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Fate of septohippocampal neurons following intracerebroventricular injections of colchicine.

Injection of colchicine into the lateral ventricles (ICV) of rats results in a selective loss of neurons immunoreactive for choline acetyltransferase (ChAT) in the medial septum (MS) and a concomitant loss of acetylcholinesterase (AChE) positive fibers in the hippocampus. To determine if this loss of cholinergic cells is due to neuronal death, septohippocampal neurons were retrogradely labeled with fluoro-gold (FG) 1 week prior to the injection of colchicine. Numbers and sizes of FG-labeled and ChAT-immunoreactive neurons were assessed 3, 6, and 10 weeks after ICV colchicine. In line with previous observations, numbers of ChAT-immunoreactive cells were reduced to fewer than 50% of control in the MS and to fewer than 60% of control in the vertical limb of the diagonal band (vDB). Three weeks after ICV colchicine, numbers of FG-labeled neurons were reduced to 48% in the MS and 24% in the vDB. By 6 weeks, the number in the MS decreased further to 31% of control, whereas the number remained at 24% in the vDB. Ten weeks after colchicine, the numbers of retrogradely labeled cells in both the MS and vDB had decreased to 11% of control. The cells which remained were not reduced in cross-sectional area or in diameter. These data suggest that the selective loss of cholinergic neurons in the MS which occurs following ICV colchicine is due to neuronal death and not just loss of ChAT expression.

Animals↗

Ventral horn motoneurons 10, 20 and 52 weeks after T-9 spinal cord transection.

To determine if transneuronal degeneration occurs in ventral horn motoneurons caudal to a spinal cord transection, we completely transected the spinal cord at T-9 in seven-week-old female rats. Ten, 20 or 52 weeks later, the motoneurons of the right sciatic nerve of transected and control rats were retrogradely labeled with Fluoro-Gold. There were no differences between control and transected rats in numbers or rostrocaudal distribution of labeled motoneurons at either 10, 20 or 52 weeks. At 20 weeks, there was no significant difference between control and transected rats in mean cross-sectional area of labeled neurons. We conclude that transneuronal degeneration did not occur.

Animals↗

Widespread dopaminergic projections of the subparafascicular thalamic nucleus in the rat.

The subparafascicular thalamic nucleus (Spf) contains a substantial number of dopaminergic neurons. The present study was designed to investigate in the rat whether or not Spf neurons projecting to a variety of central nervous system structures are dopaminergic. The following eight structures were tested for projection sites of Spf dopamine neurons: the neocortex, olfactory tubercle, nucleus accumbens, striatum, globus pallidus, amygdala, inferior olive, and spinal cord. By using a combination of fluorescent retrograde axonal tracing and immunofluorescence histochemistry for tyrosine hydroxylase, it has been revealed that the Spf provides a dopaminergic innervation, in varying degree, to each of these structures: the neocortex and spinal cord were the largest targets for dopaminergic projections from the Spf. The Spf was also found to contain significant numbers of dopaminergic neurons projecting to the olfactory tubercle and amygdala. In contrast, dopaminergic projections of Spf neurons to the nucleus accumbens, striatum, globus pallidus, and inferior olive were only minor. Furthermore, a series of fluorescent retrograde double-labeling experiments have indicated that individual Spf neurons are poorly collateralized to more than one of the eight terminal fields examined; the Spf neurons descending to the spinal cord relatively more frequently send axon collaterals ascending to the telencephalic structures, including the neocortex, olfactory tubercle, nucleus accumbens, striatum, and amygdala. The present results suggest that the Spf constitutes a major origin of widespread dopaminergic projections arising from the thalamus.

Animals↗

Evidence for connections between a discrete hypothalamic dorsochiasmatic area and the supraoptic and paraventricular nuclei.

In order to check the existence of direct or indirect connections between the hypothalamic supraoptic (SON) and paraventricular (PVN) nuclei, four retrograde traces were iontophoretically injected into these nuclei. The small injection sites were restricted to parts of the SON and PVN, enabling the identification of afferent neurons localized in their immediate vicinity. The tracer injections into any of these hypothalamic nuclei resulted in conspicuous labeling of cells gathered dorsally to the optic chiasma and the optic tract. This neuronal population was tentatively called dorsochiasmatic area. Double retrograde tracers injections into the ipsilateral SON and PVN gave evidence for some neurons containing both tracers in this dorsochiasmatic area. Otherwise, labeled parvocellular neurons were occasionally found in one PVN, after injecting retrograde tracer into either the ipsilateral SON or the contralateral PVN. As few connections exist between the four magnocellular nuclei, the dorsochiasmatic area connected with both the ipsilateral SON and PVN could play an important role in regulating the oxytocin and/or vasopressin systems.

Amidines↗

Catecholaminergic projections from the solitary tract nucleus to the perifornical hypothalamus.

The source of adrenergic and other catecholaminergic fibers innervating the perifornical lateral hypothalamus was localized in the medulla after combination of Fluoro-Gold retrograde tracing and immunohistochemistry for either tyrosine-hydroxylase or phenylethanolamine-N-methyltransferase. Following perifornical injections, Fluoro-Gold-labeled neurons were observed mainly in regions including the noradrenergic and adrenergic cell groups. In the caudal solitary tract nucleus, two kinds of doubly labeled neurons were found: a) numerous noradrenergic neurons in the A2 group at the level of, or caudal to the area postrema; b) some adrenergic neurons in the C2 group at a level immediately rostral to the area postrema. These catecholaminergic neurons connecting the caudal solitary tract nucleus to the perifornical hypothalamus might convey feeding relevant information such as glycemic level or satiety signals.

Animals↗

Evidence for reciprocal connections between the dorsochiasmatic area and the hypothalamo neurohypophyseal system and some related extrahypothalamic structures.

In the preceding article, a dorsochiasmatic area (DCh) was described that projects to both paraventricular (PVN) and supraoptic (SON) nuclei. The main afferents of the DCh, revealed by local injections of retrograde tracers, are the hypothalamic PVN and SON, lateral septal nuclei (LSV and SHy), bed nuclei of the stria terminalis (BST), anteroventral third ventricle region, particularly the median preoptic nucleus (MnPO), the subfornical organ, medial preoptic areas, arcuate hypothalamic nucleus, ventromedial hypothalamic nuclei, paraventricular thalamic nucleus, and, more caudally, several structures of the posterior hypothalamus and mesencephalon. The relations between DCh and BST, LSV, SHy, or MnPO appeared reciprocal. In view of their reciprocal relationships with the hypothalamo-neurohypophyseal system and some of their related extrahypothalamic structures, the DCh might be involved in the regulation of the vasopressin (AVP) and/or oxytocin (OT) systems, or in reproductive behavior.

Afferent Pathways↗

The parabrachio-subfornical organ projection in the rat.

Previous physiological studies have shown that both the parabrachial nucleus and the subfornical organ are involved in drinking behavior and cardiovascular controls. The purpose of the present work was to study the direct connections between these two structures by using anterograde and retrograde transport methods. A mixture of wheat germ agglutinin conjugated with horseradish peroxidase and free horseradish peroxidase or Fluorogold was injected into either the parabrachial nucleius (PBN) or the subfornical organ (SFO). The results indicated that the parabrachial nucleus sends a substantial projection to the entirety of the subfornical organ, and this input appears to be distributed to both the central and peripheral regions of this structure. Neurons that give origin to this projection are mainly located in the outer layer of the lateral division of the parabrachial nucleus, including the superior, internal, dorsal, and external lateral subnuclei. These findings suggest that, besides the already known connections, there is an additional parabrachio-subfornical pathway that may be involved in the central integration of cardiovascular function and drinking behavior.

Animals↗

Retrograde axonal transport of different fluorescent tracers from the neocortex to the suprageniculate nucleus in the rat.

The retrograde fluorescent tracers in a combination of two different dyes (Fluoro gold/Nuclear yellow or Fast blue/Fluoro gold) were used for the study of the projections from the medial geniculate body to the frontal and temporal cortices in rats. There were only single-labeled cells, no double-labeled ones in the medial geniculate body (MGB). The suprageniculate nucleus (SG) was considered to be the origin of the rat direct pathway to the frontal cortex. The present results suggest that projections from the suprageniculate nucleus to the frontal cortex and the temporal cortex consist of separate neuronal groups in the rat MGB and SG. The inputs to the SG from the auditory and oculomotor system may be processed in different ways.

Amidines↗

Postnatal development of the projection from the medial superior olive to the inferior colliculus in the rat.

Normal projection development from the medial superior olive (MSO) to the inferior colliculus (IC) was examined by injecting Fluoro-Gold (FG), a retrograde tracer, into the IC unilaterally at postnatal days 0 (P0), P3, P7 and maturity. The rats were killed 1 day after FG injection. At all ages, labeled neurons in the MSO appeared on the ipsilateral side only, as in adult controls. The total number of MSO neurons counted in Nissl-stained sections was constant throughout the postnatal periods. The labeled frequency index of MSO neurons was increased stepwise (from 35% to 90%) with increasing postnatal stages (from P0 to adulthood), suggesting differential growth of early- and late-developing axons.

Age Factors↗

Anatomical plasticity in the medial superior olive following ablation of the inferior colliculus in neonatal and adult rats.

We evaluated the consequences of unilateral ablation of the inferior colliculus (IC) upon the ascending projection from the medial superior olive (MSO) to the IC. Ablation of the IC was performed in rats aged between postnatal day 1 (P1) and maturity. All the rats were given injections of Fluoro-Gold (FG) into the ipsilateral IC at birth (P0) (before the ipsilateral IC was ablated in any case) so that growth of early-developing axons to the ipsilateral IC could be examined for any labeled neurons in the ipsilateral MSO. Upon reaching adulthood, the rats received injections of Fluoro-Ruby (FR) into the contralateral (intact) IC so that aberrant crossed projections to the intact IC could be examined for any labeled neurons in the ipsilateral MSO. These rats were killed 2 days after FR injections. The number of surviving cells in the ipsilateral MSO were counted in Nissl-stained sections for quantitative analysis of retrograde degeneration. The results show that: (1) the total number of neurons was reduced to 64-34% in the ipsilateral MSO as a result of IC ablation; (2) cell reduction by retrograde degeneration followed a U-shaped curve with a maximal effect in rats operated at P7 (reduced to 34%); (3) adult ablation of the IC led to retrograde degeneration that was less severe than that in late neonatal (P7) ablation; (4) an aberrant projection from the MSO to the contralateral IC occurred in rats operated at P1 and P3 but not in rats operated at P7 or maturity. Thus, our findings suggest that growth of late-developing axons is a major factor in the plasticity of this system of projection.

Age Factors↗

Innervation of the spleen in the rat: evidence for absence of afferent innervation.

Catecholaminergic fibers in the spleen have been well characterized in the rat and this innervation is believed to be an important source of modulation of the immune system. The presence or role of afferent feedback from the spleen has not been systematically investigated. We have examined whether the spleen receives afferent innervation from sensory ganglia and also have assessed the sources of efferent innervation to the spleen in the rat. The fluorescent retrograde anatomical tracers fluoro-gold (FGo) or fast blue (FB) were injected into the spleens of adult female rats and dorsal root, sympathetic chain, nodose, and celiac-mesenteric plexus ganglia were collected. In additional animals, the spleen was either injected with the anatomical tracer wheat germ agglutinin-horseradish peroxidase (WGA-HRP) or else regular HRP was applied to the cut end of the splenic nerve. Also, we examined the effects of cutting the splenic nerve on the retrograde labeling of cell bodies in the ganglia and on the catecholamine histochemistry of the spleen. The neuroanatomical results were based primarily upon the tracer FGo and verified that the celiac-mesenteric plexus ganglia provide a major efferent input to the spleen. Furthermore, lower thoracic sympathetic chain ganglia provide an additional and substantial efferent supply to the spleen. Cutting of the splenic nerve prevented retrograde labeling of cell bodies in the celiac-mesenteric plexus ganglia and sympathetic chain ganglia of rats injected with tracers into the spleen and also eliminated catecholamine histofluorescence in the spleen. In terms of afferent labeling, the results with FGo indicated that there were no cell bodies labeled in afferent ganglia following splenic injections.(ABSTRACT TRUNCATED AT 250 WORDS)

Amidines↗

Calcitonin gene-related peptide-like immunoreactivity in spinal cord and superior cervical ganglion of the Djungarian hamster (Phodopus sungorus).

The indirect immunofluorescent method was employed to investigate the distribution of calcitonin gene-related peptide-like immunoreactivity (CGRP-LI) in the spinal cord and superior cervical ganglion of the Djungarian hamster Phodopus sungorus. In cross-sections of the spinal cord, immunoreactive fibres and terminals were found in laminae 1 and 2 in high density, in the dorsolateral (Lissauer's) tract, in ventral and lateral horns, and in the area surrounding the central canal. A few CGRP-LI perikarya were seen in the ventral but not the dorsal horn. CGRP-LI was further observed in preganglionic sympathetic neurons which were labelled by retrograde axonal transport of fluoro-gold (FG) following injection of the substance unilaterally into the superior cervical ganglion. Preganglionic sympathetic neurons (PSN) were localized ipsilateral to the injection site mainly in the intermediolateral nucleus and the lateral funiculus of the upper thoracic segments. Most PSN exhibited CGRP-LI. Immunoreactive PSN were not seen contralaterally to the site of FG application nor in animals that did not receive injections. When the preganglionic fibres were ligated 4 days before perfusion, CGRP-LI cell bodies were found in preganglionic sympathetic neurons similar to the situation seen upon FG treatment. In the superior cervical ganglia of untreated hamsters, immunoreactive fibres were seen to enter the ganglion in which they terminated at non-immunoreactive principal ganglion cells. The present study, the first in a hamster species, describes the widespread distribution of CGRP in the spinal cord of P. sungorus and supports the view that considerable interspecies differences exist in occurrence and location of this neuropeptide.

Animals↗

Parvalbumin and calbindin in the rat claustrum: an immunocytochemical study combined with retrograde tracing frontoparietal cortex.

The distribution of the calcium binding proteins parvalbumin and calbindin D-28k was examined in the claustrum of the rat by means of immunohistochemistry. The two proteins displayed a different and largely complementary pattern of distribution. Parvalbumin-immunostaining was intense in the neuropil of the dorsal claustrum and virtually absent in the neuropil of the ventral claustrum; parvalbumin-immunoreactive neuronal cell bodies were relatively numerous in the dorsal claustrum and were detected only occasionally in the ventral region. On the other hand, calbindin-immunostaining was prevalent in the ventral claustrum; very few calbindin-positive neurons were seen in the dorsal sector of the nucleus, whereas they were relatively more numerous in the ventral claustrum. The cell bodies of the majority of the claustral parvalbumin- or calbindin-immunoreactive neurons were oval or round, but immunostained polymorphous neurons were also observed. The surface of the immunopositive dendritic branches was smooth, with no evidence of spines. Fluorescent retrograde tracing was combined with immunohistofluorescence to determine whether the parvalbumin-containing claustral cells project to the frontoparietal cortex. Neurons labelled after large fluorogold injections in frontoparietal cortical fields were highly intermingled in the dorsal claustrum with parvalbumin-immunoreactive cells but the two neuronal populations were separate. These data show that parvalbumin-immunoreactive claustral neurons do not project to the frontoparietal cortex. In addition, although these cells may project to other cortical or subcortical targets, the present findings suggest that they may represent, at least in part, local circuit claustral neurons, corresponding to the aspiny intrinsic neurons described in the rat claustrum in studies based on Golgi impregnation.

Animals↗

Nitric oxide synthase in the hypothalamo-pituitary pathways.

Several histochemical and physiological studies in the literature suggest that nitric oxide (NO) is involved in the posterior pituitary regulation. This study was set out to demonstrate the distribution of the pituitary projecting nitric oxide containing hypothalamic pathways. The fluorescent retrograde tracer fluorogold (FG) was injected into the pituitary gland in order to reveal the hypothalamic nuclei projecting to the pituitary gland. Nitric oxide synthase (NOS) was subsequently visualized from the same sections by NADPH-diaphorase histochemistry. More than 70% of the FG labelled neurons in the preoptic area, paraventricular, supraoptic, retrochiasmatic, anterior commissural and circular nuclei as well as in many other small neurosecretory centers in the hypothalamus contained also NADPH-diaphorase activity (NADPH-DA). In addition, some of the neurons in the periventricular nucleus as well as occasional neurons in the lateral hypothalamus projecting to the pituitary gland contained NADPH-DA. The present results give the first systematic neuroanatomical description of the hypothalamic NO synthase containing neurons projecting into the pituitary gland. They indicate that the pituitary receives a widely distributed NO innervation, which originates mostly in the magnocellular neurosecretory hypothalamo-pituitary system. In addition, the finding that some presumably non-neurosecretory pituitary-projecting neurons contain NO as well suggests that NO might be a more widely used regulator of the posterior pituitary secretion than previously expected.

Amino Acid Oxidoreductases↗

Projection of non-cholinergic basal forebrain neurons ensheathed with perineuronal nets to rat mesocortex.

The existence of non-cholinergic (GABAergic) components in the septo-hippocampal system but also in basal forebrain projections terminating in the olfactory bulb and certain cortical areas has been documented by several authors using retrograde and anterograde tracing techniques. On the other hand, the basal forebrain also contains a high number of mainly parvalbumin-positive neurons ensheathed by a lattice-like matrix of polyanionic proteoglycans forming so-called perineuronal nets of as yet unknown function. By a combination of retrograde tracing using Fluoro-Gold injection into mesocortical areas of rats and staining of perineuronal nets by Wisteria floribunda agglutinin (WFA) the present study describes the projection pattern and distribution of non-cholinergic projection neurons characterized by perineuronal nets in the anterior parts of the basal forebrain complex (medial septal nucleus, nucleus of the diagonal band of Broca, magnocellular preoptic nucleus). After tracer injection into the cingulate cortex labelled net-associated neurons were distributed within the rostrocaudal extension of the basal forebrain complex but were predominantly found in the horizontal limb of the diagonal band of Broca. Retrograde labelling of neurons with perineuronal nets after tracer injection into the retrosplenial cortex was more pronounced in the medial septum. Choline acetyltransferase-immunoreactive (ChAT-ir) projection neurons were in no case associated with perineuronal nets. The results demonstrate that a large portion of the non-cholinergic projection neurons of the basal forebrain are endowed with a specialized microenvironment of proteoglycans and form a strong input system of mesocortical components of the limbic system.

Animals↗

Immunohistochemical evidence for the interaction between levator ani and pudendal motor neurons in the coordination of pelvic floor and visceral activity in the squirrel monkey.

OBJECTIVE: The purpose of this study was to characterize the spinal distribution of afferent and efferent pathways that innervate the levator ani (LA) muscle in the female squirrel monkey. STUDY DESIGN: Cholera toxin B (CTB) was injected unilaterally into the LA muscle of 5 monkeys to identify primary sensory neurons in the dorsal root ganglia (DRG) and motor neurons in the spinal cord that contribute fibers to the LA nerve. Fluoro-Gold (FG) was injected into the external anal sphincter of 2 of these animals to label pudendal motor neurons (1 of these animals underwent unilateral LA neurectomy before CTB injection). Spinal cord and DRG were processed for immunofluorescence 3 to 7 days after injections. RESULTS: Retrograde transport of CTB from the LA muscle labeled primary afferent neurons in the ipsilateral DRG, their central projections, and motor neurons in the medial portion of the ipsilateral ventral horn of the spinal cord (L7-S2 segments). Injection of FG into the external anal sphincter labeled cells in Onuf's nucleus, primarily in L7. Importantly, CTB-labeled LA motor neurons were virtually absent in Onuf's nucleus, where all pudendal motor neurons are located. CTB-labeled processes were observed within Onuf's nucleus, adjacent to FG-labeled pudendal motor neurons, and appeared to derive from dendrites of LA motor neurons that project into Onuf's nucleus. CONCLUSION: The LA muscle has a distinct innervation with very little or no contribution from the pudendal nerve. The intriguing labeling of LA neural elements within a nucleus that innervates the external urethral and anal sphincters (involved in pelvic visceral control) may represent a neuroanatomic substrate for physiologic integration of spinal and supraspinal inputs for the coordination of pelvic floor and visceral activity.

Afferent Pathways↗

Antidepressant treatment with tianeptine reduces apoptosis in the hippocampal dentate gyrus and temporal cortex.

BACKGROUND: Recent clinical and preclinical studies suggest that major depression may be related to impairments of structural plasticity. Consequently, antidepressants may act by restoring altered rates of cell birth or death. Here, we investigated whether the antidepressant tianeptine would affect apoptosis in an animal model of depression, the psychosocially stressed tree shrew. METHODS: Animals were subjected to a 7-day period of psychosocial stress before the onset of daily administration of tianeptine. Stress continued throughout the 28-day treatment period. In situ end labeling was used to detect apoptosis in hippocampus and adjacent temporal cortex. RESULTS: Both stress and tianeptine treatment had a region-specific effect. Stress increased apoptosis in the temporal cortex, while it reduced it in the Ammons Horn. No significant effect was observed in the dentate gyrus. Interestingly, tianeptine treatment significantly reduced apoptosis in the temporal cortex and dentate gyrus, both in control and stressed animals, but had no effect in the Ammons Horn. Parallel Fluoro-Jade staining indicated that this apoptosis most likely represents non-neuronal cells. CONCLUSIONS: This is the first report showing an anti-apoptotic effect of tianeptine in hippocampal subfields and temporal cortex. These findings are consistent with current theories that ascribe enhanced general cell survival to antidepressant action.

Animals↗