Intrinsic and efferent connections of the endopiriform nucleus in rat.

The endopiriform nucleus is a large group of multipolar cells located deep to the piriform cortex. The function of this nucleus is unknown, but studies with animal models suggest that it plays an important role in temporal lobe epileptogenesis. To address questions concerning mechanisms of epileptogenesis and to gain insights into its normal function, efferent axons from the endopiriform nucleus were labeled by anterograde transport from small extracellular injections of Phaseolus vulgaris leucoagglutinin. Several principles of organization were derived: (1) heavy local and long intrinsic connections are present throughout the endopiriform nucleus; (2) endopiriform efferents target cortical rather than nuclear structures; (3) extensive projections from the endopiriform nucleus extend to most basal forebrain areas including the piriform cortex, entorhinal cortex, insular cortex, orbital cortex, and all cortical amygdaloid areas. The perirhinal cortex, olfactory tubercle, and most subdivisions of the hippocampal formation receive light projections; (4) projections are highly distributed spatially within all target areas; (5) efferent axons from the endopiriform nucleus are unmyelinated and give rise to boutons along their entire course rather than arborizing locally; and (6) the endopiriform nucleus and piriform cortex share target areas, but efferents from the endopiriform nucleus lack the precise laminar order of those from the piriform cortex, and provide a heavy caudal to rostral pathway that is lacking in the cortex. The significance of these findings for the triggering of generalized seizures from the deep piriform region are discussed. An hypothesis for a role of the endopiriform nucleus in memory storage is presented.     

c-fos mRNA, Fos, and Fos-related antigen induction by hypertonic saline and stress

The induction of c-fos mRNA was assessed using Northern blots and in situ hybridization in adult rats administered hypertonic saline (HS) and isotonic saline (IS). HS induced c-fos mRNA in magnocellular paraventricular nucleus (PVNm), parvocellular paraventricular nucleus (PVNp), supraoptic nucleus (SON), and lamina terminalis (LMT). This occurred within 5 min, peaked at 30-60 min, and disappeared by 180 min. Fos protein, detected using a specific monoclonal antibody, was maximal at 1-2 hr and disappeared 4-8 hr after HS administration. This confirms observations showing that the c-fos gene response is transient even in the presence of a continuing stimulus. In contrast, Fos-like immunoreactivity (FLI), detected using two polyclonal antisera, was observed in PVNm, PVNp, SON, and LMT for 1-24 hr during continuous osmotic stimulation. Moreover, FLI was observable in these structures for 7 d in rats administered HS and allowed to drink water ad libitum beginning 24 hr later. At times greater than 8 hr, FLI presumably represents Fos-related antigens (FRA), proteins immunologically and functionally related to Fos, whose expression is much more prolonged than authentic Fos following the osmotic stimulus. In addition to induction of c-fos expression in regions specifically involved in osmotic regulation, HS injections also induced c-fos in many other forebrain regions. In order to assess the induction of c-fos mRNA due to the "stress" of the injections, rats injected with isotonic saline were compared to uninjected controls. Isotonic saline injections induced c-fos mRNA in the PVNp, anterior hypothalamus, suprachiasmatic nucleus, cingulate gyrus, neocortex, ventral lateral septal nucleus, piriform cortex, hippocampal pyramidal and dentate granule neurons, paraventricular and intralaminar thalamic nuclei, bed nuclei of stria terminalis, cortical and medial amygdaloid nuclei, and other structures. In accord with other work, we interpret this pattern of c-fos expression to result from the stress of handling and injections. Since Fos and FRA probably bind to the promoters of target genes and regulate their expression, they likely mediate biochemical changes in the cells activated by the osmotic and stressful stimuli. Whereas the Fos signal is transient, FRA may act on target genes for the duration of the stimulus or longer.     

Anesthetic-dependent excitability changes in the hypothalamic ventromedial nucleus of the rat

In acute experiments in rats anesthetized with urethane, the field potentials, population spike, and unit activity evoked in the hypothalamic ventromedial nucleus (HVM) by amygdaloid stimulation are significantly increased with respect to control when preceded by a conditioning volley at 20- to 100-ms intervals. Under pentobarbital anesthesia, in contrast, the evoked responses were inhibited by the conditioning stimulus for similar interstimulus intervals. In unanesthetized animals chronically implanted with stimulating and recording electrodes, a facilitation of responses by a conditioning stimulus was observed when they were awake or anesthetized with urethane. When the same animals were anesthetized with pentobarbital the HVM evoked response was inhibited by a conditioning pulse. Frequency facilitation and post-tetanic potentiation of HVM responses were markedly enhanced under urethane, whereas in pentobarbital-anesthetized animals inhibition predominated. Picrotoxin reversed the inhibition under pentobarbital to facilitation. These results suggest that the HVM neuron population is under both excitatory and inhibitory influences from the amygdala, the former being predominant in awake and urethane-anesthetized animals and the latter being expressed under pentobarbital anesthesia and is probably mediated by γ-aminobutyric acid.     

Estrogen receptor immunoreactivity within subregions of the rat forebrain: neuronal distribution and association with perikarya containing choline acetyltransferase

Administration of the neuroactive steroid hormone estrogen has been shown to effect cholinergic basal forebrain neuronal function. Antibodies directed against the estrogen receptor alpha (ERalpha) revealed dark (type 1) and light (type 2) nuclear positive neurons within the islands of Calleja, endopiriform nucleus, lateral septum, subfields of the cholinergic basal forebrain, bed nucleus of the stria terminalis, striohypothalamic region, medial preoptic region, periventricular, ventromedial, arcuate and tuberal mammillary nuclei of the hypothalamus, reuniens and anterior medial thalamic nuclei, amygdaloid complex, piriform cortex and subfornical organ. In contrast, only a few scattered ERalpha labeled neurons were found in cortex and hippocampus. ERalpha stained cell bodies were not seen in the striatum. Counts of ERalpha labeled neurons in intact female rats revealed significantly more type 2 neurons within the basal forebrain subfields. Quantitation of ERalpha immunoreactive neurons revealed a significant decrease in the relative number of type 1 neurons within the medial septum (MS), horizontal limb of the diagonal band (HDB) and substantia innominata/nucleus basalis (SI/NB) following ovariectomy. Quantitation following choline acetyltransferease (ChAT) immunohistochemistry revealed a significant decrease in the number of ChAT positive neurons within the MS, HDB and SI/NB, but not VDB following ovariectomy. Following ovx, the percentage of double labeled cholinergic basal forebrain neurons also declined significantly within the MS, VDB, HDB and SI/NB. These observations suggest that estrogen effects a subpopulation of cholinergic basal forebrain neurons and may provide insight into the biologic actions of this steroid in Alzheimer's disease.     

The topographic organization of associational fibers of the olfactory system in the rat, including centrifugal fibers to the olfactory bulb

This study analyzed the topographic organization of the associational fibers within the olfactory cortex of the rat, by using the autoradiographic method. Small injections of 3H-leucine were placed in all of the subdivisions of the olfactory cortex, to label selectively the fibers arising in each area. Intracortical fibers were identified from all of the olfactory cortical areas except the olfactory tubercle and were classified into two major systems (the layer Ib system and the layer II-deep Ib system) on the basis of their laminar pattern of termination (see Luskin and Price, '83). The layer Ib fiber system arises in the anterior olfactory nucleus, piriform cortex, and lateral entorhinal area, and is broadly organized in relation to the lateral olfactory tract. Cortical areas deep to or near the lateral olfactory tract are preferentially interconnected with areas near the tract, while parts of the cortex lateral and caudal to the lateral olfactory tract are most heavily interconnected with areas lateral, caudal, and medial to the tract. Commissural projections from the anterior olfactory nucleus and the anterior piriform cortex match some (but not all) components of the ipsilateral layer Ib fiber system. The layer II-deep Ib fiber system arises in three small areas--the ventral tenia tecta, the dorsal peduncular cortex, and the periamygdaloid cortex. The fibers from the ventral tenia tecta terminate in layer II of the anterior olfactory nucleus and are topographically organized. The fibers from the dorsal peduncular cortex and the periamygdaloid cortex are more widely distributed, especially in the lateral and caudal parts of the cortex. Two other intracortical projections do not fit into either of these fiber systems. The nucleus of the lateral olfactory tract projects bilaterally to the islands of Calleja and the medial edge of the anterior piriform cortex. The anterior cortical nucleus projects to many parts of the olfactory cortex, but the fibers end in both superficial and deep parts of layer I (layer Ia and Ib). There are projections from several of the olfactory cortical areas to the cortical areas surrounding the olfactory cortex. Virtually all of the olfactory areas also project to the ventral and dorsal endopiriform nuclei deep to the piriform cortex and/or to the polymorph zone deep to the olfactory tubercle. In addition, projections have been demonstrated to the deep amygdaloid nuclei, especially from the more ventromedial and caudal parts of the olfactory cortex.     

Establishing aversive, but not safe, taste memories requires lateralized pontine-cortical connections

Aversive and safe taste memory processing is dramatically disrupted by bilateral lesions of the pontine parabrachial nucleus (PBN). To determine how such lesions affect patterns of neuronal activation in forebrain, lesions were combined with assessment of cFos-like immunoreactivity (FLI) in insular cortex (IC) and amygdala after conditioned taste aversion (CTA) training. Increases in FLI in amygdala and IC, which are normally seen following novel (versus familiar) CS-US pairing, were eliminated after PBN lesions. This suggests that PBN lesions prevent transmission of critical CS and US information to forebrain regions for the processing of both aversive and safe taste memories. Unilateral asymmetrical lesions of PBN and IC blocked CTA acquisition as well as normal patterns of FLI in amygdala after novel CS-US pairing, an effect not seen when unilateral lesions were confined to a single hemisphere. The crossed-disconnection experiments provide compelling evidence that functional interactions between PBN and IC are required for CTA acquisition, but not for safe taste memory formation and retrieval. The dissociation between effects of the different types of lesions on safe and aversive taste memories supports emerging evidence that the neural underpinnings of the two types of taste learning differ.     

Localization of binding sites for oxytocin in the brain of the golden hamster.

Using a radioiodinated ligand and autoradiography on film, specific binding sites for oxytocin were detected in the brain of the golden hamster. Sites were present in the endopiriform nucleus, the cingulate cortex, the islands of Calleja, the lateral septum, the dorsal hippocampus and the amygdala. The distribution of these binding sites was similar in males and females and was independent of the photoperiod. No binding sites were detected in the ventromedial hypothalamic nucleus or in the dorsal motor nucleus of the vagus nerve; areas which were labelled in the rat and where oxytocin is thought to participate in the control of sexual and autonomic functions. These data suggest that the role of oxytocin in the brain may differ among mammalian species.     

Cerebellocerebral projection from the fastigial nucleus onto the frontal eye field and anterior ectosylvian visual area in the cat

The fastigiocerebral projection in the cat was investigated electrophysiologically by recording field potentials and unit activities and also morphologically by anterograde and retrograde HRP methods. Three cortical areas mostly hidden in sulci, two in the frontal cortex and one in the insular cortex, were responsive to fastigial stimulation under pentobarbital anesthesia. The responsive areas in the frontal cortex were the ventral bank of the cruciate sulcus and the area surrounding the fundus of the presylvian sulcus; the latter area corresponds to a subregion of the frontal eye field. The responsive area in the insular cortex was the ventral bank of the anterior ectosylvian sulcus, which overlaps largely with the "anterior ectosylvian visual area." The response in the frontal cortex was a surface-positive, depth-negative wave, whereas the response in the insular cortex was a surface-negative, depth-positive wave. Anterogradely labeled terminals of the fastigiothalamic projection were most dense in the ventromedial (VM) nucleus in which retrogradely labeled neurons were numerous when WGA-HRP was injected into any one of the three cortical areas. In agreement with the results of the HRP studies, units that responded orthodromically to fastigial stimulation and antidromically to cortical stimulation were located in the thalamic VM nucleus. There was a marked difference between the frontal and insular cortices in laminar distribution of terminals of the thalamocortical projection fibers. Anterogradely labeled terminals after injection of WGA-HRP into the VM nucleus were distributed mainly in layers I and III in the frontal cortex, whereas they were distributed mainly in layer I in the insular cortex.     

The claustrum is not missing from all monotreme brains

Many authors have reported that the claustrum, which comprises the insular claustrum and the endopiriform nucleus, is missing from the monotreme forebrain. We used Nissl and myelin staining in conjunction with enzyme histochemistry for acetylcholinesterase and immunohistochemistry for parvalbumin, calbindin, calretinin and tyrosine hydroxylase to examine the brains of two monotremes, the short-beaked echidna (Tachyglossus aculeatus) and the platypus (Ornithorhynchus anatinus). We found that although the insular claustrum is a small structure in the echidna brain, it is nevertheless clearly present as loosely clustered neurons embedded in the white matter ventrolateral to the putamen and deep to the piriform and entorhinal cortices. Neurons in this region share the chemical features of the adjacent cortex (presence of a similar proportion of parvalbumin immunoreactive neurons and minimal activity for acetylcholinesterase and tyrosine hydroxylase), unlike the adjacent putamen and ventral pallidum. A putative endopiriform nucleus can be identified in the interior of the piriform lobe of the echidna as calretinin immunoreactive neurons embedded within the white matter. The situation is much less clear in the platypus, but our data suggest that there may be an insular claustrum deep to frontal cortex, separated from layer VI by only a thin layer of white matter. We could not identify an endopiriform nucleus in our platypus material. Our findings indicate that presence of the claustrum cannot be considered a feature confined to therian mammals and lend weight to arguments that this structure was present in the ancestral mammalian brain.     

The islands of Calleja complex of rat basal forebrain II: Connections of medium and large sized cells

The connections of the medium (10–20 μm) and large (20–35 μm) cells of the islands of Calleja Complex (ICC) were studied in the albino rat with anterograde and retrograde transport of horseradish peroxidase (HRP) and fluorescent tracers. The medium and large size cells were found to project to the ipsilateral olfactory tubercle, ventral pallidum, septum, piriform cortex, periamygdaloid cortex, cortical nuclei of the amygdala, ventral endopiriform nucleus, lateral hypothalamic area, Forel's field H, ventral tegmental area, supramammillary complex, and nuclei gemini of the hypothalamus, midline, intralaminar and medial thalamic nuclei, and lateral habenula. Afferents of the ICC appear to include the same nuclei with the exception of the lateral habenula. In addition, the dorsal raphe projects to the ICC. These connections are consistent with the concept that the ICC is a striato-pallidal structure.     

Retrograde transport of brain-derived neurotrophic factor (BDNF) following infusion in neo-and limbic cortex in rat: Relationship to BDNF mRNA expressing neurons

Brain-derived neurotrophic factor (BDNF) was the second member of the nerve growth factor (NGF) family to be isolated. The ability of BDNF to be retrogradely transported following intraparenchymal infusion represents a unique neurobiological tool to determine the location of putative neuron-specific BDNF-responsive neuronal systems. In the present study, we infused recombinant human (rh) BDNF into the rodent neo- and limbic cortex and used a turkey anti-BDNF antibody to determine specific populations of neurons which retrogradely transport this neurotrophin. Frontal cortex infusion retrogradely labeled neurons within the ipsilateral and contralateral frontal cortex, basal forebrain, lateral hypothalamus, centrolateral, mediodorsal, ventrolateral, ventromedial, ventral posterior, rhomboid, reuniens, and medial geniculate thalamic nuclei, and locus coeruleus. Occipital cortex infusion retrogradely labeled neurons in the frontal, temporal, occipital, and perirhinal cortices as well as the claustrum, basal forebrain, thalamus, epithalamus, hypothalamus, and raphe nuclei. Dorsal hippocampal infusion retrogradely labeled neurons within the septal diagonal band, supramammillary nucleus, and entorhinal cortex and was also transported within various hippocampal subfields. Entorhinal cortex infusion retrogradely labeled neurons within the perirhinal cortex, endopiriform nucleus, piriform cortex, dentate gyrus, presubiculum, parasubiculum, CA1-CA4 fields, amygdaloid nuclei, basal forebrain, thalamus, hypothalamus, periaqueductal gray, raphe nuclei, and locus coeruleus. Amygdala infusion labeled neurons in the endopiriform nucleus, temporal cortex, piriform cortex, paralimbic cortex, hippocampus, subiculum, entorhinal cortex, amygdala, basal forebrain, thalamus, hypothalamus, substantia nigra, pars compacta, raphe, and pontine parabrachial-nuclei. In situ hybridization experiments demonstrated that virtually all areas which retrogradely transport BDNF also express its message. Neuroanatomical distributional studies of BDNF will unravel specific central nervous system neurotrophic-responsive systems. © 1996 Wiley-Liss, Inc.     

Parabrachial nucleus projection towards the hypothalamic supraoptic nucleus: electrophysiological and anatomical observations in the rat

It has been proposed that the pontine parabrachial nucleus (PBN) participates in the regulation of body fluid balance and the release of vasopressin from the neurohypophysis, although the pathways mediating the latter response are uncertain. This study in the rat, utilizing anatomical and electrophysiological methods, describes a projection from the lateral PBN towards the hypothalamic supraoptic nucleus (SON). Rats received iontophoretic injections of the anterograde tracer Phaseolus vulgaris leucoagglutinin (PHA-L, 2% solution). After 14-17 days, rats were sacrificed and their brains prepared for immunofluorescent visualization of projections to the SON region. PHA-L-labelled terminals were found primarily in perinuclear regions immediately dorsal to the SON. In contrast, injections within the medial PBN and the nearby K?lliker-Fuse nucleus did not reveal labelling in or around the SON. Extracellular recordings from 86 of 118 antidromically identified neurons in anaesthetized rats revealed a set of complex synaptic responses after stimulation in the PBN. Excitatory responses (in 82 of 86 cells) of short (less than 100 msec, 39/82 cells) and long (greater than 100 msec, 43/82) duration were observed in both vasopressin- and oxytocin-secreting cells of the SON, while 4/86 cells displayed a depressant response to PBN stimulation. In the adjacent perinuclear zone, 22/39 nonneurosecretory cells responded with an increase in their excitability consequent to an identical stimulus. These data suggest a predominantly facilitatory influence of lateral PBN neurons on SON neurosecretory cells in the rat, and that the PBN-SON projection is an indirect one that utilizes an interneuronal network located in the perinuclear zone adjacent to the SON.     

ARC POMC mRNA and PVN alpha-MSH are lower in obese relative to lean zucker rats

The binding sites of nociceptin (also named orphanin FQ), the endogenous ligand of ORL1 (opiate receptor like 1), were localized in rat brain, using an autoradiographic procedure. High levels of binding were observed in the cingulate, retrosplenial, perirhinal, insular and occipital cortex, anterior and posteromedial cortical amygdaloid nuclei, basolateral amygdaloid nucleus, amygdaloid complex, posterior hippocampus, dorsal endopiriform, central medial thalamic, paraventricular, rhomboid thalamic, suprachiasmatic, ventromedial hypothalamic nuclei, mammillary complex, superficial gray layer of the superior colliculus, locus coeruleus, dorsal raphe nucleus. More moderate labelling was observed in the prefrontal, fronto–parietal, temporal, piriform cortex, dentate gyrus, anterior olfactory nucleus, olfactory tubercle, shell of nucleus accumbens, claustrum, lateral septum, laterodorsal thalamic, medial habenular, subthalamic, reuniens thalamic nuclei, subiculum, periaqueductal grey matter and pons. A lower binding site density was observed in the anterior and medial hippocampus, olfactory bulb, caudate putamen, the core of the nucleus accumbens, medial septum, ventrolateral, ventroposterolateral and mediodorsal thalamic nuclei, lateral and medial geniculate nuclei, hypothalamic area, substantia nigra, ventral tegmentum area and interpedoncular nucleus. A moderate and similar labelling was found in the dorsal and ventral horn of the spinal cord. No labelling was apparent in the corpus callosum. Thus, it appears that the ORL1 receptor is particularly abundant in the cerebral cortex, limbic system of the rat brain and some areas involved in pain perception.     

The topographical organization of neurons in the rat medial frontal, insular and olfactory cortex projecting to the solitary nucleus, olfactory bulb, periaqueductal gray and superior colliculus

In 19 rats two different retrograde tracers (Fast Blue, Diamidino Yellow, Rhodamine-labeled latex microspheres, or wheat germ agglutinin conjugated with HRP) were injected into the solitary nucleus (NTS) and either the olfactory bulb (OB), periaqueductal gray (PAG) or superior colliculus (SC). The pattern of retrogradely labeled neurons in the medial frontal, insular and olfactory cortices was examined to determine the topographical organization of the cell populations projecting to these subcortical targets and the extent to which they overlapped. In the medial frontal cortex (MFC) SC projections originated most dorsally, while NTS and OB projections originated most ventrally and exhibited slight overlap. PAG projections originated from virtually the entire MFC and overlapped with cells projecting to the OB, NTS and SC. These results are consistent with the role of dorsal MFC as the rat's frontal eye field and the ventral MFC as a visceral motor area. Laterally, in the insular cortex there was virtually complete overlap between cells projecting to the NTS and PAG. The extensive overlap of PAG projections with NTS projections medially and laterally and with SC projections medially suggests the PAG is involved in a variety of brain visceral and somatic functions. In the piriform cortex there was overlap between cells projecting to the OB and cells projecting to the SC; the cells projecting to the SC were located in the endopiriform nucleus, and may provide a substrate for orienting responses to odors.     

Preferential neuron loss in the rat piriform cortex following pilocarpine-induced status epilepticus

Structures within the piriform cortex (PC) including the endopiriform nucleus (DEN) and pre-endopiriform nucleus (pEn) have been implicated to be involved in seizure genesis in models of temporal lobe epilepsy. We used stereological methods to examine the specificity and extent of neuron loss in the PC of pilocarpine-treated rats. Both 7 days and 2 months post-status epilepticus rats showed significant neuron loss in the pEn and DEN, layer III of the intermediate PC, and layers II and III of the caudal PC. Total losses in the PC were 40 and 46% in 7 days and 2 months post-status epilepticus rats, respectively (p<0.01). The numbers of parvalbumin (PV)- and cholecystokinin (CCK)-immunopositive neuron profiles significantly decreased, and somatostatin (SS)-immunopositive neuron profiles tended to decrease. A large decrease in the number of PV-immunopositive neuron profiles occurred in the pEn, adjoining parts of the DEN and deep layer III of the PC, portions of the DEN bordering the claustrum and agranular insular cortex, and layer III of the caudal PC. The regions with decreased numbers of PV-, CCK-, and SS-immunopositive neuron profiles overlapped with those where many Nissl-stained neurons were lost and many degenerating cell bodies were detected. These results suggest that the decreases in the numbers of PV/SS/CCK-immunopositive neurons are related to neuron loss rather than to a low rate of synthesis of their peptides or proteins.     

Current generators and properties of late components evoked in rat olfactory cortex

Following main olfactory bulb (MOB) stimulation at frequencies of 0.1-0.3 Hz, in addition to early field potentials, a frequency-sensitive, surface negative late N2 wave (latency range: 63-96 msec) followed occasionally by a late N3 transient, was evoked in the piriform cortex and endopiriform nucleus of the rat. The N2 wave inverted polarity at the Ib-II cortical layer interface (P2 wave) and was associated with late unit discharges 200 to 1200 microns deep to the turnover point. Response probability, peak latency, recovery curve and frequency-sensitivity of the P2 wave were not significantly different in animals under urethane or pentobarbital. Current-source-density (CSD) analysis revealed that the N2 wave generators were localized to the Ib-II layer interface. Since inhibitory activity does not contribute substantially to the second derivative curve, CSD analysis strengthens the assumption that late components (LCs) are excitatory events (compound EPSPs) presumably generated on the proximal apical dendritic segments of pyramidal cells by association axons. The early "b" wave in a test response was facilitated, rather than occluded, when a LC was present in the conditioning response, or when the priming volley was delivered to the mediodorsal thalamic nucleus. Clustering of unit and field activity in two distinct periods of the evoked response separated by a prolonged interval of cell silence suggests that cortical coding of olfactory cues might be more efficiently achieved by temporal modulation of the neuronal response rather than by spatial distribution of firing patterns.     

Bursting-induced epileptiform EPSPs in slices of piriform cortex are generated by deep cells.

Previous study revealed that bursting activity generated by a variety of means in slices of piriform cortex induces persistent epileptiform EPSPs in superficial pyramidal cells by an NMDA-dependent process. The present study was undertaken to test the hypothesis that the observed epileptiform EPSPs in superficial pyramidal cells are driven by deep cells. This hypothesis was suggested by recent findings from in vitro studies of the properties of deep cells and in vivo studies indicating that the deep part of the piriform cortex or neighboring deep structures are involved in the generation of seizure activity in animal models of epilepsy. Results from simultaneous cell-pair recordings, examination of subdivided slices, and local application of excitatory and inhibitory agents provided strong evidence in support of this hypothesis. It was concluded that the endopiriform nucleus, a collection of cells immediately deep to the piriform cortex, plays a central role in generation, but that cells in the deep part of layer III and the claustrum may also contribute. Furthermore, it was found that generation of prolonged ictal-like activity only occurs in slices of piriform cortex in which the endopiriform nucleus is present. Implications of these findings for epileptogenesis are discussed.     

Convergence of autonomic and limbic connections in the insular cortex of the rat

The connnections of the insular cortex in the rate were studied by using the anterograde and retrograde transport of wheat germ agglutinin-conjugated-horseradish peroxidase. Both anterograde and retrogrde transport were seen in the ipsilateral lateral frontal, infralimbic, piriform, and perirhinal cortical areas and in the contralateral insular cortex. In the thalaamus, both types of labeling were seen in the mediodorsal and ventroposteromedial parvocellular nuclei; primarily retrograde labeling was seen in the centromedial and paracentral nuclei. In the basal forebrain, anterograde labeling was seen in the lateralpart of the bed nucleus of the stria terminalis and in the central nucleus of the amygdala, while retrogradely labeled neurons were found in the magnocellular basal nucleus and in the lateral and basolateral amygdaloid nuclei. Both types of labeling were seen in the posterior lateral hypothalamic area; the tuberomammillary nucleus contained retrogradely labeled neurons bilaterally. In the midbrain, retrogradely labeled neurons were found in the ventral tegmental area and in the dorsal and superior central raphe nuclei. In the pons, both retrogradely and anterogradely transported label was seen bilaterally in the parabrachial nucleus, primarily in the ventromedial caudal part of the medial subnucleus. Retrogradely labeled neurons were found bilaterally in the locus coeruleus. Anterograde transport was followed into the medulla, bilaterally but more heavily in the contralateral side. Labeled axons appeared to terminate in a topographic pattern in the nucleus of the solitary tract. These results indicate that the insular cortex of the rat is an important part of the highly interconnected central autonomic system. Furthermore, the autonomic representation in the insular cortex may be organized in a viscerotopic manner. The insular cortex also has connections with the limbic system and with the lateral frontal cortical system. Although it is not yet clear whether these connections converge upon the same neurons within the insular cortex, earlier physiological data suggest that each of the diverse systems of connections of this area receives relayed vagal inputs. The insular cortex of the rat may contain a primary cortical visceral representation, and its connections may underlie autonomic integration with behavioral and emotional events.     

Projections of the parabrachial nucleus in the old world monkey

The efferent projections of the pontine parabrachial nucleus (PBN) were examined in the Old World monkey (Macaca fascicularis) using tritiated amino acid autoradiography and horseradish peroxidase histochemistry. Parabrachiofugal fibers ascended to the forebrain along three pathways: the central tegmental tract, the ventral ascending catecholaminergic pathway, and a pathway located on the midline between the medial longitudinal fasciculi. The PBN projected heavily to the central nucleus of the amygdala and the lateral division of the bed nucleus of the stria terminalis and moderately to the ventral tegmental area and the substantia nigra. Light terminal label also was present within the dorsomedial, ventromedial, lateral, supramammillary, and infundibular nuclei of the hypothalamus and the annular nucleus and the dorsal raphe nucleus within the brain stem. The overall pattern of terminal label was similar to that previously reported for nonprimate species, but several differences were notable. In monkey the projection to the ventrobasal thalamus did not coincide with the region that contains gustatory-responsive neurons. In rats, these parabrachiothalamic fibers convey gustatory activity but in the monkey these fibers may carry visceral afferent information. The projections from the PBN to the hypothalamus in the monkey were neither as widespread nor as intense as in the rat, and the monkey lacks a projection from the PBN to the frontal and insular cortices.