The anterior perforated substance (APS) revisited: Commented anatomical and imagenological views

INTRODUCTION

Since 2002, when we published our article about the anterior perforated substance (APS), the knowledge about the region has grown enormously.

OBJECTIVE

To make a better description of the anatomy of the zone with new dissection material added to the previous, to sustain the anatomical analysis of the MRI employing the SPACE sequence, interacting with our imagenology colleagues. Especially, we aim to identify and topographically localize by MRI the principal structures in APS-substantia innominata (SI).

METHOD

The presentation follows various steps: (1) location and boundaries of the zone and its neighboring areas; (2) schematic description of the region with simple outlines; (3) cursory revision of the SI and its three systems; (4) serial images of the dissections of the zone and its vessels, illustrated and completed when possible, by MRI images of a voluntary experimental subject (ES).

RESULTS

With this method, we could expose most of the structures of the region anatomically and imagenologically.

DISCUSSION

The zone can be approached for dissection with magnification and the habitual microsurgical instruments with satisfactory results. We think that fibers in this region should be followed by other anatomical methods in addition to tractography. The principal structures of ventral striopallidum and extended amygdala (EA) can be identified with the SPACE sequence. The amygdala and the basal ganglion of Meynert (BGM) are easily confused because of their similar signal. Anatomical clues can orient the clinician about the different clusters of the BGM in MRI.

CONCLUSIONS

The dissection requires a previous knowledge of the zone and a good amount of patience. The APS is a little space where concentrate essential vessels for the telencephalon, "en passage" or perforating, and neural structures of relevant functional import. From anatomical and MRI points of view, both neural and vascular structures follow a harmonious and topographically describable plan. The SPACE MRI sequence has proved to be a useful tool for identifying different structures in this area as the striatopallidal and EA. Anatomical knowledge of the fibers helps in the search of clusters of the basal ganglion.

Switching to cue-directed behavior: specific for ventral striatal dopamine but not ventral pallidum/substantia innominata gaba as revealed by a swimming-test procedure in rats

In this study it was investigated whether ventral striatal dopamine-induced changes in switching to cue-directed behavioral patterns were funnelled via the rostral areas of the ventral pallidum/substantia innominata (VP/SI) complex and, if so, whether changes in switching to cue-directed behavioral patterns could be elicited in the VP/SI complex by manipulating GABAergic activity. To this end rats were bilaterally equipped with cannulae directed at the ventral striatum and/or rostral VP/SI complex and subjected to a swimming-test procedure for 6 min. Injections of the dopamine-releasing agent d-amphetamine (10 microg/0.5 microl per side) enhanced the number of different cue-directed behavioral patterns while they had no effect upon the number of different non-cue-directed behavioral patterns in line with previous studies (Life Sci - 1989 1697). This increase was attenuated by a low dose of the GABAa agonist muscimol (1 ng/0.5 microl) into the rostral VP/SI complex. This dose of muscimol when injected alone into the rostral VP/SI complex had no effect upon the number of different cue-directed behavioral patterns. Only the lowest dose of the GABAa antagonist bicuculline (10-25 ng/0.5 microl per side) into the rostral VP/SI complex slightly, and in a non-d-amphetamine-like manner, increased the number of different cue-directed behavioral patterns while none of the doses had an effect on the number of different non-cue-directed behavioral patterns. Both injections of d-amphetamine into the ventral striatum and injections of bicuculline into the rostral VP/SI complex strongly increased motor activity in the 10-min period preceding the swimming test. We conclude from the data that switching to cue-directed behavioral patterns is sensitive to manipulations with the dopaminergic activity in the ventral striatum but not with the GABAergic activity in the VP/SI complex although the VP/SI transmits it to other brain structures. In contrast motor activity is sensitive to manipulations with both ventral striatal dopamine and rostral VP/SI complex GABA.

A comparative reappraisal of projections from the superficial laminae of the dorsal horn in the rat: The forebrain

Projections to the forebrain from lamina I of spinal and trigeminal dorsal horn were labeled anterogradely with Phaseolus vulgaris-leucoagglutinin (PHA-L) and/or tetramethylrhodamine-dextran (RHO-D) injected microiontophoretically. Injections restricted to superficial laminae (I/II) of dorsal horn were used primarily. For comparison, injections were also made in deep cervical laminae. Spinal and trigeminal lamina I neurons project extensively to restricted portions of the ventral posterolateral and posteromedial (VPL/VPM), and the posterior group (Po) thalamic nuclei. Lamina I also projects to the triangular posterior (PoT) and the ventral posterior parvicellular (VPPC) thalamic nuclei but only very slightly to the extrathalamic forebrain. Furthermore, the lateral spinal (LS) nucleus, and to a lesser extent lamina I, project to the mediodorsal thalamic nucleus. In contrast to lamina I, deep spinal laminae project primarily to the central lateral thalamic nucleus (CL) and only weakly to the remaining thalamus, except for a medium projection to the PoT. Furthermore, the deep laminae project substantially to the globus pallidus and the substantia innominata and more weakly to the amygdala and the hypothalamus. Double-labeling experiments reveal that spinal and trigeminal lamina I project densely to distinct and restricted portions of VPL/VPM, Po, and VPPC thalamic nuclei, whereas projections to the PoT appeared to be convergent. In conclusion, these experiments indicate very different patterns of projection for lamina I versus deep laminae (III-X). Lamina I projects strongly onto relay thalamic nuclei and thus would have a primary role in sensory discriminative aspects of pain. The deep laminae project densely to the CL and more diffusely to other forebrain targets, suggesting roles in motor and alertness components of pain.

Amygdala response to facial expressions in children and adults

BACKGROUND

The amygdala plays a central role in the human response to affective or emotionally charged stimuli, particularly fear-producing stimuli. We examined the specificity of the amygdala response to facial expressions in adults and children.

METHODS

Six adults and 12 children were scanned in a 1.5-T scanner during passive viewing of fearful and neutral faces using an EPI BOLD sequence. All scans were registered to a reference brain, and analyses of variance were conducted on the pooled data to examine interactions with age and gender.

RESULTS

Overall, we observed predominantly left amygdala and substantia innominata activity during the presentation of nonmasked fearful faces relative to fixation, and a decrease in activation in these regions with repeated exposure to the faces. Adults showed increased left amygdala activity for fearful faces relative to neutral faces. This pattern was not observed in the children who showed greater amygdala activity with neutral faces than with fearful faces. For the children, there was an interaction of gender and condition whereby boys but not girls showed less activity with repeated exposure to the fearful faces.

CONCLUSIONS

This is the first study to examine developmental differences in the amygdala response to facial expressions using functional magnetic resonance imaging.

Organization of the basal forebrain projection to the thalamus in rats

We have examined the patterns of projections that exist between the different nuclei of the basal forebrain (BF) and the thalamus. Injections of biotinylated dextran were made into different nuclei of the BF (i.e. substantia innominata, nucleus basalis of Meynert, vertical and horizontal limbs of the diagonal band) of Sprague-Dawley rats using stereotaxic coordinates. Our results show that all of the above-mentioned BF nuclei have projections to the thalamus and that projections from different nuclei are rather similar. The bulk of the BF afferents terminate within the intralaminar, midline and mediodorsal nuclei of the dorsal thalamus and the zona incerta and reticular nucleus of the ventral thalamus. Very few terminals are ever seen in the other nuclei of the thalamus. Thus our results indicate that the BF targets particular thalamic nuclei, thereby being in a position to influence distinct thalamo-cortical pathways.

A method of basal forebrain anatomical standardization for functional image analysis

Functional as well as structural assessment of the basal forebrain has mostly focused on the dorsal caudate and putamen in axial slices where they are easily outlined or their centers located with stereotaxic methods. The more ventral extent of the basal forebrain, where the irregular form and indistinct boundaries of the nucleus accumbens and substantia innominata are difficult to trace and where the brain's ventral surface may contribute partial volume artifacts to measurement, has been less studied. We present a method based on coronal sections, landmarks placed on clearly visible anchor points, and the computational technique of thin-plate spline warping which allows the alignment of groups of individuals to common coordinates for pixel-by-pixel statistical mapping. The reliability of the landmarks across independent raters yields a median absolute difference of 1.3-1.6 mm. The validity of the method is confirmed by variance maps which reveal significant decreases in variance over spindle and bounding box alignment.

Trajectories of cholinergic pathways within the cerebral hemispheres of the human brain

All sectors of the human cerebral cortex receive dense cholinergic input. The origin of this projection is located in the Ch4 cell group of the nucleus basalis of Meynert. However, very little is known about the location of the pathways which link the cholinergic neurons of the nucleus basalis to the human cerebral cortex. This question was addressed in whole-hemisphere sections processed for the visualization of multiple cholinergic markers. Two highly organized and discrete bundles of cholinergic fibres extended from the nucleus basalis to the cerebral cortex and amygdala and were designated as the medial and lateral cholinergic pathways. These bundles contained acetylcholinesterase, choline acetyltransferase and nerve growth factor receptors, confirming their cholinergic nature and origin within the basal forebrain. The medial pathway joined the white matter of the gyrus rectus, curved around the rostrum of the corpus callosum to enter the cingulum and merged with fibres of the lateral pathway within the occipital lobe. It supplied the parolfactory, cingulate, pericingulate and retrosplenial cortices. The lateral pathway was subdivided into a capsular division travelling in the white matter of the external capsule and uncinate fasciculus and a perisylvian division travelling within the claustrum. Branches of the perisylvian division supplied the frontoparietal operculum, insula and superior temporal gyrus. Branches of the capsular division innervated the remaining parts of the frontal, parietal and temporal neocortex. Representation of these cholinergic pathways within a 3D MRI volume helped to identify white matter lesion sites that could interfere with the corticopetal flow of cholinergic pathways.

The cholinergic deficit in Alzheimer's disease

The history of the discovery of cholinergic deficit in Alzheimer's disease is briefly reviewed, focusing on the cholinergic basal forebrain. The anatomy of the structure is discussed, and the clinical implications of pathology in this population of nerve cells are presented.

Volumetric comparison of auditory brain nuclei in ear-tufted Araucanas with those in other chicken breeds

Domestic chickens of the breed Araucana have ear-tufts, which affect the structure of the ear canal. Volumes of auditory brainstem nuclei were measured in three chicken breeds in order to evaluate whether the characteristics described for ear-tufted individuals of the Araucana chicken breed (alterations in the outer and middle ear anatomy) are associated with changes in the size of the relevant auditory nuclei. Allometric comparison reveals no size reductions of the angular, laminar and superior olivary nuclei in Araucanas, compared to Japanese Bantams and Brown Leghorns, but a slight increase in the size of the magnocellular nucleus.

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

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

Double dissociation of passive avoidance and milk maze performance deficits with discrete lesions of substantia innominata or globus pallidus of rats

In three experiments, small bilateral lesions of the substantia innominata (SI), globus pallidus (GP) and central nucleus of the amygdala (ACe) produced deficits in passive avoidance of drinking (dPA) or escape performance in a milk maze (MM). Severe deficits in dPA were produced by electrolytic lesions in lateral SI or rostral ACe, and by electrolytic or ibotenic acid lesions in the heart of the SI. Such lesions produced no effects on MM performance. Lesions of the rostral SI produced no, or mild, deficits in dPA and MM performance. However, lesions of the rostral GP produced an extreme deficit in MM performance but not dPA. The milder MM deficits produced by rSI lesions appeared to reflect a spatial navigation deficit, while the more severe impairment produced by rGP lesions appeared to represent a broader disruption of instrumental behavior. SI lesions also produced a temporary cessation of drinking and a chronic decrease in body weight, both of which were associated with impaired oromotor function. Eating and drinking deficits were less severe when lesions were more lateral or rostral in SI, and absent with lesions in rostral GP or amygdala. The most important finding, however, was a double dissociation of MM performance deficits following rostral GP lesions versus passive avoidance deficits produced by SI lesions.

Microanatomical and electrophysiological changes of the rat dentate gyrus caused by lesions of the nucleus basalis magnocellularis

The effect of unilateral or bilateral lesions of the nucleus basalis magnocellularis (NBM) on the dentate gyrus of the hippocampus were assessed using microanatomical and electrophysiological techniques. NBM is the main cholinergic basal forebrain nucleus that supplies the fronto-parietal cortex. Lesions were induced using the neurotoxin ibotenic acid or a radio-frequency system and did not affect glutamic acid decarboxylase activity both in the frontal cortex and in the hippocampus. At 4 weeks after lesioning, a loss of choline acetyltransferase (ChAT) activity and of ChAT-immunoreactive fibres was observed in the frontal cortex but not in the hippocampus and no changes in the density of granule neurons of the dentate gyrus or in the hippocampal long-term potentiation (LTP) were noticeable. At 8 weeks after lesioning the loss of both ChAT activity and of ChAT-immunoreactive fibres persisted in the frontal cortex of NBM-lesioned rats. Moreover, at this time a significant decrease in the density of granule neurons in the dentate gyrus accompanied by a reduced probability of dentate LTP induction were observed in both ibotenic acid- and radio-frequency-lesioned rats. These findings have shown that although NBM does not send direct cholinergic projections to the hippocampus, lesions of this cholinergic nucleus are accompanied by delayed neurodegenerative changes involving the dentate gyrus. This suggests the occurrence of indirect connections between NBM and the hippocampus, the functional relevance of which should be explored.

Restoration of cognitive abilities by cholinergic grafts in cortex of monkeys with lesions of the basal nucleus of Meynert

Three groups of marmosets were trained to perform a series of visual discrimination tasks in a Wisconsin General Test Apparatus. Two groups then received bilateral lesions of the basal nucleus of Meynert using the excitotoxin N-methyl-D-aspartate and were found to be severely impaired on relearning a visual discrimination first learnt prior to surgery. One lesioned group then received grafts of acetylcholine-rich tissue dissected from the basal forebrain of fetal marmosets. Three months later the marmosets with lesion alone remained impaired on a number of retention and reversal tasks whereas the transplanted animals were no longer significantly impaired. Histological examination of the brains indicated that all lesioned animals had sustained substantial loss of the cholinergic neurons of the basal nucleus of Meynert (assessed by nerve growth factor receptor immunoreactivity) and that the lesion-alone animals showed marked loss of the cholinergic marker acetylcholinesterase in the dorsolateral frontal and parietal cortex. All transplanted animals had surviving graft tissue (visualized by Cresyl Violet staining, dense acetylcholinesterase staining and the presence of a limited number of nerve growth factor receptor-immunoreactive neurons) in the neocortex and 5/6 transplanted animals showed near complete restitution of acetylcholinesterase staining in frontal and parietal cortex. Examination of individual animal data showed that the animal without this restitution performed very poorly. The performance of the remaining transplanted animals was significantly better than that of the animals with lesion alone. There was a significant positive correlation between the degree of acetylcholinesterase staining and good performance on tasks sensitive to frontal lobe damage. These results demonstrate that acetylcholine-rich tissue transplanted into the neocortex of primates with damage to the cholinergic projections to the neocortex can produce substantial restitution of function provided that an appropriate level of interaction between graft and host tissue is achieved.

The nucleus basalis of Meynert of the human brain: a Golgi and electron microscope study

The nucleus basalis of Meynert of normal brains, aged from 15 to 73 years was studied in Golgi preparations and in electron microscopy. The nucleus is composed of large triangular, polyhedral and bipolar cells which are intermixed with numerous small or medium-sized spiny neurons. All of the neurons form a dense three dimensional dendritic arborization, with numerous secondary and tertiary dendritic branches studded with spines. The ultrastructural analysis revealed numerous axodendritic and axosomatic synapses between the spines. The ultrastructural analysis revealed numerous axodendritic and axosomatic synapses between the spiny neurons and the large triangular and polyhedral neurons. The presynaptic axonic profiles are plenty of ellipsoid and round synaptic vesicles. Large presynaptic terminals are seen frequently surrounded by numerous dendritic spines forming synaptic glomeruli, in all the areas of the nucleus basalis of Meynert. An age depended decrease of the number of neurons was noticed affecting mainly the population of the spiny neurons. Although in senile and presenile dementias an impressive loss of the cholinergic neurons of the nucleus basalis was reported, in normal aging the large cholinergic neurons of the nucleus basalis seems to be intact, whereas the medium and small shaped spiny neurons are decreased in number suggesting that the GABA-ergic neurons are principally affected.

Autoradiographic study of the cerebrovascular effects of stimulation of the substantia innominata: convenient stimulation paradigm

The aim of this study was to determine the distribution within the whole brain of the vascular effects of stimulation of the substantia innominata. This basal forebrain nucleus is the major cholinergic input in the neocortex in the rodent. The local cerebral blood flow was measured by the autoradiographic [14C]iodoantipyrine technique in a group of control and a group of stimulated unanesthetized rats. The substantia innominata was electrically stimulated through a chronically implanted electrode. The stimulation induced blood flow increases exceeding 200% in the hemisphere ipsilateral to the stimulation and 100% in the contralateral hemisphere compared to the control group. The ipsilateral vasodilations were observed not only in the cortical areas but also in some subcortical structures. Comparison with previous data suggests that part of the effects is due to cholinergic neurons of the substantia innominata and part to non-cholinergic neurons and indirect effects. However, only two out of eight stimulated rats displayed this response. The low reproducibility of the results is discussed, considering the stimulation paradigm which has been developed for future measurements of the cerebral glucose utilization which requires a long duration stimulation period.

Organization of the efferent projections from the pontine parabrachial area to the bed nucleus of the stria terminalis and neighboring regions: a PHA-L study in the rat

The organization of efferent projections from the pontine parabrachial (pPB) area to the forebrain rostral to the central nucleus of the amygdala (Ce) was studied in the rat by using microinjections of Phaseolus vulgaris leucoagglutinin (PHA-L), into subregions of the pPB area. The present study is a follow-up of a former study (Bernard et al. [1993] J. Comp. Neurol. 329:201-229) which examines pPB projections onto the Ce. The results demonstrate that: (1) the pPB(m) region (the medial, the ventral lateral subnuclei and the waist area) diffusely projects to the lateral division (BSTL) of the bed nucleus of the stria terminalis (BST), the Ce-BSTL continuum (including, the dorsal portion of substantia innominata, the ventral portion of globus pallidus, the fundus striatum, and the substriatal area) and to a lesser extent the agranular insular cortex; (2) the pPB(1) region [the central lateral (pPBcl) and the outer portion of external lateral subnuclei] densely projects to the dorsal lateral subnucleus of BST (BSTdl); only the pPBcl subnucleus projects to the median, the anteroventral and the periventricular nuclei of the preoptic hypothalamus; and (3) the remaining pPB area (the dorsal lateral, part of the external lateral and the external medial subnuclei) projects to the nucleus of horizontal limb of diagonal band but does not project onto the BST and the preoptic hypothalamus. It is suggested that the pPB(m)-BSTL "diffuse pathway" is mainly implicated in motivational and autonomic aspects of taste. The pPB(1)-BSTdl and hypothalamic "concentrated pathways" could be implicated in autonomic and nociceptive processes.

Quantitation and three-dimensional reconstruction of Ch4 nucleus in the human basal forebrain

The basal nucleus of Meynert, incorporating the Ch4 group of cholinergic neurons, was examined in six patients with no signs of neurological abnormalities. The ages of the patients ranged from 20 to 80 years. Despite a number of descriptions of these neurons, few age-related studies have been dedicated to the analysis of the entire anteroposterior extent of the nucleus. Staining with cresyl violet and acetylcholinesterase histochemistry, alone or in combination, was used to identify the cytoarchitectural organization of the Ch4. Computer-assisted morphometry was used for three-dimensional visualization and quantitation. The three-dimensional computer reconstructions revealed a continuous ribbon of neurons with a highly variable density. Four distinct subregions could be clearly identified in all cases by their cytoarchitecture and cellular morphology, although these subgroups were different to those previously described. There were no quantitative differences between the hemispheres in volume, density or cell number of the Ch4, although equivalent levels varied in area and density. The measures were similar in all cases with the exception of the case aged 80 years old. The data demonstrate individual variability in three dimensions and confirm previous studies that found only a mild decline of the Ch4 in old age.

The neuropharmacological restoration of cognitive functions of cats following a lesion to the basal nuclei of the forebrain (Meynert's nucleus)

The functions of generalization and abstraction in an experimental model of Alzheimer's disease (the lesion of Meynert's nuclei in cats) were studied against the background of stimulation and inhibition of the cholinergic, GABAergic, and dopaminergic systems of the brain. It was demonstrated that the cholinergic system is a key system for the formation of the function of generalization, the dopaminergic system improves simple forms of learning, while the GABAergic system is actively involved in the establishment of complex types of associations.

A novel population of tyrosine hydroxylase immunoreactive neurones in the basal forebrain of the common marmoset (Callithrix jacchus)

We have observed in the basal forebrain of the common marmoset a group of neurones which display tyrosine hydroxylase immunoreactivity (THir) with three different polyclonal antibodies and one monoclonal antibody, and which express TH mRNA as shown by in situ hybridization histochemistry. The population of cells is composed of large multipolar neurones and is located predominantly in the substantia innominata and at the ventral, medial and lateral margins of the external segment of the globus pallidus. The cell morphology and the distribution of THir cells corresponds closely to the caudal portion of the nucleus basalis of Meynert. Adjacent sections demonstrate both THir and choline acetyltransferase immunoreactivity in the cells in this group, as well as strong acetylcholinesterase activity but not dopamine immunoreactivity. These observations indicate that many cholinergic neurones in the posterior nucleus basalis of Meynert of the marmoset contain tyrosine hydroxylase, and suggest that both acetylcholine and catecholamine may be synthesised as co-localised neurotransmitters within the same magnocellular neurones. We observe no THir cells in similar areas of the basal forebrain of either rhesus or talapoin monkeys.

Effects of THA on passive avoidance retention performance of intact, nucleus basalis, frontal cortex and nucleus basalis + frontal cortex-lesioned rats

Unilateral quisqualic acid lesions of the nucleus basalis magnocellularis (NBM) produced marked choline acetyltransferase depletion (-67% ipsilateral to lesion) and impaired passive avoidance (PA) retention at 24 hours. Pretraining injections of tacrine (THA: 1, 3 and 5 mg/kg), an anticholinesterase, failed to facilitate PA retention in intact rats. However, the retention performance of NBM-lesioned rats was improved by pretraining administration of THA at 3 mg/kg but not at either 1 or 5 mg/kg. Frontal cortex lesioning did not impair PA retention, and THA at 3 mg/kg had no effect on the PA retention of frontal cortex-lesioned rats. THA at 3 mg/kg failed to improve retention performance of NBM + frontal cortex-lesioned rats. After 10 days of chronic treatment with THA, NBM lesion-induced PA retention deficits were partially restored at both 3- and 5-mg/kg doses. The results suggest that 1) the insult to cholinergic neurons in the NBM may be involved in the PA memory consolidation deficit induced by nonselective quisqualic acid lesioning; 2) the beneficial effects of THA on NBM lesion-induced PA retention deficit occur in a narrow dose range; 3) the alleviating effects of THA on NBM lesion-induced PA memory deficits are blocked by frontal cortex lesions; and 4) the dose-response window for THA-induced PA retention performance improvement is broadened by repeated treatment.

GABAergic control of basal forebrain cholinergic neurons and memory

The involvement of the GABAergic innervation of basal forebrain neurons in the rats' conditional visual discrimination performance was examined. Performance in such a task is based on the subjects's ability to retrieve information about response rules, and previous experiments have demonstrated that basal forebrain lesions interfere with this ability. Following the acquisition of the task, chronic guide cannulae were stereotaxically implanted into the substantia innominata of both hemispheres, and the animals were retrained. Administration of the GABAA-agonist muscimol into the substantia innominata (0, 25, 50 ng/0.5 microliters/hemisphere) dose-dependently decreased the number of correct responses, increased the number of errors of omission, increased response latency, but did not affect side bias. Systemic co-administration of the cholinesterase inhibitor physostigmine (0, 0.1, 0.2 mg/kg; i.p.) exclusively interacted with the effects of muscimol on correct responding. Specifically, physostigmine dose-dependently intensified and attenuated the muscimol-induced reduction in correct responding. Although it cannot be excluded that alternative neuronal mechanisms were involved in the mediation of the effects of muscimol and their interaction with physostigmine, these findings support previous evidence indicating that the activity of basal forebrain cholinergic neurons is controlled by a GABAergic input, and that this neuronal link is involved in mnemonic processing.

Configuration of the magnocellular nuclei in the basal forebrain of the human adult

With the use of gapless series of thick sections (800 microns) stained for lipofuscin pigment as a stable intraneuronal characteristic, it was found in the human brain that the three magnocellular nuclei in the basal forebrain-the medial septal nucleus, the nucleus of the diagonal band (vertical and horizontal limb) and the basal nucleus of Meynert located within the substantia innominata-were tightly connected with each other. A band-like anteromedial subnucleus and a semilunar posterolateral subnucleus could be delineated in the basal nucleus and were found to be embedded in a zone of low cell density, the substantia innominata, which medially blends into the horizontal limb of the diagonal band nucleus. A three-dimensional reconstruction was made to demonstrate the complex shape of the magnocellular basal forebrain nuclei.

Neural associations of the substantia innominata in the rat: afferent connections

The afferent connections of the substantia innominata (SI) in the rat were determined employing the anterograde axonal transport of Phaseolus vulgaris leucoagglutinin (PHA-L) and the retrograde transport of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP), in combination with histochemical procedures to characterize the neuropil of the SI and identify cholinergic cells. Both neurochemical and connectional data establish that the SI is organized into a dorsal and a ventral division. Each of these divisions is strongly affiliated with a different region of the amygdala, and, together with its amygdalar affiliate, forms part of one of two largely distinct constellations of interconnected forebrain and brainstem cell groups. The dorsal SI receives selective innervation from the lateral part of the bed nucleus of the stria terminalis, the central and basolateral nuclei of the amygdala, the fundus of the striatum, distinctive perifornical and caudolateral zones of the lateral hypothalamus, and caudal brainstem structures including the dorsal raphe nucleus, parabrachial nucleus, and nucleus of the solitary tract. Projections preferentially directed to the ventral SI arise from the medial part of the bed nucleus of the stria terminalis, the rostral two-thirds of the medial nucleus of the amygdala, a large region of the rat amygdala that lies ventral to the central nucleus, the medial preoptic area, anterior hypothalamus, medialmost lateral hypothalamus, and the ventromedial hypothalamus. Both SI divisions appear to receive afferents from the dorsomedial and posterior hypothalamus, supramammillary region, ventral tegmental area, and the peripeduncular area of the midbrain. Projections to the SI whose selectivity was not determined originate from medial prefrontal, insular, perirhinal, and entorhinal cortex and from midline thalamic nuclei. Findings from both PHA-L and WGA-HRP experiments additionally indicate that cell groups preferentially innervating a single SI division maintain numerous projections to one another, thus forming a tightly linked assembly of structures. In the rat, cholinergic neurons that are scattered throughout the SI and in parts of the globus pallidus make up a cell population equivalent to the primate basal nucleus of Meynert (Mesulam et al.: Neuroscience 10:1185-1201, '83). PHA-L-filled axons, labelled from lectin deposits in the dorsal raphe nucleus, peripeduncular area, ventral tegmental area, or caudomedial hypothalamus were occasionally seen to approach individual cholinergic neurons int he SI, and to contact the surface of such cells with axonal varicosities (putative synaptic boutons.(ABSTRACT TRUNCATED AT 400 WORDS)

Efferent connections of the substantia innominata in the rat

The efferent connections of the substantia innominata (SI) were investigated employing the anterograde axonal transport of Phaseolus vulgaris leucoagglutinin (PHA-L) and the retrograde transport of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP). The projections of the SI largely reciprocate the afferent connections described by Grove (J. Comp. Neurol. 277:315-346, '88) and thus further distinguish a dorsal and a ventral division in the SI. Efferents from both the dorsal and ventral divisions of the SI descend as far caudal as the ventral tegmental area, substantia nigra, and peripeduncular area, but projections to pontine and medullary structures appear to originate mainly from the dorsal SI. Within the amygdala and hypothalamus, which receive widespread innervation from the SI, the dorsal SI projects preferentially to the lateral part of the bed nucleus of the stria terminalis; the lateral, basolateral, and central nuclei of the amygdala; the lateral preoptic area; paraventricular nucleus of the hypothalamus; and certain parts of the lateral hypothalamus, prominently including the perifornical and caudolateral zones described previously. The ventral SI projects more heavily to the medial part of the bed nucleus of the stria terminalis; the anterior amygdaloid area; a ventromedial amygdaloid region that includes but is not limited to the medial nucleus; the lateral and medial preoptic areas; and the anterior hypothalamus. Modest projections reach the lateral hypothalamus, with at least a slight preference for the medial part of the region, and the ventromedial and arcuate hypothalamic nuclei. Both SI divisions appear to innervate the dorsomedial and posterior hypothalamus and the supramammillary region. In the thalamus, the subparafascicular, gustatory, and midline nuclei receive a light innervation from the SI, which projects more densely to the medial part of the mediodorsal nucleus and the reticular nucleus. Cortical efferents from at least the midrostrocaudal part of the SI are distributed primarily in piriform, infralimbic, prelimbic, anterior cingulate, granular and agranular insular, perirhinal, and entorhinal cortices as well as in the main and accessory olfactory bulbs. The cells of origin for many projections arising from the SI were identified as cholinergic or noncholinergic by combining the retrograde transport of WGA-HRP with histochemical and immunohistochemical procedures to demonstrate acetylcholinesterase activity or choline acetyltransferase immunoreactivity. Most of the descending efferents of the SI appear to arise primarily or exclusively from noncholinergic cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Projections between the interpeduncular nucleus and basal forebrain in the rat as demonstrated by the anterograde and retrograde transport of WGA-HRP

The distribution of anterogradely-labeled fibers and retrogradely-labeled cell bodies in the interpeduncular nucleus (IPN) was mapped after injections of wheat-germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) into various structures of the basal forebrain in adult rats. WGA-HRP injections into the medial septum/vertical limb of the diagonal band nucleus resulted in: 1) dense anterograde labeling in the rostral, intermediate, and central subnuclei; and 2) retrograde labeling in the apical and central subnuclei. Injections into the lateral septum produced: 1) no anterograde labeling in the IPN; and 2) retrograde labeling which was dense in the apical subnucleus, moderate in the central and lateral subnuclei, and light in the intermediate subnucleus. Injections into the horizontal limb of the diagonal band nucleus resulted in: 1) anterograde labeling which was most pronounced in the central, rostral, and intermediate subnuclei; and 2) retrograde labeling which was strongest in the apical, central, and lateral subnuclei. After injections into the substantia innominata-magnocellular preoptic nucleus, there was: 1) dense anterograde labeling in the rostral and central subnuclei and moderate anterograde labeling in the intermediate subnucleus; and 2) essentially no retrograde cell labeling in the IPN. These findings demonstrate that the IPN receives inputs from, and projects to specific portions of the basal forebrain. The rostral and central subnuclei are the primary targets of inputs from the basal forebrain to the IPN, and the apical subnucleus is the primary source of IPN projections to the basal forebrain.

The origins of cholinergic and other subcortical afferents to the thalamus in the rat

The origins of the cholinergic and other afferents of several thalamic nuclei were investigated in the rat by using the retrograde transport of wheat germ agglutinin conjugated-horseradish peroxidase in combination with the immunohistochemical localization of choline acetyltransferase immunoreactivity. Small injections placed into the reticular, ventral, laterodorsal, lateroposterior, posterior, mediodorsal, geniculate, and intralaminar nuclei resulted in several distinct patterns of retrograde labelling. As expected, the appropriate specific sensory and motor-related subcortical structures were retrogradely labelled after injections into the principal thalamic nuclei. In addition, other basal forebrain and brainstem structures were also labelled, with their distribution dependent on the site of injection. A large percentage of these latter projections was cholinergic. In the brainstem, the cholinergic pedunculopontine tegmental nucleus was retrogradely labelled after all thalamic injections, suggesting that it provides a widespread innervation to the thalamus. Neurons of the cholinergic laterodorsal tegmental nucleus were retrogradely labelled after injections into the anterior, laterodorsal, central medial, and mediodorsal nuclei, suggesting that it provides a projection to limbic components of the thalamus. Significant basal forebrain labelling occurred only with injections into the reticular and mediodorsal nuclei. Only injections into the reticular nucleus resulted in retrograde labelling of the cholinergic neurons in the nucleus basalis of Meynert. The results provide evidence for an organized system of thalamic afferents arising from cholinergic and noncholinergic structures in the brainstem and basal forebrain. The brainstem structures, especially the cholinergic pedunculopontine tegmental nucleus, appear to project directly to principal thalamic nuclei, thereby providing a possible anatomical substrate for mediating the well-known facilitory effects of brainstem stimulation upon thalamocortical transmission.

The organization of the nucleus basalis-neostriatum complex of the mallard (Anas platyrhynchos L.) and its connections with the archistriatum and the paleostriatum complex

The pattern of connections between the nucleus basalis, neostriatum, hyperstriatum ventrale, paleostriatum complex and archistriatum in the mallard has been analysed using Nissl material and a combination of neuroanatomical tracing procedures (autoradiography, horseradish peroxidase and horseradish peroxidase-wheat germ agglutinin histochemistry, lesion/degeneration technique). The frontal part of the mallard's telencephalon is characterized by its multilayered organization and the predominantly vertical arrangement of the connecting fiber systems. The nucleus basalis, endstation of the ascending sensory trigeminal system, is a large laminar cell area with a dorsal and a ventral layer. The overlying neostriatum frontale can be subdivided into a medial, a dorsal and a ventral intermediate, and a lateral area. The nucleus basalis has distinct connections with the ventral layer and sparse connections with the dorsal layer of the intermediate neostriatum, and abundant reciprocal connections with the ventral layer of the hyperstriatum ventrale. The ventral intermediate neostriatum also has reciprocal connections with the hyperstriatum ventrale; its projections overlap partly with those from the nucleus basalis. The ventral layer of the intermediate neostriatum frontale has a distinct projection upon the paleostriatum augmentatum. The dorsal layer sends fibers to the lateral neostriatum, to the rostral "sensorimotor" part of the archistriatum and to the lateral zone of the lobus parolfactorius. Another source of archistriatal afferents is the paleostriatum ventrale, an area that may also send fibers to the brainstem. Figure 21 summarizes the connections described in this paper. The functional significance of this organization is discussed in relation to its possible role in the guidance of pecking and other feeding behaviors in the mallard. Differences in the organization of the systems in pigeon and mallard are related to the differing degrees of visual and tactile (trigeminal) contributions to feeding in the two birds. It is suggested that the pattern of reciprocal connections between the hyperstriatum ventrale and the nucleus basalis and ventral intermediate neostriatum frontale forms the neuroanatomical substrate for a "comparator-system".

Light microscopic evidence for a substance P-containing innervation of the human nucleus basalis of Meynert

A two color histochemical/immunohistochemical method was used to demonstrate substance P and acetylcholinesterase in sections of the human nucleus basalis of Meynert (nbM). Substance P-immunoreactive terminal-like structures were found to make contact with magnocellular, acetylcholinesterase-positive perikarya and primary dendrites throughout all subdivisions of the nbM. This apparent innervation of nbM neurons was in most cases a relatively sparse one, but a small percentage of these neurons appeared to be recipients of a very heavy innervation which covered their perikarya and primary dendrites.

Cholinergic and non-cholinergic neurons of cat basal forebrain project to reticular and mediodorsal thalamic nuclei

Choline acetyltransferase immunohistochemistry combined with the retrograde transport of horseradish peroxidase showed that the reticular and mediodorsal thalamic nuclei of the cat receive an important input from cholinergic and non-cholinergic neurons of substantia innominata and adjacent structures in the basal forebrain.

Cholinergic nucleus basalis neurons may influence the cortex via the thalamus

The cholinergic neurons of the nucleus basalis of Meynert have been shown to provide the major cholinergic innervation of the cerebral cortex through which cholinergic transmission may modulate cortical activity. This study describes a projection from the cholinergic and non-cholinergic neurons of the nucleus basalis to the reticular nucleus of the thalamus, and a projection from the brainstem cholinergic neurons to the reticular nucleus as well as to other thalamic nuclei. The projection from the nucleus basalis to the reticular nucleus, which itself is synaptically interconnected with other thalamic nuclei, may provide an additional pathway for the modulation of cortical activity by the cholinergic basal forebrain and brainstem groups.

The afferent input to the magnocellular division of the mediodorsal thalamic nucleus in the monkey, Macaca fascicularis

The origin and termination of fibers to the mediodorsal thalamic nucleus, especially those to the medial, magnocellular part of the nucleus (MDm), have been studied using anterograde and retrograde axonal tracing methods, as well as electrophysiological recording. The results indicate that in addition to its well-known connections to and from the prefrontal cortex, MDm receives fibers from many parts of the basal forebrain, including the ventral pallidum and other parts of the substantia innominata, the amygdaloid complex, the primary olfactory cortex, entorhinal and perirhinal cortex, and the cortex at the pole of the temporal lobe. Lighter projections arise in the subiculum, the ventral insula, and the superior and inferior temporal gyri. The cells that project to MDm tend to be large, polymorphic neurons. Throughout most of the basal forebrain they are diffusely distributed through several nuclei or cortical layers, without obvious relation to nuclear or laminar boundaries. The major exception to this is in the ventral pallidum, where there is a dense concentration of cells that project to MDm. The lateral part of the mediodorsal nucleus (MDl) receives few if any fibers from the basal forebrain and temporal lobe, but is innervated by several brainstem structures, especially the superior colliculus, the substantia nigra, the medial vestibular nucleus, and the midbrain tegmental fields. In MDm, the fibers are distributed in irregular patches. Three-dimensional analysis indicates that these patches are often clustered into separate bands or columns at different anteroposterior levels. In addition, the strongest projections from the three major regions that innervate MDm are organized in a complex three-dimensional pattern. First, the fibers from the amygdaloid nuclei terminate most heavily (but not exclusively) in the rostral third of MDm. The parvicellular accessory basal amygdaloid nucleus and the amygdalohippocampal area project principally to the dorsal part of the nucleus. The parvicellular basal nucleus and the periamygdaloid cortex project to the ventromedial quadrant of MDm; and the magnocellular basal nucleus, the magnocellular accessory basal nucleus, and the lateral nucleus all project to the ventrolateral quadrant. Second, the substantia innominata projects preferentially to the caudal part of MDm. The medial part of the substantia innominata, especially the ventral pallidum, innervates the dorsomedial quadrant, while more caudal and lateral areas of this region project ventrolaterally. Third, the projections arising from the entorhinal and other temporal cortical areas terminate primarily in the mid-rostrocaudal level of MDm.(ABSTRACT TRUNCATED AT 400 WORDS)

The cholinergic system in aging

A morphometric analysis of neuronal loss during normal aging was performed in the nucleus basalis Meynert complex of the basal forebrain (Nbm) (nucleus septi medialis, nucleus of Broca's diagonal band, nucleus basalis) and the ciliary ganglion, a peripheral cholinergic structure, in patients free of neurological and psychiatric illness. As a basis for morphometric evaluation of the Nbm complex, a three-dimensional reconstruction of this complex structure was made. Neuronal counts in the Nbm complex and the ciliary ganglion remained stable up to the age of 60 or 50 years, respectively. After this age the number of neurons declined moderately in ciliary ganglion in all cases studied as well as in the Nbm complex in some cases (-20 and -25%, respectively, at about 90 years of age). In 3 out of 8 cases older than 60 years, neuronal counts in the Nbm complex were not reduced, so that no significant decline in neuronal number is apparent from the mean values of the 17 cases studied. No age-related changes were found in the neuronal distribution amongst the different subgroups of Nbm neurons using the alternative nomenclature of Mesulam et al. [J. comp. Neurol. 214: 170-197, 1983]. Our results provide no evidence that the cortical cholinergic projection system and peripheral cholinergic neurons might be especially vulnerable during normal aging. The severe degeneration of the cholinergic cortical projection system in SDAT is probably caused by mechanisms different from those acting during normal aging.

Basal forebrain neurons have axon collaterals that project to widely divergent cortical areas in the cat

Basal forebrain neurons with axon collaterals that project to widely divergent cortical areas were identified using retrograde transport of two labels. A proportion of neurons in the basal forebrain have axon collaterals that project to both anterior (precruciate gyrus) and posterior (marginal and suprasylvian gyri) cortical areas or to medial (precruciate gyrus) and lateral (ectosylvian and anterior suprasylvian gyri) cortical areas. These branched fibers originate from cells located predominantly in the basal nucleus of Meynert. The existence of such neurons suggests that individual basal forebrain cells are capable of influencing widespread neocortical zones in the cat.

Three-dimensional representation and cortical projection topography of the nucleus basalis (Ch4) in the macaque: concurrent demonstration of choline acetyltransferase and retrograde transport with a stabilized tetramethylbenzidine method for horseradish peroxidase

Ninety-six percent of the nucleus basalis neurons that project to the neocortex contain choline acetyltransferase. These projections from the cholinergic component of the nucleus basalis (Ch4) are topographically organized so that each cortical area receives most of its cholinergic input from a different Ch4 sector. The three-dimensional reconstruction of these sectors reveals the presence of a complex structure. A stabilization procedure that was used in these experiments maintains all the advantages of the tetramethylbenzidine method for horseradish peroxidase while eliminating the vulnerability of the reaction-product to high pH and dehydrating agents.

The nucleus basalis of Meynert

The nucleus basalis of Meynert has been studied extensively in the recent literature. Interest in this nucleus has resulted from the discovery that it is a major source of cortical cholinergic input and that there is neuronal loss in the nucleus basalis in some dementing illnesses. Consistent and severe involvement of the nucleus basalis of Meynert has been found in Alzheimer's disease and in the dementia accompanying Parkinson's disease. Occasional involvement is present in other dementing illnesses, such as progressive supranuclear palsy, Parkinsonism-Dementia complex of Guam, dementia pugilistica, Pick's disease, Korsakoff's syndrome, Down's Syndrome and Creutzfeldt-Jacob disease. Huntington's disease spares this nucleus. However, the role of the nucleus in cognitive function is as yet undetermined. Even its alteration with normal aging remains controversial. This review details the pathological studies of this region to date, with particular emphasis on the dementias. Its role in the dementias of Alzheimer's disease and Parkinson's disease is specifically addressed.

Topographical projection of cholinergic neurons in the basal forebrain to the cingulate cortex in the rat

The cholinergic innervation of the rat's posterior cingulate cortex (Brodmann's area 29) was studied using acetylcholinesterase (AChE) histochemistry. Electrolytic lesion of the ipsilateral medial septum and diagonal band region (MS-DB) reduced the diffuse AChE staining in layers I, II, III and V of the cingulate cortex. Kainic acid lesion of the ipsilateral globus pallidus and substantia innominata area (GP-SI) abolished the dense band of AChE stain in layer IV, with small reductions of AChE stain in other layers. The results indicate that the medial cholinergic pathway from MS-DB terminates diffusely in layers I, II, III and V while the lateral cholinergic pathway from the GP-SI predominantly ends in layer IV of the posterior cingulate cortex.

The afferent connections of the substantia innominata in the monkey, Macaca fascicularis

The afferent connections of the substantia innominata and the magnocellular nuclei within it (the nucleus of the horizontal limb of the diagonal band, NHDB, and the nucleus basalis of Meynert, NBM) have been studied with anterograde and retrograde axonal tracing techniques. Prominent inputs arise in the amygdaloid complex, restricted areas of the cerebral cortex, parts of the thalamus and hypothalamus, and nuclei of the lower brainstem. Autoradiographic tracing experiments indicate that the amygdaloid fibers are distributed throughout the NHDB and the NBM, and to a lesser extent to the ventral pallidum. Relatively few fibers innervate the more medially located nucleus of the vertical limb of the diagonal band (NVDB) and the medial septal nucleus. Visualization of the amygdalofugal fibers with the tracer PHA-L (Phaseolus vulgaris leuco-agglutinin) shows that they have varicosities resembling boutons en passant along their length in the substantia innominata. Retrograde tracing experiments using WGA-HRP indicate that the cells of origin of the projection from the amygdala are concentrated in the parvicellular basal nucleus, the caudal part of the magnocellular basal nucleus, the magnocellular accessory basal nucleus, and the central nucleus. Relatively few fibers to the substantia innominata arise in the rostrodorsal part of the magnocellular basal nucleus, or in the lateral or parvicellular accessory basal nuclei. Cortical cells projecting to the substantia innominata were retrogradely labeled in the orbitofrontal cortex (including areas 11-14 and 25), the rostral insula (especially the agranular area), the rostroventral temporal cortex (including areas 35, 36, and parts of TG and TE), and the piriform and entorhinal cortices. The projections from the orbital and rostral temporal cortex were confirmed with anterograde tracers. Projections to the substantia innominata were not found from the more lateral, dorsal or caudal parts of the cerebral cortex, although fibers from temporal area TA may pass through the dendritic field of the most caudal cells of the NBM. Diencephalic cells projecting to the substantia innominata are distributed diffusely throughout the preoptic area and hypothalamus, with higher concentration in the lateral preoptic area and in the pre-, supra-, and tubero-mammillary nuclei. Cells are also found in the midline thalamic nuclei and in the region between the peripeduncular and subparafascicular nuclei.(ABSTRACT TRUNCATED AT 400 WORDS)

A correlated light and electron microscopic study of identified cholinergic basal forebrain neurons that project to the cortex in the rat

Cholinergic neurons in the basal forebrain which project to the frontal cortex were studied by combining the retrograde transport of a conjugate of horseradish peroxidase and wheat germ agglutinin with choline acetyltransferase immunohistochemistry. Neurons that were both retrogradely labelled and immunoreactive were found on the medial, lateral, and ventral borders of the globus pallidus, within the globus pallidus, as well as in the substantia innominata and ventral pallidum region. The cell bodies averaged 31 by 19 micron in size and had sparsely branching dendrites. Cells which were labelled by both techniques were first characterised in the light microscope and then studied in the electron microscope. The perikarya had large amounts of cytoplasm with abundant organelles. The nuclei were indented, were usually eccentrically placed, and contained prominent nucleoli. The synaptic input onto the cell bodies and their dendrites was studied in serial sections. The synaptic input onto the perikarya and proximal dendrites was sparse but the density increased on more distal regions of the dendrites. Subjunctional bodies were associated with the postsynaptic membrane in 20-30% of the synaptic contacts and these were classified as asymmetrical; the remaining contacts could not be classified because of an association of the immunoreaction product with the postsynaptic membrane. The synaptic input to these cells was distinctly different from that onto typical globus pallidus cells, the perikarya and dendrites of which were characteristically ensheathed in synaptic boutons.

The pattern of cortical projections from the intermediate parts of the magnocellular nucleus basalis in the rat demonstrated by tracing with Phaseolus vulgaris-leucoagglutinin

The pattern and distribution of the cortical projections from intermediate parts of the cholinergic basal magnocellular nucleus were studied by anterogradely transported Phaseolus vulgaris-leucoagglutinin. This immunocytochemical tracing technique reveals the detailed morphology and distribution of efferents from this intermediate area in the nucleus basalis to the various areas and layers of cortex and amygdala. Major projections with a relatively high density of terminal boutons were found in layers I, II and VI of the frontal cortex, in layers V and VI of parietal and temporal areas, in the entire perirhinal and entorhinal cortices, and in the basolateral nucleus of the amygdaloid body. From the nucleus basalis area studied, few if any projections could be demonstrated to cingulate and occipital cortical regions.

Evidence that projections from substantia innominata to zona incerta and mesencephalic locomotor region contribute to locomotor activity

A series of anatomical, electrophysiological and behavioral experiments was carried out in the rat to investigate the possible functional significance of a recently demonstrated neural pathway from the substantia innominata of the subpallidal forebrain to the mesencephalic locomotor region. Following injections of the anterogradely transported lectin PHA into the substantia innominata labeled fibers with terminal boutons were observed in the zona incerta, dorsal to the medial part of the subthalamic nucleus, and some appeared to continue on to the pedunculopontine nucleus. Electrophysiological recordings of action potentials were made from neurons in the substantia innominata and some of these neurons were activated antidromically by single-pulse stimulation of the zona incerta and/or by single-pulse stimulation of the pedunculopontine nucleus as well. Neurons in the zona incerta responded orthodromically to stimulation of the substantia innominata. Locomotor activity was initiated by injecting picrotoxin, a GABA antagonist, unilaterally into the substantia innominata through chronic cannulae, as reported previously. This picrotoxin-initiated locomotor activity was reduced significantly when procaine (a neuronal blocker) was injected into the ipsilateral zona incerta. Injecting procaine into the contralateral zona incerta had little or no effect on the picrotoxin-initiated locomotor activity. Taken together these observations suggest the tentative working hypothesis that projections from the substantia innominata to the zona incerta as well as the pedunculopontine nucleus may contribute to the locomotor component of adaptive behaviors resulting from limbic forebrain integrative activities, an hypothesis that can now be investigated further.

Cholinergic projections from the basal forebrain to the basolateral amygdaloid complex: a combined retrograde fluorescent and immunohistochemical study

We have examined the location of cholinergic and non-cholinergic neurons that project to the rat basolateral amygdaloid nucleus by using choline acetyltransferase (ChAT) immunohistochemistry in combination with retrograde fluorescent tracing on the same tissue section. Since many tracer-and ChAT-positive neurons were identified in basal forebrain areas, including the ventral pallidum, we also stained many of the sections for glutamate decarboxylase, a suitable marker for the delineation of pallidal areas. Cholinergic neurons projecting to the basolateral amygdaloid nucleus were observed in a continuous territory stretching from the dorsal part of ventral pallidum, through sublenticular substantia innominata to ventral parts of globus pallidus and peripallidal areas. Non-cholinergic neurons projecting to the basolateral amygdaloid nucleus were found intermixed within the same structures and constitute approximately 25% of the amygdalopetal projection neurons in these ventral forebrain structures. Since amygdalopetal cholinergic neurons were demonstrated in areas generally recognized as giving rise to cholinergic projections to cerebral cortex, several retrograde double-labeling experiments with two different fluorescent tracers were performed for the purpose of detecting the possible existence of collateral projections. The results obtained showed that the cholinergic basal forebrain neurons in general project to only one forebrain region, and, furthermore, that the cholinergic system consists of partially overlapping subsets of neurons that project to various neocortical and allocortical areas and to the amygdaloid body.

Branched projections of pallidal and peripallidal neurons to neocortex and neostriatum: a double-labeling study in the cat

Double-labeling of basal forebrain neurons by retrograde axonal transport of different markers demonstrated afferents shared by the neocortex and neostriatum. A considerable double-labeled complement of neurons located in the globus pallidus (lateral pallidal segment) and the adjacent interdigitating basal nucleus of Meynert (peripallidal region) had branched axonal collaterals projecting to the precruciate, cingulate and prorean gyri as well as to the head of the caudate nucleus.

[Afferent connections of the basolateral division of the amygdaloid complex of the cat brain]

Injection of horseradish peroxidase into the basal macrocellular and lateral nuclei of the amygdaloid complex (BLAC) in the cat brain has revealed their rich thalamic afferentation. On the BLAC there are massive projections of: a) nuclei of the middle line of the precommissural pole of the dorsal thalamus (anterior parts of the paratenial, interanteromedial and reunial nuclei), as well as the whole anterior paraventricular nucleus, medial part of the ventral posteromedial nucleus; b) postcommissural nuclei of the dorsal thalamus; some "nonacustical" nuclei of the internal geniculate body (ventrolateral nucleus, medial and macrocellular parts and the most caudal end of the internal geniculate body). Rather essential are projections of the "posterior group nuclei", those of the suprageniculate nucleus, of some parts of the ventral thalamus (subparafascicular nucleus, marginal and peripeduncular nuclei) and parabrachial nucleus. Scattered single projections are obtained from all hypothalamic parts (most of all the ventromedial nucleus), reticular nuclei of the septum, substantia innominata, substantia nigra, truncal nuclei of the raphe. Variety of the dorsal thalamic nuclei, sending their fibers to the BLAC reflects variety of sensory information, that gets here, according to its modality, degree of its differentiation and integrity. A number of the dorsal thalamus nuclei, owing to abundance of labelled neurons, can be considered as special relay thalamic nuclei for the BLAC resembling corresponding relay nuclei for the new cortex.

A cytoarchitectonic and histochemical study of nucleus basalis and associated cell groups in the normal human brain

Several recent studies have reported loss of neurons in the nucleus basalis in Alzheimer's disease. However, few detailed studies of the normal distribution of these neurons in the human brain have appeared. We have used Nissl staining and acetylcholinesterase histochemical staining of the human basal forebrain, alone or in combination to identify the organization of the nucleus basalis and associated cell groups, (or collectively, the magnocellular basal nucleus) in the normal human brain. The magnocellular basal nucleus includes a series of clusters of neurons and scattered perikarya extending from the medial septum and diagonal band nucleus rostrally, through the substantia innominata to the furthest caudal extent of the globus pallidus. This distribution is similar to that which has been described in the monkey. Furthermore, acetylcholinesterase-positive fibers in the human brain are seen in the two major pathways that have been identified as carrying magnocellular basal nucleus axons to the cerebral cortex in other species. These observations suggest that the topographic organization of the magnocellular basal projection to cerebral cortex in other species probably exists in man as well. It will therefore be important in future studies of the fate of these neurons in neurological degenerative diseases to assess the loss of neurons in the different components of the magnocellular basal nucleus in relation to the clinical evidence for dysfunction in the cortical areas which they innervate.