Biomedical subjects

R H Ho

Publications and source records attributed to R H Ho.

At least 37 records · Page 2Linked to original sources

PubMed1989

Role of substance P in suppressing growth hormone release in the rat.

To evaluate a possible physiological role of endogenous substance P (SP) in the control of growth hormone (GH; somatotropin) secretion, a specific antiserum against SP (anti-SP) was injected intraventricularly (3 microliters into the third cerebral ventricle) in unanesthetized unrestrained normal male rats. Control rats received an equivalent volume of normal rabbit serum (NRS). Intraventricular injection of the NRS lowered plasma GH concentrations significantly. The lowering was detected on first measurement at 10 min after injection and was maximal at 30 min. This was followed by a return toward the initial levels. Third ventricular injection of antiserum significantly increased plasma GH in comparison with control animals injected with NRS. The effect was observed within 10-20 min, and levels remained elevated for the 120-min duration of the experiment. To confirm the possible inhibitory role of endogenous SP on GH release, 3 microliters of 0.9% NaCl (saline) alone or saline containing a specific antagonist of SP, [D-Pro2,D-Trp7,9]SP, was injected into the third ventricle of normal male rats. The antagonist also increased plasma GH significantly (P less than 0.005) within 5 min compared with values in the saline-injected control group. Levels remained elevated for 30 min but had returned toward control values 60 min after injection. In contrast, synthetic SP significantly decreased plasma GH when injected intravenously or intraventricularly compared with plasma GH in the control saline-injected group. To investigate a possible direct action of SP on GH release from the anterior pituitary gland, we incubated synthetic SP with dispersed anterior pituitary cells for 1 hr. The release of GH from incubated anterior pituitary cells was not affected at any dose of SP (10(-9) to 10(-6) M) tested. These data strongly indicate that endogenous SP has a physiological inhibitory role in the control of GH secretion at the level of the hypothalamus in the male rat.

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PubMed1989

The brainstem origin of enkephalin- and substance-P-like immunoreactive axons in the spinal cord of the North American opossum.

We have used the retrograde transport of True Blue (TB) in conjunction with immunofluorescence to determine if any of the enkephalin (ENK)- or substance P (SP)-immunoreactive axons in the spinal cord of the North American opossum originate within the brainstem. Neurons containing ENK-like immunoreactivity and TB after injections of the latter into the second or third cervical segment of the spinal cord were found within the locus coeruleus proper, the locus coeruleus pars alpha, the raphe magnus, pallidus and obscurus, and within several nuclei of the medullary reticular formation. Neurons containing SP-like immunoreactivity and TB were found in many of the same nuclei but not within the locus coeruleus proper. In general, the brainstem areas that provide ENK and SP projections to the spinal cord in marsupial opossums are comparable to those which provide similar projections in placental mammals, but differences exist. Our results are discussed in light of those differences and the probable origins of ENK and SP projections from the brainstem to different spinal targets.

Animals↗

PubMed1988

Brainstem origin of serotonin- and enkephalin-immunoreactive afferents to the opossum's cerebellum.

Previous studies have described the distribution of serotonin- and enkephalin-immunoreactive elements in the posterior lobe vermis of the opossum's cerebellum. In the present study we have used a double labeling paradigm which combines the retrograde transport of horseradish peroxidase (HRP) with serotonin and enkephalin immunohistochemistry to determine the brainstem origin of serotoninergic and enkephalinergic neurons that project to the opossum's cerebellar cortex. Subsequent to HRP injections into the posterior lobe vermis, widespread areas of the medulla and pons were found to contain retrogradely labeled neurons. Serotonin-immunoreactive somata are present primarily in the raphe nuclei and the adjacent reticular formation. Enkephalinergic neurons were numerous in the raphe nuclei, medial accessory olive, gigantocellular reticular formation, locus coeruleus, and the nucleus of the trapezoid body. However, serotoninergic neurons that project to the cerebellum were located only in the medullary pyramids and the reticular formation adjacent to the raphe. Double-labeled enkephalinergic neurons were located 1) within the medullary pyramids, 2) throughout the extent of the caudal medial accessory olive, 3) in the rostral subnucleus a of the medial accessory olive, 4) in the nucleus reticularis gigantocellularis pars ventralis, 5) in the nucleus reticularis lateralis, and 6) in the nucleus reticularis ventralis lateral to the inferior olivary complex. These results indicate that although neurons containing serotonin and enkephalin immunoreactivity may be present in some of the same pontine and medullary nuclei, those serotoninergic and enkephalinergic neurons that project to the cerebellum are present primarily in restricted and spatially separate regions of the caudal medulla.

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PubMed1988

Immunohistochemical localization of substance P, somatostatin, enkephalin, and serotonin in the spinal cord of the northern leopard frog, Rana pipiens.

Using the indirect antibody peroxidase-antiperoxidase method of Sternberger, we localized substance P (SP), somatostatin (SOM), enkephalin (ENK), and serotonin (5HT, 5-hydroxytryptamine) in the spinal cord of Rana pipiens. This is the first study to demonstrate all four substances in adjacent sections of frog spinal cord. The distribution patterns of ENK, SP, SOM, and 5HT in our study differ from that described for laminae I and II in amniotes. A high density of ENK, SP, and SOM fibers is present in a band ventral to the dorsal terminal field of cutaneous primary afferent fibers and slightly overlapping the ventral terminal field of muscle primary afferent fibers. However, a high density of 5HT fibers is present in the dorsal terminal field.

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PubMed1988

Immunocytochemical analysis of somatostatin in the hypothalamus of obese and non-obese Zucker rats.

Levels of growth hormone (GH) are reduced in the genetically obese Zucker rat, fa/fa, in comparison to lean littermates. In normal rats, GH release is regulated by stimulatory and inhibitory factors of hypothalamic origin. The present experiment focuses on hypothalamic somatostatin (SOM; growth hormone release inhibiting factor) in order to determine if abnormal hypothalamic SOM may be a correlate of depressed GH secretion in fa/fa rats. We compared immunocytochemical localization of hypothalamic SOM between 5 obese (fa/fa) Zucker rats and 5 non-obese littermates. Brain sections from pairs of animals were processed simultaneously. The distribution of SOM immunoreactive cell bodies in the hypothalamus agreed with previous reports. SOM-containing neurons in the periventricular area were counted and analyzed at 4 hypothalamic levels: (1) anterior to the suprachiasmatic nucleus (SCN); (2) through SCN; (3) between SCN and the ventromedial hypothalamic nucleus (VMH); and (4) through VMH. The greatest number of SOM-immunoreactive cell bodies was observed at levels (2) and (3). The numbers of SOM-containing cells did not differ significantly between obese and lean animals. No apparent difference in density of fiber staining was observed in the median eminence.

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PubMed1988

A temporal analysis of the origin and distribution of serotoninergic afferents in the cerebellum of pouch young opossums.

In the present study, a temporal analysis of the pattern of distribution of serotoninergic fibers and varicosities within the cerebellum of pouch young opossums was carried out. Particular attention was focused on animals ranging in age from postnatal day (PD) 21-PD 72, because there is a transient expression of serotonin immunoreactivity in the cerebellar cortex during that interval. Between PD 1-33, there is a progressive increase in serotoninergic immunoreactivity throughout the cerebellar cortex. After PD 33, there is a decrease in the relative number of immunostained fibers followed by a reorganization into the adult pattern of distribution. A double labeling paradigm, in which horseradish peroxidase, used as a retrograde marker, combined with serotonin immunohistochemistry was employed to localize serotoninergic neurons that project to the developing cerebellum. Initially (PD 9), serotoninergic cells in the medullary reticular formation and dorsolateral pontine tegmentum are double labeled. After PD 77, only neurons in the medullary reticular formation were double labeled. The course taken by serotoninergic axons from the brainstem to the cerebellum also was analyzed. Between PD 1 and PD 42, serotoninergic axons enter the cerebellum via four different routes: 1) the inferior cerebellar peduncle; 2) a pathway located lateral and rostral to the inferior cerebellar peduncle; this bundle of serotonin axons contains immunoreactive fibers that also enter the tectum (this tract is referred to as the tecto-cerebellar bundle in this report); 3) the medial aspect of the superior cerebellar peduncle; and 4) the tela choroidea. After PD 40, the latter two pathways are the primary routes by which serotoninergic fibers enter the cerebellum. The loss of serotoninergic fibers in the first two pathways coincides with the decrease in serotoninergic immunoreactivity seen in the cerebellar cortex described above. In summary, the results suggest that the serotoninergic projection to the opossum's cerebellum is remodelled during development. It is proposed that the serotonin fibers present at early stages of development may play a role in regulating specific events in cerebellar maturation. In contrast, the serotoninergic axons which have a more restricted pattern of distribution later in development, and in the adult, likely modulate neuronal activity within the cerebellum.

Afferent Pathways↗

PubMed1988

The early development of subcortical projections to presumptive somatic sensory-motor areas of neocortex in the North American opossum.

We have studied the early development of subcortical projections to presumptive somatic sensory-motor areas of neocortex in the North American opossum Didelphis virginiana. The opossum is born in a very immature state, 12-13 days after conception, and climbs into an external pouch where it is available for experimental manipulation. Using the retrograde transport of wheat germ agglutinin conjugated to horseradish peroxidase, we have obtained evidence that axons from the dorsal raphe and superior central nuclei, the substantia nigra, the locus coeruleus and the parabrachial nuclei reach presumptive somatic sensory-motor areas of neocortex by at least postnatal day (PND) 10. Axons showing serotonin-like immunoreactivity, presumably from the dorsal raphe and/or superior central nuclei, and axons containing tyrosine hydroxylase immunoreactivity, presumably from the substantia nigra and/or locus coeruleus, are present in the same areas at birth or shortly thereafter. Thalamic axons do not grow into comparable areas of neocortex until after PND 10. Such axons reach the subplate region of ventrolateral neocortex first and then proceed dorsomedially; by estimated PD (EPND) 21, they are present in presumptive layers I, V and VI, but they do not innervate an identified layer IV until EPND 48. The developmental sequences suggested by our study are compared with those reported for other species and are discussed in light of their importance in the formation of major sensory and motor circuits.

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PubMed1988

Somatostatin immunoreactive structures in the developing rat spinal cord.

Somatostatin immunoreactive (SOM-I) perikarya were first observed in the ventral horn at E12, in the presumptive intermediate gray area at E14, and in the alar plate of the rostral spinal cord at E14. In general, after their initial appearance, their density increased and then decreased during development. A moderate density of SOM-I varicosities became obvious in the superficial laminae of the E20 dorsal horn. By E12 a few SOM-I perikarya, interpreted to be dorsal root ganglia, were observed lateral to the spinal cord, and by E13, SOM immunoreactivity was visualized within the central and peripheral processes of dorsal root ganglion axons. In the marginal zone, SOM-I fibers were first demonstrable in the ventral funiculus at E14, and in the lateral funiculus at E15. After their initial appearance, their density increased and then decreased with age, with the exception of the dorsal part of the lateral funiculus where it increased at the early stages of development to an apparently stable level. The early detection of SOM immunoreactivity in specific spinal regions corresponds well with the birth dates of cells in those regions. This indicates that the SOM-I cells are capable of synthesizing the substance at least as early as they have entered their final cell division.

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PubMed1988

Catecholaminergic innervation of the spinal cord in the North American opossum, Didelphis virginiana.

Axons presumed to contain catecholamines were visualized in the spinal cord of the spinal cord of the North American opossum using antibodies to tyrosine hydroxylase (TH) by an indirect antibody peroxidase-antiperoxidase (PAP) technique. Axons showing TH-like immunoreactivity (TH-IR) coursed primarily in the dorsal part of the lateral funiculus, although they were also present more ventrally. An occasional TH-IR axon was seen in the dorsal funiculus. Within the gray matter, TH-IR axons were distributed most densely within the intermediolateral cell column (ILC). Such axons were more numerous in the presumptive sacral parasympathetic nucleus than within the adjacent gray matter, but their density was less than that within the ILC. Many TH-IR axons were also found within laminae I-V and X, but the density of innervation in the ventral horn was relatively low. The brainstem origin of TH-IR axons in the spinal cord was studied using a combination of the retrograde transport of fluorescent dyes and immunofluorescence as well as the retrograde transport of horseradish peroxidase and PAP immunohistochemistry. The injections of retrograde markers were made at either cervical, thoracic or lumbar spinal levels. With both techniques, spinally projecting TH-IR neurons were located within the nucleus periventricularis hypothalami, the nucleus paraventricularis hypothalami dorsalis, the area hypothalamica posterior, the ventral part of the nucleus coeruleus, the nucleus coeruleus pars alpha, the lateral part of the nucleus reticularis pontis, and several nuclei of the ventrolateral medulla. Few or no cells within the parabrachial area, the region of the Kölliker-Fuse nucleus or the area adjacent to the superior olivary complex (the location of the A5 group of rats) provided TH-IR projections to the spinal cord. Our results suggest that catecholaminergic projections to the spinal cord of the marsupial opossum are similar in termination and origin to those described for rats and other placental mammals, but differences do exist.

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PubMed1986

Cell bodies of origin of serotonin-immunoreactive afferents to the inferior olivary complex of the rat.

Previous studies have used immunohistochemistry to localize serotonin to distinct olivary nuclei in several mammalian species. However, the location of the cell bodies of origin for the serotoninergic projection to the inferior olive in any of these species was unknown. In the present study, a paradigm which combines transport of horseradish peroxidase (HRP) and serotonin immunohistochemistry (PAP) was used to identify the cell bodies of origin of this afferent system to the inferior olivary complex of the rat. Cells which contain both retrogradely transported HRP and brown cytoplasmic staining indicating that they are serotoninergic cells that project to the inferior olivary complex are found exclusively in an area dorsal to the rostrolateral dorsal accessory olive within the nucleus reticularis paragigantocellularis. Neurons within this nucleus were also found to be a source of serotoninergic afferents to the cerebellum and spinal cord of the rat. This raises the possibility that individual serotonin-immunoreactive neurons within this nucleus may project to all 3 areas. Future studies will be designed to address this possibility. No double-labeled cells were observed within any of the raphe nuclei.

Afferent Pathways↗

PubMed1986

Presynaptic elements formed on polylysine-coated beads contain synaptic vesicle antigens.

Cell cultures of the rat cerebellum were immunostained with antibodies to synaptic vesicle antigens, Synapsin I and SV48. Light microscopic immunocytochemistry showed that the initial appearance of demonstrable SV48 and Synapsin I immunoreactivity occurred at different times. Synapsin I immunostaining, unlike SV48 immunostaining, was first seen at 3 days in vitro as occasional punctate immunofluorescence in neurites, while SV48 immunostaining was first seen at 5 days in vitro. Both SV48 and Synapsin I punctate immunostaining became frequent at 7 days in vitro. Double labelling experiments showed coexistence of the above proteins in punctate swellings and growth cones. Using the electron microscope, either SV48 or Synapsin I immunostaining was demonstrated within presynaptic elements in the neuropil. When cultures were incubated with polylysine-coated beads, both types of immunostaining were found in the vesicle containing presynaptic elements formed on the bead surface. It is concluded that Synapsin I and SV48 are co-localized in the same populations of presynaptic elements, co-localized in some growth cones and found in presynaptic elements on beads.

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PubMed1986

Anatomical evidence for enkephalin immunoreactive climbing fibres in the cerebellar cortex of the opossum.

Enkephalin immunoreactivity is present in the cerebellum of the adult opossum within axonal arbors that resemble mature climbing fibres. In the developing cerebellum, enkephalinergic axons form pericellular nests around the perikarya of Purkinje cells in a manner which resembles developing climbing fibres seen in Golgi impregnations. Serial electron micrographs of adult climbing fibres reveal elongate enkephalin immunoreactive profiles that contain synaptic vesicles and make contact with the thorns and shafts of Purkinje cell dendrites. These results suggest that a peptide, enkephalin or an enkephalin-like substance may mediate synaptic interactions between certain populations of climbing fibres and Purkinje cells in the cerebellum of the opossum. Enkephalin immunoreactive axonal arbors, present in the molecular layer, are localized in restricted areas of vermal lobules II-VIII and X. The intermediate cortex and hemispheres are devoid of enkephalinergic climbing fibres except in restricted areas of the paramedian lobule, paraflocculus and the flocculus. In an attempt to establish the origin of enkephalin axons in the cerebellum, a double labelling technique that combines retrograde labelling of cells with horseradish peroxidase and enkephalin immunohistochemistry has been employed. Enkephalin immunoreactive neurons within specific portions of the medial accessory olive are retrogradely labelled in this paradigm. The presence of enkephalin immunoreactivity in selected climbing fibres provides evidence for chemical heterogeneity within one of the major afferent systems to the cerebellum previously thought to be uniform in its transmitter content.

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PubMed1986

Mapping of the normal distribution of substance P-like immunoreactivity in the spinal trigeminal nucleus of the cat.

Although a recent preliminary report indicated a pattern of substance P-like immunoreactivity within the spinal trigeminal nucleus that is similar to the projection sites for dental afferent fibers, details of this substance P distribution are lacking. Our purpose was to describe in cats the complete normal pattern of this immunoreactivity within each of the spinal trigeminal subnuclei. Special emphasis was given to the distribution of substance P-like immunoreactive axons and terminals located in the rostral subnucleus caudalis and the periobex region of subnucleus interpolaris, as these are regions shown to receive dental afferent fibers. Careful mapping in normal cats showed, within the resolution of the light microscope, a consistent pattern of distribution that included only a portion of the previously identified dental relay sites, but was somewhat broader in certain levels and more restricted in others. The results are compared with those provided by others from regions such as the dorsal horn and subnucleus caudalis of the spinal trigeminal nucleus. The findings also provide an anatomical basis for a recent physiologic report on specific cell types associated with dental nociceptive afferent fibers. This study also provides a baseline control for future investigations of possible changes in substance P-like immunoreactivity that follows various peripheral, including dental and central, lesions.

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PubMed1985

Enhanced survival of apparent presynaptic elements on polylysine-coated beads by inhibition of non-neuronal cell proliferation.

Increased survival of presynaptic-like neuronal profiles was found in cell cultures of rat cerebellum when the non-neuronal cell numbers were reduced with an antimitotic drug. In both treated and untreated cell cultures, neurites grew onto the polylysine-coated surface of sepharose beads and formed a swelling. The neuronal swelling contained an accumulation of synaptic vesicles and a membrane density at the site of contact with the bead and was called an apparent presynaptic element. The apparent presynaptic elements in untreated cultures increased in number from the time the beads were added to the culture to 7 days incubation and then showed a decrease to one half the 7-day value at 14 days incubation. A 75% reduction in cell division of non-neuronal cells was seen in cultures exposed to a 5 X 10(-6)M cytosine arabinoside (Ara-C) for 2 days. Adding polylysine-coated beads to cultures treated with Ara-C showed at 14 days incubation a 7-fold increase in the number of apparent presynaptic elements as compared to untreated cultures. Additional experiments examined the numbers of neurites on the beads and found only small differences between treated and untreated cultures. A decrease, however, was shown in the number of glial fibrillary acidic protein staining astrocytes on the surface of the beads in treated cultures. The reduction of astrocytes by Ara-C appeared to enhance the survival of apparent presynaptic elements but did not enhance the growth of neurites. These results suggest that proliferating non-neuronal cells at a site of injury in the central nervous system may inhibit the formation of synaptic contacts and the growth of neurites through the site of injury.

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PubMed1985

Localization of serotonin immunoreactivity in the opossum cerebellum.

We have used the indirect antibody peroxidase-antiperoxidase technique to analyze the course of serotonin (5-hydroxytryptamine; 5HT) fibers to the deep cerebellar nuclei; the distribution of serotonin within the nuclei; the continued course of 5HT fibers to the cerebellar cortex; and the lobular and laminar distribution of this indoleamine in the cerebellar cortex. Only rarely are fibers found in either the restiform body or the brachium pontis. However, a distinct bundle of serotoninergic axons is present in the medial aspect of the brachium conjunctivum. Axons arise from this bundle and course dorsally into the neuropil of the deep cerebellar nuclei. The densest immunostaining is present in posterior and ventral regions of all four cerebellar nuclei. Within the nuclei large (24% of total) and small (76% of total) varicosities are present. The average distance between varicosities on individual axons is 3.85 micron (S.D. = 1.2). The innervation of the cerebellar cortex is derived primarily from fibers that course through the deep nuclei. At levels caudal to the deep nuclei a single midsagittal band courses into lobules VIII and IX. In the cerebellar cortex, serotoninergic axons and varicosities are present in all lobules; however, the fiber density is not uniform. The densest distribution is present in vermal lobule VIII and the dorsal folia of lobule IX. Within the granule cell layer of lobules VIII and IX, immunoreactive elements form a midsagittal band, and to a lesser degree, two parasagittal bands. Beaded serotoninergic fibers course through the deep and middle portion of the granule cell layer and give rise to a plexus at the border between the Purkinje cell and granule cell layers. Within this plexus axons extend long distances in the transverse and sagittal planes. Long beaded axons oriented in the transverse plane of the folia are also present in the deep molecular layer. A few radial serotoninergic fibers ascend to the pial surface and give rise to very short tangential branches. In all three cortical layers, both large (19% of total) and small (81% of total) varicosities are present. The average distance between varicosities on individual fibers is 5.3 micron (S.D. = 2.2).(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1985

The distribution and origin of serotonin immunoreactivity in the rat cerebellum.

The distribution of serotonin immunoreactivity in the rat cerebellum was studied using the indirect antibody peroxidase-antiperoxidase (PAP) technique of Sternberger. Furthermore, the origin of these chemically defined cerebellar afferents was studied using a procedure which combines the retrograde transport of horseradish peroxidase (HRP) with the PAP technique. Serotoninergic fibers and varicosities distribute throughout the cerebellar cortex. However, within the cortex there are density variations in the distribution of this indoleamine to the granule cell and molecular layers as well as differences in the spatial orientation of labeled elements, especially in the latter lamina. Serotonin-positive fibers are also present in the Purkinje cell layer. Some of the fibers pass from this layer into the overlying molecular layer while others form a plexus around the somata of Purkinje cells. Subsequent to injections of HRP into the vermis and immediately adjacent portions of the cerebellar cortex, several reticular and raphe nuclei (n.) were found to project to the cerebellum including the paramedian reticular nucleus, n. raphe pallidus, n. raphe obscurus, n. raphe magnus, n. reticularis gigantocellularis, n. reticularis paragigantocellularis, n. pontis oralis, n. reticularis tegmenti pontis and n. centralis superioris. Double-labeling experiments, however, reveal that the neurons giving rise to serotoninergic afferents to the cerebellum are located almost exclusively in the n. reticularis gigantocellularis, the n. reticularis paragigantocellularis and the n. pontis oralis. In conclusion, the findings of the present study further support the view that the cerebellar cortex is not uniform in its histological structure. Although serotoninergic elements are distributed throughout the cerebellar cortex, there are lobular variations in the laminar distribution of this indoleamine. These data suggest that serotonin may be exerting its physiological effect on different populations of cortical neurons in different lobules. Thus this putative neurotransmitter may play different roles in the circuitry of the cerebellum in disparate regions of the cortex. Further, the data obtained in the double-label experiments demonstrate a fairly restricted origin for serotoninergic afferents in the medullary and pontine reticular formation. Moreover, the majority are not located in the raphe nuclei.

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PubMed1985

An immunohistochemical study of serotonin development in the opossum cerebellum.

In the present study we have used the indirect antibody peroxidase anti-peroxidase technique to analyze the development of serotonin in the cerebellum of pouch young opossums ranging in age from birth (postnatal day (PD) 1) - to PD 47. The pathways by which serotoninergic axons enter the cerebellum appear to change during development. Between PD 1 and PD 11 varicose serotoninergic fibers course though the continuity between the tectum and the dorsal medial aspect of the cerebellar plate and distribute primarily to the intermediate zone. By PD 11 serotoninergic fibers enter the cerebellum via a connecting band between the cerebellum and the dorsal lateral aspect of the rostral medulla. Fibers entering the cerebellum via this later route course around the lateral recess of the fourth ventricle and initially distribute to ventral and lateral areas of the cerebellum. At later developmental ages (PD 14-PD 47) serotoninergic fibers are present in: 1) the cellular zone of migration between the Purkinje cell layer and deep nuclei; 2) the Purkinje cell layer; 3) the internal granule cell layer; and 4) the deep cerebellar nuclei. The external granule cell and the molecular layers rarely contain serotoninergic fibers. The present study has shown that serotonin is present in the cerebellar anlage on PD 1 (within 13 days of conception). This is prior to the arrival of other major afferent systems (King et al. 1982; Bishop et al. 1983; Martin et al. 1983; Morgan et al. 1983). Further, serotoninergic axons reach the cerebellum via different routes at different stages of development. The presence of serotonin in the intermediate zone early in development supports the hypothesis that it may influence neuronal migration and differentiation (Lauder and Krebs 1976). Axons containing serotonin and arriving later in development may function in synaptic transmission, a role proposed for this indoleamine in the adult (Strahlendorf et al. 1979).

Animals↗

PubMed1985

Serotonergic innervation of the forebrain in the North American opossum.

The forebrain distribution of axons showing serotonin-like immunoreactivity was studied in the North American opossum. Serotonergic innervation of the hypothalamus was extensive, particularly within the ventromedial nucleus, the periventricular nucleus and the rostral supraoptic nucleus. Serotonergic axons were also present within the fields of Forel and zona incerta, but they tended to avoid parts of the subthalamic nucleus. In the thalamus serotonergic innervation was dense within the midline nuclei (e.g. the central, intermediate dorsal and rhomboid nuclei) and the ventral lateral geniculate nucleus, but relatively sparse in some of the nuclei more readily associated with specific functions (e.g. the ventrobasal nucleus). Serotonergic axons innervate most areas of the rostral and dorsal forebrain. Areas containing the heaviest innervation included the interstitial nucleus of the stria terminalis and the lateral septal nucleus. Serotonergic innervation of the neocortex varied markedly from region to region and within different layers of the same regions. The retrograde transport of True Blue combined with immunofluorescence for localization of serotonin revealed that serotonergic axons within the forebrain arise mainly within the dorsal raphe and superior central nuclei, but that some originate within the midbrain and pontine reticular formation and the locus coeruleus, pars alpha. Neurons of the raphe magnus and obscurus also innervate the forebrain, but few of them are serotonergic. The use of horseradish peroxidase as a retrograde marker provided evidence that raphe projections to the forebrain are topographically organized. Our results suggest that serotonergic projections to the forebrain, like those to the spinal cord, are connectionally heterogeneous.

Animals↗