Nerve cells immunoreactive for p62 in select hypothalamic and brainstem nuclei of controls and Parkinson's disease cases.

The protein p62 plays an important role in the proteasomal and/or autophagic clearance of misfolded and aggregation-prone proteins. Immunoreactivity for p62, however, not only characterizes pathological proteinaceous inclusions but also occurs in the form of homogeneous nerve cell labeling in brains of both healthy and diseased individuals, e.g., in the vagal dorsal motor nucleus and other subcortical nuclei. In sporadic Parkinson's disease (PD), the pathological process initially involves preganglionic neurons of the parasympathetic and sympathetic system and probably advances caudo-rostrally from there along the neuroaxis. Since all subsequently affected nuclei (lower raphe nuclei, magnocellular reticular formation, locus coeruleus, and central subnucleus of the amygdala) generate descending projections that terminate in the vagal dorsal motor nucleus and intermediolateral column, it has been conjectured that retrograde axonal transport and transsynaptic transmission of a pathogen contribute to the pathogenesis of PD. The hypothalamic paraventricular nucleus also sends projections to the preganglionic nuclei under consideration and, thus, should belong to the nuclei endangered by the pathological process. However, it remains uninvolved for the duration of the disorder. For this reason, we performed a retrospective study of the relevant nuclei in a cohort of 36 individuals, including 17 with clinically documented PD, one case with incidental Lewy body disease (ILBD), and 18 controls using p62-immunocytochemistry. Remarkably, the neurosecretory cells of the paraventricular nucleus were among the sites showing homogeneous p62-immunolabeling with the greatest consistency. Its p62-immunoreactive profile may indicate that the hypothalamic paraventricular nucleus is somehow capable of effectively metabolizing misfolded proteins and/or preventing their aggregation.

Electron-microscopic examination of effects of yokukansan, a traditional Japanese medicine, on degeneration of cerebral cells in thiamine-deficient rats.

We previously demonstrated that yokukansan ameliorated not only learning disturbance but also behavioral and psychological symptoms of dementia-like behaviors (anxiety, aggressiveness) and neurological symptoms (opisthotonus) induced in rats by dietary thiamine deficiency (TD). In the present study, the effects of yokukansan on degeneration of cerebral cells were further examined electron-microscopically during pre-symptomatic and symptomatic stages in TD rats. In the pre-symptomatic TD stage, which appeared as increase in aggressive behaviors on the 21st and 28th days of TD diet-feeding, severe edematous degeneration of astrocytes was detected by electron microscopy, although the changes were not observed by light microscopy. In the symptomatic TD stage (the 34th day) characterized by development of neurological symptoms, severe sponge-like degeneration and multiple hemorrhages in the parenchyma were obvious by light microscopy. The electron-microscopic examination showed degeneration in neurons, oligodendroglias, and myelin sheaths in addition to astrocytes. TD rats, which exhibited multiple hemorrhages light microscopically, showed severe edematous changes and hypertrophy of the foot processes of astrocytes surrounding blood vessels. Administration of yokukansan ameliorated not only the TD-induced aggressive behavior and neurological symptoms but also degeneration of the cerebral cells. These results suggest that the inhibitory effect of yokukansan on degeneration in various brain cells might be closely related to the amelioration of aggression and neurological symptoms in TD rats.

Ultrastructural study of the effects of cyclosporine in the brainstem of Wistar rats submitted to the ethidium bromide demyelinating model.

The ethidium bromide-demyelinating model (EB) was used to study remyelination in the brainstem under the use of cyclosporine (CsA). Wistar rats were submitted to intracisternal injection of 0.1% EB or 0.9% saline solution, and others were taken as histologic controls (group I). Within those injected with EB, some have not received immunosuppressive treatment (II); some were treated by intraperitonial route with CsA (III.E-10 mg/kg/day). Rats from group III.C were injected with saline solution and treated with CsA. The animals were perfused from 15 to 31 days post-injection collecting brainstem sections for light and transmission electron microscopy studies. After EB injection it was noted the presence of macrophages and non-degraded myelin debris, demyelinated axons, oligodendrocyte or Schwann cell remyelinated axons, groups of infiltrating pial cells, hypertrophic astrocytes and few lymphocytes. Tissue repair of EB-induced lesions in group III.E was similar to that of group II, but with the presence of a higher density of oligodendrocytes near remyelinating areas.

Ultrastructural study of the effects of cyclosporine in the brainstem of Wistar rats submitted to the ethidium bromide demyelinating model / Estudo ultra-estrutural dos efeitos da ciclosporina no tronco encefálico de ratos Wistar submetidos ao modelo desmielinizante do brometo de etídio

The ethidium bromide-demyelinating model (EB) was used to study remyelination in the brainstem under the use of cyclosporine (CsA). Wistar rats were submitted to intracisternal injection of 0.1 percent EB or 0.9 percent saline solution, and others were taken as histologic controls (group I). Within those injected with EB, some have not received immunosuppressive treatment (II); some were treated by intraperitonial route with CsA (III.E - 10 mg/kg/day). Rats from group III.C were injected with saline solution and treated with CsA. The animals were perfused from 15 to 31 days post-injection collecting brainstem sections for light and transmission electron microscopy studies. After EB injection it was noted the presence of macrophages and non-degraded myelin debris, demyelinated axons, oligodendrocyte or Schwann cell remyelinated axons, groups of infiltrating pial cells, hypertrophic astrocytes and few lymphocytes. Tissue repair of EB-induced lesions in group III.E was similar to that of group II, but with the presence of a higher density of oligodendrocytes near remyelinating areas.

Empregou-se o modelo desmielinizante do brometo de etídio (BE) com o objetivo de estudar a remielinização no tronco encefálico frente ao uso de ciclosporina (CsA). Foram utilizados ratos Wistar, submetidos à injeção de BE a 0,1 por cento ou de solução salina na cisterna pontina, assim como controles histológicos (grupo I). Dos animais injetados com BE, alguns não receberam tratamento imunossupressor (II); outros foram tratados por via intraperitoneal com CsA (III.E - 10 mg/kg/dia). O grupo III.C incluiu animais injetados com salina e tratados com CsA. Os animais foram perfundidos dos 15 aos 31 dias pós-injeção, com colheita de material do tronco encefálico para estudos de microscopia de luz e eletrônica de transmissão. Após injeção de BE, foram observados macrófagos e restos de mielina não-degradada, axônios desmielinizados ou remielinizados por oligodendrócitos e por células de Schwann, grupos de células piais infiltrantes, astrócitos hipertróficos e poucos linfócitos. O processo de reparo das lesões no grupo III.E apresentou-se similar ao do grupo II, porém com maior densidade de oligodendrócitos próximos às áreas de remielinização.

Vesicular glutamate transporters define two sets of glutamatergic afferents to the somatosensory thalamus and two thalamocortical projections in the mouse.

The ventral posterior nucleus of the thalamus (VP) receives two major sets of excitatory inputs, one from the ascending somatosensory pathways originating in the dorsal horn, dorsal column nuclei, and trigeminal nuclei, and the other originating from the cerebral cortex. Both systems use glutamate as neurotransmitter, as do the thalamocortical axons relaying somatosensory information from the VP to the primary somatosensory cortex (SI). The synapses formed by these projection systems differ anatomically, physiologically, and in their capacity for short-term synaptic plasticity. Glutamate uptake into synaptic vesicles and its release at central synapses depend on two isoforms of vesicular glutamate transporters, VGluT1 and VGluT2. Despite ample evidence of their complementary distribution, some instances exist of co-localization in the same brain areas or at the same synapses. In the thalamus, the two transcripts coexist in cells of the VP and other nuclei but not in the posterior or intralaminar nuclei. We show that the two isoforms are completely segregated at VP synapses, despite their widespread expression throughout the dorsal and ventral thalamus. We present immunocytochemical, ultrastructural, gene expression, and connectional evidence that VGluT1 in the VP is only found at corticothalamic synapses, whereas VGluT2 is only found at terminals made by axons originating in the spinal cord and brainstem. By contrast, the two VGluT isoforms are co-localized in thalamocortical axon terminals targeting layer IV, but not in those targeting layer I, suggesting the presence of two distinct projection systems related to the core/matrix pattern of organization of thalamocortical connectivity described in other mammals.

The brain is getting ready for dinner.

Every evening, as we get ready for dinner, in addition to the routine behaviors of preparing the meal itself, we also prepare our bodies to cope with the upcoming meal. This could take the form of making restaurant reservations, changing into appropriate attire, washing hands, priming ourselves with an aperitif, or even consciously avoiding snacks as the meal approaches. A study by Johnstone and colleagues in this issue of Cell Metabolism (Johnstone et al., 2006) provides evidence that in parallel to our learned preparatory behaviors, our central nervous system is going through comparable motions as it gets ready for the anticipated meal.

Neuronal activation in the hypothalamus and brainstem during feeding in rats.

We trained rats to a regime of scheduled feeding, in which food was available for only 2 hr each day. After 10 days, rats were euthanized at defined times relative to food availability, and their brains were analyzed to map Fos expression in neuronal populations to test the hypothesis that some populations are activated by hunger whereas others are activated by satiety signals. Fos expression accompanied feeding in several hypothalamic and brainstem nuclei. Food ingestion was critical for Fos expression in noradrenergic and non-noradrenergic cells in the nucleus tractus solitarii and area postrema and in the supraoptic nucleus, as well as in melanocortin-containing cells of the arcuate nucleus. However, anticipation of food alone activated other neurons in the arcuate nucleus and in the lateral and ventromedial hypothalamus, including orexin neurons. Thus orexigenic populations are strongly and rapidly activated at the onset of food presentation, followed rapidly by activity in anorexigenic populations when food is ingested.

Brainstem axonal degeneration in mice with deletion of selenoprotein p.

Selenoprotein P is an abundant extracellular protein that is expressed in liver, brain, and other tissues. Studies in mice with the selenoprotein P gene deleted (Sepp-/- mice) have implicated the protein in maintaining brain selenium. Sepp-/- mice fed a normal or low selenium diet develop severe motor impairment and die, but Sepp-/- mice fed a high selenium diet remain clinically unimpaired. As an initial step to evaluate the effect of selenoprotein P deletion on central nervous system architecture, the brains and cervical spinal cords of Sepp-/- and Sepp+/+ mice fed low or high selenium diets were examined by light and electron microscopy. Brains of Sepp-/- mice demonstrated no gross abnormalities. At the light microscopic level, however, Sepp-/- mice fed either the selenium deficient diet or the high selenium diet had enlarged dystrophic axons and degenerated axons in their brainstems and cervical spinal cords. No axonal lesions were observed in the Sepp+/+ mice fed either diet. Electron microscopy demonstrated that the enlarged axons in the Sepp-/- mice were packed with organelles, suggesting a deficit in fast axonal transport. The similar severity of axonal lesions observed in Sepp-/- mice fed the 2 diets suggests that axonal dystrophy is a common phenotype for deletion of selenoprotein P regardless of selenium intake and that additional studies will be required to determine the pathogenesis of the neurological signs and mortality observed in Sepp-/- mice fed a low selenium diet.

Input of orexin/hypocretin neurons revealed by a genetically encoded tracer in mice.

The finding of orexin/hypocretin deficiency in narcolepsy patients suggests that this hypothalamic neuropeptide plays a crucial role in regulating sleep/wakefulness states. However, very little is known about the synaptic input of orexin/hypocretin-producing neurons (orexin neurons). We applied a transgenic method to map upstream neuronal populations that have synaptic connections to orexin neurons and revealed that orexin neurons receive input from several brain areas. These include the amygdala, basal forebrain cholinergic neurons, GABAergic neurons in the preoptic area, and serotonergic neurons in the median/paramedian raphe nuclei. Monoamine-containing groups that are innervated by orexin neurons do not receive reciprocal connections, while cholinergic neurons in the basal forebrain have reciprocal connections, which might be important for consolidating wakefulness. Electrophysiological study showed that carbachol excites almost one-third of orexin neurons and inhibits a small population of orexin neurons. These neuroanatomical findings provide important insights into the neural pathways that regulate sleep/wakefulness states.

Histological findings at the boundary of craniopharyngiomas.

Although a craniopharyngioma is grossly well circumscribed, microscopically the borders are frequently irregular and may be associated with gliosis in the adjacent brain tissue. In the current study, we investigated the histology of the interface between craniopharyngiomas and surrounding normal structures such as the hypothalamus and pituitary gland. Histologically, we classified the findings at the boundary of craniopharyngiomas into three types. In type 1, a relatively thick capsule-like tissue was identified at the boundary between the craniopharyngioma and surrounding normal structure composed of tumor cells and inflammatory changes. In type 2, a craniopharyngioma had a relatively clear cleavage between the surrounding gliosis. In type 3, the boundary had some interdigitation of the tumor in the surrounding gliotic layer adjacent to the craniopharyngioma. In types 1 and 3, surgeons may fail to accomplish complete resection of the tumor. These histological features may result in recurrence of craniopharyngioma even after gross total resection.

Ultrastructural localization of parkin in the rat brainstem, thalamus and basal ganglia.

The parkin gene encodes a 52 kd putative E3 ubiquitin-protein ligase involved in an autosomal recessive form of early onset parkinsonism. Parkin ultrastructural localization was studied by immunohistochemistry in the adult rat brain and in a parkin inducible PC12 cell line (HS22). In the rat brain, parkin immunoreactivity was detected in neuronal and glial cell bodies and in nerve processes. In the neurons, it was mostly localized on the periphery of large vesicles, some rare mitochondria and endoplasmic reticulum in the cell bodies, and on the periphery of large vesicles in the dendrites and terminals of the neurons. In addition, parkin immunoreactivity was also found around synaptic vesicles in the presynaptic elements of some axons. In HS22 cells over-expressing parkin, the distribution of the protein was similar to that observed in the perikarya of the labeled neurons.

Immunoelectron-microscopic demonstration of NACP/alpha-synuclein-epitopes on the filamentous component of Lewy bodies in Parkinson's disease and in dementia with Lewy bodies.

We examined brains from Parkinson's disease and from dementia with Lewy bodies (LBs) by using antibodies to NACP/alpha-synuclein. Immunohistochemically, all of the antibodies against the amino-terminal region, NAC domain, and carboxyl-terminal region of NACP labeled not only LBs, pale bodies (PBs), and dystrophic neurites, but also fine thread-like structures in the neuronal perikarya (perikaryal threads) in the hypothalamus and brainstem nuclei. On electron microscopy, immunoreactive products were found to label the 9 to 12 nm-thick filamentous component (LB-filaments) of LBs, PBs, and perikaryal threads. The NACP-immunoreactive perikaryal threads, consisting of small bundles of LB-filaments and randomly oriented LB-filaments, presumably represent an initial stage of LB- or PB-formation. The present study indicates that the entire molecule of NACP is involved in the neuronal filament-aggregating processes of LB disorders.

Gene expression of central and peripheral renin-angiotensin system components upon dietary sodium intake in rats.

The effects of dietary sodium intake on the gene expression of the renin-angiotensin system (RAS) were investigated in rat central and peripheral tissues in a single set of experiment. Northern and reverse transcriptase-polymerase chain reaction (RT-PCR) techniques were used to detect mRNA expression in rats fed a low- or a high-sodium diet (5 or 500 mmol Na+/kg diet) for 20 days. Plasma and renal renin levels were elevated in rats maintained on the low-sodium diet. Sodium deprivation enhanced the expression of angiotensinogen, renin, AT1A and AT1B receptor subtypes in the hypothalamus, but suppressed them in the brainstem. Kidney and adrenal levels of those mRNAs were also enhanced in the sodium-restricted rats. Both AT1A and AT1B mRNAs changed in a similar magnitude in each tissue examined upon dietary sodium intake. AT1A was the predominant receptor subtype of AT1 in all the tissues examined in the present study except the adrenal gland. The present study demonstrated that dietary sodium modulated the gene expression of the RAS components in the central and peripheral tissues. It also showed that the RAS components in the brainstem and hypothalamus were differentially expressed upon sodium deprivation. This suggests different roles of the RAS in these tissues in maintaining body fluid homeostasis in response to different sodium intakes.

Ultrastructural and quantitative study of atypical age-related bodies in the hamster brain.

Atypical bodies (ABs), related to aging, are described in the central nervous system of normal aged hamsters. Our study used ultrastructural microscopy and quantitative stereology analysis to study these structures in the hypothalamus and brain stem of 3, 6, 12, 18, 24 and 30 month-old hamsters. We found that these complex bodies have an oval or a round profile with a core of fibrillar or tubular structures rounded by a cytoplasmic crown. We frequently observed accumulations of organelles displaying evidence of degeneration. We found that these structures did not appear until 12 months and their frequency increased with age from 12 to 30 months. Their size can range from 3 to 10 microns, although the median size is 6.5 +/- 0.49 microns in diameter. There is a significant correlation between the quantity of these ABs and the animal's age. Their appearance in both hamster and human normal aging can provide an appropriate animal model to yield more information about the normal aging process. This knowledge of the normal aging process in hamsters may also give new insights into which processes in the human brain occur with normal aging and which ones may be exacerbated as in Alzheimer's disease.

Differential gene expression of growth hormone (GH)-releasing hormone (GRH) and GRH receptor in various rat tissues.

Growth hormone (GH)-releasing hormone (GRH) acts on specific receptors in the anterior pituitary to stimulate the synthesis and release of GH. Recent reports suggest that GRH is also synthesized in extrahypothalamic tissues. To evaluate the potential roles of extrahypothalamic GRH, we studied the gene expression of GRH and GRH receptors in various rat tissues by reverse transcribed (RT)-polymerase chain reaction (PCR). Total RNA was extracted from twenty-three rat organs and RT-PCR was performed with GRH and GRH receptor primers. Highly-sensitive RT-PCR-Southern blotting showed that GRH and GRH receptor mRNA coexist in the widespread tissues (14 of 25 tissues). GRH mRNA was relatively abundant in the cerebral cortex, brain stem, testis, and placenta, while GRH receptor mRNA was abundant in renal medulla and renal pelvis. Northern blot hybridization using poly A+ RNA indicated that the transcript of GRH receptor gene found in the renal medulla was similar to the longer transcript (about 4 Kb) of pituitary GRH receptor in the size. These results suggest that GRH plays a potential role not only in the neuroendocrine axis, but also in the autocrine and paracrine systems in extrahypothalamic tissues.

GABAA-receptor heterogeneity in the adult rat brain: differential regional and cellular distribution of seven major subunits.

GABAA-receptors display an extensive structural heterogeneity based on the differential assembly of a family of at least 15 subunits (alpha 1-6, beta 1-3, gamma 1-3, delta, rho 1-2) into distinct heteromeric receptor complexes. The subunit composition of receptor subtypes is expected to determine their physiological properties and pharmacological profiles, thereby contributing to flexibility in signal transduction and allosteric modulation. In heterologous expression systems, functional receptors require a combination of alpha-, beta-, and gamma-subunit variants, the gamma 2-subunit being essential to convey a classical benzodiazepine site to the receptor. The subunit composition and stoichiometry of native GABAA-receptor subtypes remain unknown. The aim of this study was to identify immunohistochemically the main subunit combinations expressed in the adult rat brain and to allocate them to identified neurons. The regional and cellular distribution of seven major subunits (alpha 1, alpha 2, alpha 3, alpha 5, beta 2,3, gamma 2, delta) was visualized by immunoperoxidase staining with subunit-specific antibodies (the beta 2- and beta 3-subunits were covisualized with the monoclonal antibody bd-17). Putative receptor subtypes were identified on the basis of colocalization of subunits within individual neurons, as analyzed by confocal laser microscopy in double- and triple-immunofluorescence staining experiments. The results reveal an extraordinary heterogeneity in the distribution of GABAA-receptor subunits, as evidenced by abrupt changes in immunoreactivity along well-defined cytoarchitectonic boundaries and by pronounced differences in the cellular distribution of subunits among various types of neurons. Thus, functionally and morphologically diverse neurons were characterized by a distinct GABAA-receptor subunit repertoire. The multiple staining experiments identified 12 subunit combinations in defined neurons. The most prevalent combination was the triplet alpha 1/beta 2,3/gamma 2, detected in numerous cell types throughout the brain. An additional subunit (alpha 2, alpha 3, or delta) sometimes was associated with this triplet, pointing to the existence of receptors containing four subunits. The triplets alpha 2/beta 2,3/gamma 2, alpha 3/beta 2,3/gamma 2, and alpha 5/beta 2,3/gamma 2 were also identified in discrete cell populations. The prevalence of these seven combinations suggest that they represent major GABAA-receptor subtypes. Five combinations also apparently lacked the beta 2,3-subunits, including one devoid of gamma 2-subunit (alpha 1/alpha 2/gamma 2, alpha 2/gamma 2, alpha 3/gamma 2, alpha 2/alpha 3/gamma 2, alpha 2/alpha 5/delta).(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of target deprivation on the morphology and survival of adult dorsal column nuclei neurons.

During development, interaction with target cells plays a critical role in the regulation of survival of afferent neurons. In an attempt to define the role of target cells in the adult central nervous system, the somatodendritic morphology and survival of adult cuneate neurons deprived of their targets by in situ injection of kainic acid in the rat thalamus were studied. In neuron-specific, enolase-immunostained sections, a 20% decrease in the mean longest diameter of the labeled cells was detected at 4 months postlesion. This somatic atrophy was accompanied by a loss of distal dendritic arborizations as observed after labeling by intracellular diffusion of horseradish peroxidase. Cytochrome oxidase staining did not reveal detectable alterations of the metabolic activity of these neurons, and an ultrastructural study also failed to demonstrate major changes in the neuronal somata. Cell counts indicated a much delayed death of 25% of the neurons at 10 months postlesion, whereas no neuronal death was detected at 7 months. The glial cells appeared unaltered both in number and in immunolabeling when using OX-42 antibodies or antiglial fibrillary acidic protein (anti-GFAP) antibodies. Results obtained in this time-course study indicate that neuronal death and alteration of the somatodendritic morphology are much delayed events after excitotoxic loss of targets. Somatodendritic atrophy occurs several months postlesion, and neuronal death occurs close to 1 year after lesion. These results suggest that the hypothesis of a necessary continuous trophic support by target cells does not hold as firmly for the adult central nervous system as during development.

Structural characterization by affinity cross-linking of glucagon-like peptide-1(7-36)amide receptor in rat brain.

Specific binding of glucagon-like peptide (GLP)-1(7-36)amide was detected in several rat brain areas, with the highest values being found in hypothalamic nuclei and the nucleus of the solitary tract. In hypothalamus and brainstem homogenate binding of 125I-GLP-1(7-36)amide was time, temperature, and protein content dependent and was inhibited by unlabeled proglucagon-derived peptides. The rank order of potency was GLP-1(7-36)amide >> GLP-1(1-36)amide > GLP-1(1-37) approximately equal to GLP-2 > glucagon. Scatchard analysis of the steady-state binding data was consistent with the presence of both high- and low-affinity binding sites in hypothalamus and brainstem. Brain 125I-GLP-1(7-36)amide-binding protein complexes were covalently cross-linked using disuccinimidyl suberate and analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. A single radiolabeled band of M(r) 56,000 identified in both hypothalamus and brainstem homogenates was unaffected by reducing agents. An excess of unlabeled GLP-1(7-36)amide abolished the band labeling, whereas glucagon had no effect. Other unlabeled GLPs inhibited M(r) 56,000 complex labeling with the following order of potency: GLP-1(1-36)amide > GLP-1(1-37) > GLP-2. The binding of 125I-GLP-1(7-36)amide and the intensity of the cross-linked band were similarly inhibited in a dose-response manner by increasing concentrations of unlabeled GLP-1(7-36)amide. Covalent M(r) 56,000 125I-GLP-1(7-36)amide-binding protein complexes solubilized by Triton X-100 were adsorbed onto wheat germ agglutinin.(ABSTRACT TRUNCATED AT 250 WORDS)

GABAergic terminals in nucleus magnocellularis and laminaris originate from the superior olivary nucleus.

The auditory brainstem nuclei, angularis (NA), magnocellularis (NM), and laminaris (NL) of the chicken, Gallus, contain terminals that stain for antibodies against the inhibitory neurotransmitter, gamma-aminobutyric acid (GABA). Some of these terminals originate from cells surrounding nucleus magnocellularis. Results from this study indicate that the majority of the GABAergic terminals found in NA, NM and NL originate from the superior olivary nucleus (SON). Injections of cholera toxin and horseradish peroxidase show that superior olivary nucleus (SON) neurons, which respond to pure tones, project bilaterally to NA, NM, and NL. NA and NL are reciprocally connected with the SON. More NA cells project to the SON than NL cells. While SON neurons project to NM, NM neurons do not project axons back to the SON. The configuration of SON terminals in NA, NM and NL matches the pattern of GABA-immunoreactive puncta seen in these three nuclei: they surround individual NM cells, congregate in the dendritic neuropil of NL, and blanket the NA. The data indicate that NA, NM and NL may be affected by two different inhibitory cell types: local interneurons and SON neurons. Patterns of connectivity described in this report suggest that the activity of NA cells could influence NM and NL cell physiology. Specifically, increases in NA cell activity could augment the effects of GABAergic SON neurons on NM and NL. Hence, binaural perception in the chicken may be more dependent upon changes in intensity cues than previously believed.

Visualization of neurons filled with biotinylated-lucifer yellow following identification of efferent connectivity with retrograde transport.

A new method is described that allows identification of neurons by retrograde transport, intracellular injection of biotin-labeled Lucifer Yellow, and a histochemical reaction of the biotin. Cells in the inferior colliculus that project to the ipsilateral thalamus are identified by injection of rhodamine-labeled latex beads into the medial geniculate body and retrograde transport in vivo. Several days later, the brains are fixed with aldehydes, and the inferior colliculus is cut on a vibratome. The rhodamine-labeled cells are observed with epi-fluorescent optics, impaled with intracellular pipettes under visual control, and injected with 9% Lucifer Yellow dilithium salt and 1% Lucifer Yellow cadaverine biotin-X. The biotinylated Lucifer Yellow is visualized by incubation of the slice overnight in avidin-biotin-HRP complex in the presence of 0.1% Triton X-100 at 4 degrees C. A diaminobenzidine reaction with simultaneous cobalt and nickel intensification follows. This method produces well-filled neuronal cell bodies, dendrites, and spines for light microscopic analysis. The non-fluorescent reaction product in these intracellularly filled cells may permit transmitter immunohistochemistry and synaptic fine structure to be studied in combination with neural connections and dendritic morphology.