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PubMed1993

Enhancement of the acoustic startle response by stimulation of an excitatory pathway from the central amygdala/basal nucleus of Meynert to the pontine reticular formation.

The acoustic startle response (ASR) is a simple motor reaction to intense and sudden acoustic stimuli. The neural pathway underlying the ASR in rats is already fairly well understood. As the ASR is subject to a variety of modulations, this reaction can serve as a model for vertebrate neuroethologists to investigate the neural mechanisms mediating sensorimotor transfer and their extrinsic modulation. We report here on experiments in rats which were undertaken in order to investigate the neural mechanisms underlying the enhancement of the ASR. An increased amplitude of the ASR can be observed during states of conditioned and unconditioned fear. By employing neuroanatomical tract-tracing methods, we describe a pathway from neurons of the medial division of the central amygdaloid nucleus (cA) and the basal nucleus of Meynert (B) to the caudal pontine reticular nucleus (PnC), an important relay station in the acoustic startle pathway. Extracellular recordings from acoustically responsive neurons in the PnC showed that electrical stimulation of the cA/B facilitates the tone-evoked response of these neurons. Behavioural tests following chemical stimulation of the cA/B with NMDA (N-methyl-d-aspartate) in awake rats indicated that activation of this pathway increases the ASR. The lack of sufficient spatial resolution of our stimulation techniques did not allow us to differentiate the relative contributions of the cA and the B to this effect. As the amygdaloid complex has been implicated in emotional behaviour, particularly in the mediation of fear, these findings substantiate the concept that the amygdaloid complex plays a key role for the enhancement of the ASR by conditioned and unconditioned fear.

Amygdala↗
PubMed1994

Vestibular nucleus projections to nucleus tractus solitarius and the dorsal motor nucleus of the vagus nerve: potential substrates for vestibulo-autonomic interactions.

Autonomic effects of vestibular stimulation are important components of phenomena as diverse as acute vestibular dysfunction and motion sickness. However, the organization of neural circuits mediating these responses is poorly understood. This study presents evidence for direct vestibular nucleus projections to brain stem regions that mediate autonomic function. One group of albino rabbits received injections of Phaseolus vulgaris leucoagglutinin into the vestibular nuclei. The tracer was visualized immunocytochemically with standard techniques. Anterogradely labeled axons from the caudal medial vestibular nucleus (cMVN) and inferior vestibular nucleus (IVN) could be traced bilaterally to nucleus tractus solitarius (NTS). Fewer axons ended near the somata of neurons in the dorsal motor nucleus of the vagus nerve (DMX). A second group of rabbits received pressure or iontophoretic injections of cholera toxin B-HRP or Fluoro-Gold into a region including NTS and DMX. Retrogradely labeled neurons were observed bilaterally in the caudal half of cMVN and ipsilaterally in IVN. The labeled somata were small and they tended to occupy the center of cMVN in transverse sections. These previously unreported vestibular nucleus projections to NTS and DMX are a potential substrate for vestibular influences on autonomic function. In particular, they may contribute to both cardiovascular control during head movements (e.g., orthostatic reflexes) and autonomic manifestions of vestibular dysfunction, motion sickness and exposure to altered gravitational environments.

Animals↗
PubMed1991

Pallidotectal projection to the inferior colliculus of the rat.

After injection of fluorescent tracer into the inferior colliculus (IC), retrogradely labeled cells were observed not only in the temporoauditory cortex (ACx) and the substantia nigra pars lateralis, but also in the globus pallidus (GP). These labeled GP cells were localized exclusively in the caudal portion of the GP, which has been known to project to the ACx. Employing a retrograde fluorescent double labeling technique, the GP-IC neurons were found to be distributed in a separate manner from the GP-ACx neurons within the caudal GP. The present study provides further anatomical evidence that the caudal GP has a functional role in auditory processing.

Amidines↗
PubMed1989

Relationship of afferent inputs to the lattice of high NADPH-diaphorase activity in the mouse superior colliculus.

In the intermediate gray layer of the superior colliculus there is a lattice of high NADPH-diaphorase activity which represents the terminal distribution of a number of extrinsic afferent systems. These include inputs from the dorsal cholinergic column and cells in the precommissural nucleus and dorsolateral wedge of the central gray substance. Other afferents that terminate in the intermediate gray layer, such as the input from the nucleus of the brachium of the inferior colliculus (BIN), are almost completely segregated from the above inputs and show very little overlap with the NADPH-diaphorase lattice. It is suggested that the input from the precommissural nucleus and central gray substance may have a role in nociception while the input from BIN may provide an important source of auditory information.

Animals↗
PubMed1993

Asymmetry is present in the thalamofugal visual projections of female chicks.

Asymmetry of the thalamofugal visual projections of the chick has been previously reported to exist in males but not females. Using a larger sample size and a double-labelling procedure, projections to the visual Wulst were labelled with the retrograde tracers True Blue and Fluoro-gold and the ratio of contralateral projections to ipsilateral projections was calculated. We found that asymmetry does exist in female chicks, but to a lesser degree than in males.

Animals↗
PubMed1993

Transsynaptic induction of c-fos in basal forebrain, diencephalic and midbrain neurons following AMPA-induced activation of the dorsal and ventral striatum.

In these experiments, induction of the immediate early gene c-fos following excitation of striatal neurons has been used to investigate the organization of the ventral and dorsal striatopallidal systems and the relationship between striatal neurons and cholinergic neurons of the nucleus basalis magnocellularis (of Meynert, nbM). The results demonstrate that FOS immunoreactivity (ir) can be detected in ventral and dorsal striatal neurons following infusions of the non-N-methyl-D-aspartic acid (NMDA) glutamate receptor agonist alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA). This activation and increased expression of FOS in striatal neurons was itself associated with the sustained appearance of FOS-ir in neurons of the ipsilateral ventral and dorsal pallidum, subthalamic nucleus and some thalamic nuclei. Infusions of AMPA into the ventral striatum (VS), but not the dorsal striatum (DS), also resulted in the appearance of FOS-ir in a proportion (17%) of the cholinergic neurons of the nbM. By combining the retrograde transport of Fluoro-Gold with FOS immunocytochemistry, it was also possible to demonstrate that approximately 46% and 58% of the pallidal neurons containing FOS-ir after infusions of AMPA into the VS or DS, respectively, directly project to the subthalamic nucleus. Taken together, these observations suggest that visualizing the protein product of transsynaptic c-fos induction provides an effective way to study the topographic and transsynaptic, within-system consequences of striatal activation.

Animals↗
PubMed1996

Morpholological analyses of galaninergic inputs to the rat spinal parasympathetic nucleus.

We examined the characteristic features of galanin (GAL)-containing nerve afferents in the intermediolateral nucleus (IML) of the rat lumbosacral spinal cord (L6, S1), i.e., spinal parasympathetic nucleus, by immunocytochemistry at both light and electron microscopic levels. Firstly, the types of synapses formed by GAL-immunoreactive (IR) axon terminals and their post- or presynaptic elements were examined in random ultrathin sections. A total of 109 synapses were examined. Axodendritic (71%) and axo-somatic (20%) synapses were always of the asymmetrical type. Axo-axonic synapses (9%) were occasionally found; GAL-IR axon terminals were either postsynaptic (3%) or presynaptic (6%) to non-IR axon terminals. By confocal laser microscopy, many GAL-IR axon terminals were seen close to cell bodies and proximal dendrites of the IML neurons that were retrogradely labeled with Fluoro-Gold injected into the pelvic ganglion. Some GAL-IR axon terminals were identified to be presynaptic to them under the electron microscope, by restaining for GAL immunoreactivity with the immunoperoxidase method. These findings suggest that the GAL afferents are involved in the parasympathetic motor regulation of pelvic organs via their central synaptic influences upon preganglionic neurons. Finally, hemi-transection of the upper lumbar segments (L1-L3) or unilateral dorsal rhizotomy (L5-S2) did not significantly alter the immunoreactivity for GAL in the IML. These results suggest that GAL afferents do not originate from regions rostral to the IML nor from the dorsal root ganglion, but probably from GAL cells located at least within the lower lumbar segments and/or sacral spinal cord.

Animals↗
PubMed1991

Midbrain central gray GABAA receptor activation enhances, and blockade reduces, sexual behavior in the female rat.

The inhibitory neurotransmitter, GABA, has been implicated in the control of lordosis behavior. Previous studies indicate that modulation of GABAA transmission can have dual effects on lordosis, being facilitative in the ventromedial hypothalamus and inhibitory in the preoptic area. The midbrain central gray (MCG) is also known to be an important neural site for regulating lordosis as well as defensive and escape behaviors, and plays an integral role in the control of nociception. Because of the multitude of behaviors regulated at the level of the MCG, we utilized a two-chamber testing apparatus that allowed simultaneous measurement of the females' proceptive (hopping and darting), receptive and rejection behaviors, as well as an index of nociception and general motor activity. We found that microinfusion of the GABAA antagonist, bicuculline, into the MCG of steroid-primed female rats resulted in a significant decrease in lordosis and proceptive behaviors at 5 min post-infusion. There was full recovery to pretest levels by 60 min. Furthermore, microinfusion of the GABAA agonist, muscimol, to estrogen-treated females that displayed low levels of receptivity and high levels of rejection behavior during a pretest, resulted in a significant increase in lordosis responding and a decrease in rejection behaviors. Neither drug significantly affected time spent in the vicinity of the male, motor activity or vocalizations. It is concluded that the decrease in lordosis resulting from blockade of GABA transmission is not solely due to the induction of antagonistic behaviors since there was no increase in rejections after bicuculline administration. The current findings are consistent with the interpretation that GABA facilitates lordosis in the MCG via disinhibition.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Zinc-containing telencephalic connections to the rat striatum: a combined Fluoro-Gold tracing and histochemical study.

The organization of telencephalic zinc-containing neurons projecting to the rat striatum was investigated by combining intrastriatal injections of the retrograde fluorescent tracer Fluoro-Gold with histochemistry revealing zinc-containing neurons and terminals. Throughout the ipsilateral and contralateral neocortex, corticostriatal zinc-containing neurons with striatal projections were located predominantly at the border between deep layer V and superficial layer VI. Additional, but fewer zinc-containing neurons were located in layers II, III and deep layer VI of the ipsilateral neocortex. The main neocortical source of zinc-containing afferents to the striatum were the frontal motor cortices. Smaller contingents of zinc-containing projections arose from the motor cortical forelimb and hindlimb areas and the parietal cortical areas. In the cingulate cortex, zinc-containing neurons with striatal projections were found predominantly in the ipsilateral layers II and III, with only few neurons in the ipsilateral layer VI and in the contralateral layers II, III and VI. Subcortically, zinc-containing neurons belonging to the amygdalostriatal projection were found bilaterally in the basolateral and basomedial nuclei of the amygdala. Zinc has been found to modulate the response of many ligand- and voltage-gated ion channels, including both GABA receptors and NMDA-, AMPA- and kainate-type glutamate receptors. The present findings raise the possibility that zinc in the corticostriatal projections might play a role in the selective, possibly excitotoxic, cell death of GABAergic projections seen in Huntington's disease.

Animals↗
PubMed1994

Regeneration of dorsal root axons into experimentally altered glial environments in the rat spinal cord.

Exposure of the lumbar spinal cord of rats to X-rays 3 days after birth results in changes in the composition of central glia. Shortly after irradiation, there is both retardation of central myelin formation and a loss of integrity of the astrocyte-derived glia limitans on the dorsal surface of the cord. Subsequently, Schwann cells invade, undergo division and myelinate axons in the dorsal funiculi in the irradiated region of the cord, creating there an environment similar to that of peripheral nerve. The present study was undertaken to compare the ability of lesioned dorsal root axons to grow back into the altered glial environments that exist within the spinal cord after irradiation. This regrowth was assessed by injecting Fluoro-Gold into the spinal cord and subsequently examining neurons in the dorsal root ganglia (DRG) for the presence of this label. Numbers of retrogradely labeled neurons were counted in the DRG in both injured and contralateral non-injured sides. Non-irradiated control rats had almost no labeled DRG neurons on the injured side, whereas Fluoro-Gold labeled neurons were observed in substantial numbers in the DRG on the injured side of irradiated rats. There was a definite trend in the data, indicating that the longer the interval between irradiation and root injury, the greater the number of labeled neurons. Since the Fluoro-Gold labeling technique does not allow for visualization of the labeled axons within the spinal cord, a few animals were used to assess anterograde labeling with wheat germ agglutinin-conjugated horseradish peroxidase (WGA-HRP/HRP) from the dorsal root into the spinal cord.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Segregation of lemniscal inputs and motor cortex outputs in cat ventral thalamic nuclei: application of a novel technique.

A double labeling method that permits accurate delineation of the terminals of medial lemniscal fibers was used to determine whether thalamic neurons projecting to motor cortex in the cat are in a position to be contacted by such terminals. Thalamic neurons in the VL nucleus were retrogradely labeled by injections of fluorogold placed in the cytoarchitectonically defined area 4, while lemniscal axons and their terminal boutons were anterogradely labeled, in a Golgi-like manner, from injections of Fast Blue placed under physiological control in different parts of the contralateral dorsal column nuclei. In additional experiments, spinothalamic fibers were similarly labeled by injections of Fast Blue in the spinal cord. The results reveal that there is no significant overlap in the distributions of lemniscal terminals and motor cortex-projecting neurons and that no somata or proximal dendrites of motor cortex-projecting neurons are in a position to receive lemniscal terminals. Spinothalamic terminals, on the other hand, end in clusters around motor cortex-projecting neurons in the VL nucleus as well as in other nuclei and are a more likely route for short latency somatosensory inputs to the motor cortex.

Amidines↗
PubMed1988

Local connections in transplanted and normal cerebral cortex of rats.

Injections of the fluorescent tracer Fluoro-Gold were made in transplanted and normal cerebral cortex of rats in order to investigate and compare the local connectivities of both. In the normal somatosensory cortex, small injections in superficial layers (I to III) produced retrograde cell labeling below the injection site in two bands: in layer V and in the deep part of layer VI. Pieces of embryonic rat neocortical tissue were transplanted into a cavity made in the somatosensory cortex of young adult rats. After a survival period of 2-3 months, small injections of Fluoro-Gold were made in the superficial part of the grafts. These injections revealed multiple clusters of intratransplant-projecting cells. No callosal or thalamic neurons were labeled in these experiments. On occasion, a bilaminated pattern of retrograde cell labeling was observed inside the transplants. In both transplanted and normal cortices, pyramidal and non-pyramidal cells were retrograde-labeled. We conclude that in the neocortical transplants there is a pattern of local connectivity that is reminiscent of the pattern of intracortical connectivity in the normal neocortex in at least two aspects: first, the retrograde-labeled cells tended to form clusters or bands; second, both pyramidal and non-pyramidal cells were labeled.

Animals↗
PubMed1989

Demonstration of axonal branching of fibres from certain precerebellar nuclei to the cerebellar cortex and nuclei: a retrograde fluorescent double-labelling study in the cat.

The projections from certain brain stem precerebellar nuclei to the cerebellar cortex and nuclei have been examined in the cat by using the retrograde fluorescent double-labelling technique. Crystalline Fluoro-Gold was implanted into the left cerebellar nuclei from the contralateral side and rhodamine-B-isothiocyanate was injected into the overlying cerebellar cortex. The inferior olive, the lateral reticular nucleus, and the reticular tegmental pontine nucleus all contained double- as well as single-labelled neurons, and it was concluded that these nuclei have a high number of neurons whose axons branch to both the cerebellar cortex and nuclei. The neurons in the paramedian reticular nucleus and the pontine nuclei proper appear to project only to the cerebellar cortex.

Animals↗
PubMed1989

Transplanted rat retinae do not project in a topographic fashion on the host tectum.

We report here that transplanted rat retinae do not project in a topographically organized fashion onto the host tectum. In fact, following the injection of two small non-overlapping regions of the host tectum, one with Fluorogold, the other with Rhodamine conjugated latex microspheres, groups of ganglion cells labelled with either dye are found interspersed throughout the ganglion cell layer of the retinal transplant. The absence of topography in the projections of transplanted retinae offers a new opportunity to examine the mechanisms which lead to topographically ordered projections in normal development.

Animals↗
PubMed1994

Vagal innervation of the rat pylorus: an anterograde tracing study using carbocyanine dyes and laser scanning confocal microscopy.

In an attempt to identify the distribution and structure of vagal fibers and terminals in the gastroduodenal junction, vagal efferents were labeled in vivo by multiple injections of the fluorescent carbocyanine dye DiA into the dorsal motor nucleus (dmnX), and vagal afferents were anterogradely labeled by injections of DiI into the nodose ganglia of the same or separate rats. Thick frontal cryostat sections were analysed either with conventional or laser scanning confocal microscopy, using appropriate filter combinations and/or different wavelength laser excitation to distinguish the fluorescent tracers. Vagal efferent terminal-like structures were present in small ganglia within the circular sphincter muscle, which, in the absence of a well-developed, true myenteric plexus at this level, represent the myenteric ganglia. Furthermore, vagal efferent terminals were also present in submucosal ganglia, but were absent from mucosa, Brunner's glands and circular muscle fibers. Vagal afferent fibers and terminal-like structures were more abundant than efferents. The most prominent afferent terminals were profusely branching, large net-like aggregates of varicose fibers running within the connective tissue matrix predominantly parallel to the circular sphincter muscle bundles. Profusely arborizing, highly varicose endings were also present in large myenteric ganglia of the antrum and duodenum, in the modified intramuscular ganglia, and in submucosal ganglia. Additionally, afferent fibers and terminals were present throughout the mucosal lining of the gastroduodenal junction. The branching patterns of some vagal afferents suggested that individual axons produced multiple collaterals in different compartments. NADPH-diaphorase positive, possibly nitroxergic neurons were present in myenteric ganglia of the immediately adjacent antrum and duodenum, and fine varicose fibers entered the sphincter muscle from both sides, delineating the potential vagal inhibitory postganglionic innervation. These morphological results support the view of a rich and differentiated extrinsic neural control of this important gut region as suggested by functional studies.

Animals↗
PubMed1995

Nitric oxide nerves in the uterus are parasympathetic, sensory, and contain neuropeptides.

Nitric oxide (NO) is synthesized in neurons and is a potent relaxor of vascular and nonvascular smooth muscle. The uterus contains abundant NO-synthesizing nerves which could be autonomic and/or sensory. This study was undertaken to determine: 1) the source(s) of NO-synthesizing nerves in the rat uterus and 2) what other neuropeptides or transmitter markers might coexist with NO in these nerves. Retrograde axonal tracing, utilizing Fluorogold injected into the uterine cervix, was employed for identifying sources of uterine-projecting neurons. NO-synthesizing nerves were visualized by staining for nicotinamide adenine dinucleotide phosphate (reduced)-diaphorase (NADPH-d) and immunostaining with an antibody against neuronal/type I NO synthase (NOS). NADPH-d-positive perikarya and terminal fibers were NOS-immunoreactive (-I). Some NOS-I/NADPH-d-positive nerves in the uterus are parasympathetic and originate from neurons in the pelvic paracervical ganglia (PG) and some are sensory and originate from neurons in thoracic, lumbar, and sacral dorsal root ganglia. No evidence for NOS-I/NADPH-d-positive sympathetic nerves in the uterus was obtained. Furthermore, double immunostaining revealed that in parasympathetic neurons, NOS-I/NADPH-d-reactivity coexists with vasoactive intestinal polypeptide, neuropeptide Y, and acetylcholinesterase and in sensory nerves, NOS-I/NADPH-d-reactivity coexists with calcitonin gene-related peptide and substance P. In addition, tyrosine hydroxylase(TH)-I neurons of the PG do not contain NOS-I/NADPH-d-reactivity, but some TH-I neurons are apposed by NOS-I varicosities. These results suggest NO-synthesizing nerves in the uterus are autonomic and sensory, and could play significant roles, possibly in conjunction with other putative transmitter agents, in the control of uterine myometrium and vasculature.

Amino Acid Oxidoreductases↗
PubMed1993

Occurrence, distribution and neurochemical features of small intestinal neurons projecting to the cranial mesenteric ganglion in the pig.

The small intestine of the pig has been investigated for its topographical distribution of enteric neurons projecting to the cranial mesenteric ganglion, by using Fast Blue or Fluorogold as a retrogradely transported neuronal tracer. Contrary to the situation in small laboratory animals such as rat and guinea-pig, the intestinofugally projecting neurons in the porcine small intestine were not restricted to the myenteric plexus, but were observed in greater numbers in ganglia of the outer submucous plexus. The inner submucous plexus was devoid of labelled neurons. Retrogradely labelled neurons were mostly found, either singly or in small aggregates, in ganglia located within a narrow border on either side of the mesenteric attachment. For both nerve networks, their number increased from duodenum to ileum. All the retrogradely labelled neurons exhibited a multidendritic uniaxonal appearance. Some of them displayed type-III morphology and stained for serotonin. This study indicates that, in the pig, not only the myenteric plexus but also one submucous nerve network is involved in the afferent component of intestino-sympathico-intestinal reflex pathways. The finding that some of the morphologically defined type-III neurons participate in these reflexes is in accord with the earlier proposal that type-III neurons are supposed to fulfill an interneuronal role, whether intra- or extramurally.

Amidines↗
PubMed1994

Co-localization of nitric oxide synthase and vasoactive intestinal peptide immunoreactivity in neurons of the major pelvic ganglion projecting to the rat rectum and penis.

Nitric oxide synthase (NOS)- and vasoactive intestinal peptide (VIP)-immunoreactive neurons projecting to the upper rectum or penis were examined using retrograde tracing combined with immunohistochemistry in the major pelvic ganglion of male rats. Five days after injection of Fluoro-Gold (FG) into the upper rectum or penis, the major pelvic ganglion was treated with colchicine. FG injected into the upper rectum labelled many ganglion neurons in the major pelvic ganglion. Immunohistochemistry showed that 37% of FG-labelled neurons were immunoreactive for NOS and 33% for VIP. After injection of FG into the penis, 41% of FG-labelled neurons were immunoreactive for NOS and 25% for VIP. Serial cryostat sections stained for NOS and VIP, respectively, showed the co-localization of NOS and VIP in the ganglion cells projecting to the rectum and penis. In the major pelvic ganglion of the colchicine-treated animals, about 17% of the ganglion cells were immunoreactive for NOS and 32% were immunoreactive for VIP. These neurons were small in diameter (less than 30 microns). A histogram showing cell sizes in cross-sectional areas of NOS-immunoreactive neurons coincided with that of VIP-immunoreactive neurons. Most of the NOS- and VIP-immunoreactive neurons were less than 600 microns. These results indicate that small neurons containing both NOS and VIP in the major pelvic ganglion project to the rectum and penis. In the penile erectile tissues and enteric ganglia, NO and VIP may be released from the same axons and may act concomitantly on the target tissue.

Amino Acid Oxidoreductases↗