Efferent projections of Vglut2, Foxp2, and Pdyn parabrachial neurons in mice.

The parabrachial nucleus (PB) is a complex structure located at the junction of the midbrain and hindbrain. Its neurons have diverse genetic profiles and influence a variety of homeostatic functions. While its cytoarchitecture and overall efferent projections are known, we lack comprehensive information on the projection patterns of specific neuronal subtypes in the PB. In this study, we compared the projection patterns of glutamatergic neurons here with a subpopulation expressing the transcription factor Foxp2 and a further subpopulation expressing the neuropeptide Pdyn. To do this, we injected an AAV into the PB region to deliver a Cre-dependent anterograde tracer (synaptophysin-mCherry) in three different strains of Cre-driver mice. We then analyzed 147 neuroanatomical regions for labeled boutons in every brain (n = 11). Overall, glutamatergic neurons in the PB region project to a wide variety of sites in the cerebral cortex, basal forebrain, bed nucleus of the stria terminalis, amygdala, diencephalon, and brainstem. Foxp2 and Pdyn subpopulations project heavily to the hypothalamus, but not to the cortex, basal forebrain, or amygdala. Among the few differences between Foxp2 and Pdyn cases was a notable lack of Pdyn projections to the ventromedial hypothalamic nucleus. Our results indicate that genetic identity determines connectivity (and therefore, function), providing a framework for mapping all PB output projections based on the genetic identity of its neurons. Using genetic markers to systematically classify PB neurons and their efferent projections will enhance the translation of research findings from experimental animals to humans.

Tau pathology spread in PS19 tau transgenic mice following locus coeruleus (LC) injections of synthetic tau fibrils is determined by the LC's afferent and efferent connections.

Filamentous tau inclusions are hallmarks of Alzheimer's disease (AD) and other neurodegenerative tauopathies. An increasing number of studies implicate the cell-to-cell propagation of tau pathology in the progression of tauopathies. We recently showed (Iba et al., J Neurosci 33:1024-1037, 2013) that inoculation of preformed synthetic tau fibrils (tau PFFs) into the hippocampus of young transgenic (Tg) mice (PS19) overexpressing human P301S mutant tau induced robust tau pathology in anatomically connected brain regions including the locus coeruleus (LC). Since Braak and colleagues hypothesized that the LC is the first brain structure to develop tau lesions and since LC has widespread connections throughout the CNS, LC neurons could be the critical initiators of the stereotypical spreading of tau pathology through connectome-dependent transmission of pathological tau in AD. Here, we report that injections of tau PFFs into the LC of PS19 mice induced propagation of tau pathology to major afferents and efferents of the LC. Notably, tau pathology propagated along LC efferent projections was localized not only to axon terminals but also to neuronal perikarya, suggesting transneuronal transfer of templated tau pathology to neurons receiving LC projections. Further, brainstem neurons giving rise to major LC afferents also developed perikaryal tau pathology. Surprisingly, while tangle-bearing neurons degenerated in the LC ipsilateral to the injection site starting 6 months post-injection, no neuron loss was seen in the contralateral LC wherein tangle-bearing neurons gradually cleared tau pathology by 6-12 months post-injection. However, the spreading pattern of tau pathology observed in our LC-injected mice is different from that in AD brains since hippocampus and entorhinal cortex, which are affected in early stages of AD, were largely spared of tau inclusions in our model. Thus, while our study tested critical aspects of the Braak hypothesis of tau pathology spread, this novel mouse model provides unique opportunities to elucidate mechanisms underlying the selective vulnerability of neurons to acquire tau pathology and succumb to or resist tau-mediated neurodegeneration.

Efferent projections of the suprachiasmatic nucleus based on the distribution of vasoactive intestinal peptide (VIP) and arginine vasopressin (AVP) immunoreactive fibers in the hypothalamus of Sapajus apella.

The suprachiasmatic nucleus (SCN), which is considered to be the master circadian clock in mammals, establishes biological rhythms of approximately 24 h that several organs exhibit. One aspect relevant to the study of the neurofunctional features of biological rhythmicity is the identification of communication pathways between the SCN and other brain areas. As a result, SCN efferent projections have been investigated in several species, including rodents and a few primates. The fibers originating from the two main intrinsic fiber subpopulations, one producing vasoactive intestinal peptide (VIP) and the other producing arginine vasopressin (AVP), exhibit morphological traits that distinguish them from fibers that originate from other brain areas. This distinction provides a parameter to study SCN efferent projections. In this study, we mapped VIP (VIP-ir) and AVP (AVP-ir) immunoreactive (ir) fibers and endings in the hypothalamus of the primate Sapajus apella via immunohistochemical and morphologic study. Regarding the fiber distribution pattern, AVP-ir and VIP-ir fibers were identified in regions of the tuberal hypothalamic area, retrochiasmatic area, lateral hypothalamic area, and anterior hypothalamic area. VIP-ir and AVP-ir fibers coexisted in several hypothalamic areas; however, AVP-ir fibers were predominant over VIP-ir fibers in the posterior hypothalamus and medial periventricular area. This distribution pattern and the receiving hypothalamic areas of the VIP-ir and AVP-ir fibers, which shared similar morphological features with those found in SCN, were similar to the patterns observed in diurnal and nocturnal animals. This finding supports the conservative nature of this feature among different species. Morphometric analysis of SCN intrinsic neurons indicated homogeneity in the size of VIP-ir neurons in the SCN ventral portion and heterogeneity in the size of two subpopulations of AVP-ir neurons in the SCN dorsal portion. The distribution of fibers and morphometric features of these neuronal populations are described and compared with those of other species in the present study.

Regulation of body temperature and brown adipose tissue thermogenesis by bombesin receptor subtype-3.

Bombesin receptor subtype-3 (BRS-3) regulates energy homeostasis, with Brs3 knockout (Brs3(-/y)) mice being hypometabolic, hypothermic, and hyperphagic and developing obesity. We now report that the reduced body temperature is more readily detected if body temperature is analyzed as a function of physical activity level and light/dark phase. Physical activity level correlated best with body temperature 4 min later. The Brs3(-/y) metabolic phenotype is not due to intrinsically impaired brown adipose tissue function or in the communication of sympathetic signals from the brain to brown adipose tissue, since Brs3(-/y) mice have intact thermogenic responses to stress, acute cold exposure, and ß3-adrenergic activation, and Brs3(-/y) mice prefer a cooler environment. Treatment with the BRS-3 agonist MK-5046 increased brown adipose tissue temperature and body temperature in wild-type but not Brs3(-/y) mice. Intrahypothalamic infusion of MK-5046 increased body temperature. These data indicate that the BRS-3 regulation of body temperature is via a central mechanism, upstream of sympathetic efferents. The reduced body temperature in Brs3(-/y) mice is due to altered regulation of energy homeostasis affecting higher center regulation of body temperature, rather than an intrinsic defect in brown adipose tissue.

Efferent projections of neuropeptide Y-expressing neurons of the dorsomedial hypothalamus in chronic hyperphagic models.

The dorsomedial hypothalamus (DMH) has long been implicated in feeding behavior and thermogenesis. The DMH contains orexigenic neuropeptide Y (NPY) neurons, but the role of these neurons in the control of energy homeostasis is not well understood. NPY expression in the DMH is low under normal conditions in adult rodents but is significantly increased during chronic hyperphagic conditions such as lactation and diet-induced obesity (DIO). To understand better the role of DMH-NPY neurons, we characterized the efferent projections of DMH-NPY neurons using the anterograde tracer biotinylated dextran amine (BDA) in lactating rats and DIO mice. In both models, BDA- and NPY-colabeled fibers were limited mainly to the hypothalamus, including the paraventricular nucleus of the hypothalamus (PVH), lateral hypothalamus/perifornical area (LH/PFA), and anteroventral periventricular nucleus (AVPV). Specifically in lactating rats, BDA-and NPY-colabeled axonal swellings were in close apposition to cocaine- and amphetamine-regulated transcript (CART)-expressing neurons in the PVH and AVPV. Although the DMH neurons project to the rostral raphe pallidus (rRPa), these projections did not contain NPY immunoreactivity in either the lactating rat or the DIO mouse. Instead, the majority of BDA-labeled fibers in the rRPa were orexin positive. Furthermore, DMH-NPY projections were not observed within the nucleus of the solitary tract (NTS), another brainstem site critical for the regulation of sympathetic outflow. The present data suggest that NPY expression in the DMH during chronic hyperphagic conditions plays important roles in feeding behavior and thermogenesis by modulating neuronal functions within the hypothalamus, but not in the brainstem.

Calcitonin gene-related peptide in the bed nucleus of the stria terminalis produces an anxiety-like pattern of behavior and increases neural activation in anxiety-related structures.

Calcitonin gene-related peptide (CGRP) evokes anxiety-like responses when infused into the lateral ventricle of rats. Because the bed nucleus of the stria terminalis (BNST) lies immediately adjacent to the lateral ventricle, is rich in CGRP receptors, and has itself been implicated in anxiety, we evaluated the hypothesis that these effects are attributable to stimulation of CGRP receptors within the BNST itself. Bilateral intra-BNST, but not dorsal, CGRP infusions (0, 200, 400, 800 ng/side) enhanced startle amplitude in a dose-dependent manner, and produced an anxiety-like response on the elevated plus maze. Intra-BNST infusion of the CGRP antagonist, αCGRP(8-37), blocked the effect of CGRP on startle, and also blocked startle potentiation produced by exposure to trimethylthiazoline (a component of fox feces that induces anxiety-like behavior in rats). Intra-BNST, but not dorsal, CGRP infusions also increased c-Fos immunoreactivity in a number of anxiety-related brain areas (central nucleus of the amygdala, locus ceruleus, ventrolateral septal nucleus, paraventricular hypothalamic nucleus, lateral hypothalamus, lateral parabrachial nucleus, dorsal raphe nucleus, and nucleus accumbens shell), all of which receive direct projections from the BNST. Together, the results indicate that the activation of BNST CGRP receptors is both necessary and sufficient for some anxiety responses and that these effects may be mediated by activation of a wider network of BNST efferent structures. If so, inhibition of CGRP receptors may be a clinically useful strategy for anxiety reduction.

Specific and complementary roles for nitric oxide and ATP in the inhibitory motor pathways to rat internal anal sphincter.

BACKGROUND: The neurotransmitters mediating inhibitory pathways to internal anal sphincter (IAS) have not been fully characterized. Our aim was to assess the putative release of nitric oxide, purines and vasoactive intestinal peptide (VIP) from inhibitory motor neurons (MNs) and their role in the myogenic tone, resting membrane potential (RMP) of smooth muscle cells (SMC), spontaneous inhibitory junction potentials (sIJP), mechanical relaxation, and IJP induced by electrical field stimulation (EFS) or nicotine. METHODS: Rat IAS strips were studied using organ baths, microelectrodes, and immunohistochemistry. KEY RESULTS: Internal anal sphincter strips developed active myogenic tone (0.31 g), enhanced and stabilized by prostaglandin F(2α) (PGF2α). L-NNA (1 mmol L(-1)) depolarized SMC and increased tone but did not modify sIJP. In contrast, the specific P2Y(1) receptor antagonist MRS2500 (1 µmol L(-1)) did not modify the RMP or the basal tone but abolished sIJP. Electrical field stimulation and nicotine (10 µmol L(-1)) caused IAS relaxation (-45.9%VS-52.2%), partially antagonized by L-NNA (35%-45%, P ≤ 0.05) and fully abolished by MRS2500 (P ≤ 0.001). Electrical field stimulation induced a biphasic inhibitory junction potential (IJP), the initial fast component was selectively blocked by MRS2500 and the sustained slow component was blocked by L-NNA. Vasoactive intestinal peptide 6-28 (0.1 µmol L(-1)) or α-chymotrypsin (10 U mL(-1)) did not modify the RMP, sIJP, EFS-induced IJP, or relaxation. P2Y(1) receptors were immunolocalized in the circular SMC of IAS. CONCLUSIONS & INFERENCES: The effects of inhibitory MNs on rat IAS are mediated by a functional co-transmission process involving nitrergic and purinergic pathways through P2Y(1) receptors with specific and complementary roles on the control of tone, sIJP, and hyperpolarization and relaxation of IAS following stimulation of inhibitory MNs.

Paraventricular oxytocinergic hypothalamic prevention or interruption of long-term potentiation in dorsal horn nociceptive neurons: electrophysiological and behavioral evidence.

Spinal long-term potentiation (LTP) elicited by noxious stimulation enhances the responsiveness of dorsal horn nociceptive neurons to their normal input, and may represent a key mechanism of central sensitization by which acute pain could turn into a chronic pain state. This study investigated the electrophysiological and behavioral consequences of the interactions between LTP and descending oxytocinergic antinociceptive mechanisms mediated by the hypothalamic paraventricular nucleus (PVN). PVN stimulation or intrathecal oxytocin (OT) reduced or prevented the ability of spinal LTP to facilitate selectively nociceptive-evoked responses of spinal wide dynamic range (WDR) neurons recorded in anesthetized rats. In a behavioral model developed to study the effects of spinal LTP on mechanical withdrawal thresholds in freely moving rats, the long-lasting LTP-mediated mechanical hyperalgesia was transiently interrupted or prevented by either PVN stimulation or intrathecal OT. LTP mediates long-lasting pain hypersensitivity that is strongly modulated by endogenous hypothalamic oxytocinergic descending controls.

Cholecystokinin action on layer 6b neurons in somatosensory cortex.

Layer 6b in neocortex is a distinct sublamina at the ventral portion of layer 6. Corticothalamic projections arise from 6b neurons, but few studies have examined the functional properties of these cells. In the present study we examined the actions of cholecystokinin (CCK) on layer 6b neocortical neurons using whole-cell patch clamp recording techniques. We found that the general CCK receptor agonist CCK8S (sulfated CCK octapeptide) strongly depolarized the neurons, and this action persisted in the presence of tetrodotoxin, suggesting a postsynaptic site of action. The excitatory actions of CCK8S were mimicked by the selective CCK(B) receptor agonist CCK4, and attenuated by the selective CCK(B) receptor antagonist L365260, indicating a role for CCK(B) receptors. Voltage-clamp recordings revealed that CCK8S produced a slow inward current associated with a decreased conductance with a reversal potential near the K(+) equilibrium potential. In addition, intracellular cesium also blocked the inward current, suggesting the involvement of a K(+) conductance, likely K(leak). Our data indicate that CCK, acting via CCK(B) receptors, produces a long-lasting excitation of layer 6b neocortical neurons, and this action may play a critical role in modulation of corticothalamic circuit activity.

Hypothalamospinal oxytocinergic antinociception is mediated by GABAergic and opiate neurons that reduce A-delta and C fiber primary afferent excitation of spinal cord cells.

Recent results implicate a new original mechanism involving oxytocin (OT), as a mediator via descending fibers of the paraventricular hypothalamic nucleus (PVN), in antinociception and analgesia. In rats electrical stimulation of the PVN or topical application of OT selectively inhibits A-delta and C fiber responses in superficial dorsal horn neurons, and this inhibition is reversed by a selective OT antagonist. However, little is known about the mechanisms and the spinal elements participating in this phenomenon. Here we show that topical application of bicuculline blocks the effects produced by PVN electrical stimulation or OT application. PVN electrical stimulation also activates a subpopulation of neurons in lamina II. These PVN-On cells are responsible for the amplification of local GABAergic inhibition. This result reinforces the suggestion that a supraspinal descending control of pain processing uses a specific neuronal pathway in the spinal cord in order to produce antinociception involving a GABAergic interneuron. Moreover, the topical administration of naloxone or a mu-opiate receptor antagonist beta-funaltrexamine only partially blocks the inhibitory effects produced by OT application or PVN electrical stimulation. Thus, this OT mechanism only involves opiate participation to a minor extent. The OT-specific, endogenous descending pathway represents an interesting mechanism to resolve chronic pain problems in special the neuropathic pain.

Activation of orexin/hypocretin projections to basal forebrain and paraventricular thalamus by acute nicotine.

Orexin/hypocretin neurons of the lateral hypothalamus/perifornical area project to a diverse array of brain regions and are responsive to a variety of psychostimulant drugs. It has been shown that orexin neurons are activated by systemic nicotine administration suggesting a possible orexinergic contribution to the effects of this drug on arousal and cognitive function. The basal forebrain and paraventricular nucleus of the dorsal thalamus (PVT) both receive orexin inputs and have been implicated in arousal, attention and psychostimulant drug responses. However, it is unknown whether orexin inputs to these areas are activated by psychostimulant drugs such as nicotine. Here, we infused the retrograde tract tracer cholera toxin B subunit (CTb) into either the basal forebrain or PVT of adult male rats. Seven to 10 days later, animals received an acute systemic administration of (-) nicotine hydrogen tartrate or vehicle and were euthanized 2h later. Triple-label immunohistochemistry/immunofluorescence was used to detect Fos expression in retrogradely-labeled orexin neurons. Nicotine increased Fos expression in orexin neurons projecting to both basal forebrain and PVT. The relative activation in lateral and medial banks of retrogradely-labeled orexin neurons was similar following basal forebrain CTb deposits, but was more pronounced in the medial bank following PVT deposits of CTb. Our findings suggest that orexin inputs to the basal forebrain and PVT may contribute to nicotine effects on arousal and cognition and provide further support for the existence of functional heterogeneity across the medial-lateral distribution of orexin neurons.

V1R and V2R segregated vomeronasal pathways to the hypothalamus.

The vomeronasal system is segregated from the epithelium to the bulb. Two classes of receptor neurons are apically and basally placed in the vomeronasal epithelium, express Gi2alpha and Goalpha proteins and V1R and V2R receptors and project to the anterior and posterior portions of the accessory olfactory bulb, respectively. Apart from common vomeronasal recipient structures in the amygdala, only the anterior accessory olfactory bulb projects to the bed nucleus of the stria terminalis and only the posterior accessory olfactory bulb projects to the dorsal anterior amygdala. The efferent projections from these two amygdaloid structures to the hypothalamus were investigated. These two vomeronasal subsystems mediated by V1R and V2R receptors were partially segregated, not only in amygdala, but also in the hypothalamus.

Glutamatergic pallidothalamic projections and their implications in the pathophysiology of Parkinson's disease.

GABAergic projections emitted from the entopeduncular nucleus (ENT) and the substantia nigra pars reticulata (SNr) innervate different thalamic nuclei and they are known to be hyperactive after dopaminergic depletion. Here we show that isoform 2 of the vesicular glutamate transporter (VGLUT2) is expressed by neurons in the ENT nucleus but not in the SNr. Indeed, dual in situ hybridization demonstrated that the ENT nucleus contains two different subpopulations of projection neurons, one single-expressing GAD65/67 mRNAs and another one that co-expresses either of the GAD isoforms together with VGLUT2 mRNA. Unilateral dopaminergic depletion induced marked changes in pallidothalamic-projecting neuron gene expression, resulting in increased expression of GAD65/67 mRNAs together with a clear down-regulation of VGLUT2 mRNA expression. Our results indicate that the increased thalamic inhibition typical of dopamine depletion might be explained by a synergistic effect of increased GABA outflow coupled to decreased glutamate levels, both neurotransmitters coming from ENT neurons.

Collapsin response mediator protein-4 (CRMP-4) expression in posthaching development of song control nuclei in Bengalese finches.

CRMP-4 is regarded to play a role in neuronal differentiation, neurite growth and synapse formation. It has been shown to express in brain areas undergoing plastic changes or neuronal generation. Bird song is a learned, complex behavior. During song learning, some neural changes occur dramatically within song nuclei in neuron number, neuronal morphology, and synaptic formation or rearrangements. In order to get insights into the potential functions of CRMP-4 in the posthatching development of song nuclei during song learning, we examined the expression of CRMP-4 protein and mRNA in song control nuclei of Bengalese finch (Lonchura striata) from posthatching days (P) 10 to adulthood. Our study showed that cells positive for CRMP-4 protein and mRNA were distributed in song nuclei nearly in all the studied groups. The numbers of CRMP-4 cells in most of studied song nuclei changed significantly with age. They reached the peak at P15 in the lateral magnocellular nucleus of anterior nidopallium (LMAN) and the caudal medial nidopallium (NCM), or at P25 in HVC, Area X and the dorsolateral nucleus of the medial anterior thalamus (DLM). They then continued to decrease till adulthood. CRMP-4 protein and mRNA were both relatively high expressed during the post-hatch development of song control nuclei and song learning (P20-60), suggesting that CRMP-4 is involved in these activities. Although CRMP-4 protein and mRNA largely decreased at adulthood, they continued to express moderately, revealing that CRMP-4 may play a role in the maintenance of adult song nuclei.

Morphometric analysis of the AMPA-type neurons in the Deiter's vestibular complex of the chick brain.

Chicken (Gallus gallus) brains were used to investigate the typology and the immunolabel pattern for the subunits composing the AMPA-type glutamate receptors (GluR) of hindbrain neurons of the dorsal (dND) and ventral nuclei (vND) of the Deiter's vestibular complex (CD), which is the avian correspondent of the lateral vestibular nucleus (LVN) of mammals. Our results revealed that neurons of both divisions were poor in GluR1. The vND, the GluR2/3+ and GluR4+ label presented no area or neuronal size preference, although most neurons were around 75%. The dND neurons expressing GluR2/3 are primarily around 85%, medium to large-sized 85%, and predominantly 60% located in the medial portion of the rostral pole and in the lateral portion of the caudal pole. The majority of dND neurons containing GluR4 are also around 75%, larger (70% are large and giant), exhibiting a distribution that seems to be complementary to that of GluR2/3+ neurons. This distinct arrangement indicates functional differences into and between the DC nuclei, also signaling that such variation could be attributed to the diverse nature of the subunit composition of the GluRs. Discussion addresses the morphological and functional correlation of the avian DC with the LVN of mammals in addition to the high morphological correspondence, To include these data into the modern comparative approach we propose to adopt a similar nomenclature for the avian divisions dND and vND that could be referred as dLVN and vLVN.

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.

Efferent association pathways originating in the caudal prefrontal cortex in the macaque monkey.

The efferent association fibers from the caudal part of the prefrontal cortex to posterior cortical areas course via several pathways: the three components of the superior longitudinal fasciculus (SLF I, SLF II, and SLF III), the arcuate fasciculus (AF), the fronto-occipital fasciculus (FOF), the cingulate fasciculus (CING F), and the extreme capsule (Extm C). Fibers from area 8Av course via FOF and SLF II, merging in the white matter of the inferior parietal lobule (IPL) and terminating in the caudal intraparietal sulcus (IPS). A group of these fibers turns ventrally to terminate in the caudal superior temporal sulcus (STS). Fibers from the rostral part of area 8Ad course via FOF and SLF II to the IPS and IPL and via the AF to the caudal superior temporal gyrus and STS. Some fibers from the rostral part of area 8Ad are conveyed to the medial parieto-occipital region via FOF, to the STS via Extm C, and to the caudal cingulate gyrus via CING F. Fibers from area 8B travel via SLF I to the supplementary motor area and area 31 in the caudal dorsal cingulate region and via the CING F to cingulate areas 24 and 23 and the cingulate motor areas. Fibers from area 9/46d course via SLF I to the superior parietal lobule and medial parieto-occipital region, via SLF II to the IPL. Fibers from area 9/46v travel via SLF III to the rostral IPL and the frontoparietal opercular region and via the CING F to the cingulate gyrus.

Distribution of hypothalamic, hippocampal and other limbic peptidergic neuronal cell bodies giving rise to retinopetal fibers: anterograde and retrograde tracing and neuropeptide immunohistochemical studies.

In our present work utilizing the retrograde or anterograde transport of tracers (biotinylated dextran amine and Fluorogold, respectively) we have provided direct evidence for the cells of origin of the limboretinal pathway in rats and their termination in the retina using light microscopic approach. Administration of biotinylated dextran amine into the vitreous body resulted in nerve cell body labeling in several structures: the supraoptic and paraventricular nuclei, the hippocampus (CA1, CA3), the dentate gyrus, the indusium griseum, the olfactory tubercle, and the medial habenula, all of them belong to the limbic system. We estimated that the total number of retrogradely labeled cells is 1495+/-516. We have seen fiber labeling in the retinorecipient suprachiasmatic nucleus and in the primary visual center, the lateral geniculate body, but labeled nerve cell bodies in these structures were never seen. Iontophoretic application of Fluorogold into the hippocampal formation, where the major part of the biotinylated dextran amine-labeled cell bodies was observed, resulted in labeled fibers in the optic nerve and in the retina indicating that the retrogradely labeled cells in the hippocampus and the dentate gyrus among others are the cells of origin of the centrifugal visual fibers. Sections showing biotinylated dextran amine labeling were stained for vasoactive intestinal polypeptide, pituitary adenylate cyclase activating polypeptide or luteinizing hormone-releasing hormone immunoreactivity using immunohistochemistry. Some biotinylated dextran amine-labeled cells also showed vasoactive intestinal polypeptide, pituitary adenylate cyclase activating polypeptide or luteinizing hormone-releasing hormone immunoreactivity. We conclude that the limboretinal pathway exists and that the cells of origin are partially vasoactive intestinal polypeptide, pituitary adenylate cyclase activating polypeptide or luteinizing hormone-releasing hormone immunoreactive.

Projections from the entorhinal cortex, perirhinal cortex, presubiculum, and parasubiculum to the medial thalamus in macaque monkeys: identifying different pathways using disconnection techniques.

The projections from the perirhinal cortex, entorhinal cortex, parasubiculum, and presubiculum to the thalamus were examined using both anterograde and retrograde tracers. Attention focused on the routes taken by these projections, which were delineated by combining surgical tract section with the placement of a tracer. Projections to the anterior thalamic nuclei almost exclusively used the fornix. These relatively light projections, which arose from all areas of the entorhinal cortex, from the presubiculum, parasubiculum, and area 35 of the perirhinal cortex, terminated mainly in the anterior ventral nucleus. In contrast, the projections to the lateral dorsal nucleus from the entorhinal cortex, presubiculum and parasubiculum were denser than those to the anterior thalamic nuclei. The projections to the lateral dorsal nucleus used two routes. While nearly all of the projections from the subicular complex used the fornix, many of the entorhinal cortex projections passed caudally in the temporopulvinar bundle to reach the lateral dorsal nucleus. The perirhinal cortex, as well as the entorhinal cortex, also projects to nucleus medialis dorsalis. These projections exclusively used the external capsule and thence the inferior thalamic peduncle. Other temporal-thalamic projections included those to the medial pulvinar, via the temporopulvinar bundle, from the perirhinal and entorhinal cortices, and those to the paraventricular nucleus from the entorhinal cortex. By identifying these routes, it is possible to appreciate how different lesions might disconnect temporal-diencephalic pathways and so contribute to memory disorders.

Stimulation of the lateral hypothalamus produces antinociception mediated by 5-HT1A, 5-HT1B and 5-HT3 receptors in the rat spinal cord dorsal horn.

The lateral hypothalamus is part of an efferent system that modifies pain at the spinal cord dorsal horn, but the mechanisms by which lateral hypothalamus-induced antinociception occur are not fully understood. Previous work has shown that antinociception produced from electrical stimulation of the lateral hypothalamus is mediated in part by spinally projecting 5-hydroxytryptamine (5-HT) neurons in the ventromedial medulla. To further examine the role of the lateral hypothalamus in antinociception, the cholinergic agonist carbamylcholine chloride (125 nmol) was microinjected into the lateral hypothalamus of female Sprague-Dawley rats and nociceptive responses measured on the tail-flick and foot-withdrawal tests. Intrathecal injections of the selective 5-HT1A, 5-HT1B, 5-HT3 receptor antagonists, WAY 100135, SB-224289, and tropisetron, respectively, and the non-specific antagonist methysergide, were given. Lateral hypothalamus stimulation with carbamylcholine chloride produced significant antinociception that was blocked by WAY 100135, tropisetron, and SB-224289 on both the tail-flick and foot-withdrawal tests. Methysergide was not different from controls on the tail flick test, but increased foot-withdrawal latencies compared with controls. These results suggest that the lateral hypothalamus modifies nociception in part by activating spinally projecting serotonin neurons that act at 5-HT1A, 5-HT1B, and 5-HT3 receptors in the dorsal horn.