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E C Azmitia

Publications and source records attributed to E C Azmitia.

At least 91 records · Page 5Linked to original sources
PubMed1987

Postnatal changes in serotonin receptors following prenatal alterations in serotonin levels: further evidence for functional fetal serotonin receptors.

Recent work by ourselves and others has indicated that serotonin (5-HT) acts as a regulator of neuronal growth in fetal tissue, probably through an action on the high affinity 5-HT receptors known to be present. In order for our hypothesis to be correct, these receptors must be shown to be functional in fetal tissue. Furthermore, since 5-HT has a dual role in neuronal development, these receptors must be functional both in the region of the serotonergic cell body (brainstem) and in projection areas (forebrain). We have tested the functional status of fetal 5-HT receptors by testing their ability to adapt to changes in the level of 5-HT. Pregnant rats were treated with saline, p-chlorophenylalanine (a 5-HT depletor) or 5-methoxytryptamine (a 5-HT agonist) and the characteristics of the high affinity 5-HT receptors in the rat pups determined using a binding assay with [3H]5-HT. Our results show that both forebrain and brainstem receptors respond to alterations in transmitter level in a manner similar to adult brain. Thus, fetal 5-HT receptors are functional and capable of playing a role in neuronal development.

5-Methoxytryptamine↗
PubMed1987

Target cell stimulation of dissociated serotonergic neurons in culture.

Dissociated mesencephalic raphe cells from fetal rats (14-18 days) were grown in culture in 96 well Linbro plates. The maturation of serotonergic cells was qualitatively studied using immunocytochemistry with a serotonin antibody and quantitatively by measuring the retention of radioactivity following incubation in the presence of a low concentration of [3H]5-hydroxytryptamine (6 X 10(-8) M). The 5-hydroxytryptamine immunoreactive neurons showed specific staining in the perikaryon, nucleus, dendrites, axons and growth cones. These neurons formed varicose fibers and growth cones after 18 h in culture and survived for up to 21 days in culture. Each serotonergic neuron concentrated approximately 1 fmol of serotonin after 20 min of incubation. Maturation of mesencephalic serotonergic neurons was increased in co-cultures of both normal (hippocampus, cerebral cortex, olfactory bulb and striatum) and abnormal (spinal cord) target neurons. The best stimulation was produced by dissociated hippocampal neurons (14-18 days of gestation) on mesencephalic raphe cells (14 days of gestation) after 4 days in culture. This stimulation was seen in culture conditions which favored neuronal but not glial survival. Our results obtained using cultures of dissociated serotonergic cells are consistent with an expansive network pattern developed by this chemical transmitter system in the adult brain.

Animals↗
PubMed1987

Stimulation of serotonergic neuronal maturation after fetal mesencephalic raphe transplantation into the 5,7-DHT-lesioned hippocampus of the adult rat.

Neurotoxin lesioning of 5-HT fibers selectively induced the homotypic collateral sprouting of spared 5-HT fibers in the hippocampus. We have used this model to investigate the possibility that the neurotoxin-primed hippocampus will enhance the development of transplanted fetal serotonergic neurons in the brain. The neurotoxin 5,7-DHT, when microinjected into the FF, produced a specific and partial depletion of 5-HT in the hippocampus of adult rats. The ability of the 5,7-DHT-primed hippocampus to selectively support the neurochemical maturation of fetal serotonergic cells was tested by assaying the transplanted fetal raphe or LC 1 month after neuronal transplantation. The neurochemical maturation of fetal 5-HT and NE neurons was dramatically different when they were transplanted in the 5,7-DHT-FF-lesioned hippocampus as compared to the normal hippocampus. The transplanted 5-HT neurons had 480% more SHAU of [3H]5-HT and had a 250% greater content of 5-HT in the partially denervated hippocampus than in the normal hippocampus after 1 month. Furthermore, extracts obtained from lesioned hippocampus enhanced the 5-HT content of 5-HT neurons transplanted in the normal hippocampus, to a level similar to that seen in neurons transplanted in the lesioned hippocampus. In contrast, the implanted NE neurons of fetal LC had a lower NE level in the 5-HT partially denervated hippocampus than in normal hippocampus after 1 month in the host site. The growth of the NE transplants was not facilitated by the vacant postsynaptic space produced by the 5,7-DHT lesion. These results suggest that the 5-HT denervation triggered a trophic signal selectively enhancing the development of the 5-HT neurons but not the NE neurons. Our results are consistent with previous studies showing homotypic collateral sprouting in 5,7-DHT-primed hippocampus.

5,7-Dihydroxytryptamine↗
PubMed1986

Autoregulation of fetal serotonergic neuronal development: role of high affinity serotonin receptors.

A microculture technique was used to study the factors regulating the development of fetal rat serotonergic neurons. Mesencephalic raphe cells from E14 rats co-cultured with hippocampal cells from E18 were grown for up to 4 days in the presence of various agents known to alter serotonergic function in the mature brain. Pargyline (a non-specific monoamine oxidase inhibitor) alone and with serotonin (10(-8) to 10(-6) M) both inhibited growth of serotonergic neurons as assessed by uptake of [3H]serotonin. 5-methoxytryptamine (5-MT), a serotonin agonist with selectivity for serotonin autoreceptors, inhibited growth at low concentrations, but this inhibition was overcome at higher concentrations. Using immunocytochemistry with a primary anti-serotonin antibody, 5-MT was observed to produce stunted processes, increase autoinnervation and lead to neuronal death. A model is proposed whereby high affinity serotonin receptors in fetal brainstem tissue and in fetal forebrain tissue regulate direction and extent of growth. We have confirmed the presence of these receptors using a direct binding assay.

5-Methoxytryptamine↗
PubMed1986

Induced homotypic sprouting of serotonergic fibers in hippocampus. II. An immunocytochemistry study.

The dorsal hippocampus of the rat normally receives its 5-HT innervation from two homologous groups of cells in the median raphe nucleus via the cingulum bundle-induseum griseum (CB-IG) and the fornix-fimbria (FF) (J. Comp. Neurol., 179 (1978) 641-667 and Brain Res. Bull., 10 (1983) 445-451). 5-HT immunoreactive (IR) fibers are distributed in a laminar pattern in the hippocampus. These fibers have large varicosities and are densely distributed in the infragranular layer of dentate gyrus, in the stratum lacunosum-moleculare of the cornu Ammonis and in the area fasciola cinerea (FC). The present study provides evidence that the density of the 5-HT-IR fibers in the dorsal hippocampus is greatly decreased but maintained a similar laminar pattern 3 days after lesioning by microinjection of 4 micrograms of 5,7-dihydroxytryptamine (5,7-DHT) into the CB-IG. An apparently normal density and distribution pattern of the 5-HT-IR fiber is seen by 42 days postlesion. The FC in the hippocampus is among the first regions reinnervated by 5-HT-IR fibers with very dense and large varicosities. The restitution of 5-HT-IR fibers in the dorsal hippocampus after the 5,7-DHT lesion in the CB-IG is accompanied by a marked increase in the number and intensity of 5-HT-IR fibers in the FF. No evidence of a regeneration of 5-HT-IR fibers is seen distal to the injection site in the CB-IG. These observations provide direct evidence for homotypic collateral sprouting in the CNS induced by removal of a single fiber type.

5,7-Dihydroxytryptamine↗
PubMed1986

Fetal raphe neurons grafted into the hippocampus develop normal adult physiological properties.

Embryonic midbrain raphe was grafted into serotonin-deficient adult rat hippocampus. Serotonin-containing neurons in the graft survive for at least 6 months after grafting. Grafted neurons develop physiological properties, not present on the day of grafting, identical to those of normal adult serotonin-containing neurons. These include (a) high input resistance and slow membrane time constant, (b) lack of inward rectification in response to hyperpolarizing current pulses and (c) a potent, 4-aminopyridine-sensitive transient outward rectification. The grafted neurons innervate the host tissue with axons that have a slow conduction velocity and refractoriness. It is suggested that grafted CNS neurons may possess normal physiological properties.

Animals↗
PubMed1986

[3H]5-hydroxytryptamine binding to brain astroglial cells: differences between intact and homogenized preparations and mature and immature cultures.

[3H]5-hydroxytryptamine ([3H]serotonin) binds with high affinity (KD 2-12 nM) to a finite number of sites on brain astroglial cells. The number of binding sites in the C6 glioma line is decreased significantly (Bmax = 315 versus 30 fmol/mg) by homogenization. In intact primary cultures, derived from newborn rat brain, the number of binding sites is far greater in cultures of immature astrocytes than in cultures treated with dibutyryl cyclic AMP (Bmax = 1,520 versus 580 fmol/mg). A role for these receptors in development is suggested.

Animals↗
PubMed1986

The primate serotonergic system: a review of human and animal studies and a report on Macaca fascicularis.

This chapter has reviewed biochemical and morphological studies of the human and monkey serotonergic system. In addition, the serotonin-producing neurons of M fascicularis were analyzed, using immunocytochemistry, radioautography, and measurements of synaptosomal serotonin reuptake and supernatant tryptophan hydroxylase activity. The major sections of the chapter covered cell bodies, pathways, subcortical distribution, and cortical distribution, and a gross brain dissection guide of M fascicularis is included. An atlas of the 5-HT-IR cell bodies was presented in Figures 7 to 33. Rostral and caudal groups of nuclei were discussed. The rostral group consists principally of the nuclei raphe dorsalis (B7 and B6), centralis superior (B8, B5, and part of B7), and prosupralemniscus (B9). These groups ascend mainly in tracts lying outside the medial forebrain bundle (MFB). In M fascicularis, 25% of the fibers within the MFB are myelinated. The caudal 5-HT-IR nuclei consist principally of the nuclei in a dorsal cluster (raphe obscurus, B2) and in a ventral cluster (pallidus, B1, and magnus B3). The dorsal 5-HT-IR cells in raphe obscurus are associated with the MLF, and cells extend into cervical spinal cord (lamina IX and X) with the descending MLF and the TTS. Fibers from the raphe obscurus innervate the motoneurons in both the cranial nuclei (X, XII) and the ventral horn. The ventral 5-HT-IR cells lie mainly medial to the medial leminiscal fibers. A large number of these cells extend laterally into paragigantocellularis lateralis and here extend caudally lying below the lateral reticular nuclei. Cells from this group are seen dorsally joining the internal arcuate fibers. The raphe magnus of the ventral cluster projects to the dorsal horn and is believed to mediate the serotonin-induced analgesia. The descending fibers from both of these clusters are occasionally myelinated. Also, in our tryptophan- and pargyline-pretreated monkeys, small 5 HT-IR cells were visible in the area postrema. Human and monkey biochemical data (detailed summary in Tables 1-6) provide evidence for the presence of serotonin fibers in all cortical and subcortical regions. In subcortical regions, the midbrain, medulla, amygdala, and substantia nigra have the highest, whereas the cerebellum, spinal cord, and ventral pons have the lowest amount of serotonin and its metabolite, 5-HIAA. In the basal ganglion, the globus pallidus has the highest rate of 5-HT synthesis. The temporal lobe receives the most serotonin of the major cortical lobes.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1985

Characterization of specific binding sites labeled by [3H]LSD in coronal sections of paraformaldehyde-fixed rat brain.

Specific, high-affinity binding of [3H]lysergic acid diethylamide (LSD) in coronal sections of paraformaldehyde-fixed rat brain is described. Intracardiac perfusion of paraformaldehyde selectively altered 40% of the total binding sites normally labeled by [3H]LSD in unfixed sections. Competition by unlabeled LSD and serotonin (5-HT) was not altered by the fixation procedure. Competition by spiperone, however, revealed that the fixation procedure preferentially altered sites for which spiperone has high affinity. This technique should facilitate the combination of neuroanatomical techniques such as radioautography and immunocytochemistry.

Animals↗
PubMed1985

The effect of adrenalectomy and corticosterone on homotypic collateral sprouting of serotonergic fibers in hippocampus.

Lesioning of serotonergic (5-HT) fibers using 5,7-dihydroxytryptamine (5,7-DHT) in one of the two median raphe-hippocampal pathways induced homotypic sprouting from the other. We have utilized this model with the horseradish peroxidase (HRP) tracing technique to test the effects of an adrenal corticosteroid-corticosterone on homotypic sprouting in female adult rats. Removal of the adrenal glands does not interfere with the 5,7-DHT destruction of 5-HT fibers observed at 3 days. However, the animals without circulating adrenal steroids do not show the increase of the HRP-labeled cells normally seen 21 days after the 5,7-DHT lesions. Furthermore, s.c. implantation of corticosterone pellets was able to completely restore homotypic sprouting of 5-HT fibers in the hippocampus.

5,7-Dihydroxytryptamine↗
PubMed1984

Facilitated sexual behavior reversed and serotonin restored by raphe nuclei transplanted into denervated hypothalamus.

Fetal raphe cells transplanted into the hypothalamus reversed facilitation of feminine sexual behavior in rats with brain lesions induced by 5,7-dihydroxytryptamine. Immunocytochemical and chemical analyses of serotonin indicate that reinnervation of the ventromedial nucleus of the hypothalamus by the transplants is associated with behavioral recovery. The findings suggest that transplanted fetal tissue can exert functional regulation over an innate, complex, hormone-dependent behavior in adult rats.

5,7-Dihydroxytryptamine↗
PubMed1984

Induced homotypic collateral sprouting of serotonergic fibers in the hippocampus of rat.

The organization of the raphe cells efferent to the dorsal hippocampus (DHipp) has been shown to consist of two homologous groups of cells in the median raphe nucleus (MRN). Their axons project by way of the cingulum bundle (CB) and the fornix-fimbria (FF)58. A group of neurons located in the interfascicular part of the dorsal raphe nucleus (IFN) was found to use the CB route exclusively. Quantitation of the HRP-labeled cells in the MRN neurons projecting to the DHipp decreased by 55% and 92% 3 days following CB and CB-FF 5,7-DHT injections respectively. There was a significant increase in HRP-labeled neurons in the MRN at 21 and 42 days compared to 3 days after CB injection (a 2% decrease at 21 days and 38% increase at 42 days compared to sham injected). No change in the number of labeled MRN cells was seen at these long-term time points after combined CB-FF 5,7-DHT microinjections. The labeled cells in the MRN increased in size in the long survival group of CB lesioned animals. The labeled cells localized in the IFN which were lost after CB 5,7-DHT injections did not reappear after long-term survival. These results indicate that CB 5-HT fibers do not regenerate into the DHipp, but FF 5-HT fibers increase their terminal territory by collateral sprouting in response to homotypic denervation.

5,7-Dihydroxytryptamine↗
PubMed1984

An immunocytochemical study of the serotonergic innervation of the thalamus of the rat.

The serotonergic innervation of the rat thalamus was studied with an indirect immunocytochemical technique using an antiserum raised against a serotonin-hemocyanin conjugate in animals pretreated with L-tryptophan and a monoamine oxidase (MAO) inhibitor. When pretreatment was not used there was a decrease in the number of immunoreactive fibers observed in the thalamic region. Innervation was greatest in nucleus ventralis corporis geniculati lateralis, and in the following midline nuclei: nucleus periventricularis, nucleus rhomboideus, and nucleus reuniens. Also well labeled were nucleus anterior ventralis, the intralaminar nuclei, and nucleus lateralis dorsalis. Moderate innervation was found in nucleus reticularis, nucleus anterior dorsalis, nucleus ventralis medialis, nucleus lateralis pars posterior, the posterior complex, and in nucleus dorsalis corporis geniculati lateralis. Very few serotonergic fibers were observed in nucleus paratenialis, nucleus gelatinosus, nucleus anterior medialis, nucleus medialis dorsalis, nucleus ventralis, nucleus ventralis pars dorsomedialis, or in nucleus corporis geniculati medialis. Serotonin immunoreactivity was also noted in a number of fiber bundles in the thalamic region. These include the fasciculus retroflexus, the fasciculus mamillothalamicus, the stria medullaris, and the stria terminalis. These results differ from those of previous descriptions of the serotonergic innervation of thalamic nuclei most notably in the midline nuclei and in the posterior complex. In this study the midline nuclei, nucleus rhomboideus, and nucleus reuniens were more densely innervated than had been described, and in the posterior complex a moderate, rather than sparse, innervation was observed. The more densely innervated nuclei of the anterior and lateral nuclear groups, nucleus lateralis dorsalis and nucleus anterior ventralis, also contained a greater number of labeled fibers than had been indicated.

Animals↗
PubMed1984

5-HT-Immunoreactive fibers in the trigeminal nuclear complex of the rat.

The distribution of serotonin immunoreactive (5-HT-IR) fibers in the trigeminal nuclear complex of the rat was mapped. In the sensory nuclei, innervation appeared to be dense in areas primarily related to nociceptive afferent activity, and sparse in areas primarily related to nonnociceptive afferent activity. Specifically, the marginal and gelatinosa layers of the spinal subnucleus caudalis contained many 5-HT-IR fibers while few labeled fibers were seen in the magnocellular portion of subnucleus caudalis or in the principal sensory nucleus. The spinal subnuclei oralis and interpolaris were sparsely innervated except for a few areas which contained more 5-HT-IR fibers. The motor nucleus contained as many immunoreactive fibers as the subnucleus caudalis, although fibers in the motor nucleus were thicker and varicosities more irregularly spaced than in caudalis.

Animals↗