilateral tectobulbar tract as well as in the structures receiving input from the more superficial layers. These results are compared to the results of similar analyses of the superior colliculus in mammals.

Animals↗
PubMed1976

Projections of the locus coeruleus and adjacent pontine tegmentum in the cat.

The projections of the locus coeruleus and adjacent pontine tegmentum have been studied using anatomical and physiological methods in the cat. Axonal trajectories were traced using either the Fink-Heimer I method following electrolytic lesions, or the autoradiographic method after injection of tritiated proline into the nucleus. Results with both methods were similar. Axons of locus noeruleus neurons ascended ipsilaterally through the mesencephalon lateral to the medial longitudinal fasiculus, ventrolateral to the central gray. In the caudal diencephalon, the ascending fibers entered the centrum medianum-parafascicular complex where they diverged into two fascicles: a dorsal fascicle which terminated in the intralaminar nuclei of the thalamus, and a ventral fascicle which gave off fibers to the ventrobasal complex and reticular nucleus of the thalamus while continuing centrolaterally into the lateral hypothalamus medial to the internal capsule. Fibers of the ventral fascicle ascended in the lateral hypothalamus and zona incerta and were traced through the preoptic region into the septum. Fibers could not be consistently traced to the cerebral cortex, and were not seen at all in the cerebellum. Throughout the ascending course of the path from the locus coeruleus, axons were given off to the pretectal area, the medial and lateral geniculate nuclei and the amygdala; fibers passed contralaterally through the posterior commissure, the midline thalamus, and the supraoptic commissure. Fibers descending from the locus coeruleus surrounded the intramedullary portion of the facial nerve and further caudally were observed ventrolateral to the hypoglossal and dorsal vagal nuclei. The axonal trajectories visualized with degeneration and autoradiographic methods followed closely those previously shown for reticular formation neurons, but were also similar to locus coeruleus projections revealed by histofluorescence methods. After injections of horseradish peroxidase into the centrum medianum-parafascicular complex, lateral hypothalamus or preoptic region, labeled neurons were located in the locus coeruleus, nucleus subcoeruleus, and lateral parabrachial nucleus. Reticular formation neurons were not labeled. Neurons in locus coeruleus and adjacent pontine tegmentum could be antidromically activated by stimulation in the rostral midbrain or caudal diencephalon. Our data indicate that both adrenergic and non-adrenergic neurons of the dorsolateral pontine tegmentum have similar projections.

Afferent Pathways↗
PubMed1977

Cells of origin and terminal distribution of descending projections of the rat somatic sensory cortex.

The retrograde, horseradish peroxidase technique has been used to demonstrate the cells of origin of corticofugal fiber systems arising in the rat somatic sensory cortex and projecting to the striatum, diencephalon, brainstem, and spinal cord. Correlative experiments conducted with the anterograde, autoradiographic method have been used to confirm the terminal distribution of many of these fiber systems. Corticofugal pathways directed to subcortical structures arise in the first and second somatic sensory areas exclusively from pyramidal cells of the infragranular layers, V and VI. Fibers which descend to the midbrain, pons, medulla and spinal cord arise exclusively from the largest pyramidal cells, the somata of which are found in the deep part of layer V (layer VB). There is some evidence for a sublaminar organization of the different classes of efferent cells within this layer. Fibers projecting to the diencephalon arise from somata situated throughout layer VI and to a lesser extent in layer V. Corticostriatal fibers arise only from cells with somata in layer V, but the somata are more superficially situated than those of the other classes of corticofugal neurons. The laminar distribution of the somata of corticofugal neurons differs considerably from that of commissural and ipsilateral corticocortical neurons.

Animals↗