Galanin immunoreactivity within the primate basal forebrain: Evolutionary change between monkeys and apes

Galanin immunoreactivity (GAL-ir) is differentially expressed within the basal forebrain of monkeys and humans. Most monkey magnocellular basal forebrain neurons colocalize GAL-ir. In contrast, virtually no human magnocellular basal forebrain neurons express GAL-ir. Rather, an extrinsic galaninergic fiber plexus innervates these neurons in humans. The present study examined the expression of GAL-ir within the basal forebrain of apes to establish the phylogenetic level at which this transformation occurs. The staining patterns of GAL-ir within the basal forebrain of both lesser (gibbons) and great (chimpanzee and gorilla) apes were compared to that previously observed within monkeys and humans. All apes displayed a pattern of basal forebrain GAL-ir indistinguishable from humans. GAL-ir was not expressed within ape basal forebrain magnocellular neurons as seen in monkeys. Rather like humans, a dense collection of GAL-ir fibers was seen in close apposition to magnocellular perikarya. In addition, a few GAL-ir parvicellular neurons were scattered within the ape basal forebrain. These data indicate that the evolutionary change in the expression of GAL-ir within the primate basal forebrain occurs at the branch point of monkeys and apes. © 1993 Wiley-Liss, Inc.     

Telencephalic cholinergic system of the New World monkey (Cebus apella): morphological and cytoarchitectonic assessment and analysis of the projection to the amygdala

While the cholinergic projection from the nucleus basalis to the cortical mantle has received considerable attention, a similar projection to the magnocellular basal nucleus of the amygdala has not been studied in such detail. The present study analyzed the cholinergic basal forebrain projection to the amygdala in the Cebus apella monkey by using combined tract-tracing and immunocytochemical techniques. As a foundation for this assessment, the morphological and cytoarchitectonic organization of the cholinergic telencephalic system of the New World C. apella monkey was examined by using choline acetyltransferase (ChAT) immunocytochemistry. Although there were minor differences, the telencephalic cholinergic system of Cebus monkeys is similar to that seen in Old World nonhuman primates. ChAT-immunoreactive neurons were observed throughout the Ch1-4 regions of the basal forebrain, with subdivisions of the Ch4 region similar to those previously described (Mesulam et al., '83a). Most cholinergic neurons were hyperchromic and magnocellular; however, some neurons were parvicellular. Like most species, cholinergic neurons were also observed throughout the striatum. However, unlike in rodents, cholinergic perikarya were not observed within the cortex or hippocampus. To analyze the cholinergic fiber projections from the basal forebrain to the amygdala, monkeys received an intraamygdaloid injection of the retrograde tracer horseradish peroxidase conjugated to wheat germ agglutinin. Retrogradely labeled neurons that colocalized ChAT or acetylcholinesterase (AChE) were found predominantly in the anterolateral portion of the CH4 region. Fewer double-labeled neurons were found in the anteromedial and intermediate portion of CH4 and in the CH3 region. Neurons that exhibited retrograde labeling were only occasionally discerned in the posterior portions of the CH4 region, in the medullary laminae of the globus pallidus, or lodged within the internal capsule. These data are discussed in terms of the putative role this cholinergic input might play in cognitive processing in primates.     

Nerve growth factor-like immunoreactive profiles in the primate basal forebrain and hippocampal formation

The distribution of nerve growth factor (NGF), the prototypic neurotrophin, within the basal forebrain and hippocampal formation of young adult monkeys and aged humans was characterized with and affinity purified polyclonal β-NGF antibody raised against mouse β-NGF. In the basal forebrain of both primates, a granular NGF-like immunoreactive (ir) reaction product was observed within neurons of the medial septum, nucleus of the diagonal band, and nucleus basalis of Meynert. NGF-like immunoreactivity exclusively colocalized within p75 NGF receptor (NGFR) containing basal forebrain neurons. The intensity of NGF immunolabeling varied between cell bodies. Many NGF-ir perikarya were highly immunoreactive. In other basal forebrain neurons, NGF-like immunoreactivity was either undetectable or minimally expressed. In the hippocampus of both species, NGF-like immunoreactivity was mainly localized within the hilus of the dentate gyrus and within CA3 and CA2 hippocampal subfields. A marked diminution in NGF-like staining was seen in CA1. Within the hippocampal formation, NGF-like immunoreactivity was heaviest within the neuropil of stratum radiatum, intermediate in stratum oriens, and lightest in stratum pyramidal. NGF-like immunoreactivity was not found within the granule or pyramidal cells of the dentate gyrus and hippocampal formation, respectively. These findings demonstratre the presence of an NGF-like antigen in association with monkey and human magnocellular basal forebrain neurons and within their hippocampal target sites. This lends support to the hypothesis that NGF is internalized from sources located within target regions of the primate cholinergic basal forebrain neurons and is retrogradely transported to these cell bodies where the NGF trophic effect likely occurs.     

Nerve growth factor mRNA-containing cells are distributed within regions of cholinergic neurons in the rat basal forebrain

It has been proposed that nerve growth factor (NGF) provides critical trophic support for the cholinergic neurons of the basal forebrain and that it becomes available to these neurons by retrograde transport from distant forebrain targets. However, neurochemical studies have detected low levels of NGF mRNA within basal forebrain areas of normal and experimental animals, thus suggesting that some NGF synthesis may actually occur within the region of the responsive cholinergic cells. In the present study with in situ hybridization and immunohistochemical techniques, the distribution of cells containing NGF mRNA within basal forebrain was compared with the distribution of cholinergic perikarya. The localization of NGF mRNA was examined by using a ³⁵S-labeled RNA probe complementary to rat preproNGF mRNA and emulsion autoradiography. Hybridization of the NGF cRNA labeled a large number of cells within the anterior olfactory nucleus and the piriform cortex as well as neurons in a continuous zone spanning the lateral aspects of both the horizontal limb of the diagonal band of Broca and the magnocellular preoptic nucleus. In the latter regions, large autoradiographic grain clusters labeled relatively large Nissl-pale nuclei; it did not appear that glial cells were autoradiographically labeled. Comparison of adjacent tissue sections processed for in situ hybridization to NGF mRNA and immunohistochemical localization of choline acetyltransferase (ChAT) demonstrated overlapping fields of cRNA-labeled neurons and ChAT-immunoreactive perikarya in both the horizontal limb of the diagonal band and magnocellular preoptic regions. However, no hybridization of the cRNA probe was observed in other principal cholinergic regions including the medial septum, the vertical limb of the diagonal band, or the nucleus basalis of Meynert. These results provide evidence for the synthesis of NGF mRNA by neurons within select fields of NGF-responsive cholinergic cells and suggest that the generally accepted view of “distant” target-derived neurotrophic support should be reconsidered and broadened.     

Cholinergic systems in the rat brain: I. Projections to the limbic telencephalon

The cholinergic projections to the limbic telecephalon in the rat were investigated by use of fluorescent tracer histology in combination with choline-O-acetyltransferase (ChAT) immunohistochemistry and acetylcholinesterase (AChE) histochemistry (pharmacohistochemical regimen). Propidium iodide or Evans Blue was infused into the olfactory bulb, hippocampus, dorsal retrohippocampal region, amygdala, and the entorhinal, perirhinal, pyriform, insular, and cingular cortices. Retrogradely transported fluorescent labels and ChAT and/or AChE were microscopically analyzed on the same brain section. Virtually all of the cholinergic projections to the limbic telencephalon derived from the basal forebrain cholinergic system composed of neurons associated with the medial septal nucleus, nuclei of the vertical and horizontal limbs of the diagonal band, the magnocellular preoptic area, the subpallidal substantia innominata and its rostral extension into the regions of the ventral pallidum laterally and the lateral preoptic area medially, and the nucleus basalis. The cingulate cortex received a small cholinergic projection from the dorsolateral tegmental nucleus in the brainstem. All of the presumed cholinergic innervation of the olfactory bulb, hippocampus, and dorsal retrohippocampal area and the majority of cholinergic afferents to posterior cingulate and entorhinal cortices derived from the medial septal nucleus, vertical and horizontal limbs of the diagonal band, magnocellular preoptic area, and rostral substantia innominata. Putative cholinergic afferents to the amygdala and to pyriform, insular, perirhinal, and anterior cingulate cortices orginated from ChAT-positive cells concentrated more caudally in the basal forebrain cholinergic system. Within the basal forebrain, no simple topographic pattern emerged to explain the cholinergic innervation of the limbic telencephalon, although an essentially reverse rostrocaudal organization was observed for afferents to the cingular region. It was noted, however, that most regions of the limbic telencephalon received cholinergic input from rostral portions of the basal forebrain cholinergic system, an observation inviting speculation that anterior aspects of the basal forebrain provide cholinergic afferents primarily to limbic structures in the telencephalon whereas more caudal portions are the source of cholinergic fibers preferentially innervating non-limbic regions. Of the total number of projection neurons innervating a given region of the limbic telencephalon, a greater proportion was ChAT-positive if phylogenetically newer target structures were innervated.(ABSTRACT TRUNCATED AT 400 WORDS)     

Distribution of galaninergic immunoreactivity in the brain of the mouse

The distribution of galaninergic immunoreactive (-ir) profiles was studied in the brain of colchicine-pretreated and non-pretreated mice. Galanin (GAL)-ir neurons and fibers were observed throughout all encephalic vesicles. Telencephalic GAL-ir neurons were found in the olfactory bulb, cerebral cortex, lateral and medial septum, diagonal band of Broca, nucleus basalis of Meynert, bed nucleus of stria terminalis, amygdala, and hippocampus. The thalamus displayed GAL-ir neurons within the anterodorsal, paraventricular, central lateral, paracentral, and central medial nuclei. GAL-ir neurons were found in several regions of the hypothalamus. In the midbrain, GAL-ir neurons appeared in the pretectal olivary nucleus, oculomotor nucleus, the medial and lateral lemniscus, periaqueductal gray, and the interpeduncular nucleus. The pons contained GAL-ir neurons within the dorsal subcoeruleus, locus coeruleus, and dorsal raphe. In the medulla oblongata, GAL-ir neurons appear in the anterodorsal and dorsal cochlear nuclei, salivatory nucleus, A5 noradrenergic cells, gigantocellular nucleus, inferior olive, solitary tract nucleus, dorsal vagal motor and hypoglossal nuclei. Only GAL-ir fibers were seen in the lateral habenula nucleus, substantia nigra, parabrachial complex, cerebellum, spinal trigeminal tract, as well as the motor root of the trigeminal and facial nerves. GAL-ir was also observed in several circumventricular organs. The widespread distribution of galanin in the mouse brain suggests that this neuropeptide plays a role in the regulation of cognitive and homeostatic functions.     

Peptidergic neurons in the basal forebrain magnocellular complex of the rhesus monkey

The basal forebrain magnocellular complex of primates is defined by the presence of large, hyperchromic, usually cholinergic neurons in the nucleus basalis of Meynert and nucleus of the diagonal band of Broca. Because there is growing evidence for noncholinergic neuronal elements in the basal forebrain complex, five neuropeptides and the enzyme choline acetyltransferase were studied immunocytochemically in this region of rhesus monkeys. Galaninlike immunoreactivity coexists with choline-acetyl-transferase-like immunoreactivity in most large neurons and in some smaller neurons of the primate nucleus basalis and nucleus of the diagnonal band. Four other peptides show immunoreactivity in more limited regions of the basal forebrain complex, usually in separate smaller, noncholinergic neurons. Numerous small, somatostatinlike-immunoreactive neurons occupy primarily anterior and intermediate segments of the nucleus basalis, especially laterally and ventrally. Somewhat fewer, small neuropeptide Y-like-immunoreactive somata are found in the same regions. Neurons that show neurotensinlike immunoreactivity are slightly larger than cells that contain immunoreactivity for somatostatin or neuropeptide Y, but these neurons also occur mainly in anterior and intermediate parts of the nucleus basalis. Overall, the usually small, leucine-enkephalin-like-immunoreactive neurons are infrequent in the basal forebrain complex and are most abundant in the rostral intermediate nucleus basalis. Thus, neurons that appear to contain somatostatin, neuropeptide Y, neurotensin, or enkephalin mingle with cholinergic/galaninergic neurons only in some subdivisions of the nucleus basalis/nucleus of the diagonal band, and their distributions suggest that some of these small neurons could be associated with structures that overlap with cholinergic neurons of the labyrinthine basal forebrain magnocellular complex. We also have found light microscopic evidence for innervation of basal forebrain cholinergic neurons by boutons that contain galanin-, somatostatin-, neuropeptide Y-, neurotensin-, or enkephalinlike immunoreactivity. The origins and functions of these putative synapses remain to be determined.     

Organization of ascending hypothalamic projections to the rostral forebrain with special reference to the innervation of cholinergic projection neurons

Axonal projections from hypothalamic nuclei to the basal forebrain, and their relation to cholinergic projection neurons in particular, were studied in the rat by using the anterograde tracer Phaseolus vulgaris-leucoagglutinin (PHA-L) in combination with choline acetyltransferase (ChAT) immunocytochemistry. Discrete iontophoretic PHA-L injections were delivered to different portions of the caudal lateral hypothalamus, as well as to various medial hypothalamic areas, including the ventromedial, dorsomedial, and paraventricular nuclei, and anterior hypothalamic and medial preoptic areas. The simultaneous detection of PHA-L-labeled fibers/terminals and ChAT-positive neurons was performed by using nickel-enhanced diaminobenzidine (DAB) and nonenhanced DAB as chromogens. Selected cases were investigated at the electron microscopic level. Ascending hypothalamic projections maintained an orderly lateromedial arrangement within the different components of the medial forebrain bundle, as well as with respect to their terminal projection fields (e.g., within the bed nucleus of the stria terminalis and lateral septal nucleus). The distribution pattern of hypothalamic inputs to cholinergic projection neurons corresponded to the topography of ascending hypothalamic axons. Axons originating from neurons in the far-lateral hypothalamus reached cholinergic neurons in a zone that extended from the dorsal part of the sublenticular substantia innominata (SI) caudolaterally, to the lateral portion of the bed nucleus of the stria terminalis rostromedially, encompassing a narrow band along the ventral part of the globus pallidus and medial portion of the internal capsule. Axons originating from cells in the medial portion of the lateral hypothalamus reached cholinergic cells primarily in more medial and ventral parts of the SI, and in the magnocellular preoptic nucleus and horizontal limb of the diagonal band nucleus (HDB). Axons from medial hypothalamic cells appeared to contact cholinergic neurons primarily in the medial part of the HDB, and in the medial septum/vertical limb of the diagonal band complex. Electron microscopic double-labeling experiments confirmed contacts between labeled terminals and cholinergic cells in the HDB and SI. Individual hypothalamic axons established synapses with both cholinergic and noncholinergic neuronal elements in the same regions. These findings have important implications for our understanding of the organization of afferents to the basal forebrain cholinergic projection system.     

Distribution of beta-nerve growth factor receptors in the human basal forebrain

The distribution of neurons expressing the receptor for beta-nerve growth factor has been examined immunohistochemically in serial coronal sections of basal forebrain from aged normal human subjects. Neurons expressing the receptor were observed in the nucleus of the diagonal band of Broca and in the anterior, the intermediate, and the posterior portions of the nucleus basalis of Meynert. Neurons could also be seen in the medial septal nucleus and embedded in myelinated fibre tracts such as those of the external capsule, cingulum, medullary laminae of the globus pallidus, ansa penduncularis, ansa lenticularis, and anterior commissure. In situ hybridization with a 35S cDNA probe to the human beta-nerve growth factor receptor confirms a neuronal location as the site of synthesis of beta-nerve growth factor receptors in the nucleus basalis of Meynert in a fifth brain. A high percentage of Nissl-stained hyperchromic magnocellular neurons expressed the receptor for beta-nerve growth factor, suggesting that most neurons in the human cholinergic magnocellular basal forebrain system express these receptors. Recent data suggest that beta-nerve growth factor functions as a neurotrophic factor in basal forebrain cholinergic neurons. In Alzheimer's disease there is known to be a reduction in cholinergic function and an apparent loss of neurons in the cholinergic nucleus basalis of Meynert. For this reason we have examined the distribution of receptors for beta-nerve growth factor in the normal human basal forebrain in order to form a basis for comparison to those with Alzheimer's disease.     

Nucleus basalis (Ch4) and cortical cholinergic innervation in the human brain: observations based on the distribution of acetylcholinesterase and choline acetyltransferase

The nucleus basalis (NB) of the human brain is a large, complex, and highly differentiated structure. Many of its neurons are magnocellular, hyperchromic, isodendritic, acetylcholinesterase-rich, and choline-acetyltransferase-positive. Concurrent histochemical and immunological staining demonstrated that all choline-acetyltransferase-positive NB neurons in the human brain also contain acetylcholinesterase enzyme activity. Only a small minority of acetylcholinesterase-rich magnocellular cell bodies in the NB failed to show choline acetyltransferase immunoreactivity. Sections that were counterstained for Nissl substance showed that 80-90% of all magnocellular neurons in the NB were choline-acetyltransferase-positive and therefore cholinergic. These characteristics, which are very similar to those of the NB in the monkey brain, justified the designation of these cholinergic neurons in the human brain as the Ch4 (or NB-Ch4) complex. On morphological grounds, the compact parts of the human NB-Ch4 complex were divided into distinct sectors which appeared to show a greater level of differentiation than in the monkey brain. In addition to the compact sectors, interstitial elements of NB Ch4 were embedded within adjacent fiber bundles. The putative cortical projections from NB-Ch4 were identified in the form of acetylcholinesterase-rich fibers. These fibers formed a dense plexus in all cortical regions but also displayed laminar and regional variations. Limbic and paralimbic areas had higher concentrations of these fibers than the immediately adjacent neocortical association areas. Alzheimer's disease was associated with a marked depletion of cortical acetylcholinesterase. Two cases of Alzheimer's disease with relatively selective NB-Ch4 cell loss supported the hypothesis that the corticopetal cholinergic pathways in the human brain may have a topographical organization similar to that in the monkey brain.     

Loss of nerve growth factor receptor-containing neurons in Alzheimer's disease: a quantitative analysis across subregions of the basal forebrain

Magnocellular neurons comprising the Ch1-Ch4 regions of the basal forebrain provide topographic cholinergic innervation to the cerebral cortex, thalamus, and basolateral nucleus of the amygdala. Most quantitative studies analyzing the status of these neurons in Alzheimer's disease (AD) have employed Nissl-stained preparations. These studies principally analyzed large neurons of a prespecified cell diameter. Since basal forebrain neurons atrophy in Alzheimer's disease, an immunocytochemical marker for these neurons would appear to be a better alternative for determining whether there is regionally specific degeneration of cholinergic neurons across subregions of the basal forebrain. Brain sections from seven AD and five aged-matched control patients were immunocytochemically stained with a monoclonal antibody raised against the receptor for nerve growth factor (NGF), a probe which has previously been demonstrated to extensively and exclusively colocalize with cholinergic basal forebrain neurons in humans (17, 25, 35). NGF receptor-immunoreactive neurons within the hippocampal projecting nuclei of the medial septum (Ch1) and vertical limb of the diagonal band (Ch2) were minimally affected in AD as compared to control cases. In contrast, the Ch4 region demonstrated a significant loss of NGF receptor-immunoreactive neurons in AD that inversely correlated (-0.786) with the duration of the disease process. All four subregions of Ch4 were affected in the AD cases with the anterolateral (76.4%), intermediate (62.1%) and posterior divisions (76.5%) demonstrating the greatest reduction in NGF receptor-immunoreactive neurons. Nissl-counterstained sections failed to reveal magnocellular neurons which were not immunoreactive for the NGF receptor, suggesting that reductions in immunocytochemically stained neurons reflects neuron loss and not the failure of viable neurons to synthesize NGF receptors. These data indicate that cholinergic basal forebrain neurons which project to the amygdala, as well as to the temporal, frontobasal, and frontodorsal cortices, are most affected in AD.     

Basal forebrain efferents to the medial dorsal thalamic nucleus in the rhesus monkey

Thalamic efferent connections of the basal forebrain (BF); medial septal nucleus (MS), vertical limb of the diagonal band (VDB), horizontal limb of the diagonal band (HDB), nucleus basalis (NB), and ventral pallidum (VP) were investigated in twelve rhesus monkeys. In five animals, injections of radioactively labeled amino acids were placed in the BF. In four animals, the injections involved different divisions of the NB, HDB, and the most ventral part of the VDB. In those four cases, labeled fibers in the medial forebrain bundle were observed traveling caudally towards the hypothalamus where some turned dorsally to enter the inferior thalamic peduncle. These fibers terminated in the ventral half of the magnocellular part of the medial dorsal thalamic nucleus (MDmc). In a fifth case, the amino acid injection involved most of the MS and the VDB. Labeled fibers traveled caudally from the injection site and entered the stria medullaris. These fibers then traveled caudally before turning ventrally to terminate in the dorsal half of MDmc. To determine which of the diverse neuronal types in the BF gives rise to these thalamic projections, in two monkeys injections of horseradish peroxidase (HRP) were placed into MDmc. Labeled neurons were observed throughout the full extent of the NB, the VDB, the MS, and part of the VP. In order to determine the extent of the cholinergic input to MDmc from the BF, one of the HRP cases was processed for the simultaneous visualization of HRP, and acetylcholinesterase (AChE), the hydrolytic enzyme for acetylcholine, and a second case was processed for simultaneous visualization of HRP, and choline acetyltransferase (ChAT), the synthetic enzyme for acetylcholine. We observed that 30-50% of the HRP-labeled neurons were putatively cholinergic. In order to determine if the NB projection to MD is a collateral of the NB projection to orbital frontal cortex, one fluorescent retrograde tracer was injected into the orbital frontal cortex and one into MD. This case showed that approximately 5% of the BF neurons that project to MDmc also project to the orbital frontal cortex. These results confirm a significant subcortical projection by which the cholinergic system of the basal forebrain may influence higher cortical functions through the thalamus.     

Codistribution of GABA- with acetylcholine-synthesizing neurons in the basal forebrain of the rat

In recent years, GABAergic neurons have been identified in the basal forebrain where cholinergic cortically projecting neurons are located and known to be important in mechanisms of cortical activation. In the present study in the rat, the relationship of the GABA-synthesizing neurons to the acetylcholine-synthesizing neurons was examined by application of a sequential double staining immunohistochemical procedure involving the peroxidase-antiperoxidase technique for glutamic acid decarboxylase (GAD) and choline acetyltransferase (ChAT). In these double and adjacent single immunostained series of sections, the GAD+ and ChAT+ cells were mapped, counted and measured with the aid of a computerized image analysis system. Through the entire basal forebrain, there was no evidence for colocalization of GAD and ChAT in the same neurons. Instead, a large population of GAD-immunoreactive neurons is codistributed with ChAT-immunoreactive neurons and outnumbers them by a factor of two: approximately 39,000 GAD+ cells to 18,000 ChAT+ cells. Although the GAD+ and ChAT+ neurons lie intermingled within fascicles of the major longitudinal and transverse forebrain fiber systems in subregions of the basal forebrain, the GAD+ cells are more highly concentrated within different sectors of the pathways and regions than the ChAT+ cells. Although GAD+ neurons resemble ChAT+ neurons in certain regions, both being bi- or multipolar and, on average, medium-sized cells, the GAD+ neurons are, in the majority (51%), small-sized cells ( < 15 μm in length) and as a population significantly smaller than the ChAT+ neurons. These results suggest that many GABAergic neurons may represent interneurons in the basal forebrain and potentially exert an inhibitory influence on adjacent cortically projecting cholinergic neurons. Medium- to large GAD+ cells, which resemble similar ChAT+ cells, are also present and represent the majority of the GAD+ cells in the nucleus of the diagonal band of Broca, magnocellular preoptic nucleus, and olfactory tubercle, but represent the minority in the anterior and posterior substantia innominata and globus pallidus. Given their prominent size, such GABAergic cells may also exert an inhibitory influence outside the basal forebrain as projection neurons and potentially in parallel with cholinergic neurons, to certain regions of the cerebral cortex. Accordingly, GABAergic cells may be considered as constituents of the magnocellular basal nucleus and potentially important elements within the ventral extrathalamic relay from the brainstem reticular formation to the cerebral cortex. © 1993 Wiley-Liss, Inc.     

Plasticity of Galaninergic Fibers Following Neurotoxic Damage within the Rat Basal Forebrain: Initial Observations

Galanin immunoreactive fibers hypertrophy and hyperinnervate remaining cholinergic basal forebrain neurons within the septum–diagonal band complex in Alzheimer's disease. The present investigation determined whether a similar hyperinnervation of galanin immunoreactive fibers occurs following intraparenchymal injections of ibotenic acid within the cholinergic medial septum or diagonal band nucleus in young adult rats. Sections through the medial septum and the diagonal band were either concurrently immunostained for galanin and the low-affinity p75 neurotrophin receptor (an excellent marker of cholinergic basal forebrain neurons) or single stained for choline acetyltransferase. Following chemical lesion, an increase in the density of galanin immunoreactivity was seen within the medial septum on the lesion, as opposed to the contralateral control side. In contrast, within diagonal band-lesioned animals, the increase in galanin immunoreactivity was low to moderate. In either lesion paradigm we did not observe hyperinnervation of remaining cholinergic basal forebrain neurons. In fact, there was no correlation between the galanin hypertrophy and the amount of cholinergic cell loss. We hypothesize that galanin hyperinnervation within the cholinergic basal forebrain may provide a protective effect by down-regulating acetylcholine release following brain insult.     

Distribution of parvalbumin-immunoreactive cells and fibers in the monkey temporal lobe: The amygdaloid complex

The calcium-binding protein parvalbumin was immunohistochemically localized in the monkey amygdaloid complex. Parvalbumin-immunoreactive neuronal cell bodies, fibers, and terminals were observed in several amygdaloid nuclei and cortical areas. Three types of aspiny neurons, ranging from small spherical cells (Type 1) to large multipolar cells (Type 2) and fusiform cells (Type 3) were observed in most amygdaloid regions, though the proportions of the cell types were different in each region. The density of parvalbumin-immunoreactive fibers and terminals tended to parallel the density of labeled cell bodies. The highest densities of parvalbumin profiles were observed in the nucleus of the lateral olfactory tract, the periamygdaloid cortex (PAC2), the magnocellular division of the basal nucleus, the ventrolateral portion of the lateral nucleus, and the accessory basal nucleus. The regions containing the lowest densities of parvalbumin-positive profiles were the medial nucleus, anterior cortical nucleus, central nucleus, and the paralaminar nucleus. In regions with fiber and terminal labeling, pericellular networks of fibers, reminiscent of basket cell terminations, were commonly observed to surround unstained neuronal cell bodies and proximal dendrites. In the magnocellular division of the basal nucleus, and to a lesser extent in the lateral nucleus, parvalbuminlabeled “cartridges” of axo-axonic terminals were observed on the initial segments of unlabeled cells. Parvalbumin-positive varicosities were also commonly observed in close apposition to the soma and dendrites of parvalbumin-immunoreactive cells. Given the close correspondence between the distribution of parvalbumin-positive neurons and a subset of GABAergic neurons in many brain regions, these data provide a first indication of the organization of the inhibitory circuitry of the primate amygdaloid complex. © 1993 Wiley-Liss, Inc.     

Development of galanin-like immunoreactivity in the brain of the brown trout (Salmo trutta fario), with some observations on sexual dimorphism

The development of galanin-like immunoreactive (GAL-ir) cells and fibers was investigated in the brain of brown trout embryos, alevins, juveniles, and adults (some spontaneously releasing their gametes). The earliest GAL-ir neurons appeared in the preoptic region and the primordial hypothalamic lobe of 12-mm embryos. After hatching, new GAL-ir neurons appeared in the lateral, anterior, and posterior tuberal nuclei, and in late alevins, GAL-ir neurons appeared in the area postrema. In juveniles, further GAL-ir populations appeared in the nucleus subglomerulosus and magnocellular preoptic nucleus. The GAL-ir neuronal groups present in juveniles were also observed in sexually mature adults, although the area postrema of males lacked immunoreactive neurons. Moreover, spawning males exhibited GAL-ir somata in the olfactory bulb and habenula, which were never observed in adult females or in developing stages. In adults, numerous GAL-ir fibers were observed in the ventral telencephalon, preoptic area, hypothalamus, neurohypophysis, mesencephalic tegmentum, ventral rhombencephalon, and area postrema. Moderate to low GAL-ir innervation was seen in the olfactory bulbs, dorsomedial telencephalon, epithalamus, medial thalamus, optic tectum, cerebellum, and rhombencephalic alar plate. There were large differences among regions in the GAL-ir innervation establishment time. In embryos, GAL-ir fibers appeared in the preoptic area and hypothalamus, indicating early expression of galanin in hypophysiotrophic centers. The presence of galanin immunoreactivity in the olfactory, reproductive, visual, and sensory-motor centers of the brain suggest that galanin is involved in many other brain functions. Furthermore, the distribution of GAL-ir elements observed throughout trout development indicates that galaninergic system maturation continues until sexual maturity.     

Distribution of 125I-neurotensin binding sites in human forebrain: comparison with the localization of acetylcholinesterase

The distribution of 125I-neurotensin binding sites was compared with that of acetylcholinesterase reactivity in the human basal forebrain by using combined light microscopic radioautography/histochemistry. High 125I-neurotensin binding densities were observed in the bed nucleus of the stria terminalis, islands of Calleja, claustrum, olfactory tubercle, and central nucleus of the amygdala; lower levels were seen in the caudate, putamen, medial septum, diagonal band nucleus, and nucleus basalis of Meynert. Adjacent sections processed for cholinesterase histochemistry demonstrated a regional overlap between the distribution of labeled neurotensin binding sites and that of intense acetylcholinesterase staining in all of the above regions, except in the bed nucleus of the stria terminalis, claustrum, and central amygdaloid nucleus, where dense 125I-neurotensin labeling was detected over areas containing only weak to moderate cholinesterase staining. At higher magnification, 125I-neurotensin-labeled binding sites in the islands of Calleja, supraoptic nucleus of the hypothalamus, medial septum, diagonal band nucleus, and nucleus basalis of Meynert were selectively associated with neuronal perikarya found to be cholinesterase-positive in adjacent sections. Moderate 125I-neurotensin binding was also apparent over the cholinesterase-reactive neuropil of these latter three regions. These data suggest that neurotensin (NT) may directly influence the activity of magnocellular cholinergic neurons in the human basal forebrain, and may be involved in the physiopathology of dementing disorders such as Alzheimer's disease, in which these neurons have been shown to be affected.     

Noncollateral projections of basal forebrain neurons to frontal and parietal neocortex in primates

To test the hypothesis that axons of the basal forebrain cholinergic system collateralize to innervate widely separated areas of cortex, two distinct, retrogradely transported fluorescent dyes were injected into discrete neocortical regions of three macaques. In two monkeys, True Blue was injected into parietal cortex and Nuclear Yellow into frontal cortex; in a third monkey, placement of the dyes was reversed. Following these large (3-10 microliters total) injections, neurons single labeled with either Nuclear Yellow or True Blue were seen throughout most of the ipsilateral nucleus basalis of Meynert and nucleus of the diagonal band of Broca. Neurons projecting to either frontal or parietal cortex were most heavily concentrated in the anteromedial aspect of the basal forebrain. A small number of labeled neurons was also seen in the contralateral basal forebrain. Cells single labeled with either True Blue or Nuclear Yellow were frequently adjacent to one another, but in no case was a neuron labeled with both dyes. Thus, individual neurons of the basal forebrain complex do not appear to innervate both frontal and parietal lobes of monkeys. This finding is consistent with recent studies in rodents which suggest that basal forebrain neurons innervate relatively small, restricted cortical fields.     

Tyrosine-hydroxylase-containing neurons in the primate basal forebrain magnocellular complex.

Immunocytochemistry and in situ hybridization for tyrosine hydroxylase (TH) were used to study the distribution of putative catecholaminergic neurons in the basal forebrain magnocellular complex (BFMC) of monkeys and humans. Magnocellular TH-expressing neurons in the primate BFMC are distributed along a rostrocaudal gradient, with the largest proportion of these cells located in the medial septal nucleus and nucleus of the diagonal band of Broca; smaller TH-containing neurons generally follow the same distribution. These findings suggest that, within rostromedial segments of the BFMC, there is a distinct subpopulation of neurons that express catecholamine-synthesizing enzymes. Further research is necessary to establish whether these neurons utilize one or more catecholamines as neurotransmitters.