Striatal and central extended amygdala parts of the interstitial nucleus of the posterior limb of the anterior commissure: evidence from tract-tracing techniques in the rat.

The interstitial nucleus of the posterior limb of the anterior commissure (IPAC) lies at the junction of the striatopallidal system and the lateral bed nucleus of the stria terminalis-central amygdaloid nucleus continuum (i.e., the central extended amygdala; EAc). Its efferent connections were investigated in the rat with anterograde (Phaseolus vulgaris leucoagglutinin) and retrograde (Fluoro-Gold and cholera toxin B subunit) tracers and compared with those of the central amygdaloid nucleus. Our anterograde tracing experiments reveal that the projections of the medial IPAC largely reciprocate its afferent connections (Shammah-Lagnado et al. [1999] Neuroscience 94:1097-1123) and are very similar to those of the medial part of the central amygdaloid nucleus. The lateral IPAC, on the other hand, innervates the pallidal complex, substantia nigra and retrorubral field. Local connections are found within medial IPAC and within lateral IPAC, but the two divisions are not interconnected. Our retrograde tracing experiments confirm that IPAC projections to EAc components, parabrachial area, and nucleus of the solitary tract originate chiefly from the medial division, whereas both medial and lateral divisions innervate the retrorubral field. Moreover, in sections processed for choline acetyltransferase, the strong projections from caudal IPACm to the posterior basolateral amygdaloid nucleus and the amygdalopiriform transition area were found to arise chiefly from cholinergic cells. Overall, our results suggest that the medial IPAC is intimately related to the EAc, whereas the lateral IPAC represents a striatal territory.

Supracapsular bed nucleus of the stria terminalis contains central and medial extended amygdala elements: evidence from anterograde and retrograde tracing experiments in the rat.

Neurons that accompany the stria terminalis as it loops over the internal capsule have been termed collectively the supracapsular bed nucleus of the stria terminalis (BSTS). They form two cell columns, a lateral column and a considerably smaller medial column. The lateral column merges rostrally with the lateral bed nucleus of the stria terminalis and caudally with the central amygdaloid nucleus (central extended amygdala components). The medial column is continuous with the medial bed nucleus of the stria terminalis and the medial amygdaloid nucleus (medial extended amygdala districts). The connections of the BSTS were investigated in the rat by placing injections of Phaseolus vulgaris-leucoagglutinin (PHA-L) or retrograde tracers in different parts of the extended amygdala or in structures related to the extended amygdala. BSTS inputs and outputs were identified, respectively, by the presence of varicose fibers and retrogradely labeled neurons within the stria terminalis. The results suggest that the medial-to-lateral compartmentalization of BSTS neurons reflects their close alliance with the medial and central divisions of the extended amygdala. The medial BSTS contains primarily elements that correspond to the posterodorsal part of the medial amygdaloid nucleus and the medial column of the posterior division of the medial bed nucleus of the stria terminalis, and the lateral BSTS contains elements that correspond to the medial and lateral parts of the central amygdaloid nucleus and lateral bed nucleus of the stria terminalis. These results add strong support to the concept of the extended amygdala as a ring-like macrostructure around the internal capsule, and they are of theoretical interest for the understanding of the organization of the basal forebrain.

Basal forebrain in the context of schizophrenia.

The human basal forebrain has been notoriously difficult to analyze, and it was only in the last part of the twentieth Century that its various components came into sharper focus. It has now been demonstrated that the main parts of what was previously referred to as the 'substantia innominata' (a neurological equivalent of the geographer's 'terra incognita') belong to nearby and better defined anatomical systems. These include the ventral aspects of the basal ganglia, i.e. the ventral striatopallidal system, extensions of the centromedial amygdala that links it via subpallidal cell columns to the bed nucleus of stria terminalis, i.e. the extended amygdala, and a more or less continuous collection of aggregated and non-aggregated, predominantly large, hyperchromatic projections neurons referred to as the basal nucleus of Meynert. Following a pictorial survey of the basal forebrain, the anatomy of these three systems are described with special emphasize on clinically relevant details. Sections devoted to clinical-anatomical correlations emphasize the potential significance of the basal forebrain in the context of schizophrenia. The functional-pathological importance of the cortico-subcortical re-entrant circuits through the ventral striatopallidal system is well recognized in the field of neuropsychiatry. Less appreciated is the fact that both the ventral striatum and the extended amygdala contain prominent collections of islands with small neurons, which have collectively been referred to as 'interface islands'. The abundance of neuroactive substances in the interface islands, and the potential for significant postnatal development of the neurons in these islands make them especially intriguing in the context of the developmental hypothesis of schizophrenia. The basal nucleus of Meynert is also of special interest. Involvement of the basal nucleus of Meynert and its related circuits may well be one of the main reasons for attentional dysfunction and cognitive symptoms in this complex disorder. Finally, we emphasize that changes in the neuronal circuits related to the ventral striatopallidal system, extended amygdala and basal nucleus of Meynert in all likelihood provide the anatomical substrate through which pathologic activities in the medial temporal lobe and prefrontal-orbitofrontal structures are translated into disruption of a number of functions ranging from motor activities and basic drives, to personality changes involving stress, mood and higher cognitive functions.

The concepts of the ventral striatopallidal system and extended amygdala.

The concepts of the ventral striatopallidal system and extended amygdala have significantly improved our understanding of basal forebrain organization. As a result of these and other advances during the last twenty years, many of the most prominent basal forebrain structures, including the nucleus accumbens, olfactory tubercle, and amygdaloid body, have all but lost their relevance as independent functional anatomical units. In order to appreciate the distinct differences that exist between the ventral striatopallidal system and the extended amygdala, and as a way of explaining the choice of the terms ventral striatopallidal system and extended amygdala, we will review the discovery and subsequent elaboration of these two systems. On the background of these discussions, we will then proceed to dispel some recently published misgivings regarding the usefulness of the extended amygdaloid concept.

Afferent connections of the interstitial nucleus of the posterior limb of the anterior commissure and adjacent amygdalostriatal transition area in the rat.

The interstitial nucleus of the posterior limb of the anterior commissure is, like the striatum, very rich in tyrosine hydroxylase and acetylcholinesterase, but on the basis of most other neurochemical criteria displays features that are typical of the extended amygdala (Alheid, de Olmos and Beltramino, 1995). Its afferent connections were examined in the rat with retrograde (cholera toxin B subunit) and anterograde (Phaseolus vulgaris leucoagglutinin) tracers and compared to those of the neighboring amygdalostriatal transition area and central amygdaloid nucleus. Deposits of cholera toxin B subunit in the interstitial nucleus of the posterior limb of the anterior commissure result in retrograde labeling that is similar to that seen after cholera toxin B subunit injections in the central amygdaloid nucleus. Retrogradely labeled cells are found in insular, infralimbic, prelimbic, piriform, amygdalopiriform transition, entorhinal and perirhinal cortices, as well as in temporal field CA1 of Ammon horn and ventral subiculum, amygdala (nucleus of the lateral olfactory tract, anterior amygdaloid area, anterior cortical, posterolateral cortical, anterior and posterior basomedial, intercalated cells, basolateral and lateral nuclei), and extended amygdala, primarily in its central division. The latter includes the lateral bed nucleus of the stria terminalis, dorsal portions of the sublenticular region, the lateral pocket of the supracapsular bed nucleus of the stria terminalis and the central amygdaloid nucleus. Retrogradely labeled cells are also seen in midline thalamic nuclei, lateral hypothalamus, ventral tegmental area, retrorubral field, dorsal raphe nucleus, pedunculopontine and dorsolateral tegmental nuclei, locus coeruleus and parabrachial area. The central extended amygdala, lateral hypothalamus and parabrachial area display a substantial retrograde labeling only when the injection involves districts of the interstitial nucleus of the posterior limb of the anterior commissure apposed to the pallidum, i.e. its medial part. Our anterograde results confirm that projections from the lateral bed nucleus of the stria terminalis and central amygdaloid nucleus to the interstitial nucleus of the posterior limb of the anterior commissure target its medial part. They also indicate that structures which provide major afferents to the central extended amygdala (the lateral and posterior basolateral amygdaloid nuclei and the amygdalopiriform transition area) innervate chiefly the medial part of the interstitial nucleus of the posterior limb of the anterior commissure and, to a much lesser degree, its lateral part. The piriform cortex, which has well-acknowledged projections to the ventral striatum, innervates only the rostral sector of the interstitial nucleus of the posterior limb of the anterior commissure. Taken together, these data indicate that the medial part of the interstitial nucleus of the posterior limb of the anterior commissure is closely related to the central extended amygdala. Rostral and lateral parts of the interstitial nucleus of the posterior limb of the anterior commissure, on the other hand, appear as transitional territories between the central extended amygdala and ventral striatum. The afferent connections of the zone traditionally termed amygdalostriatal transition area are in general similar to those of the caudate-putamen, which does not receive projections from the central extended amygdala. After cholera toxin B subunit injections in the caudoventral globus pallidus, a dense retrograde labeling is observed in the amygdalostriatal transition area and overlying striatum, but not in the interstitial nucleus of the posterior limb of the anterior commissure. Our results suggest that the interstitial nucleus of the posterior limb of the anterior commissure and the amygdalostriatal transition area are engaged in distinct forebrain circuits; the former is a dopamine-rich territory intimately related to the central ext

The neuronal organization of the supracapsular part of the stria terminalis in the rat: the dorsal component of the extended amygdala.

In the present normal anatomical light and electron microscopic study in the rat, histochemical (Nissl, Timm, Golgi) or immunocytochemical (microtubule-associated protein type 2, glutamate decarboxylase, glutamate receptor subunit 1, synaptophysin) stains were used to analyse neurons embedded within the stria terminalis and their associated neuropil. These cells are closely related to the bed nucleus of the stria terminalis and the centromedial amygdala, and have been termed the "supracapsular part of the bed nucleus of the stria terminalis". The largest part of this neuronal complex is located in the ventrolateral part of the stria, where it appears as a round or oval "lateral pocket" in virtually any type of light microscopic preparation because of its collection of neuronal cell bodies and dense neuropil, in addition to a lacework of unmyelinated axons. A much smaller but still distinct "medial pocket" is located in the medial corner of the stria. The large lateral subdivision of the supracapsular stria terminalis is directly continuous with the lateral bed nucleus of the stria terminalis and extends to the central amygdaloid nucleus, containing a column of neurons that is only broken up into cell clusters at the most caudal levels of the stria as it drops vertically toward the amygdala. The considerably smaller medial subdivision appears, in turn, to be directly continuous with the medial part of the bed nucleus of the stria terminalis. The medial column tapers off more rapidly than the lateral part, so that as the middle levels are approached, only small interrupted clusters of cells are seen. Solitary neurons can also be found in practically every part of the stria terminalis except among the ventrally located axons of the commissural component. Most of the neurons are small to medium in size, as viewed in transverse sections of the stria, but larger neurons are also encountered. In sections parallel to the stria, many neurons are fusiform in appearance. The dendrites are often aligned in a longitudinal fashion; many of the dendrites related to the cells in the lateral pocket are moderately to densely spined, whereas those in the medial pocket are more sparsely spined. The neuropil in both the lateral and medial pockets is characterized by boutons, bundles of unmyelinated axons, and dendrites. Based on their vesicle content, the boutons are divided into three major types: (A) round or slightly oval, agranular vesicles of uniform size; (B) pleomorphic, agranular vesicles, many of which are flattened; and (C) pleomorphic agranular vesicles, some of which are considerably larger than the ones in type B boutons. Type A boutons establish contacts with both dendritic spines and shafts, whereas types B and C usually contact dendritic shafts and sometimes somata. These synaptic components are similar to those described earlier for the central and medial amygdaloid nuclei. Overall, our results support the contention advanced in 1923 by Johnston [J. comp. Neurol. 35, 337481] that the cells accompanying the stria terminalis are interconnecting columns of a macrostructure encompassing the bed nucleus of the stria terminalis and centromedial amygdala. More recently, it has been appreciated that columns of neurons below the globus pallidus also belong to this macrostructure [Alheid G. F. et al. (1995) In The Rat Nervous System, 2nd edn, pp. 495 578, Academic, San Diego; de Olmos J. S. et al. (1985) In The Rat Nervous System, pp. 223-334, Academic, Sydney], which has been named the "extended amygdala".

The accumbens: beyond the core-shell dichotomy.

This article highlights recent discoveries related to the accumbens and closely associated structures, with special reference to their importance in neuropsychiatry. The development of "striatal patches" in the accumbens is reviewed in a series of pictures. Neuronal ensembles are discussed as potentially important functional-anatomical units. Attention is also drawn to recent discoveries related to the neuronal circuits that the primate accumbens establishes with the mesencephalic dopamine system. On the basis of histological and neurochemical differences, the accumbens has been divided into core and shell compartments. In the context of this article, the shell, which is an especially diversified part of the accumbens, is the subject of special attention because of its close relation to the extended amygdala and distinctive response to antipsychotic and psychoactive drugs.

Substantia innominata: a notion which impedes clinical-anatomical correlations in neuropsychiatric disorders.

Comparative neuroanatomical investigations in primates and non-primates have helped disentangle the anatomy of the basal forebrain region known as the substantia innominata. The most striking aspect of this region is its subdivision into two major parts. This reflects the fundamental organizational scheme for this portion of the forebrain. According to this scheme, two major subcortical telencephalic structures, i.e. the striatopallidal complex and extended amygdala, form large diagonally oriented bands. The rostroventral extension of the pallidum accounts for a large part of the rostral subcommissural substantia innominata, while the sublenticular substantia innominata is primarily occupied by elements of the extended amygdala. Also dispersed across this region is the basal nucleus of Meynert, which is part of a more or less continuous collection of cholinergic and non-cholinergic corticopetal and thalamopetal cells, which stretches from the septum diagonal band rostrally to the caudal globus pallidus. The basal nucleus of Meynert is especially prominent in the primate, where it is sometimes inappropriately applied as a synonym for the substantia innominata, thereby tacitly ignoring the remaining components. In most mammals, the extended amygdala presents itself as a ring of neurons encircling the internal capsule and basal ganglia. The extended amygdala may be further subdivided, i.e. into the central extended amygdala (related to the central amygdaloid nucleus) and the medial extended amygdala (related to the medial amygdaloid nucleus), which generally form separate corridors both in the sublenticular region and along the supracapsular course of the stria terminalis. The extended amygdala is directly continuous with the caudomedial shell of the accumbens, and to some extent appears to merge with it. Together the accumbens shell and extended amygdala form an extensive forebrain continuum, which establishes specific neuronal circuits with the medial prefrontal-orbitofrontal cortex and medial temporal lobe. This continuum is particularly characterized by a prominent system of long intrinsic association fibers, and a variety of highly differentiated downstream projections to the hypothalamus and brainstem. The various components of the extended amygdala, together with the shell of the accumbens, are ideally structured to generate endocrine, autonomic and somatomotor aspects of emotional and motivational states. Behavioral observations support this proposition and demonstrate the relevance of these structures to a variety of functions, ranging from the various elements of the reproductive cycle to drug-seeking behavior. The neurochemical and connectional features common to the accumbens shell and the extended amygdala are especially relevant to understanding the etiology and treatment of neuropsychiatric disorders. This is discussed in general terms, and also in specific relation to the neurodevelopmental theory of schizophrenia and to the neurosurgical treatment of neuropsychiatric disorders.

Efferent connections of the caudal part of the globus pallidus in the rat.

The efferent connections of the caudal pole of the globus pallidus (GP) were examined in the rat by employing the anterograde axonal transport of Phaseolus vulgaris leucoagglutinin (PHA-L), and the retrograde transport of fluorescent tracers combined with choline acetyltransferase (ChAT) or parvalbumin (PV) immunofluorescence histochemistry. Labeled fibers from the caudal GP distribute to the caudate-putamen, nucleus of the ansa lenticularis, reuniens, reticular thalamic nucleus (mainly its posterior extent), and along a thin strip of the zona incerta adjacent to the cerebral peduncle. The entopeduncular and subthalamic nuclei do not appear to receive input from the caudal GP. Descending fibers from the caudal GP course in the cerebral peduncle and project to posterior thalamic nuclei (the subparafascicular and suprageniculate nuclei, medial division of the medial geniculate nucleus, and posterior intralaminar nucleus/peripeduncular area) and to extensive brainstem territories, including the pars lateralis of the substantia nigra, lateral terminal nucleus of the accessory optic system, nucleus of the brachium of the inferior colliculus, nucleus sagulum, external cortical nucleus of the inferior colliculus, cuneiform nucleus, and periaqueductal gray. In cases with deposits of PHA-L in the ventral part of the caudal GP, labeled fibers in addition distribute to the lateral amygdaloid nucleus, amygdalostriatal transition area, cerebral cortex (mainly perirhinal, temporal, and somatosensory areas) and rostroventral part of the lateral hypothalamus. Following injections of fluorescent tracer centered in the lateral hypothalamus, posterior intralaminar nucleus, substantia nigra, pars lateralis, or lateral terminal nucleus, a substantial number of retrogradely labeled cells is observed in the caudal GP. None of these cells express ChAT immunoreactivity, but, except for the ones projecting to the lateral hypothalamus, a significant proportion is immunoreactive to PV. Our results indicate that caudal GP efferents differ from those of the rostral GP in that they project to extensive brainstem territories and appear to be less intimately related to intrinsic basal ganglia circuits. Moreover, our data suggest a possible participation of the caudal GP in feedback loops involving posterior cortical areas, posterior striatopallidal districts, and posterior thalamic nuclei. Taken as a whole, the projections of the caudal GP suggest a potential role of this pallidal district in visuomotor and auditory processes.

Amygdaloid input to transiently tyrosine hydroxylase immunoreactive neurons in the bed nucleus of the stria terminalis of the rat.

Several studies have reported transient expression of tyrosine hydroxylase in a subpopulation of neurons in the bed nucleus of stria terminalis of preadolescent rats. The tyrosine hydroxylase immunoreactive (TH) neurons, which are of small to medium size and often display a typical bipolar configuration, are confined to the intermediate part of the lateral bed nucleus. By the use of a combination of experimental tracer techniques and immunocytochemical methods, we have demonstrated that these neurons receive a significant number of amygdaloid afferents, which establish mostly symmetric synaptic contacts on the cell bodies and sparsely spined dendritic shafts of the TH neurons. TH neurons also receive a small number of tyrosine hydroxylase-positive terminals of unspecified origin.

A new PCR-based typing of the Rodgers and Chido antigenic determinants of the fourth component of human complement.

The Rodgers (Rg) and Chido (Ch) blood groups are antigenic determinants of the fourth component of human complement C4. They are associated with the two isotypes of C4, C4A and C4B, respectively. They serve as markers to distinguish C4A from C4B as well as for the definition of subtypes of common and rare allotypes. As an alternative to the serological typing method using human alloantisera, a PCR typing procedure with sequence-specific primers (PCR-SSP) was designed. The method was tested on selected DNA samples from individuals with well-defined C4 allotypes. No false-positive or false-negative typing results were obtained and all the determinant combinations could be distinguished. The PCR genotyping allowed the detection of all Rg/Ch sequence determinants of each isotype. Thus, reverse antigenicity could also be established in the presence of other C4 allotypes without a segregation study. To exclude the possibility that PCR-typed determinants originate from a non-expressed C4 null gene, a sequence-specific PCR was established detecting a 2-bp insertion in exon 29 described previously as a cause for C4A non-expression. PCR Rg/Ch genotyping provides a fast and efficient method for routine typing in HLA haplotype and disease association studies.

Silver staining as a tool for neurotoxic assessment.

There is no denying that the silver methods lost their dominant role as tract-tracing methods in the past 10 to 15 years. But it seems equally clear that the silver technique is headed for a dramatic revival in many fields of neuroscience, where the scope and localization of neuronal degeneration are a central issue. Together with the immunostaining of proteins formed or altered in traumatized neurons, the modern silver techniques provide neurotoxicologists and neuropathologists with unparalleled opportunities to detect and study injured and dying neurons. Characterized by great sensitivity and distinct rendition of the morphology of degenerating neurons and their processes, the reduced silver methods constitute the ideal tool for screening irreversible neuronal damage caused by neurotoxic substances including drugs of abuse. Those interested in the rapidly expanding fields of "excitotoxicity" and neurodegenerative disorders (Taylor 1991) are also likely to find increasing use for the silver methods. The pattern of degeneration in so-called "system degenerations" may be predetermined by the neuronal connections (Saper et al. 1987), and as the disease progresses from the destruction of the originally affected neuron population, closely related systems and pathways may be recruited into the pathophysiologic cascade. Any type of trauma to the CNS has the potential to produce this type of "domino effect" of degeneration, through which additional systems are progressively recruited into a degenerative chain reaction of transneuronal degeneration. In other words, even longstanding disorders may exhibit signs of more recent degeneration, and the proper use of silver methods at autopsy may give some important clues regarding the etiology of disease; it may also provide new insights about the anatomy of the human brain. Little can be said at present about the chemical basis of argyrophilia in degenerating and "reactive" neurons, but there is every reason to pay more attention to this subject. One can expect that a continuing and concerted effort will result in a rational understanding of the molecular biological and physicochemical events that fortuitously provide the basis for the selective impregnation of degenerating neuronal elements. This knowledge can be the basis for the development of even more reliable and simple, yet sensitive, silver methods suited for neurotoxic risk assessment on a large scale.

Specificity in the efferent projections of the nucleus accumbens in the rat: comparison of the rostral pole projection patterns with those of the core and shell.

The efferent connections of the rostral pole of the rat accumbens, where distinct core and shell subterritories can not be identified, were examined with the aid of the anterogradely transported plant lectin, Phaseolus vulgaris-leucoagglutinin (PHA-L), for comparison with the previously reported projection patterns of the accumbal core and shell. Injection sites and transported PHA-L were evaluated with the aid of reference to adjacent sections processed to display substance P or calbindin 28 kD immunoreactivities, i.e., markers that demonstrate the core and shell. Lateral parts of the rostral pole gave rise to a "core-like" projection system that involved the rostroventral globus pallidus, subcommissural ventral pallidum, entopeduncular nucleus and an adjacent part of the lateral hypothalamus, lateral ventral tegmental area, dorsal pars compacta, and structures in the lateral mesencephalic tegmentum and central grey. The medial part of the rostral pole gave rise to a "shell-like" innervation of the subcommissural ventral pallidum, lateral preoptic region, lateral hypothalamus, ventral tegmental area, dorsalmost pars compacta, retrorubral field, lateral midbrain tegmentum, and central grey. In contrast to the large numbers of axon varicosities observed through the entire length of lateral hypothalamus following shell injections, dense accumulations of axon collaterals and varicosities in hypothalamus were limited to the levels of origin of the stria medullaris bundle and entopeduncular nucleus and to the posterlateral region following medial injections. The medial part of the rostral pole contributed some projections to preoptic and sublenticular regions, but not to the bed nucleus of the stria terminalis. Noteworthy concentrations of calbindin immunoreactive cells observed in the lateral rostral pole correlate with the origin of the "basal ganglia-like" projection system, provoking the speculation that ventral striatal calbindin immunoreactive cells contribute principally to basal ganglia-like projections while cells lacking calbindin immunoreactivity contribute to the innervation of hypothalamus and midbrain tegmentum.

Patterns of glucose use after bicuculline-induced convulsions in relationship to gamma-aminobutyric acid and mu-opioid receptors in the ventral pallidum--functional markers for the ventral pallidum.

Bicuculline-induced convulsions increased glucose use throughout the brain and sharply demarcated the ventral pallidum and globus pallidus. Glucose use in the nucleus accumbens also increased after bicuculline-induced convulsions, except for a circumscribed region in the dorsomedial shell. Since the projection from the nucleus accumbens to the ventral pallidum contains gamma-aminobutyric acid (GABA) and the opioid peptide, enkephalin, the pattern of increased glucose use in the ventral pallidum and nucleus accumbens after bicuculline-induced convulsions was compared to the topography of GABAA and mu-opioid receptors. The pattern of glucose use in the nucleus accumbens and ventral pallidum resembled the topography of GABAA, but differed from that of mu-opioid receptors. Bicuculline may disinhibit GABAergic efferents to the ventral pallidum resulting in a dramatic increase in glucose use within striatopallidal synaptic terminals as well as in local terminals of the pallidal projection neurons.

Identification of the recombination site within the steroid 21-hydroxylase gene (CYP21) of the HLA-B47,DR7 haplotype.

The HLA haplotype A3-Cw6-B47-C4A91-BQ0-DR7 is associated with congenital adrenal hyperplasia (CAH), since it only carries the dysfunctional steroid 21-hydroxylase A pseudogene as well as the 5' adjacent complement C4A gene. The recombination site leading to the deletion of the complement C4B and steroid 21-hydroxylase B genes in this haplotype was studied by determining the 21-hydroxylase genomic DNA sequence in comparison to the standard CYP21A- and CYP21B-specific sequences. A 200-bp region between exons 7 and 8 was identified as a possible recombination site. Thus the deleted area comprises the 3' end of the CYP21A pseudogene, the entire C4B gene and the 5' end of the CYP21B gene. The findings were confirmed by PCR amplification of a 1.8-kb fragment of the CYP21 gene. This PCR system is specific for CYP21A/B recombinant genes and may be used for screening among CAH patients carrying this type of deletion.

Specificity in the projection patterns of accumbal core and shell in the rat.

The efferent projections of the core and shell areas of the nucleus accumbens were studied with a combination of anterograde and retrograde tract-tracing methods, including Phaseolus vulgaris-leucoagglutinin, horseradish peroxidase and fluorescent tracers. Both the core and shell regions project to pallidal areas, i.e. ventral pallidum and entopeduncular nucleus, with a distinct topography in the sense that the core projection is located in the dorsolateral part of ventral pallidum, whereas the shell projects to the medial part of the subcommissural ventral pallidum. Both regions of the accumbens also project to mesencephalon with a bias for the core projection to innervate the substantia nigra-lateral mesencephalic tegmentum, and for the shell projection to reach primarily the ventral tegmental-paramedian tegmentum area. The most pronounced differences between core and shell projections exist in regard to the hypothalamus and extended amygdala. Whereas the core projects primarily to the entopeduncular nucleus including a part that invades the lateral hypothalamus, the shell, in addition, projects diffusely throughout the rostrocaudal extent of the lateral hypothalamus as well as to the extended amygdala, especially its sublenticular part. Both the core and shell of the accumbens have unmistakable striatal characteristics both histologically and in their connectional patterns. The shell, however, has additional features that are reminiscent of the recently described extended amygdala [Alheid G.F. and Heimer L. (1988) Neuroscience 27, 1-39; de Olmos J.S. et al. (1985) In The Rat Nervous System, pp. 223-334]; in fact, the possibility exists that the shell represents a transitional zone that seems to characterize most of the fringes of the striatal complex, where it adjoins the extended amygdala.