Ventral mesencephalic neurons containing both cholecystokinin- and tyrosine hydroxylase-like immunoreactivities project to forebrain regions

The coexistence of cholecystokinin- and tyrosine hydroxylase-like immunoreactivities within neurons of the rat ventral mesencephalon was analyzed by using an indirect immunofluorescence technique for the simultaneous demonstration of two antigens in the same tissue section. A high degree of colocalization was observed in the substantia nigra pars compacta, in which 80-90% of all labeled neurons at rostral and up to 70% at intermediate levels contained both cholecystokinin and tyrosine hydroxylase. At caudal levels, the incidence of colocalization declined to approximately 30-50%. All of the immunoreactive perikarya in the substantia nigra pars lateralis were labeled with both substances. Other areas of the ventral midbrain that exhibited a moderate proportion of neurons immunoreactive for both cholecystokinin and tyrosine hydroxylase included the ventral tegmental area, interfascicular nucleus, and rostral and caudal linear nuclei. In addition, coexistence was occasionally observed within neurons of the central and ventral periaqueductal gray matter, supramammillary region, peripeduncular region, retrorubral field, and extremely rarely, within the substantia nigra pars reticulata. Cell bodies containing tyrosine hydroxylase-like immunoreactivity (indicative of dopamine) usually outnumbered those containing the peptide except in the supramammillary region and in the ventral periaqueductal gray matter, where the cholecystokinin perikarya were present in higher numbers. The double-labeling colocalization technique was combined with fluorescence retrograde tracing to determine some of the forebrain projections of these neurons. Ventral midbrain neurons containing both cholecystokinin and tyrosine hydroxylase were found to project to the caudate-putamen, nucleus-accumbens, prefrontal cortex, and amygdala. These projections originated from neurons located predominantly in the substantia nigra pars compacta and the ventral tegmental area. Thus, cholecystokinin occurs within the well-known dopaminergic nigrostriatal pathway in the rat. Overall, these results demonstrate that a significant proportion of the dopamine neurons giving rise to the ascending mesotelencephalic projections also contain the peptide cholecystokinin.     

Direct comparison of projections from the central amygdaloid region and nucleus accumbens shell

Certain neurochemical and connectional characteristics common to extended amygdala and the nucleus accumbens shell suggest that the two represent a single functional-anatomical continuum. If this is so, it follows that the outputs of the two structures should be substantially similar. To address this, projections from the caudomedial shell and central nucleus of the amygdala, a key extended amygdala structure, were demonstrated in Sprague-Dawley rats with different anterograde axonal tracers processed separately to exhibit distinguishable brown and blue-black precipitates. The caudomedial shell projection is strong in the ventral pallidum and along the medial forebrain bundle through the lateral preopticohypothalamic continuum into the ventral tegmental area, distal to which it thins abruptly. The central nucleus projects strongly to the bed nucleus of the stria terminalis and the sublenticular extended amygdala, but substantially to the lateral hypothalamus only at levels behind the rostral part of the entopeduncular nucleus. Innervation of the ventral tegmental area by the central amygdala is minimal, but the lateral one-third of the substantia nigra, pars compacta and an adjacent lateral part of the retrorubral field receive substantial central amygdala input. Central amygdaloid projections are robust in caudal brainstem sites, such as the reticular formation, parabrachial nucleus, nucleus of the solitary tract and dorsal vagal complex, all of which receive little input from the accumbens. The substantial differences in the output systems of the caudomedial shell of accumbens and central amygdala suggest that the two represent distinct functional-anatomical systems.     

Cholinergic innervation of the human striatum, globus pallidus, subthalamic nucleus, substantia nigra, and red nucleus.

The anatomical organization of cholinergic markers such as acetylcholinesterase, choline acetyltransferase, and nerve growth factor receptors was investigated in the basal ganglia of the human brain. The distribution of choline acetyltransferase-immunoreactive axons and varicosities and their relationship to regional perikarya showed that the caudate, putamen, nucleus accumbens, olfactory tubercle, globus pallidus, substantia nigra, red nucleus, and subthalamic nucleus of the human brain receive widespread cholinergic innervation. Components of the striatum (i.e., the putamen, caudate, olfactory tubercle, and nucleus accumbens) displayed the highest density of cholinergic varicosities. The next highest density of cholinergic innervation was detected in the red nucleus and subthalamic nucleus. The level of cholinergic innervation was of intermediate density in the globus pallidus and the ventral tegmental area and low in the pars compacta of the substantia nigra. Immunoreactivity for nerve growth factor receptors (NGFr) was confined to the cholinergic neurons of the basal forebrain and their processes. Axonal immunoreactivity for NGFr was therefore used as a marker for cholinergic projections originating from the basal forebrain (Woolf et al., '89: Neuroscience 30:143-152). Although the vast majority of striatal cholinergic innervation was NGFr-negative and, therefore, intrinsic, the striatum also contained NGFr-positive axons, indicating the existence of an additional cholinergic input from the basal forebrain. This basal forebrain cholinergic innervation was more pronounced in the putamen than in the caudate. The distribution of NGFr-positive axons suggested that the basal forebrain may also project to the globus pallidus but probably not to the subthalamic nucleus, substantia nigra, or red nucleus. The great majority of cholinergic innervation to these latter three structures and to parts of the globus pallidus appeared to come from cholinergic neurons outside the basal forebrain, most of which are probably located in the upper brainstem. These observations indicate that cholinergic neurotransmission originating from multiple sources is likely to play an important role in the diverse motor and behavioral affiliations that have been attributed to the human basal ganglia.     

Complementary Distribution of Calbindin D-28k and Parvalbumin in the Basal Forebrain and Midbrain of the Squirrel Monkey

The distribution of cell bodies expressing either calbindin D-28k or parvalbumin immunoreactivity in the basal forebrain and midbrain of squirrel monkeys (Saimiri sciureus) was studied on contiguous sections incubated with monoclonal antibodies raised against calbindin or parvalbumin. In the nucleus accumbens, medium-sized calbindin-positive neurons formed two cell bridges joining the ventral part of the striatum to the olfactory tubercle, whereas medium-sized parvalbumin-positive cells in the same area were much less numerous and more uniformly distributed. The medial and dorsal septal nuclei contained a small number of elongated calbindin-positive neurons and only a few parvalbumin-immunoreactive cells. In the nucleus of the diagonal band of Broca, calbindin and parvalbumin were found to label two distinct but closely intermingled neuronal populations. In the striatum, medium-sized calbindin-immunoreactive cells occurred in very large numbers and appeared to be confined to the extrastriosomal matrix. Medium-sized, parvalbumin-immunoreactive neurons were also present in the striatum but they were less numerous than the calbindin-positive cells. The calbindin-positive neurons in the dorsal portion of the striatum were less intensely stained than those in the ventral portion, whereas this pattern did not occur for neurons expressing parvalbumin immunoreactivity. At the pallidal level, neurons in both segments were devoid of calbindin but displayed a very strong parvalbumin immunoreactivity. Most of the large neurons of the nucleus basalis of Meynert were strongly calbindin-immunoreactive and many of them invaded dorsally the medullary laminae of the pallidal complex. The neurons of the subthalamic nucleus were markedly enriched with parvalbumin but displayed only light calbindin staining. In the substantia nigra/ventral tegmental area complex, calbindin-immunoreactive cells abounded in the ventral tegmental area and in the dorsal tier of the pars compacta of the substantia nigra, but were absent in the ventral tier of the pars compacta and in the entire pars reticulata of the substantia nigra. In contrast, numerous parvalbumin-immunoreactive neurons occurred in the pars reticulata and pars lateralis, but none were found in the pars compacta and ventral tegmental area. These findings reveal that the patterns of calbindin and parvalbumin distribution in primate basal forebrain and midbrain are strikingly complementary, suggesting a synergistic role for these calcium-binding proteins in basal forebrain and midbrain function.     

Neurotensin in projection neurons of the striatum and nucleus accumbens, with reference to coexistence with enkephalin and GABA: an immunohistochemical study in the cat

Neurotensin-like immunoreactivity (NT-LI) was demonstrated in projection neurons of the striatum and nucleus accumbens in the cat by combining immunohistochemistry and the fluorescent retrograde neuronal labeling method. In colchicine-treated cats, many neurons with NT-LI were found in the caudate nucleus, nucleus accumbens, and putamen. Most of these neurons were medium-sized neurons with spiny dendrites. NT-LI of neuronal elements in the caudate nucleus and nucleus accumbens formed dense aggregates with irregular figures, which appeared to correspond to the striosomes of Graybiel et al. (Proc. Natl. Acad. Sci. USA 75:5723-5726, '78; Exp. Brain Res. 34:189-195, '79; Neuroscience 6:377-397, '81). Fibers with NT-LI were distributed massively to the globus pallidus and ventral midbrain regions, but not to the entopeduncular nucleus. In the ventral midbrain regions, many fine varicose fibers with NT-LI were distributed to the pars compacta and pars lateralis of the substantia nigra, ventral tegmental area, and retrorubral area. In the pars reticulata of the substantia nigra, however, fibers with NT-LI were rather sparse. Examination of consecutive sections immunostained for NT, enkephalin (Enk), GABA, and substance P (SP) revealed that 50% of neurons with NT-LI in the caudate nucleus and nucleus accumbens exhibited Enk-LI, 15% showed GABA-LI, and 5% manifested both Enk-LI and GABA-LI; no NT-positive neurons in the striatum and nucleus accumbens showed SP-LI. No morphological differences were found between NT-positive neurons with Enk-LI and/or GABA-LI and those without Enk-LI and GABA-LI. Most neurons with NT-LI in the striatum and nucleus accumbens were retrogradely labeled with True Blue injected into the globus pallidus, pars compacta and pars lateralis of the substantia nigra, and ventral tegmental area. After hemitransection severing neuronal connections between the ventral midbrain regions and the forebrain structures, fibers with NT-LI and those with Enk-LI in the ventral midbrain regions were markedly reduced in number.(ABSTRACT TRUNCATED AT 400 WORDS)     

Visualization of a dopamine D1 receptor mRNA in human and rat brain.

Using 32P-labeled oligonucleotides derived from the coding region of human dopamine D1 receptor mRNA we have localized in the human and rat brain the cells containing the mRNAs coding for this receptor. Dopamine D1 receptor mRNA in human brain was found to be contained in the neurons of the caudate and putamen nuclei as well as in the nucleus accumbens, some cortical regions and some nuclei of the amygdala. In the rat brain, cells containing D1 receptor mRNA were enriched in caudate-putamen and accumbens nuclei, olfactory tubercle, islands of Calleja, some cortical areas and in several thalamic nuclei. Moreover, in both species, it was absent from the neurons of the substantia nigra both pars compacta and pars reticulata and ventral tegmental area as well as from the globus pallidus pars lateralis and medialis in human and globus pallidus and entopeduncular nucleus in rat. In general, a good agreement was found with the distribution of binding sites labeled with the D1 antagonist SCH 23390. The main exception was the absence of D1 receptor mRNA in globus pallidus and substantia nigra, regions where high densities of receptor sites are found. These data support the notion that sites in these two regions are localized to projections from striatal neurons and that dopaminergic neurons do not express this receptor.     

A PHA-L analysis of ascending projections of the dorsal raphe nucleus in the rat.

Ascending projections from the dorsal raphe nucleus (DR) were examined in the rat by using the anterograde anatomical tracer, Phaseolus vulgaris leucoagglutinin (PHA-L). The majority of labeled fibers from the DR ascended through the forebrain within the medial forebrain bundle. DR fibers were found to terminate heavily in several subcortical as well as cortical sites. The following subcortical nuclei receive dense projections from the DR: ventral regions of the midbrain central gray including the 'supraoculomotor central gray' region, the ventral tegmental area, the substantia nigra-pars compacta, midline and intralaminar nuclei of the thalamus including the posterior paraventricular, the parafascicular, reuniens, rhomboid, intermediodorsal/mediodorsal, and central medial thalamic nuclei, the central, lateral and basolateral nuclei of the amygdala, posteromedial regions of the striatum, the bed nucleus of the stria terminalis, the lateral septal nucleus, the lateral preoptic area, the substantia innominata, the magnocellular preoptic nucleus, the endopiriform nucleus, and the ventral pallidum. The following subcortical nuclei receive moderately dense projections from the DR: the median raphe nucleus, the midbrain reticular formation, the cuneiform/pedunculopontine tegmental area, the retrorubral nucleus, the supramammillary nucleus, the lateral hypothalamus, the paracentral and central lateral intralaminar nuclei of the thalamus, the globus pallidus, the medial preoptic area, the vertical and horizontal limbs of the diagonal band nuclei, the claustrum, the nucleus accumbens, and the olfactory tubercle. The piriform, insular and frontal cortices receive dense projections from the DR; the occipital, entorhinal, perirhinal, frontal orbital, anterior cingulate, and infralimbic cortices, as well as the hippocampal formation, receive moderately dense projections from the DR. Some notable differences were observed in projections from the caudal DR and the rostral DR. For example, the hippocampal formation receives moderately dense projections from the caudal DR and essentially none from the rostral DR. On the other hand, virtually all neocortical regions receive significantly denser projections from the rostral than from the caudal DR. The present results demonstrate that dorsal raphe fibers project significantly throughout widespread regions of the midbrain and forebrain.     

A catecholaminergic projection from the ventral tegmental area to the diagonal band of broca: Modulation by neurotensin

The ventral tegmental area contains a high density of dopaminergic perikarya having ascending projections to a number of limbic forebrain regions. In this study, we use combined retrograde labeling with horseradish peroxidase (HRP) and immunohistochemical staining for tyrosine hydroxylase to examine the catecholaminergic projection from the ventral tegmental area to the diagonal band of Broca. When injection of HRP was restricted to the diagonal band, only neurons in the nucleus linearis, nucleus interfascicularis and ventromedial portion of the nucleus paranigralis were labeled. In contrast, HRP injection into the adjacent nucleus accumbens labeled neurons throughout these nuclei, plus the nucleus parabrachialis pigmentosus, nucleus retroruber and substantia nigra, pars compacta. Approximately 60% of neurons in the ventral tegmental area labeled from the diagonal band contained tyrosine hydroxylase, compared with 79% of the neurons labeled from the nucleus accumbens. Neurotensin is a tridecapeptide found in the ventral tegmental area which has been shown to activate dopamine neurons projecting to the nucleus accumbens. In this study, microinjection of neurotensin into ventral tegmental nuclei which contained neurons retrogradely labeled from the diagonal band significantly elevated the levels of dopamine metabolites, 3,4-dihydroxyphenylacetic acid and homovanillic acid, in the diagonal band. The results of this study demonstrate that a catecholaminergic projection exists from the ventral tegmental area to the diagonal band of Broca, and that this pathway can be stimulated by intra-ventral tegmental injection with neurotensin.     

Compartmental distribution of ventral striatal neurons projecting to the mesencephalon in the rat.

The ventral striatum is characterized by an intricate neurochemical compartmentation that is reflected in the distribution of most of its afferent fiber systems. In the present study, the compartmental relationships of ventral striatal neurons projecting to the mesencephalon were studied by combining tract tracing with the immunohistochemical localization of leu-enkephalin. Injections of the retrograde tracer cholera toxin subunit B were placed at various sites in the ventral mesencephalon. The anterograde tracer Phaseolus vulgaris leucoagglutinin was injected in single compartments in the rostrolateral part of the nucleus accumbens. The projections from the ventral striatum to the dopaminergic cell groups in the ventral mesencephalon and those to the substantia nigra pars reticulata originate from distinct subpopulations of ventral striatal neurons that respect neurochemically defined compartmental boundaries. In the "shell" of the nucleus accumbens, neurons that project to the dopaminergic cell groups are located outside areas of high cell density and weak enkephalin immunoreactivity (ENK-IR). Rostrolaterally in the "core" of the nucleus accumbens, neurons inside large areas of strong ENK-IR surrounding the anterior commissure project to the dorsomedial part of the substantia nigra pars reticulata, whereas neurons outside these areas innervate the ventral tegmental area and/or the medial part of the substantia nigra pars compacta. By contrast, more caudally in the dorsal part of the nucleus accumbens and in the ventral part of the caudate-putamen, the relationships are reversed: neurons in- or outside small patches of strong ENK-IR project respectively to the pars compacta or the pars reticulata of the substantia nigra. Since the thalamic and cortical afferents of the ventral striatum are compartmentally ordered as well, the present results imply that through the ventral striatal compartments information from disparate combinations of cortical and thalamic sources may be conveyed to distinct mesencephalic targets. The component of the ventral striatomesencephalic system reaching the dopaminergic cell groups A10, A9, and A8 may modulate the dopaminergic input to virtually the entire striatum. The other component can, by way of the pars reticulata of the substantia nigra, participate in nigrothalamic and nigrotectal output pathways of the basal ganglia.     

An autoradiographic study of the projections of the central nucleus of the monkey amygdala

The efferent connections of the central nucleus of the monkey amygdala have been studied using the autoradiographic method for tracing axonal projections. Small injections of 3H-amino-acids which are largely confined to the central nucleus lead to the labeling of several brainstem nuclei as far caudally as the spinomedullary junction. Specifically, in the forebrain, the central nucleus projects heavily to the bed nucleus of the stria terminalis, the basal nucleus of Meynert, the nucleus of the horizontal limb of the diagonal band, and more lightly to the substantia innominata and the preoptic area. In the hypothalamus, label is found over the dorsomedial nucleus, the perifornical region, the lateral hypothalamus, the supramammillary area, and most heavily in the paramammillary nucleus. In the thalamus, all components of the nucleus centralis medialis and the nucleus reuniens receive fibers from the central nucleus and there is a light projection to the medial pulvinar nucleus. In the mesencephalon, there is heavy labeling dorsal to the substantia nigra ad over the peripeduncular nucleus and lighter labeling within the substantia nigra pars compacta and the ventral tegmental area; the midbrain central gray is also labeled. More caudally, fibers from the central nucleus travel in the lateral tegmental reticular fields and contribute collaterals to the raphe nuclei, the cuneiform nucleus, and the central gray substance. Perhaps one of the heaviest terminal zones is the parabrachial region of the pons, both the lateral and the medial nuclei of which receive a prominent central nucleus projection. Only the ventral aspect of the adjacent locus coeruleus appears to receive a substantial input, but there is labeling also over the area of the nucleus subcoeruleus. Finally, there is heavy labeling around the dorsal motor nucleus of the vagus and over the parvocellular component of the nucleus of the solitary tract. A number of intra-amygdaloid connections between the basal and lateral nuclei of the amygdala and the central nucleus are also described. The present findings, taken together with recently reported widespread projections from the temporal association cortex to the amygdala, point out a potentially trisynaptic route between neocortical association regions and a variety of brainstem nuclei, many of which are related to autonomic function.     

Efferent connections of the substantia nigra and ventral tegmental area in the rat

Small injections of tritiated leucine and proline confined to the ventral tegmental area (AVT) were found to label fibers ascending: (a) to the entire ventromedial half of the striatum, but most massively to the ventral striatal zone that includes the nucleus accumbens; (b) to the thalamus: lateral habenular nucleus, nuclei reuniens and centralis medius, and the most medial zone of the mediodorsal nucleus; (c) to the posterior hypothalamic nucleus and possibly the lateral hypothalamic and preoptic region; (d) to the nuclei amygdalae centralis, lateralis and medialis; (e) to the bed nucleus of the stria terminalis, the nucleus of the diagonal band, and the medial half of the lateral septal nucleus; (f) to the anteromedial (frontocingulate) cortex; and (g) to the entorhinal area. Further AVT efferents descend to the medial half of the midbrain tegmentum including an anterior region of the median raphe nucleus, to the ventral half of the central grey substance including the dorsal raphe nucleus, to the parabrachial nuclei, and to the locus coeruleus. Similar injections centered in the pars compacta of the substantia nigra (SNC) label fibers that are distributed in the striatum in an orderly medial-to-lateral arrangement, and almost entirely avoid the nucleus accumbens and olfactory tubercle. With the exception of the lateral quarter of the substantia nigra, which apparently does not project to the extreme rostral pole of the striatum, each small SNC locus, regardless of its anteroposterior localization, distributes nigrostriatal fibers throughout the length of the striatum. Descending SNC efferents are distributed to the same general regions that receive descending AVT projections, except that no SNC fibers appear to enter the locus coeruleus. Isotope injections confined to the pars reticulata (SNR) label sparse nigrostriatal fibers, and numerous nigrothalamic fibers ascending mainly to the nucleus ventromedialis and in lesser number to the parafascicular nucleus and the paralamellar zone of the nucleus mediodorsalis. Descending SNR fibers leave the nigra as a voluminous fiber bundle that bifurcates into a large nigrotectal and a smaller nigrotegmental component, the latter terminating largely in the pedunculopontine nucleus of the pontomesencephalic tegmentum.     

Distribution of cholecystokinin-like-immunoreactive neurons in the guinea pig forebrain

The distribution of cholecystokinin (CCK)-immunoreactive nerve fibers and cell bodies was studied in the forebrain of control and colchicine-treated guinea pigs by using an antiserum directed against the carboxyterminus of CCK octapeptide (CCK-8) in the indirect immunoperoxidase technique. Virtually all forebrain areas examined contained immunoreactive nerve fibers. A dense innervation was visualized in; neocortical layers II-III, piriform cortex, the medial amygdala, the medial preoptic area, a circumventricular organ-like structure located at the top of the third ventricle in the preoptic area, the subfornical organ, the posterior bed nucleus of the stria terminalis, the posterior globus pallidus (containing labeled woolly fiber-like profiles), the ventromedial hypothalamus, the median eminence, and the premammillary nucleus. A moderately dense innervation was visualized elsewhere excepted in the septum and thalamus where labeled axons were comparatively few. Immunoreactive perikarya were abundant in: neocortex (especially layers II-III), piriform cortex, amygdala, the median preoptic nucleus, the bed nucleus of the stria terminalis, the hypothalamic paraventricular (parvicellular part), arcuate, and dorsomedial (pars compacta) nuclei, the dorsal and perifornical hypothalamic areas, and throughout the thalamus. Areas also containing a moderate number of labeled cell bodies were the medial preoptic area, the globus pallidus, the caudate-putamen, and the periventromedial area in the hypothalamus. Immunostained perikarya were absent or only occasionally observed in the septum, the suprachiasmatic nucleus, the magnocellular hypothalamoneurohypophyseal nuclei, and the ventral mesencephalon. In the adenohypophysis, corticomelanotrophs were labeled in both males and females, and thyrotrophs were labeled in females only. This distribution pattern of CCK-8 immunoreactivity is compared to those previously recorded in other mammals. This shows that very few features are peculiar to the the guinea pig. It is discussed whether some interspecific differences in immunostaining are real rather than methodological.     

Synaptic innervation of midbrain dopaminergic neurons by glutamate-enriched terminals in the squirrel monkey

The excitatory amino acid, glutamate, has long been thought to be a transmitter that plays a major role in the control of the firing pattern of midbrain dopaminergic neurons. The present study was aimed at elucidating the anatomical substrate that underlies the functional interaction between glutamatergic afferents and midbrain dopaminergic neurons in the squirrel monkey. To do this, we combined preembedding immunocytochemistry for tyrosine hydroxylase and calbindin D-28k with postembedding immunostaining for glutamate. On the basis of their ultrastructural features, three types (so-called types I, II, and III) of glutamate-enriched terminals were found to form asymmetric synapses with dendrites and perikarya of midbrain dopaminergic neurons. The type I terminals accounted for more than 70% of the total population of glutamate-enriched boutons in contact with dopaminergic cells in the dorsal and ventral tiers of the substantia nigra pars compacta as well as in the ventral tegmental area, whereas 5–20% of the glutamatergic synapses with dopaminergic neurons involved the two other types of terminals. The major finding of our study is that the glutamate-enriched boutons were involved in 70% of the axodendritic synapses in the ventral tegmental area. In contrast, less than 40% of the boutons in contact with dopaminergic dendrites were immunoreactive for glutamate in the dorsal and ventral tiers of the substantia nigra pars compacta. Approximately 50% of the terminals in contact with the perikarya of the different populations of midbrain dopaminergic neurons displayed glutamate immunoreactivity. In conclusion, our findings provide the first evidence that glutamate-enriched terminals form synapses with midbrain dopaminergic neurons in primates. The fact that the proportion of glutamatergic boutons in contact with dopaminergic cells is higher in the ventral tegmental area than in the substantia nigra pars compacta suggests that the different groups of midbrain dopaminergic neurons are modulated differently by extrinsic glutamatergic afferents in primates. © 1996 Wiley-Liss, Inc.     

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.     

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. © 1993 Wiley-Liss, Inc.     

Localization of preproenkephalin mRNA in the rat brain and spinal cord by in situ hybridization

To determine the localization in rat brain and spinal cord of individual neurons that contain the messenger RNA coding for the opioid peptide precursor preproenkephalin, we performed in situ hybridization with a tritiated cDNA probe complementary to a protion of preproenkephalin mRNA. We observed autoradiographic signal over the cytoplasm of neurons of many regions of the central nervous system. Several types of controls indicated specificity of the labeling. Neurons containing preproenkephalin mRNA were found in the piriform cortex, ventral tenia tecta, several regions of the neocortex, nucleus accumbens, olfactory tubercle, caudate-putamen, lateral septum, bed nucleus of the stria terminalis, diagonal band of Broca, preoptic area, amygdala (especially central nucleus, with fewer labeled neurons in all other nuclei), hippocampal formation, anterior hypothalamic nucleus, perifornical region, lateral hypothalamus, paraventricular nucleus, dorsomedial and ventromedial hypothalamic nuclei, arcuate nucleus, dorsal and ventral premamillary nuclei, medial mamillary nucleus, lateral geniculate nucleus, zona incerta, periaqueductal gray, midbrain reticular formation, ventral tegmental area of Tsai, inferior colliculus, dorsal and ventral tegmental nuclei of Gudden, dorsal and ventral parabrachial nuclei, pontine and medullary reticular formation, several portions of the raphe nuclei, nucleus of the solitary tract, nucleus of the spinal trigeminal tract (especially substantia gelatinosa), ventral and dorsal cochlear nuclei, medial and spinal vestibular nuclei, cuneate and external cuneate nuclei, gracile nucleus, superior olive, nucleus of the trapezoid body, some deep cerebellar nuclei, Golgi neurons in the cerebellum, and most laminae of the spinal cord. In most of these brain regions, the present results indicate that many more neurons contain preproenkephalin mRNA than have been appreciated previously on the basis of immunocytochemistry.     

The efferent projections of the periaqueductal gray in the rat: A Phaseolus vulgaris-leucoagglutinin study. I. Ascending projections

This study has examined the ascending projections of the periaqueductal gray in the rat. Injections of Phaseolus vulgaris-leucoagglutinin were placed in the dorsolateral or ventrolateral subregions, at rostral or caudal sites. From either region, fibers ascended via two bundles. The periventricular bundle ascended in the periaqueductal and periventricular gray matter. At the posterior commissure level, this bundle divided into a dorsal component that terminated in the intralaminar and midline thalamic nuclei, and a ventral component that supplied the hypothalamus. The ventral bundle formed in the deep mesencephalic reticular formation and supplied the ventral tegmental area, substantia nigra pars compacta, and the retrorubral field. The remaining fibers were incorporated into the medial forebrain bundle. These supplied the lateral hypothalamus and forebrain structures, including the preoptic area, the nuclei of the diagonal band, and the lateral division of the bed nucleus of the stria terminalis. The dorsolateral subregion preferentially innervated the centrolateral and paraventricular thalamic nuclei and the anterior hypothalamic area. The ventrolateral subregion preferentially innervated the parafascicular and central medial thalamic nuclei, the lateral hypothalamic area, and the lateral division of the bed nucleus of the stria terminalis. Although the dorsolateral and ventrolateral subregions gave rise to differential projections, the projections from both the rostral and caudal parts of either subregion were similar. This suggests that the dorsolateral and ventrolateral subregions are organized into longitudinal columns that extend throughout the length of the periaqueductal gray. These columns may correspond to those demonstrated in recent physiological studies. © 1995 Willy-Liss, Inc.     

Afferents of vocalization-controlling periaqueductal regions in the squirrel monkey

In order to determine the input of vocalization-controlling regions of the midbrain periaqueductal gray (PAG), wheat germ agglutinin-horseradish peroxidase was injected in six squirrel monkeys (Saimiri sciureus) at PAG sites yielding vocalization when injected with the glutamate agonist homocysteic acid. Brains were scanned for retrogradely labeled areas common to all six animals. The results show that the vocalization-eliciting sites receive a widespread input, with the heaviest projections coming from the surrounding PAG, dorsomedial and ventromedial hypothalamus, medial preoptic region, substantia nigra pars diffusa, zona incerta and reticular formation of the mesencephalon, pons, and medulla. The heaviest cortical input reaches the PAG from the mediofrontal cortex. Moderate to weak projections come from the insula, lateral prefrontal, and premotor cortex as well as the superior and middle temporal cortex. Subcortical moderate to weak projections reach the PAG from the central and medial amygdala, nucleus of the stria terminalis, septum, nucleus accumbens, lateral preoptic region, lateral and posterior hypothalamus, globus pallidus, pretectal area, deep layers of the superior colliculus, the pericentral inferior colliculus, mesencephalic trigeminal nucleus, locus coeruleus, substantia nigra pars compacta, dorsal and ventral raphe, vestibular nuclei, spinal trigeminal nucleus, solitary tract nucleus, and nucleus gracilis. The input of the periaqueductal vocalization-eliciting regions thus is dominated by limbic, motivation-controlling afferents; input, however, also comes from sensory, motor, arousal-controlling, and cognitive brain areas.     

Midbrain dopaminergic neurons (nuclei A8, A9, and A10): Three-dimensional reconstruction in the rat

The dopaminergic neurons in the midbrain of the rat are located in three cell groups: nucleus A8 cells in the retrourbal field, nucleus A9 cells in the substantia nigra, and nucleus A10 cells in the ventral tegmental area and related nuclei. The purpose of the present study was to map and quantify the midbrain dopaminergic neurons in two and three dimensions in the rat brain, using immunohistochemical staining and computer imaging techniques. The cells were identified with an antibody against tyrosine hydroxylase, and counted in six midbrain nuclei: the retrorubral field, substantia nigra pars compacta, substantia nigra pars reticulata, central linear nucleus, ventral tegmental area, and interfascicular nucleus. Outlines were traced around the perimeters of the coronal tissue sections, and the locations of all immunoreactive ventral midbrain cells were mapped. On one side of the brain there are approximately 1,300 nucleus A8 cells, 10,500 nucleus A9 cells, and 10,200 nucleus A10 cells. The 2- and 3-dimensional reconstructions illustrate the region-specific density of dopaminergic neurons throughout the midbrain cell complex, and provide a visual appreciation of the location and distribution of the three dopaminergic cell groups in relation to their position in the midbrain. Information about the number and location of midbrain dopaminergic neurons will be useful in conjunction with future studies that characterize these cells more specifically, for example, in terms of their co-transmitters, and afferent and efferent projections. © 1993 Wiley-Liss, Inc.     

Autoradiographic evidence for nicotine receptors on nigrostriatal and mesolimbic dopaminergic neurons

Rats received unilateral injections of 6-hydroxydopamine into the medial forebrain bundle, resulting in an ipsilateral loss of striatal dopamine and of dopaminergic perikarya. A concimitant reduction of displaceable tritiated nicotine binding was observed autoradiographically in the ipsilateral substantia nigra, ventral tegmental area, striatum, nucleus accumbens, and olfactory tubercle. Thus, nicotine receptors appear to be located on nigrostriatal and mesolimbic dopaminergic neurons at the level of perikarya and terminals.