The distribution and cellular localization of the serotonin 1C receptor mRNA in the rodent brain examined by in situ hybridization histochemistry. Comparison with receptor binding distribution

The regional distribution and cellular localization of mRNA coding for the serotonin 1C receptor were investigated in tissue sections of mouse and rat brain by in situ hybridization histochemistry. Several 32P-labelled riboprobes derived from mouse genomic clones were used. The serotonin 1C receptor binding sites were visualized autoradiographically and quantified using [3H]mesulergine as ligand, in the presence of spiperone to block serotonin 1C receptors. Strong hybridization signal was observed in the choroid plexus of all brain ventricles. High levels of hybridization were also seen in the anterior olfactory nucleus, pyriform cortex, amygdala, some thalamic nuclei, especially the lateral habenula, the CA3 area of the hippocampal formation, the cingulate cortex, some components of the basal ganglia and associated areas, particularly the nucleus subthalamicus and the substantia nigra. The midbrain and brainstem showed moderate levels of hybridization. The distribution of the serotonin 1C receptor mRNA corresponded well to that of the serotonin 1C receptors. The highest levels of serotonin 1C receptor binding were observed in the choroid plexus. In addition, significant levels of the serotonin 1C receptor binding were seen in the anterior olfactory nucleus, pyriform cortex, nucleus accumbens, ventral aspects of the striatum, paratenial and paracentral thalamic nuclei, amygdaloid body and substantia nigra pars reticulata. The cingulate and retrosplenial cortices as well as the caudal aspects of the hippocampus (CA3) were also labelled. Binding in brainstem and medulla was low and homogeneously distributed. No significant binding was seen in the habenular and subthalamic nuclei. Similar findings were obtained in rat brain. These results demonstrate that, in addition to their enrichment in the choroid plexus, the serotonin 1C receptor mRNA and binding sites are heterogeneously distributed in the rodent brain and thus could be involved in the regulation of many different brain functions. The combination of in situ hybridization histochemistry with receptor autoradiography opens the possibility of examining the regulation of the serotonin 1C receptor synthesis after pharmacological or physiological alterations.     

Localization of neuropeptide receptor mRNA in rat brain: initial observations using probes for neurotensin and substance P receptors.

The expression of receptors for neurotensin and substance P was examined in rat brain and spinal cord using in situ hybridization with synthetic oligonucleotide probes. Strong hybridization signals for neurotensin receptor mRNA were observed over neurons i.a. in the diagonal band, medial septal nucleus, nucleus basalis magnocellularis, suprachiasmatic nucleus, supramammillary area, substantia nigra and ventral tegmental area. Strong hybridization signals for substance P receptor mRNA were observed over scattered, large neurons in the striatum, and in the spinal cord over neurons in the dorsal horn, the area around the central canal and preganglionic autonomic neurons. Thus, discrete neurons in several brain regions express a G-protein-coupled receptor with which endogenous neurotensin and substance P may interact.     

Expression and glucocorticoid regulation of natriuretic peptide clearance receptor (NPR-C) mRNA in rat brain and choroid plexus

The natriuretic peptide clearance receptor (NPR-C) binds atrial natriuretic peptide, brain natriuretic peptide and C-type natriuretic peptide with high affinity. This receptor lacks an intracellular guanylate cyclase domain, and is believed to exert biological actions by sequestration of released natriuretic peptides and/or inhibition of adenylate cyclase. The present report summarizes the first detailed mapping of NPR-C mRNA in rat brain. In situ hybridization analysis revealed high levels of NPR-C mRNA expression in frontal and retrosplenial granular cortices, medial preoptic nucleus, ventral cochlear nucleus and choroid plexus. NPR-C mRNA expression was also observed in deep layers of neocortex and limbic cortex, posterior cortical amygdala, ventral subiculum, amygdalohippocampal area, and dentate gyrus. Positive hybridization signal was observed in both anterior and intermediate lobes of the pituitary gland. Regulatory studies indicated that expression of NPR-C mRNA was increased in the medial preoptic nucleus of adrenalectomized rats, suggesting negative glucocorticoid regulation. No changes in NPR-C mRNA expression were observed in frontal cortex or choroid plexus. These results suggest a role for the NPR-C in modulation of natriuretic peptide availability and/or adenylate cyclase activity in a subset of central natriuretic peptide circuits concerned with cortical, olfactory and neuroendocrine functions. Response of the NPR-C gene to changes in circulating hormones suggests the capacity for glucocorticoid modulation of natriuretic peptide action at the receptor level.     

Electrical activity generated in subicular and entorhinal cortices after electrical stimulation of the lateral and basolateral amygdala of the rat

Evoked field potentials and extracellular unitary activity were recorded from entorhinal lateral and subicular ventral cortices under conditions of amygdala stimulation in equithesin-anesthetized rats. The stimulation of the lateral and basolateral nuclei of the amygdaloid complex evoked field potentials consisting of negative-positive waves in layers III-VI and positive-negative deflections in the superficial layers of the ventral subdivision of the entorhinal cortex. The stimulation of the lateral nucleus evoked similar potentials in the dorsal subdivision of this cortex. And the stimulation of the lateral and basolateral nuclei of the amygdala evoked negative-positive field potentials in layer III of the subicular cortex. Cellular activity of the entorhinal and subicular cells evoked by stimulation of the lateral and basolateral nuclei consisted of an excitatory response followed by a prolonged suppression period. This activation coincided with the negative potential recorded in the deeper layers of these cortices. Such observations provide support for amygdaloid projection to the entorhinal and subicular cortices as recent anatomical findings suggested. The functional significance of these observations indicate an amygdaloid influence on entorhinal-hippocampal neurotransmission as well as on the ventral subiculum which provides the major output from the hippocampus.     

Comparison of substance P and enkephalin distribution in rat brain: an overview using radioimmunocytochemistry

The distribution of substance P and leucine enkephalin in mid- and fore-brain areas of the rat was studied using a radioimmunocytochemical method. The secondary antibody was labeled with 125I and the sections apposed to LKB Ultrofilm or emulsion-dipped. In alternate sections an extensive distribution of substance P and enkephalin immunoreactive material was seen in frontal, cingulate, retrosplenial, and entorhinal cortices. Substance P and enkephalin exhibited a remarkable overlap in many of these cortical areas as well as in the nucleus accumbens, caudate, portions of the hypothalamus, amygdala, thalamus and central gray. Differences in distribution were seen in the retrosplenial cortex, septum, ventromedial hypothalamus, hippocampus, the substantia nigra and the superior colliculus. The results provide a detailed immunohistochemical demonstration of the laminar patterns of substance P and enkephalin in the cortex of the rat. The results are discussed in terms of the interaction of substance P and enkephalin. The matches and mismatches of immunoreactive substance P and enkephalin and the locations of their receptors are also examined.     

Distribution of neurotensin binding sites in rat brain: a light microscopic radioautographic study using monoiodo [125I]Tyr3-neurotensin

The topographic distribution of specifically labeled neurotensin binding sites was examined by light microscopic radioautography in rat brain sections incubated with monoiodo [125I]Tyr3-neurotensin. Preliminary experiments indicated that under the present experimental conditions [125I]neurotensin specifically binds to a single apparent population of sites with a dissociation constant of 7.7 +/- 0.3 nM, and that fixation of the labeled sections with glutaraldehyde ensures regionally proportional retention of more than 70% of bound [125I]neurotensin molecules. High concentrations of [125I]neurotensin binding sites were detected in the olfactory bulb and tubercle, parts of the neocortex, the lateral septum, the diagonal band of Broca, the caudate putamen, the amygdala, the dentate gyrus, the anterior dorsal nucleus of the thalamus, the suprachiasmatic nucleus of the hypothalamus, the medial habenula, the zona incerta, the substantia nigra and the ventral tegmental area. In certain areas, such as in the diagonal band of Broca, the substantia innominata, the nucleus basalis and the pars compacta of the substantia nigra, discrete accumulations of silver grains were apparent over neuronal perikarya and their proximal dendrites. In most areas, however, the label appeared more or less uniformly distributed over nerve cell bodies and surrounding neuropil. In several instances, the labeling conformed with the distribution of cell bodies of origin and terminal aborizations of specific projection systems, suggesting that neurotensin receptors might be distributed both proximally and distally on the plasma membrane of certain neurons. Such putative "neurotensinoceptive" projection systems might involve part of the mesostriatal, mesocortical and mesolimbic dopamine systems, as well as the raphe-prosencephalic serotonin system and the habenulo-interpeduncular and basal forebrain-cortical cholinergic systems. Finally, areas of dense [125I]neurotensin labeling often corresponded to zones previously shown to exhibit intense acetylcholinesterase staining, suggesting the existence of a possible link between the expression of neurotensin binding sites and that of acetylcholinesterase in certain neuronal populations.     

Cholinergic and non-cholinergic projections from the rat basal forebrain revealed by combined choline acetyltransferase and Phaseolus vulgaris leucoagglutinin immunohistochemistry

A two-color fluorescence method is described for demonstrating immunohistochemically the anterogradely transported plant lectin Phaseolus vulgaris leucoagglutinin (PHAL, fluorescein isothiocyanate label) and choline acetyltransferase (ChAT, rhodamine label) on the same rat brain section. Application of this method to the study of projection neurons in the vertical and horizontal limbs of the diagonal band, the substantia innominata and nucleus basalis revealed that both cholinergic and non-cholinergic pathways followed similar trajectories to their targets. These included: projections from the vertical, and, to a lesser extent, horizontal limb of the diagonal band coursing through the dorsal fornix, alveus and fimbria to the hippocampus; fibers from the vertical and horizontal limbs of the diagonal band traveling anteriorly to the anterior olfactory nucleus, posterolaterally to the entorhinal cortex, and anterodorsally into the cingulum to the cingulate and retrosplenial, and, in some cases, the frontal and occipital cortices; projections, mostly non-cholinergic, from the substantia innominata traveling laterally to the piriform cortex and amygdala, and anteriorly to the anterior olfactory nucleus and olfactory bulb; and fibers from cells in the nucleus basalis coursing dorsally to the frontal and parietal cortices or laterally to the basolateral amygdala and piriform, insular and temporal cortices. Some axon terminations ended at right angles to the parent axon shaft in short protuberances resembling terminal boutons.     

Substantia nigra and ventral tegmental area projections to cortex: topography and collateralization

The substantia nigra and ventral tegmental area of the rat were examined by retrograde transport methods to determine the topography and collateralization patterns of projections to cortex and certain subcortical sites. The topographical relationships between cells and their terminal fields were confirmed and clarified by the horseradish peroxidase retrograde transport technique. The collateralization of axons was analyzed by the use of multiple fluorescent tracers. These experiments indicated that individual ventral tegmental area cells do not collateralize extensively to either subcortical or cortical terminal fields. Substantia nigra cells, however, give rise to more highly collateralized axons and single cells may simultaneously innervate different regions of cortex as well as subcortical sites. Substantia nigra cells can be divided with respect to their cortical collateralization patterns into three groups: (1) those that innervate cingulate cortices, (2) those that project to prefrontal and suprarhinal cortices, and (3) those that innervate entorhinal cortex.     

Transient increase in glutamic acid decarboxylase mRNA in the cerebral cortex following focal cortical lesion in the rat

Summary In situ hybridization histochemistry (ISHH) was used to study the expression of glutamic acid decarboxylase (GAD) mRNA changes in the rat cerebral cortex following unilateral frontal and somatosensory cortical lesion by devascularisation. 4 days after the lesion, a significant transient increase in GAD mRNA level in the ipsilateral cortex was observed when compared with contralateral, ipsi-sham operated and ipsi-normal control cortices. The change occurred throughout the ipsilateral neocortex, with no significant difference between the magnitude of increase in frontal, parieto-occipital, parieto-temporal, cingulate or retrosplenial areas; no obvious change was seen in pyriform, entorhinal or hippocampal cortices. This unexpected GAD mRNA increase in neocortex may be part of a long term adaptive functional alteration and changes in the gene expression of the cerebral cortex following focal cortical injury.A preliminary report of these findings was presented at the annual general meeting of the Anatomical Society of Great Britain and Ireland     

Neurotensin receptors in Parkinson's disease and progressive supranuclear palsy: an autoradiographic study in basal ganglia

The technique of receptor autoradiography was used to study the distribution of neurotensin receptors in post mortem brain tissues from patients affected by Parkinson's disease, progressive supranuclear palsy and from age-matched controls. [125I]Neurotensin was used as ligand. Significant receptor decreases were found in the substantia nigra, both pars compacta and reticulata, and in the putamen in Parkinson's disease and progressive supranuclear palsy. In addition, significant decreases of neurotensin receptors were found in the ventral tegmental area, nucleus accumbens and dorsal part of caudate head in patients with Parkinson's disease but not in patients with progressive supranuclear palsy, indicating differential involvement of neurotensin receptors in these two neurological disorders. In addition, both in Parkinson's disease and progressive supranuclear palsy the decrement of striatal neurotensin binding sites was less than expected from the reported decrease of dopamine content in this nucleus, suggesting only partial localization of neurotensin receptors on mesostriatal dopaminergic projections.     

The topographic order of inputs to nucleus accumbens in the rat

Afferents to the nucleus accumbens have been studied with the retrograde transport of unconjugated wheatgerm agglutinin as detected by immunohistochemistry using the peroxidase-antiperoxidase method, in order to define precisely afferent topography from the cortex, thalamus, midbrain and amygdala. Cortical afferent topography was extremely precise. The largest number of cells was found following injections to the anterior accumbens. Anteromedial injections labelled a very large extent of the subiculum and part of the entorhinal cortex. Anterolateral injections produced less subicular and entorhinal label but also labelled the posterior perirhinal cortex. Posteromedial injections labelled only the ventral subiculum and a few cells in the adjacent medial entorhinal cortex. Posterolateral injections labelled few lateral entorhinal neurones but did label a long anteroposterior strip of perirhinal cortex. Prefrontal cortex label was found only after anterior accumbens injections. In the amygdala labelled neurones were found in cortical, central, lateral posterior, anteromedial and basolateral nuclei. Basolateral amygdala projected chiefly to the anteromedial accumbens and central nucleus to anterolateral accumbens. Only a weak amygdala label was found after posterior accumbens injections. In the ventral tegmental area, the midline interfascicular nucleus projected only to medial accumbens. The paranigral ventral tegmentum projected chiefly to the medial accumbens and the parabrachial area chiefly to the lateral accumbens. In the thalamus, heaviest label was found after anterior accumbens injections. Most cells were found in the paraventricular, reuniens and rhomboid nuclei and at posterior thalamic levels lying medial to the fasciculus retroflexus. There was only restricted topography found from thalamic sites. Retrograde label was also found in the ventral pallidum and lateral hypothalamus. Single small injection sites within accumbens received input from the whole anteroposterior extent of the thalamus and ventral tegmentum. The medial accumbens was found to have a close relationship to habenula, globus pallidus and interfascicular nucleus. It appeared that the heaviest volume of inputs projected to anteromedial accumbens, where output from hippocampus (CAI), subiculum, entorhinal and prefrontal cortices converged with output from amygdala, midline thalamus and ventral tegmentum.     

Cortical afferents of the nucleus accumbens in the cat,studied with anterograde and retrograde transport techniques

The cortical afferentation of the nucleus accumbens in the cat was studied with the aid of retrograde tracing techniques. Retrograde experiments were carried out with horseradish peroxidase or one of the fluorescent tracers Bisbenzimid, Nuclear Yellow and Fast Blue. In the anterograde experiments [³H]leucine and [³⁵S]methionine were used as tracers.Following injections in the nucleus accumbens, retrogradely-labelled cells were found in the medial frontal cortex, the anterior olfactory nucleus, the posterior part of the insular cortex, the endopiriform nucleus, the amygdalo-hippocampal area, the entorhinal and perirhinal cortices and the subiculum of the hippocampal formation. In the medial frontal cortex most of the labelled cells were found in layers III and V of the prelimbic area (area 32 of Brodmann), but retrogradely-filled neurons were also present in the infralimbic area and in the caudoventral part of the lateral bank of the proreal gyrus. Retrogradely-labelled cells in the entorhinal and perirhinal cortices were located in the deep cellular layers. Following large injections in the nucleus accumbens, retrograde labelling in the subiculum extended from the most dorsal, septal pole to the most ventral, temporal pole.Injections of anterograde tracers were placed in the frontal cortex, the entorhinal and perirhinal cortices and the hippocampal formation. The prelimbic area was found to project via the internal capsule to mainly the rostral half of the nucleus accumbens, whereas in the caudal half of the nucleus only a lateral region receives frontal cortical fibres. Following injections in the infralimbic area only fibres passing through the nucleus accumbens were labelled. Afferents from the entorhinal and perirhinal cortices reach the nucleus accumbens by way of the external capsule and terminate mainly in a ventral zone of the nucleus accumbens.Afferents from the entorhinal area are distributed to the entire accumbens, whereas the termination field of the perirhinal afferents is largely restricted to the lateral part of the nucleus accumbens. Both the frontal cortex and the entorhinal and perirhinal cortices appear to project also to the nucleus caudatus and the tuberculum olfactorium. These cortical areas also project to the contralateral striatum.Both anterograde and retrograde tracing experiments demonstrated a topographical relationship between the subiculum and the nucleus accumbens. The ventral pole of the subiculum projects via the fornix to the medial part of the caudal half of the nucleus accumbens and to a small dorsomedial area in its rostral half. Successively more dorsal portions in the subiculum project to successively more ventrolateral parts in the rostral nucleus accumbens. The projection from the hippocampus was found to extend also to the tuberculum olfactorium. The results of the present study do not provide unambiguous criteria for the delimitation of the nucleus accumbens in the cat.     

Ascending projections of presumed dopamine-containing neurons in the ventral tegmentum of the rat as demonstrated by horseradish peroxidase

The projections of presumed dopamine-containing neurons in the zona compacta of the substantia nigra and the ventral tegmental area were examined by stereotaxic injections of horseradish peroxidase into diverse cortical and subcortical regions which are known to include dopamine-containing terminals. Neurons in the lateral half of the substantia nigra pars compacta were labelled after injections into the caudolateral aspect of the caudate-putamen, while neurons in the medial part of the substantia nigra pars compacta and lateral aspect of the ventral tegmental area projected to the anteromedial portion of the caudate putamen. Injections of horseradish peroxidase into the amygdala resulted in the appearance of reactive neurons in the anterior portion of the ventral tegmental area, but the more caudally located entorhinal cortex received projections from the posterior half of the ventral tegmental area. Injections of horseradish peroxidase into the frontal cortex, anterior to the genu, produced scattered labelled cells in the rostral half of the ventral tegmental area, whereas more posterior injections into the cingulate cortex resulted in the appearance of reactive cells which were confined to the medial one-quarter of the substantia nigra pars compacta. The near-midline structure, the lateral septum, was innervated by neurons with cell bodies primarily in the medial half of the ventral tegmental area. Injections of horseradish peroxidase into the nucleus accumbens, which contains very high levels of dopamine, resulted in the appearance of many labelled neurons throughout the ventral tegmental area and some reactive neurons in the medial part of the substantia nigra pars compacta. A few labelled cells were also occasionally observed in the contralateral ventral tegmental area after accumbens injections.These results suggest that although there is considerable overlap, and that the same subdivisions within the substantia nigra pars compacta and the ventral tegmental area appear to innervate diverse regions of the forebrain, there also exists a general topographical organization with respect to the projections of these neurons.Injections of horseradish peroxidase into some of the forebrain regions also resulted in the appearance of reactive cells in mesencephalic nuclei not known to contain dopaminergic perikarya. For example, labelled cells were observed in the supramamillary nucleus after injections into the frontal cortex, entorhinal cortex, accumbens and lateral septum. Injections into the amygdala produced reactive cells in the suprageniculate nucleus, the peripeduncular nucleus, and the magnocellular nucleus of the medial geniculate. These latter results are discussed with reference to the possibility that such pathways may mediate the responsiveness of cells in the amygdala to a wide range of sensory stimuli.     

Cortical projections of the anterior thalamic nuclei in the cat

Summary Unilateral stereotaxic lesions were made in the anterior thalamic nuclei of the cat, and the ensuing terminal degeneration traced to the medial cortex by the methods of Nauta-Gygax and Fink-Heimer. The anterodorsal nucleus projects to the retrosplenial, postsubicular and presubicular areas. These projections appear to be organized in the dorsoventral direction. The posterior portion of the retrosplenial area receives no fibers from the anterodorsal nucleus. Fibers from this nucleus are distributed largely in layer I and in layer III and the deep portion of layer II of the posterior limbic cortex. The anteroventral nucleus sends fibers to the cingular area and parts of the retrosplenial, postsubicular and presubicular areas. These projections appear to be organized in a topical manner mediolaterally. When the lesion involves the parvocellular part of the nucleus, degeneration spreads to the lower lip, bank and fundus of the splenial sulcus. There appears to be an anteroposterior organization in the cortical projections of the anteroventral nucleus. Fibers from the anteroventral nucleus are distributed most profusely in layers IV and III and in the superficial portion of layer I of the posterior limbic cortex. The anteromedial nucleus sends fine fibers to the anterior limbic region and to the cingular, retrosplenial, postsubicular and presubicular areas. The cortical projections of the anteromedial nucleus appear to be topographically organized in the dorsoventral direction. Fibers from the anteromedial nucleus are distributed largely in cortical layers V and VI of the anterior and posterior limbic regions.Abbreviations used in Figures a anterior - AD anterodorsal nucleus - AM anteromedial nucleus - AMD dorsolateral part of anteromedial nucleus - AMV ventromedial part of anteromedial nucleus - AV anteroventral nucleus - AVM magnocellular part of anteroventral nucleus - AVP parvocellular part of anteroventral nucleus - CC corpus callosum - Cg cingular area - CM medial central nucleus - Il infralimbic area - LA anterior limbic region - LD dorsal lateral nucleus - MD dorsal medial nucleus - Of orbitofrontal region - p posterior - Pr presubicular area - Prag precentral agranular area - Ps postsubicular area - Pt paratenial nucleus - Pv anterior paraventricular nucleus - R reuniens nucleus - Rs retrosplenial area - Rt thalamic reticular nucleus - SC cruciate sulcus - SM stria medullaris - Sm submedial nucleus - SS splenial sulcus - VA ventral anterior nucleus - VL ventral lateral nucleus - VM ventral medial nucleus     

Excitatory amino acid projections to the nucleus accumbens septi in the rat: a retrograde transport study utilizing D[3H]aspartate and [3H]GABA

Afferents to the nucleus accumbens septi utilizing glutamate or aspartate have been investigated in the rat by autoradiography following injection and retrograde transport of D[3H]aspartate. Parallel experiments with the intra-accumbal injection of [3H]GABA were employed to establish the transmitter-selective nature of the retrograde labelling found with D[3H]aspartate. The topography of cortical and thalamic perikarya labelled by D[3H]aspartate was extremely precise. D[3H]Aspartate labelled perikarya were found in layer V of agranular insular cortex; bilaterally within prelimbic and infralimbic subareas perikarya, but predominantly ipsilaterally. Ipsilateral labelling was observed in dorsal, ventral and posterior agranular insular cortices, and in perirhinal cortex. Injections into ventral accumbens labelled perikarya in ipsilateral entorhinal cortex, while infusion of D[3H]aspartate into anterior caudate-putamen resulted in labelling of perikarya in ipsilateral cingulate and lateral precentral cortices. Following infusion of D[3H]aspartate, ipsilateral midline thalamic nuclei contained the highest density of labelled perikarya; infusions centred on nucleus accumbens resulted in heavy retrograde labelling of the parataenial nucleus, but labelling was sparse from a lateral site and not observed after injection into anterior caudate-putamen. Less prominent labelling of perikarya was seen in other thalamic nuclei (mediodorsal, central medial, rhomboid, reuniens and centrolateral), mostly near the midline. Perikaryal labelling was also found in the ipsilateral amygdaloid complex, particularly in basolateral and lateral nuclei. Only weak labelling resulted in ventral subiculum. Numerous labelled cells were present bilaterally in anterior olfactory nucleus, although perikarya were more prominent ipsilaterally. Labelled perikarya were not consistently observed in other regions (ventral tegmental area, medial substantia nigra, raphe nuclei and locus coeruleus) known to innervate nucleus accumbens. Presumptive anterograde labelling was detected in ventral pallidum/substantia innominata, ventral tegmental area and medial substantia nigra. [3H]GABA was generally not retrogradely transported to the same regions labelled by D[3H]aspartate; an exception being the anterior olfactory nucleus, where large numbers of labelled perikarya were found. [3H]GABA failed to label perikarya in thalamus and amygdala, and a topographic distribution of label was absent in neocortex.(ABSTRACT TRUNCATED AT 400 WORDS)     

Efferent connections of dorsal and ventral agranular insular cortex in the hamster, Mesocricetus auratus

The anterior portion of rodent agranular insular cortex consists of a ventral periallocortical region (AIv) and a dorsal proisocortical region (AId). Each of these two cortical areas has distinct efferent connections, but in certain brain areas their projection fields are partially or wholly overlapping. Bilateral projections to layers I, III and VI of medial frontal cortex originate in the dorsal agranular insular cortex and terminate in the prelimbic, anterior cingulate and medial precentral areas; those originating in ventral agranular insular cortex terminate in the medial orbital, infralimbic and prelimbic areas. The dorsal and ventral regions of the agranular insular cortex project topographically to the ipsilateral cortex bordering the rhinal fissure, which includes the posterior primary olfactory, posterior agranular insular, perirhinal and lateral entorhinal areas. Fibers to these lateral cortical areas were found to travel in a cell-free zone, between cortical layer VI and the claustrum, which corresponds to the extreme capsule. The dorsal and ventral regions send commissural projections to layer I, lamina dissecans and outer layer V, and layer VI of the contralateral homotopical cortex, via the corpus callosum. Projections from the ventral and dorsal regions of the agranular insular cortex to the caudatoputamen are topographically arranged and terminate in finger-like patches. The ventral, but not the dorsal region, projects to the ventral striatum and ventral pallidum. The thalamic projections of the ventral and dorsal regions are largely overlapping, with projections from both to the ipsilateral reticular nucleus and bilaterally to the rhomboid, mediodorsal, gelatinosus and ventromedial nuclei. The heaviest projection is that to the full anteroposterior extent of the medial segment of the mediodorsal nucleus. Brainstem areas receiving projections from the ventral and dorsal regions include the lateral hypothalamus, substantia nigra pars compacta, ventral tegmental area and dorsal raphe nucleus. In addition, the ventral region projects to the periaqueductal gray and the dorsal region projects to the parabrachial and ventral pontine nuclei.These efferent connections largely reciprocate the afferent connections of the ventral and dorsal agranular insular cortex, and provide further support for the concept that these regions are portions of an outer ring of limbic cortex which plays a critical role in the expression of motivated, species-typical behaviors.     

Cellular localization and distribution of dopamine D(4) receptors in the rat cerebral cortex and their relationship with the cortical dopaminergic and noradrenergic nerve terminal networks

The role of the dopamine D(4) receptor in cognitive processes and its association with several neuropsychiatric disorders have been related to its preferential localization in the cerebral cortex. In the present work we have studied in detail the regional and cellular localization of the dopamine D(4) receptor immunoreactivity (IR) in the rat cerebral cortex and its relationship to the dopaminergic and noradrenergic nerve terminal networks, since both dopamine and noradrenaline have a high affinity for this receptor. High levels of D(4) IR were found in motor, somatosensory, visual, auditory, temporal association, cingulate, retrosplenial and granular insular cortices, whereas agranular insular, piriform, perirhinal and entorhinal cortices showed low levels. D(4) IR was present in both pyramidal and non-pyramidal like neurons, with the receptor being mainly concentrated to layers II/III. Layer I was observed to be exclusively enriched in D(4) IR branches of apical dendrites. Finally, mismatches were observed between D(4) IR and tyrosine hydroxylase and dopamine beta-hydroxylase IR nerve terminal plexuses, indicating that these receptors may be activated at least in part by dopamine and noradrenaline operating as volume transmission signals. The present findings support a major role of the dopamine D(4) receptor in mediating the transmission of cortical dopamine and noradrenaline nerve terminal plexuses.     

Neurodegeneration and prolonged immediate early gene expression throughout cortical areas of the rat brain following acute administration of dizocilpine

N-methyl-d-aspartate receptor antagonist drugs (NMDA-A), such as dizocilpine (MK801), induce long-lasting behavioral disturbances reminiscent to psychotic disorders in humans. To identify cortical structures affected by NMDA-A, we used a single dose of MK801 (10 mg/kg) that caused low and high neurodegeneration in intact and orchiectomized male rats, respectively. Degenerating somas (neuronal death) and axonal/synaptic endings (terminal degeneration) were depicted by a silver technique, and functionally affected cortical neuronal subpopulations by Egr-1, c-Fos, and FosB/ΔFosB-immunolabeling. In intact males, MK801 triggered a c-Fos induction that remained high for more than 24 h in selected layers of the retrosplenial, somatosensory and entorhinal cortices. MK801-induced neurodegeneration reached its peak at 72 h. Degenerating somas were restricted to layer IV of the granular subdivision of the retrosplenial cortex, and were accompanied by suppression of Egr-1 immunolabeling. Terminal degeneration extended to selected layers of the retrosplenial, somatosensory and parahippocampal cortices, which are target areas of retrosplenial cortex. Induction of FosB/ΔFosB by MK801 also extended to the same cortical layers affected by terminal degeneration, likely reflecting the damage of synaptic connectivity. In orchiectomized males, the neurodegenerative and functional effects of MK801 were exacerbated. Degenerative somas in layer IV of the retrosplenial cortex significantly increased, with a parallel enhancement of terminal degeneration and FosB/ΔFosB-expression in the mentioned cortical structures, but no additional areas were affected. These observations reveal that synaptic dysfunction/degeneration in the retrosplenial, somatosensory and parahippocampal cortices might underlie the long-lasting impairments induced by NMDA-A.     

Inputs from the olfactory bulb and olfactory cortex to the entorhinal cortex in the cat

Summary The spatial organization and laminar distribution of projections from the olfactory bulb and the anterior (PPCa) and posterior (PPCp) divisions of the prepiriform cortex to the entorhinal cortex were studied with anterograde (³H-leucine) and retrograde (WGA-HRP) tracing techniques. After ³H-leucine injections into the olfactory bulb transported labeling was seen over the lateral entorhinal area, except its most medial part, and over the rostral part of the medial entorhinal area. The labeling covers exclusively layer Ia. The lateral and medial entorhinal areas are also reached by fibers from the prepiriform cortex. The projection to the medial entorhinal area has not been described previously. Following injections of ³H-leucine into the PPCa transported labeling is present over the entire expanse of the entorhinal cortex and is located over layer Ib with the greatest density in its superficial part. Injections of ³H-leucine into the PPCp give rise to transported labeling over much of the entorhinal cortex. No labeling was found over the most medial parts of the medial subdivision (VMEA) of the lateral entorhinal area and the medial entorhinal area. Labeling occupies layer Ib, especially its middle part, and layers II and III. Both PPCa and PPCp appear to project most heavily to the dorsal (DLEA) and ventral (VLEA) subdivisions of the lateral entorhinal area. From the retrograde experiments it can be inferred that cells of layers II and III of the PPCa project predominantly to the DLEA, whereas those of the PPCp project predominantly to the VLEA. The MEA receives its heaviest projection from layer II of both PPCa and PPCp. In control experiments with ³H-leucine injections into the endopiriform nucleus it was found that this nucleus projects to the entire expanse of the entorhinal cortex. The fibers distribute to all layers with the exception of layer Ia.Abbreviations AI agranular insular cortex - AL lateral nucleus of the amygdala - BL basolateral nucleus of the amygdala - BM basomedial nucleus of the amygdala - C claustrum - CoA cortical nucleus of the amygdala - DLEA dorsal division of the lateral entorhinal cortex - END endopiriform nucleus - H hippocampus - I granular insular cortex - lot lateral olfactory tractus - MCL mitral cell layer of the olfactory bulb - MEA medial entorhinal area - OB olfactory bulb - PPCa anterior part of the prepiriform nucleus - PPCp posterior part of the prepiriform nucleus - VLEA ventral division of the lateral entorhinal cortex - VMEA ventromedial division of the lateral entorhinal cortex - 35 area 35 of the perirhinal cortex - 36 area 36 of the perirhinal cortex