Brainstem innervation of prefrontal and anterior cingulate cortex in the rhesus monkey revealed by retrograde transport of HRP

The cells of origin of projections from the brainstem to the dorsolateral and orbital prefrontal granular cortex and to the anterior cingulate cortex of the rhesus monkey were analyzed by means of retrograde axonal transport of the enzyme horseradish peroxidase (HRP). Following injections in various portions of the dorsolateral prefrontal and in the cingulate cortex, HRP-positive neurons were found in three main locations: (1) the ventral midbrain including the anterior ventral tegmental area, the medial one-third of the substantia nigra pars compacta, and the retrorubral nucleus; (2) the central superior nucleus and the dorsal raphe nucleus, primarily in its caudal subdivision; and (3) the locus coeruleus and adjacent medial parabrachial nucleus. Labeled neurons in the raphe nuclei and locus coeruleus were distributed bilaterally. A basically similar pattern of labeled somata was found in the brainstem with HRP injections in the orbital prefrontal cortex. Scattered HRP-positive cells were found throughout the ipsilateral ventral tegmental area and in ventromedial portions of the retrorubral nucleus, and a large number of HRP-positive cells were distributed bilaterally in the dorsal raphe and central superior nuclei as well as the dorsolateral pontine tegmentum. However, in contrast to the results obtained with injections on the dorsolateral and medial aspects of the hemisphere, labeled neurons were not found in any portion of the substantia nigra. The neurons labeled retrogradely after injection of HRP in these various regions of the frontal lobe in rhesus monkey correspond both in location and morphology to the monoamine-containing neurons of the brainstem and are thus very likely the source of dopamine, norepinephrine, and serotonin found in the frontal cortex of the same species.     

Prefrontal cortical projections to the striatum in macaque monkeys: evidence for an organization related to prefrontal networks

The organization of projections from the prefrontal cortex (PFC) to the striatum in relation to previously defined "orbital" and "medial" networks within the PFC were studied in monkeys using anterograde and retrograde tracing techniques. The results indicate that the orbital and medial networks connect to different striatal regions. The ventromedial striatum (the medial caudate nucleus, accumbens nucleus, and ventral putamen) receives input predominantly from the medial PFC (mPFC) and orbital areas 12o, Iai, and 13a, which constitute the "medial" network. More specifically, caudal medial areas 32, 25, and 14r project to the medial edge of the caudate nucleus, accumbens nucleus, and ventromedial putamen, whereas rostral areas 10o, 10m, and 11m are restricted to the medial edge of the caudate. Projections from orbital areas 12o, 13a, and Iai extend more laterally into the lateral accumbens and the ventral putamen. Area 24 gives rise to a divided pattern of projections, including fibers to the ventromedial striatum, apparently from area 24b, and fibers to the dorsolateral striatum, apparently from area 24c. Other areas of orbital cortex (11l, 12m, 12l, 13m, 13l, Ial, and Iam) that constitute the "orbital" network project primarily to the central part of the rostral striatum. This region includes the central and lateral parts of the caudate nucleus, and the ventromedial putamen, on either side of the internal capsule. The results support the subdivision of the orbital and medial PFC into "medial" and "orbital" networks and suggest that the prefrontostriatal projections reflect the functional organization of the PFC rather than topographic location.     

Distribution of dopaminergic fibers in the central division of the extended amygdala of the rat

The distribution of dopaminergic fibers in the principal components of the central extended amygdala (central amygdaloid nucleus (Ce), substantia innominata, and bed nucleus of the stria terminals (BNST)), was studied using immunocytochemistry against tyrosine hydroxylase, dopamine β-hydroxylase and dopamine. Dopamine fibers were found most densely distributed in the dorsolateral subdivision of the BNST and the lateral part of the Ce. Smaller numbers of dopaminergic fibers were found in the rest of the central extended amygdala. In contrast, dopamine β-hydroxylase fibers were virtually absent from the dorsolateral bed nucleus of the stria terminalis and lateral part of the central amygdaloid nucleus, but were distributed in a moderate density in the medial part of Ce, dorsal substantia innominata and posterolateral BNST. Our results show that dopamine fibers are most concentrated over those regions of the central extended amygdala with large numbers of GABAergic neurons whose projections remain within the central extended amygdala, while noradrenergic fibers are most heavily concentrated over those regions containing a large proportion of brainstem projection neurons. That dopamine fibers are concentrated over regions with GABAergic medium spiny neurons suggests that those regions might be organized as a striatal parallel.     

Loss of dopamine terminals in the medial prefrontal cortex increased the ratio of DOPAC to DA in tissue of the nucleus accumbens shell: role of stress

We examined whether dopamine depletion in the medial prefrontal cortex of the rat differentially affects basal and evoked dopamine and 3,4-dihydroxyphenylacetic acid (DOPAC) content in the subareas of the neostriatum and nucleus accumbens. Loss of ≈80% of tissue dopamine content in the medial prefrontal cortex did not significantly alter basal tissue concentrations of dopamine or DOPAC or the DOPAC : dopamine ratio in either the nucleus accumbens core or shell or the medial or lateral neostriatum. However, tail pressure stress significantly increased the DOPAC : dopamine ratio in the nucleus accumbens shell of lesioned rats. Because dorsal and ventral areas of the medial prefrontal cortex preferentially innervate the core and shell, respectively, we sought to determine whether the selective effect of lesions on dopamine terminals in the shell of the nucleus accumbens are paralleled by greater dopamine loss in the ventral medial prefrontal cortex. 6-Hydroxydopamine decreased tissue concentrations of dopamine in both the dorsal (−74%) and ventral medial prefrontal cortex (−68%). In lesioned rats, few tyrosine hydroxylase-immunoreactive fibers remained in the dorsal medial prefrontal cortex whereas a dense innervation remained in the ventralmost area. The present data suggest that the influence of mesocortical dopamine neurons on the dopamine projection to the nucleus accumbens shell is expressed only under conditions of stress. Furthermore, lesion-induced alterations in dopamine neurons projecting to the nucleus accumbens shell are not due to a more extensive loss of dopamine terminals in the ventral than in the dorsal medial prefrontal cortex.     

The medial geniculate body of the tree shrew, Tupaia glis. I. Cytoarchitecture and midbrain connections.

In this study of the medial geniculate body in the tree shrew eight subdivisions are identified on the basis of differences recognized in Nissl-stained material. Experiments using the methods of anterograde and retrograde axonal transport and anterograde degeneration show that each subdivision has a unique pattern of connections with the midbrain. The ventral division of the medial geniculate body contains at least two subdivisions, the ventral nucleus and the caudomarginal nucleus. The ventral nucleus is characterized by densely-packed cells and receives topographically organized projections from the central nucleus of the inferior colliculus. The caudomarginal nucleus, on the other hand, receives its major midbrain projections from the medial nucleus in the inferior colliculus. In the dorsal division four subdivisions are distinguished. The suprageniculate nucleus contains large, loosely-packed cells and receives projections from the deep layers of the superior colliculus and from the midbrain tegmentum. The dorsal nucleus receives projections from the midbrain tegmentum. The deep dorsal and anterodorsal nuclei have neurons which resemble those in the dorsal nucleus. Both receive projections from the roof nucleus of the inferior colliculus but the deep dorsal nucleus receives an additional projection from the parabrachial tegmentum. The medial division has a rostral and a caudal subdivision. The ascending projections to the rostral nucleus are from the lateral zone in the inferior colliculus and from the spinal cord. The caudal nucleus contains cells with large somas and receives projections from most of the midbrain areas which project to the other subdivisions of the medial geniculate body.     

Newly paired zebra finches have higher dopamine levels and immediate early gene Fos expression in dopaminergic neurons

Most birds are socially monogamous, yet little is known about the neural pathways underlying avian monogamy. Recent studies have implicated dopamine as playing a role in courtship and affiliation in a socially monogamous songbird, the zebra finch (Taeniopygia guttata). In the present study, we sought to understand the specific contribution to pair formation in zebra finches of the mesolimbic dopaminergic pathway that projects from the midbrain ventral tegmental area to the nucleus accumbens. We observed that paired birds had higher levels of dopamine and its metabolite 3,4‐dihydroxyphenylacetic acid in the ventral medial striatum, where the nucleus accumbens is situated, than unpaired birds. Additionally, we found that the percentage of dopaminergic neurons expressing immediate early gene Fos, a marker of neuronal activity, was higher in the ventral tegmental area of paired birds than in that of unpaired birds. These data are consistent with a role for the mesolimbic dopaminergic pathway in pair formation in zebra finches, suggesting the possibility of a conserved neural mechanism of monogamy in birds and mammals.     

Efferent connections of the basal forebrain in the cat: the nucleus accumbens.

The efferent connections of the nucleus accumbens in the cat were studied with radioautographic methods. Injections of [³H]leucine were placed throughout the extent of this structure in adult cats. The results revealed the presence of a topographical organization of the projections from the nucleus accumbens to the brain stem. Fibers arising from the dorsomedial sector of the nucleus accumbens project through the medial aspect of the medial forebrain bundle to the rostral end of the ventral tegmental area. Fibers arising from the ventromedial sector of the nucleus accumbens project to slightly more caudal and lateral parts of the ventral tegmentum. In contrast, fibers which arise from lateral parts of the nucleus accumbens project through the lateral aspect of the medial forebrain bundle and medial tip of the internal capsule to terminate primarily within the pars reticulata of the substantia nigra and central tegmental field. The data also suggest that fibers from this part of the nucleus accumbens probably terminate within the dorsolateral aspect of the substantia innominata and adjacent parts of the pallidum. These findings indicate that the nucleus accumbens is linked to both the limbic system and the basal ganglia.     

Midbrain acetylcholine and glutamate receptors modulate accumbal dopamine release

This study determined the role of ventral tegmental area acetylcholine and glutamate receptors in modulating laterodorsal tegmentum stimulation-evoked dopamine efflux in the nucleus accumbens. Rapid changes in dopamine oxidation current were measured at carbon fiber microelectrodes using fixed potential amperometry in urethane anesthetized male mice. Intraventral tegmental area infusions of the muscarinic acetylcholine receptor antagonist scopolamine, the nicotinic acetylcholine receptor antagonist mecamylamine, or the ionotropic glutamate receptor antagonist kynurenate significantly diminished dopamine efflux in the nucleus accumbens evoked by brief electrical stimulation of the laterodorsal tegmentum. These findings suggest that acetylcholine and ionotropic glutamate receptors influence rapid dopaminergic activity and thus the communication of behaviorally relevant information from ventral tegmental area dopamine cells to forebrain areas.     

Self-stimulation of the nucleus accumbens and ventral tegmental area of tsai attenuated by microinjections of spiroperidol into the nucleus accumbens

The contribution of dopaminergic neurons to self-stimulation of the ventral tegmental area, nucleus accumbens and prefrontal cortex was investigated. The ventral tegmental area is the site of non-striatal dopaminergic neurons and their axons project to the nucleus accumbens and prefrontal cortex. Injections of spiroperidol, a dopamine antagonist, into the nucleus accumbens significantly reduced self-stimulation of the ipsilateral ventral tegmental area but did not influence self-stimulation of the contralateral ventral tegmental area. Injections of spiroperidol into the prefrontal cortex did not reduce self-stimulation of the ipsilateral or contralateral ventral tegmental area. Electrical stimulation of sites in the nucleus accumbens positive for self-stimulation antidromically activated neurons of the ventral tegmental area, and a reduction of discharge of these neurons following administration of apomorphine suggested that they were dopaminergic neurons. These observations provide additional evidence implicating dopaminergic neurons in brain-stimulation reward and suggest that dopaminergic neurons contribute to self-stimulation of the nucleus accumbens but not the prefrontal cortex.     

Comparative analysis of dopamine and tyrosine hydroxylase immunoreactivities in the brain of two amphibians, the anuran Rana ridibunda and the urodele Pleurodeles waltlii.

To gain more insight into the dopaminergic system of amphibians and the evolution of catecholaminergic systems in vertebrates in general, the distribution of dopamine and tyrosine hydroxylase immunoreactivity was studied in the brains of the anuran Rana ridibunda and the urodele Pleurodeles waltlii. In both species, dopamine-immunoreactive (DAi) cell bodies were observed in the olfactory bulb, the preoptic area, the suprachiasmatic nucleus, the nucleus of the periventricular organ and its accompanying cells, the nucleus of the posterior tubercle, the pretectal area, the midbrain tegmentum, around the solitary tract, in the ependymal and subependymal layers along the midline of the caudal rhombencephalon, and ventral to the central canal of the spinal cord. Tyrosine hydroxylase (TH) immunohistochemistry revealed a similar pattern, although some differences were noted. For example, with the TH antibodies, additional cell bodies were stained in the internal granular layer of the olfactory bulb and in the isthmal region, whereas the same antibodies failed to stain the liquor contacting cells in the nucleus of the periventricular organ. Both antisera revealed an almost identical distribution of fibers in the two amphibian species. Remarkable differences were observed in the forebrain. Whereas the nucleus accumbens in Rana contains the densest DAi plexus, in Pleurodeles the dopaminergic innervation of the striatum prevails. Moreover, cortical structures of the newt contain numerous DAi fibers, whereas the corresponding structures in the frog are devoid of immunoreactivity. The dopaminergic system in amphibians appears to share many features not only with other anamniotes but also with amniotes.     

Compartmental organization of the ventral striatum of the rat: immunohistochemical distribution of enkephalin, substance P, dopamine, and calcium-binding protein

In the caudate-putamen of the rat a patch/matrix organization can be recognized on the basis of the immunohistochemical distribution of several markers, which include enkephalin, substance P, dopamine, and calcium-binding protein. In the present experiments the distributional relations of these markers were investigated in the nucleus accumbens. The distribution of enkephalin fibers shows different inhomogeneities according to their location in the nucleus. Rostrally, heavily labeled areas stand out against a moderately stained background, whereas caudally, in medial and ventral parts of the nucleus, lightly stained areas delineate regions in the moderately stained neuropil. In the distribution of substance P, areas with high staining intensity were observed in the medial and ventral parts of the nucleus accumbens. Inhomogeneities in the distribution of strong dopamine immunoreactivity consist of weakly immunoreactive areas throughout the rostrocaudal extent of the nucleus accumbens and extremely heavily labeled areas in the medial and ventral parts of the nucleus. Calcium-binding protein immunoreactivity can only be detected in dorsal parts of the nucleus. The generally intense immunostaining for calcium-binding protein is interspersed with "blanks" of weak immunoreactivity. The heavily and moderately labeled enkephalin areas each maintain specific relations with inhomogeneities in the distribution of substance P, dopamine, and calcium-binding protein. Rostrally, the heavily labeled enkephalin areas coincide with areas strongly immunostained for calcium-binding protein and with lightly stained areas in the dopamine and substance P immunoreactivity patterns. In the same region lightly stained areas in the enkephalin distribution match heavily labeled substance P areas. Caudally, in the border region of the nucleus accumbens and the caudate-putamen, the heavily labeled enkephalin areas are either related to "blanks" or to the intense staining regions in the calcium-binding protein immunoreactivity distribution. The moderately labeled enkephalin areas caudomedially in the nucleus accumbens are in register with the heavily labeled regions in the distribution of substance P and with the extremely heavily labeled regions in the distribution of dopamine. Relations with connectivity are discussed and the inhomogeneities are compared to those in the caudate-putamen. It is concluded that in the ventral striatum either one patch and one matrix compartment exist with different immunohistochemical relationships or there are several compartments with different immunohistochemical characteristics and different input-output relations.     

Projections of the visual cortex to the lateral geniculate and posterior thalamic nuclei in the cat

Fiber degeneration in the cat following lesions of various parts of areas 17, 18 and 19 was traced to the lateral geniculate and posterior thalamic nuclei by the method of Nauta and Gygax. Area 17 lying in the lateral and posterolateral gyri projects to the most medial parts of laminae A, A1 and central interlaminar nucleus (NIC). Area 17 in the suprasplenial gyrus sends fibers to the medial and middle parts of laminae A and A1 and the underlying part of NIC, while that in the splenial gyrus gives off fibers to the dorsolateral and ventrolateral parts of laminae A, A1 and NIC. These data indicate that there is a mediolateral organization in the projection from area 17 to the dorsal lateral geniculate nucleus. A topical organization exists also in the anteroposterior direction; the anterior, middle and posterior parts of area 17 project to the corresponding portion of the dorsal nucleus. Area 18 gives rise to fibers that pass between the medial interlaminar nucleus (NIM) and lamina A1 into the dorsolateral part of NIM, the medial part of NIC and the medial ends of laminae A and A1. The projections of area 18 to the dorsal nucleus are also organized in the anteroposterior dimension. Area 19 sends fibers to the major part of NIM, except to its most ventral and dorsolateral parts, and to the medialmost parts of NIC and lamina B. The majority of these fibers run along the medial aspect of NIM, but a few fibers pass ventrolaterally between NIM and lamina A1. It should be mentioned that NIM receives fibers not only from area 19 in the lateral and the posterior suprasylvian gyri, but also from area 19 in the medial cortex. As with areas 17 and 18, the corticogeniculate projections of area 19 are organized in an anteroposterior dimension. The ventral lateral geniculate nucleus also receives fibers from areas 17 and 19. The anterior part of area 17 projects only very few fibers to the ventral nucleus, but the posterior part gives off many fibers to the external layer of the nucleus. Area 17 fibers from the posterolateral gyrus are distributed in the dorso-medial part of the external layer and those from the suprasplenial gyrus enter the ventral and medial portion of the layer. In contrast most of area 18 and that part of area 19 in the lateral gyrus project no fibers to the ventral nucleus. The other parts of area 19 give off fibers to the internal layer and the adjoining portion of the external layer of the ventral nucleus. There appears to be an anteroposterior organization of the projection of the visual cortex on the ventral nucleus. The posterior thalamic nucleus receives fibers from areas 18 and 19 and part of area 17. Area 18 sends fibers to the medial and ventromedial part of the posterior nucleus, while most of area 19 projects fibers to the dorsal and middle part of the nucleus. Area 17 lying in the upper portion of the posterolateral gyrus and the suprasplenial and splenial gyri projects to the dorsomedial and medial part of the posterior nucleus.     

Functional organization of the medial geniculate body''s subdivisions of the awake squirrel monkey

The response properties of 138 cells in the medial geniculate body (MGB), of the awake squirrel monkey (Saimiri sciureus), to 7 species-specific vocalizations were studied. Cells were divided into 4 subgroups: 26 in the ventral, 24 in the medial and 46 in the lateral subdivision. Forty-two cells located on the borders between the subdivisions represent the fourth group. No significant differences were found between the subdivisions with respect to their selectivity, nor did cells in any subdivision respond preferentially to any particular vocalization. On the other hand, the response patterns of the ventral and the lateral subdivisions showed significant differences (P < 0.001, X²-test) from those of the medial subdivision. Most of the cells in the medial subdivision (87.5%) responded with similar response pattern to the 7 vocalizations (mainly ‘on’ or ‘sustain’), while most of the cells in the ventral and the lateral subdivisions (61.5% and 69.6% respectively) responded with complex, time-locked and different patterns to the various vocalizations. Cells that exhibited a response characterized as an intermediate between the two types were accumulated mainly on or close to the borders between the medial and the other subdivisions of the MGB. The possible role of each response patterns is discussed with respect to the projection of the subdivisions to the cortex.     

Immunohistochemical localization of substance P and enkephalin in the nucleus tractus solitarii of the rhesus monkey, Macaca mulatta

The nucleus tractus solitarii in the monkey Macaca mulatta was found to have several subdivisions based upon cytoarchitectonics and immunohistochemistry. Subdivisions that could be identified included commissural, medial, parvicellular, dorsolateral, ventrolateral, intermediate, and interstitial. Substance P and enkephalin immunoreactivity was localized within discrete regions of the nucleus tractus solitarii, by means of the peroxidase-antiperoxidase technique. Substance P immunoreactivity occurred most frequently in the interstitial subdivision of the nucleus tractus solitarii. Moderate accumulations of substance P immunoreactivity were present in the commissural, medial, parvicellular, dorsolateral, and intermediate subdivisions, but very little was present in the ventrolateral subdivision. Enkephalin immunoreactivity followed the staining patterns of substance P; however, the amounts of enkephalin immunoreactivity were less than amounts for substance P. Following colchicine treatment, large numbers of enkephalin-immunoreactive neurons were distributed throughout all subdivisions, many being located in the parvicellular and medial subdivisions. The few substance P-immunoreactive neurons found were restricted to the parvicellular subdivision. The distribution of substance P and enkephalin immunoreactivity in M. mulatta is very similar to that described in the cat and rat. In addition, the extensive overlap of the distribution of these two putative neurotransmitters provides morphological evidence for their possible participation in the autonomic regulation within the nucleus tractus solitarii.     

Immunocytochemical localization of the dopamine transporter in human brain.

The dopamine transporter (DAT) was localized in normal human brain tissue by light microscopic immunocytochemistry by using highly specific monoclonal antibodies. Regional distribution of DAT was found in areas with established dopaminergic circuitry, e.g., mesostriatal, mesolimbic, and mesocortical pathways. Mesencephalic DAT-immunoreactivity was enriched in the dendrites and cell bodies of neurons in the substantia nigra pars compacta and ventral tegmental area. Staining in the striatum and nucleus accumbens was dense and heterogeneous. Mesocortical DAT immunoreactivity in motor, premotor, anterior cingulate, prefrontal, entorhinal/perirhinal, insular, and visual cortices was detected in scattered varicose and a few nonvaricose fibers. Varicose fibers were relatively enriched in the basolateral and central subnuclei of amygdala, with sparser fibers in lateral and basomedial subnuclei. Double-labeling studies combining DAT and tyrosine hydroxylase (TH) immunostaining in the ventral mesencephalon showed two subpopulations of dopaminergic neurons differentiated by the presence or absence of DAT-immunoreactivity in the A9 and A10 cell groups. In other dopaminergic cell groups (All, A13-A15), TH-positive hypothalamic neurons showed no detectable DAT-immunoreactivity. However, fine DAT-immunoreactive axons were scattered throughout the hypothalamus, particularly concentrated along the medial border, with more coarse axons present along the lateral border. These findings demonstrate that most mesotelencephalic dopamine neurons of human brain express high levels of DAT throughout their entire somatodendritic and axonal domains, whereas a smaller subpopulation of mesencephalic dopamine cells and all hypothalamic dopamine cell groups examined express little or no DAT. These data indicate that different subpopulations of dopaminergic neurons use different mechanisms to regulate their extracellular dopamine levels.     

Efferent connectivity of the hippocampal formation of the zebra finch (Taenopygia guttata): An anterograde pathway tracing study using Phaseolus vulgaris leucoagglutinin

The avian hippocampal formation (HP) is considered to be homologous to the mammalian hippocampus, being involved in memory formation and spatial memory in particular. The subdivisions and boundaries of the pigeon hippocampus have been defined previously by various morphological methods to detect further similarities with the mammalian homologue. We studied the efferent projections of the zebra finch hippocampus by applying Phaseolus vulgaris leucoagglutinin, and three main subdivisions were distinguished on the basis of the connectivity patterns. Dorsolateral injections gave rise to projections innervating the rostralmost extension of the HP, a laminar complex including the dorsal and ventral hyperstriata and the lamina frontalis superior, the rostral lobus parolfactorius, the medial and ventral paleostriatal regions, the lateral septal nucleus, the nucleus of the diagonal band, the dorsolateral corticoid area, the archistriatum posterius, and the nucleus taeniae in the telencephalon. In the diencephalon, labelled axons were seen in the periventricular and lateral hypothalamus, including the lateral mammillary nuclei, and in the dorsolateral and the dorsomedial posterior thalamic nuclei, whereas, in the midbrain, only the area ventralis of Tsai contained hippocampal fibres. With the exception of the bilateral archistriatal efferents, all projections were ipsilateral. Dorsomedial injections gave rise to a local fibre system that was almost completely restricted to the ipsilateral hippocampal formation. In addition, lectin-containing fibres continued in the dorsal septal region and a thin band in the hyperstriatum accessorium, adjacent to the lateral ventricle. Ventral injections gave rise to axons innervating the dorsolateral subdivision ipsilaterally and bilaterally the medial septal nuclei and the contralateral ventral hippocampus. © 1996 Wiley-Liss, Inc.     

Basal ganglia organization in amphibians: Afferent connections to the striatum and the nucleus accumbens

As part of a research program to determine if the organization of basal ganglia (BG) of amphibians is homologous to that of amniotes, the afferent connections of the BG in the anurans Xenopus laevis and Rana perezi and the urodele Pleurodeles waltl were investigated with sensitive tract-tracing techniques. Hodological evidence is presented that supports a division of the amphibian BG into a nucleus accumbens and a striatum. Both structures have inputs in common from the olfactory bulb, medial pallium, striatopallial transition area, preoptic area, ventral thalamus, ventral hypothalamic nucleus, posterior tubercle, several mesencephalic and rhombencephalic reticular nuclei, locus coeruleus, raphe, and the nucleus of the solitary tract. Several nuclei that project to both subdivisions of the BG, however, show a clear preference for either the striatum (lateral amygdala, parabrachial nucleus) or the nucleus accumbens (medial amygdala, ventral midbrain tegmentum). In addition, the anterior entopeduncular nucleus, central thalamic nucleus, anterior and posteroventral divisions of the lateral thalamic nucleus, and torus semicircularis project exclusively to the striatum, whereas the anterior thalamic nucleus, anteroventral, and anterodorsal tegmental nuclei provide inputs solely to the nucleus accumbens. Apart from this subdivision of the basal forebrain, the results of the present study have revealed more elaborate patterns of afferent projections to the BG of amphibians than previously thought. Moreover, regional differences within the striatum and the nucleus accumbens were demonstrated, suggesting the existence of functional subdivisions. The present study has revealed that the organization of the afferent connections to the BG in amphibians is basically similar to that of amniotes. According to their afferent connections, the striatum and the nucleus accumbens of amphibians may play a key role in processing olfactory, visual, auditory, lateral line, and visceral information. However, contrary to the situation in amniotes, only a minor involvement of pallial structures on the BG functions is present in amphibians. J. Comp. Neurol. 378:16–49, 1997. © 1997 Wiley-Liss, Inc.     

Variations in extracellular levels of dopamine, noradrenaline, glutamate, and aspartate across the sleep--wake cycle in the medial prefrontal cortex and nucleus accumbens of freely moving rats

We used intracerebral microdialysis coupled with electrophysiologic recordings to determine relative changes in the concentrations of several neurotransmitters in the medial prefrontal cortex and nucleus accumbens of freely moving rats during waking, slow-wave sleep, and rapid eye movement (REM) sleep. The concentrations of noradrenaline, dopamine, glutamate, and aspartate in 2-min dialysate samples were analyzed by capillary electrophoresis combined with laser-induced fluorescence detection. Changes in glutamate and aspartate concentrations were found only in the nucleus accumbens, in which a decrease was obtained during both slow-wave sleep and REM sleep compared to waking. A progressive reduction in the release of noradrenaline was observed from waking to REM sleep in both structures. In contrast, dopamine concentrations were higher during waking and REM sleep compared to that during slow-wave sleep. The latter results demonstrate that contrary to the findings of earlier electrophysiologic studies carried out on ventral tegmental area dopaminergic neurons, changes in the release of dopamine in projection areas occur across the sleep-wake cycle. The elevated levels of dopamine during waking and REM sleep in the medial prefrontal cortex and the nucleus accumbens could result from changes during these two states in afferent modulation at the level of cell bodies or at the level of dopaminergic terminals.     

Biochemical mapping of the noradrenergic ventral bundle projection sites: Evidence for a noradrenergic-dopaminergic interaction

Norepinephrine (NE) and dopamine (DA) concentration and dopamine turnover were measured 12 days after a unilateral or bilateral noradrenergic ventral bundle (VB) transection to determine the noradrenergic projection sites and possible interactions with dopaminergic systems.Both bilateral and unilateral VB transection resulted in a significant reduction of NE of the nucleus accumbens, lateral septal nucleus, medial forebrain bundle, ventromedial nucleus, dorsomedial nucleus and medial amygdaloid nucleus. Bilateral transection also decreased NE content of the median eminence and the periventricular and arcuate nuclei. In the medial preoptic nucleus, the nucleus interstitialis striae terminalis and the central gray catecholamine area, bilateral transection significantly decreased NE concentrations while unilateral lesions had no significant effect. The anterior hypothalamic, lateral preoptic, and paraventricular nuclei responded to bilateral VB transection with a decrease in NE concentration and to unilateral lesion with a bilateral increase in NE. In the dorsal hippocampus and the caudate nucleus, bilateral lesions had no effect on NE concentrations while unilateral transection significantly decreased NE concentrations. Regions in which neither bilateral nor unilateral VB transection produced a significant change in NE content are the olfactory tubercle, the nucleus tractus diagonalis, substantia nigra pars compacta and reticulata, ventral tegmental area, habenula, superior colliculus, and the cingulate and piriform cortices.Transection of the noradrenergic ventral bundle also produced changes in dopaminergic systems suggesting a noradrenergic-dopaminergic interaction. Bilateral VB transection decreased the dopamine concentration and turnover in the nucleus accumbens, increased steady-state levels and turnover in the nucleus tractus diagonalis and increased dopamine concentration in the lateral septum. Unilateral VB transection decreased DA concentration bilaterally in the caudate nucleus, olfactory tubercle, nucleus accumbens and the nucleus interstitialis striae terminalis but increased concentrations in the substantia nigra pars reticulata (ipsilateral) and in the ventral tegmental area (bilateral). These results indicate a broad projection field for the noradrenergic ventral bundle and suggest a noradrenergic-dopaminergic interaction.