Topography of choline acetyltransferase-containing neurons in the forebrain of the rat

Topography of choline acetyltransferase immunoreactive neurons and fibers in the rat spinal cord

The topography of choline acetyltransferase immunoreactivity was studied in the rat spinal cord with a monoclonal antibody. Cholinergic fibers were most prominent in lamina III of the dorsal horn and originated from cholinergic neurons within the spinal cord. Lamina X, which was rich in cholinergic neurons and fibers, provided cholinergic interconnections between the dorsal, intermediate and ventral gray. Within the ventral gray, choline acetyltransferase immunoreactive boutons were found on motor neurons. This study suggests that the cholinergic innervation of the spinal cord arises from neurons intrinsic to the spinal cord. The cholinergic neurons within the spinal cord may provide several, overlapping levels of regulation of spinal cord neurons.

The localization of central cholinergic neurons

Over the past decade our understanding of the localization of central cholinergic neurons has greatly increased. Interest in these systems has also intensified due to the involvement of cholinergic mechanisms in Alzheimer's disease. The distribution of central cholinergic neurons is reviewed, focusing on recent work in experimental animals. The pharmacohistochemical procedure for acetylcholinesterase and the development of antibodies to choline acetyltransferase are two of the major technical advances that have shaped our knowledge of the distribution of central cholinergic neurons. The results, advantages and limitations of both techniques are discussed. A discussion of the phenomenon of coexistence of acetylcholine with neuroactive peptides in central neurons is also included.

Positron emission tomography and the possible origins of cytopathology in Alzheimer's disease

The local cerebral metabolic rate for glucose (LCMRgl), as determined by positron emission tomography (PET), declines in the cerebral cortex in Alzheimer's disease; the severity of the decline parallels the severity of the dementia and correlates with regional cortical neuronal loss and glial proliferation. The cholinergic cells of the medial basal forebrain show a pathological dropout in Alzheimer's disease which accounts for the decline in choline acetyltransferase in the cerebral cortex and hippocampus. It is proposed that these cholinergic cells serve both as an acquisition and readout device for memory; reconstruction of real time events can thus be created in the areas of neocortex where consciousness resides. Alzheimer's disease may have a toxic, genetic or infectious origin; electron microscopic evidence is presented for the possible presence of viral particles of the double stranded DNA type in Alzheimer's brain tissue.

Basal forebrain neurons projecting to the rat frontoparietal cortex: electrophysiological and pharmacological properties

Neurons located in the ventromedial globus pallidus (nucleus basalis) and substantia innominata, that were antidromically driven by electrical stimulation of the frontoparietal cortex, were recorded in the urethane anesthetized rat. The basalocortical neurons (BCNs) were antidromically driven with latencies of 1.1-13.5 ms, giving conduction velocities of 0.6-6.8 m/s. Many BCNs had regular patterns of spontaneous discharge (mean spontaneous activity: 20 impulses/s). Most BCNs were not responsive to non-noxious peripheral somatic stimulation. BCNs were readily excited by the iontophoretic application of glutamate and strongly inhibited by GABA. Eighty-five percent of the BCNs could be excited by acetylcholine. They could also be excited by cholinergic agonists. Muscarinic agonists excited a higher proportion of BCNs than nicotinic agonists. Excitatory responses to acetylcholine, carbachol and muscarinic agonists were abolished by atropine.

Galanin-like immunoreactivity in cholinergic neurons of the septum-basal forebrain complex projecting to the hippocampus of the rat

It is now well recognized that there are several groups of cholinergic neurons in the basal forebrain with direct projections to various cortical regions. Immunohistochemical investigations of the distribution of the neuropeptide galanin (GAL) have shown that two of these brain areas, the medial septum and diagonal band, contained large numbers of GAL-immunoreactive neurons. In the present study, double staining techniques using antibodies raised against choline acetyltransferase (ChAT) revealed that GAL- and ChAT-like immunoreactivities are colocalized within a subpopulation of the cholinergic neurons within the medial septum and diagonal band. This colocalization of GAL- and ChAT-immunoreactivities was not seen to occur within other groups of forebrain cholinergic neurons. Immunohistochemistry carried out subsequent to injections of fluorescent retrograde tracers into the hippocampal formation revealed that both ChAT/GAL- and ChAT-containing neurons project to the hippocampal formation. The question of GAL as a modulator of cholinergic transmission in this projection is discussed.

Distribution of cholinergic muscarinic binding sites in guinea-pig brain as determined by in vitro autoradiography of [3H]N-methyl scopolamine binding

The distribution of muscarinic binding sites was analyzed in regions of the guinea-pig brain with semi-quantitative densitometry of [3H]N-methyl scopolamine binding, a muscarinic antagonist. In the rostral forebrain, high levels of binding were detected in the caudate putamen, nucleus accumbens and olfactory tubercle while intermediate levels of binding were observed in the medial and lateral septum, bed nucleus, and vertical and horizontal limbs of the diagonal band. The hypothalamus displayed binding that ranged from low levels in the preoptic area to intermediate levels in the mammillary nucleus. In limbic areas such as the thalamus, amygdala and hippocampus, a heterogeneous pattern of binding was evident in various subregions which tended to correspond with known innervation by cholinergic afferents. In the midbrain, binding was high in the superficial layer of the superior colliculus and the medial geniculate while intermediate binding was recorded in the lateral geniculate and the lateral aspect of the central gray. The pattern of muscarinic binding observed in the brain of the guinea-pig is similar to distributions of this binding site previously reported in the rat brain and the human brain.

Stability of numbers but not size of mouse forebrain cholinergic neurons to 53 months

In normal mammalian aging there is a reduction of cholinergic markers in a variety of regions. To determine whether this reduction is related to reduced numbers of basal forebrain cholinergic neurons, we counted the number and measured the sizes of the magnocellular acetylcholinesterase-positive neurons in this region of 7, 15, and 53-month-old C57Bl/6NNIA mice. Data were collected from coded slides containing the medial septum, nucleus of the diagonal band, magnocellular preoptic nucleus, and nucleus basalis magnocellularis. There was no decline in numbers of basal forebrain acetylcholinesterase-positive neurons in any of the regions studied. However, cell sizes showed a progressive age-related decline which was greatest in the nucleus basalis magnocellularis.

The efferent projections from the reticular formation and the locus coeruleus studied by anterograde and retrograde axonal transport in the rat

Following injections of [3H]leucine into the formatio reticularis gigantocellularis (Rgc), reticularis pontis caudalis (Rpc), reticularis pontis oralis (Rpo), reticularis mesencephali (Rmes), or the locus coeruleus (LC) of the rat, autoradiographic study revealed prominent reticuloreticular projections from all areas and secondary projections onto cranial nerve motor nuclei from most areas within the brain stem. Common long descending projections extended the full length of the spinal cord terminating in the ventromedial ventral horn and intermediate zone and more sparsely in the base of the dorsal horn and (particularly from Rgc) the region of the motoneurons. Common long ascending projections extended into the forebrain via Forel's tegmental fascicles. A dorsal branch of fibers innervated the intralaminar and midline nuclei of the thalamus. The major fiber system continued forward through Forel's fields and ascended into the pallidum from Rpo, Rmes, and LC and into the neostriatum from Rmes and LC. Fascicles from all areas also ascended in the medial forebrain bundle through the lateral hypothalamus to the lateral preoptic area, substantia innominata, and nuclei of the diagonal band. From Rpo, Rmes, and LC, fibers continued forward to reach the cerebral cortex, where the innervation was sparse and discrete from Rpo and Rmes but moderate and ubiquitous from LC. Retrograde transport of true blue and/or nuclear yellow revealed inverse gradients along the brain stem longitudinal axis of interdigitated cells respectively projecting caudally into the spinal cord (with the greatest number of cells in Rgc, Rpc, and Rpo) and rostrally into the diencephalon (with the greatest number of cells in Rmes and LC), with very few cells projecting both to the spinal cord and the diencephalon. From the basal forebrain, a large number of reticular and LC cells were retrogradely labelled, whereas from the frontal cortex, a much smaller number of reticular cells was labelled. These results document the widespread efferent projections from the reticular formation and overlapping, yet more extensive, projections from the LC.

Memory impairments following basal forebrain lesions

The functional contribution of the nucleus basalis magnocellularis (NBM) and medial septal area (MSA) to memory was evaluated in 4 behavioral tasks. The tasks were postoperative acquisition of a win-stay spatial discrimination in a T-maze, a win-shift spatial discrimination on a radial arm maze, active avoidance in a shuttle box, and passive avoidance in a shuttle box. Bilateral lesions were made by injecting ibotenic acid (IBO) into the NBM or MSA. Control rats received operations in which no neurotoxin was injected. When compared to controls, rats with lesions in either the NBM or MSA had significantly impaired choice accuracy in the T-maze and radial maze tasks, took significantly fewer trials to reach criterion in the acquisition, but not the retention of an active avoidance task, and significantly more trials to reach criterion in the passive avoidance task. The results show that equivalent behavioral changes are obtained from lesions in the NBM and MSA in tasks that vary in their type of motivation, reinforcement, response-reinforcement contingency, and response. These behavioral changes suggest that the NBM and MSA may both be involved in memory.

Basal forebrain lesions produce a dissociation of trial-dependent and trial-independent memory performance

The behavioral effects of lesions in the basal forebrain (BF) of rats were evaluated using two tasks. The BF lesions included both the nucleus basalis magnocellularis (NBM) and the medial septal area (MSA). The first task was a Stone maze, which has 14 consecutive choice points and is a task of complex, trial-independent memory. BF lesions did not impair choice accuracy in this task. The second task was a win-shift spatial discrimination in a radial arm maze, which requires trial-dependent memory. BF lesions produced a significant decrease in choice accuracy in this task. These results demonstrate that BF lesions impair trial-dependent (working) memory but not trial-independent reference memory, and that task difficulty is not the sole factor determining whether BF lesions produce behavioral impairments.

Effect of unilateral decortication on choline acetyltransferase activity in the nucleus basalis and other areas of the rat brain

Acetyl-coenzyme A: choline O-acetyltransferase (EC 2.3.1.6) (ChAT) enzyme activity was measured in the nucleus basalis and other microscopically identified brain areas at various times after unilateral cortical lesions were made in the rat. Initially, a significant decrease in ChAT activity was detected in the nucleus basalis ipsilateral to the lesion. However, after 120 days ChAT activity had apparently recovered, as levels of the enzyme at that time were not significantly different from control values. No changes in ChAT activity could be detected in any of the other brain areas similarly studied. The significance of these findings and their relationship to the morphological changes seen in neurones of the nucleus basalis after cortical lesions are discussed.

A photographic perspective on the origins, form, course and relations of the acetylcholinesterase-containing fibres of the dorsal tegmental pathway in the rat brain

The dorsal tegmental pathway in the rat brain has been studied using acetylcholinesterase (AChe) staining alone, after lesions, and combined with the horseradish-peroxidase (HRP) tracing method. This paper characterises in photographs, diagrams and text the origins, form, extent and relations of its visible AChe-staining fibres in 3 planes. This record should provide a template for further investigations. The pathway largely takes origin from ChAT-containing pedunculopontine (PPTg) and laterodorsal (LDT) nuclei; some non-cholinergic cell groups may also contribute, notably locus coeruleus (LC). It takes the form of a horizontally disposed fan which radiates from the pontomesencephalic area to the forebrain. Its lateral portion is bunched and consists mainly of cholinergic fibres whereas the cholinergic status of its fully unfurled intermediate and partly unfurled medial contingents (which mainly accompany the central tegmental tract) is more doubtful. The changing form and relations of PPTg and LDT are adumbrated including that of the microcellular nucleus (MI) to the former and of Barrington's detrusor nucleus (B) which is unstained, to the latter. Functional overlapping between non-cholinergic and cholinergic nuclei in the peribrachial region are noted and some correlations adduced.

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.

Disruption of central cholinergic systems in the rat by basal forebrain lesions or atropine: effects on feeding, sensorimotor behaviour, locomotor activity and spatial navigation

Rats with ibotenic acid lesions of the nucleus basalis magnocellularis, the origin of the extrinsic cholinergic innervation of the cortex, were examined for changes in feeding, sensorimotor behaviour, nocturnal locomotor activity, and place navigation in the Morris swimming pool task, in comparison with control rats and rats receiving the muscarinic antagonist, atropine. The lesions produced acute feeding impairments, marked by weight loss and vigorous active rejection of food and water lasting 2-4 days, sensorimotor impairments in placing and orienting, and overnight hyperactivity. A similar hyperactivity was induced by atropine, lasting approximately 6 h following the injection. Rats with lesions or receiving atropine were similarly impaired in the acquisition of the spatial navigation task, they failed to reach control levels of efficiency even once they had acquired the task, and they showed small but significant retention impairments when pretrained in the absence of either treatment. The results are discussed in terms of the lesions producing a disruption of cortical cholinergic systems, with implications for the clinical disorder of senile dementia of the Alzheimer type, and in terms of possible associated disruption to non-cholinergic systems.

The cytoarchitecture, histochemistry and projections of the tuberomammillary nucleus in the rat

The normal morphology, efferent projections and possible neurotransmitter content of neurons in the tuberomammillary nucleus (caudal magnocellular nuclei of Bleier et al.) [Bleier, Cohn and Siggelkow (1979) In Anatomy of the Hypothalamus, Vol. 1, pp. 137-220] have been examined in the adult male rat. In Nissl-stained sections, the nucleus can be divided into a dorsomedial, ventral and diffuse part, each of which consists of large, darkly stained neurons cradling the mammillary body. The ventral part is by far the largest and consists of some 2500 neurons on each side of the brain. Immunohistochemical studies indicate that a majority of the large neurons in all three parts of the nucleus stain with antisera against glutamate decarboxylase and [Met]enkephalyl-Arg6-Phe7 heptapeptide and that a smaller subset of these neurons (about 10%) also stain with an antiserum against substance P. Single injections of retrogradely transported fluorescent tracers were made into 18 different sites in 86 animals and the results indicate that all three parts of the tuberomammillary nucleus on one side of the brain send fibers to or through various parts of the neocortex, hippocampal formation, amygdala, basal ganglia, thalamus, superior colliculus and cerebellum on both sides of the brain and that the projection neurons are not organized in a highly topographic way. Injections of two different fluorescent tracers in the same animal indicate that individual neurons in the nucleus may give rise to both ascending and descending projections, as well as projections to widely divergent parts of the forebrain. Together with previous results, this evidence suggests that the tuberomammillary nucleus has widespread projections to the numerous brain structure located in the forebrain and in the caudal medulla (it may not project to the spinal cord), and that its axons may release a mixture of neuroactive substances including gamma-amino butyrate and several peptides. Although its functional significance remains to be investigated, morphological evidence suggests that the tuberomammillary nucleus may constitute one of a series of neurotransmitter-specific cell groups in the brainstem and basal forebrain with diffuse efferent projections that may be involved in the modulation of attention or behavioral state, rather than the processing of specific sensory or motor information.

Immunocytochemical localization of choline acetyltransferase within the rat neostriatum: a correlated light and electron microscopic study of cholinergic neurons and synapses

Monoclonal antibodies to choline acetyltransferase (ChAT) were used in an immunocytochemical study to characterize putative cholinergic neurons and synaptic junctions in rat caudate-putamen. Light microscopy (LM) revealed that ChAT-positive neurons are distributed throughout the striatum. These cells have large oval or multipolar somata, and exhibit three to four primary dendrites that branch and extend long distances. Quantitative analysis of counterstained preparations indicated that ChAT-positive neurons constitute 1.7% of the total neuronal population. Electron microscopy (EM) of immunoreactive neurons initially studied by LM revealed somata characterized by deeply invaginated nuclei and by abundant amounts of organelle-rich cytoplasm. Surfaces of ChAT-positive neurons are frequently smooth, but occasional somatic protrusions and dendritic spines occur. Although infrequently observed, axons of ChAT-positive neurons branch, receive synapses, and become myelinated. Unlabeled boutons make both symmetrical and asymmetrical synapses with ChAT-positive somata and proximal dendrites, but are more numerous on distal dendrites. In addition, some unlabeled terminals form asymmetrical synapses with ChAT-positive somata and dendrites that are distinguished by prominent subsynaptic dense bodies. Light microscopy demonstrated a dense distribution of ChAT-positive fibers and punctate structures in the striatum, and these structures appear to correlate, respectively, with labeled preterminal axons and presynaptic boutons identified by EM. ChAT-positive boutons contain pleomorphic vesicles, and make symmetrical synapses primarily with unlabeled dendritic shafts. Furthermore, they establish synaptic contacts with somata, dendrites and axon initial segments of unlabeled neurons that ultrastructurally resemble medium spiny neurons. These observations, together with the results of other investigations, suggest that medium spiny GABAergic projection neurons receive a cholinergic innervation that is probably derived from ChAT-positive striatal cells. The results of this study also indicate that cholinergic neurons within caudate-putamen belong to a single population of cells that have large somata and extensive sparsely spined dendrites. Such neurons, in combination with dense concentrations of ChAT-positive fibers and terminals, are the likely basis for the large amounts of ChAT and acetylcholine detected biochemically within the neostriatum.

Septohippocampal neurons in the rat: an in vivo intracellular study

In vivo intracellular recordings were obtained from septohippocampal neurons identified by their antidromic response to electrical stimulation of the fimbria in rats anesthetized with pentobarbital or urethane. Beside the antidromic response, fimbria stimulation evoked a short-latency depolarizing potential (EPSP) followed by an hyperpolarizing potential which reversed polarity when recorded with KCl-filled electrodes. This IPSP is therefore likely to be chloride-dependent. It was followed by a long-lasting (80-250 ms) depolarizing potential often associated with a burst of spikes. Septohippocampal neurons therefore receive an inhibitory, chloride-mediated, input which itself triggers a long-lasting excitatory event. These results are consistent with extracellular observations. Their significance in the septohippocampal circuitry is discussed.

Degeneration of cholinergic neurons in the basal nucleus following kainic or N-methyl-D-aspartic acid application to the cerebral cortex in the rat

The effect on cholinergic neurons in the basal nucleus of exposing the cortex to excitotoxic amino acids was examined in the rat. Kainic or N-methyl-D-aspartic acid were applied extradurally over the cerebral cortex of one side. This resulted in a severe depletion in the numbers of neurons in the underlying cortex. The immunohistochemically identified cholinergic neurons of the ipsilateral basal nucleus showed a significant shrinkage, -31% of their mean cell area, which was comparable with the retrograde degeneration seen following direct mechanical damage of the cortex. These findings suggest that cholinergic neurons of the basal nucleus can undergo transneuronal retrograde degeneration.

Profound disturbances of spontaneous and learned behaviors following lesions of the nucleus basalis magnocellularis in the rat

It has been shown that a marked decline in the cortical activity of the cholinergic synthesizing enzyme choline-acetyltransferase (ChAT), accompanied by a severe neuronal loss in the nucleus basalis magnocellularis of Meynert occurs in the brains of patients with senile dementia of the Alzheimer type. However, the functional role of these neurons is largely unknown. In fact, very few studies have been done in animals. In this paper we report the behavioral effects of the lesion of the nucleus basalis magnocellularis in the rat either by radiofrequency current or by ibotenic acid injection at the level of the cell bodies. The two kinds of lesion lead to a profound disturbance of spontaneous and learned behaviors. There is a complete disorganization of behavior which is evidenced by an enhanced locomotor activity, an alteration in alimentary and hoarding behavior. In addition, we observed a deterioration of spatial memory and an incapacity to reverse a previously learned response. Biochemical assay showed that radiofrequency and ibotenic acid lesions produced a decrease of ChAT activity in the prefrontal and sensorimotor cortices and in amygdala without affecting the hippocampus or striatum. Ibotenic acid lesions seem to specifically destroy the cell bodies of the nucleus basalis magnocellularis since the dopaminergic and noradrenergic fibers of passage remained intact as measured by the unchanged level of endogenous catecholamine concentration in the terminal region in the prefrontal cortex. Presently, it cannot be said that the behavioral syndrome results solely from the lesion of the cholinergic neurons. Also, it is likely that the lesion of the nucleus basalis magnocellularis in the rat does not exactly reproduce the behavioral syndrome observed in Alzheimer's disease in man. However, this experimental approach in leading to a better knowledge of the functioning of these neurones could improve our understanding of this disease.

Hypertrophy of cholinergic neurones of the rat basal nucleus following section of the corpus callosum

The effect of division of the corpus callosum on immunohistochemically identified cholinergic neurones of the basal nucleus has been examined in rats. Following callosal section the cholinergic cell bodies on both sides are significantly larger (25%) than those in normal animals. This hypertrophy persists for at least 62 days after operation, the longest survival time examined. It is greatest when the animal is operated on in infancy, but it occurs at all ages examined. The enlargement is similar to that seen in the cells of the same nucleus on one side following contralateral cortical damage.

Organization of cerebral cortical afferent systems in the rat. II. Hypothalamocortical projections

The organization of hypothalamic projections to the cerebral cortex in the rat has been studied using retrograde and anterograde tracer methods. Four separate populations of hypothalamic neurons, which constitute a major source of diffuse cortical innervation, were identified: Tuberal lateral hypothalamic (LHAt) neurons which innervate the cerebral cortex tend to cluster in the perifornical region, in the zona incerta, and along the medial edge of the cerebral peduncle, at levels roughly coextensive with the ventromedial hypothalamic nucleus. Most of these neurons project to the ipsilateral cortex; a small percentage innervate the contralateral cortex, but this varies among cortical terminal fields. The perifornical neurons are organized in a roughly topographic medial-to-lateral relationship with respect to their cortical terminal fields. Field of Forel (FF) neurons, which project primarily to the frontal cortex of the ipsilateral hemisphere, are located just ventral to the medial edge of the medial lemniscus, at the level of the ventromedial basal thalamic nucleus. The more laterally placed neurons innervate the lateral frontal, insular and perirhinal cortex; the more medial neurons, around the mammillothalamic tract, innervate the medial frontopolar, prelimbic, infralimbic, and anterior cingulate cortex. Posterior lateral hypothalamic (LHAp) neurons form a dense cluster spanning the lateral hypothalamus, from the cerebral peduncle to the posterior hypothalamic area at premammillary levels, and extending into the supramammillary nucleus and the adjacent ventral tegmental area. LHAp neurons innervate the entire cerebral cortex, predominantly on the ipsilateral side. Populations of LHAp neurons projecting to different cortical target areas show considerable spatial overlap, but computer plots of the centers of these populations demonstrate a strict topographic relationship with respect to the cerebral cortex. Tuberomammillary (TMN) neurons form a sheet along the ventrolateral surface of the premammillary hypothalamus. About twice as many TMN neurons innervate the ipsilateral, as compared to the contralateral hemisphere; it is not known whether single neurons project to both hemispheres. No topographic organization of the TMN cortical projection is apparent. Injections of different-colored fluorescent dyes into various cortical areas demonstrate that hypothalamic neurons in general have rather restricted cortical terminal fields. Only occasional neurons are found, primarily in LHAt, which are double labeled by injections into different cytoarchitectonic areas.(ABSTRACT TRUNCATED AT 400 WORDS)

Basal forebrain innervation of rodent neocortex: studies using acetylcholinesterase histochemistry, Golgi and lesion strategies

Acetylcholinesterase (AChE)-rich projections from basal forebrain to neocortex cerebri were characterized in the present study. The purpose was to investigate 3 aspects of these projections in rats and mice that have been incompletely described in previous work: intracortical organization of the fibers, subcortical pathways and axonal branching patterns of individual basal forebrain neurons. AChE histochemistry, lesions and Golgi impregnations were the principal strategies employed in this light microscopic study. The moderately dense, AChE-stained innervation of neocortex can be altered by intracortical lesions. The results depended on the region involved and the orientation of the lesion. Sagittal knife cuts had barely detectable effects, regardless of sites. Coronal knife cut lesions in medial cortex resulted in substantial loss of staining in cingulate and medial occipital fields. In contrast, coronal lesions of lateral or anterior cortex produce only small zonal reductions in staining. The interpretation of the latter findings that we favor is that AChE-rich basal forebrain fibers enter lateral/anterior cortex and branch densely there, but in tangentially limited and overlapping terminal domains. Observations on the topography and targets of AChE-rich basal forebrain cortical afferents revealed that the fibers could be grouped based on certain characteristics. Three sets of fibers were distinguishable: anterior pathway innervating cortex of the frontal pole. These fibers were traceable to the region of the substantia innominata/nucleus basalis. They crossed the neostriatum and external capsule in the sagittal plane, forming in 3 dimensions an orderly sheet-like array of fibers bridging the anteroventral surface of the neostriatum with nearby polar cortex medial pathway innervating cingulate and medial occipital cortex. Emerging predominantly from the region of the diagonal band, the fibers run caudally as a triangular bundle in deep layer VI of cingulate cortex. lateral pathway innervating most of remaining lateral neocortex. The fibers radiate out from substantia innominata/nucleus basalis with a complex 3-dimensional organization. In all pathways, fibers enter and initially run within layer VI before ascending pialward, although the intracortical course in layer VI differs between pathways. These fibers primarily terminate in layer V with a secondary concentration in layer I. However, the latter appears to receive substantial AChE-stained inputs from other sources, possibly intracortical, as well. The pathways overlap at their respective boundary zones. This system is comparably organized in rats and mice.(ABSTRACT TRUNCATED AT 400 WORDS)

Distribution of central cholinergic neurons in the baboon (Papio papio). I. General morphology

The morphological characteristics of cholinergic neurons in the central nervous system (CNS) of the baboon (Papio papio) were studied by choline acetyltransferase (ChAT) immunohistochemistry and acetylcholinesterase (AChE) pharmacohistochemistry. The distributions of central cholinergic neurons as visualized by these two histochemical techniques were similar in most, but not all regions of the brain and spinal cord. Based upon these observations, central cholinergic neurons that are immunoreactive to ChAT and intensely stained for AChE by the pharmacohistochemical procedure can be divided into four major groups: (1) those in the caudate nucleus, putamen, nucleus accumbens and anterior perforated substance. These ChAT-containing and AChE-intense neurons are large and multipolar, and are scattered throughout these structures. (2) The rostral cholinergic column, which consists of a continuous mass of cholinergic perikarya situated in the medial septal nucleus, nucleus of the diagonal band, and nucleus basalis (Meynert). The ChAT-immunoreactive and AChE-intense cell bodies of the nucleus basalis are a prominent feature in the basal forebrain of the baboon. The labeled neurons are large, multipolar, and hyperchromic and show a tendency to aggregate in cell clusters. These cells are distributed within the full extent of the substantia innominata, often being associated with subcortical fiber networks such as the medullary laminae of the globus pallidus. (3) The caudal cholinergic column, which consists of a continuous group of cholinergic neurons in the caudal midbrain and pontine tegmentum. The rostral component of this group of cells is the nucleus tegmenti pedunculopontinus (subnucleus compacta) and it extends caudally to include the laterodorsal tegmental nucleus. Compared to that in other species the nucleus tegmenti pedunculopontinus in the baboon appears to occupy a relatively greater volume and is composed of a greater number of cholinergic neurons. The cells of the caudal column are large and hyperchromic. (4) Nuclei of origin of somatic and visceral efferents of the cranial nerves (III, IV, V, VI, VII, IX, X, XI, XII) and spinal nerves. In addition to these major cholinergic cell groups, a small population of ChAT-positive and AChE-intense cell bodies can be observed at the floor of the fourth ventricle and in lamina VII and X of the cervical cord. The present findings indicate that although some differences exist, the overall distribution and morphological features of cholinergic cell bodies identified in the baboon brain and spinal cord are similar to those demonstrated previously in investigations of the rhesus monkey and nonprimates.

Anti-acetylcholine antibodies and first immunocytochemical application in insect brain

A specific immunological approach was developed to enable acetylcholine (ACh) to be visualized in biological tissues. A variety of ACh-like immunogens were synthesized, and injected into rabbits. Antibody specificity was tested using an enzyme-linked immunosorbent assay (ELISA) method. The most immunoreactive ACh derivative was found to be choline-glutaryl-lysine. A mixture of allyl alcohol and formaldehyde was found to be the best fixative of ACh in tissues. The specificity of this antibody recognition was tested in vitro and in immunochemistry. There was excellent agreement between the in vitro results and the ACh staining. Moreover, visualization using these anti-ACh antibodies appeared identical to the results using anti-choline acetyltransferase antibodies.

Evidence for the presence of cholinergic nerves in cerebral arteries: an immunohistochemical demonstration of choline acetyltransferase

The presence of cholinergic nerves in cerebral arteries of several species was investigated by an immunohistochemical method using antibodies against choline acetyltransferase (ChAT). In cats, pigs, rats, and dogs, ChAT immunoreactivities were found to be associated with large bundles and single fibers in the circle of Willis and anterior cerebral, middle cerebral, and basilar arteries. In the rabbit, the ChAT-immunoreactive (ChAT-I) nerves were also observed in the circle of Willis and anterior and middle cerebral arteries, but only few or none were found in the basilar and vertebral arteries. The ChAT-I nerves were found only in the adventitial layer of vessels examined. Superior cervical ganglionectomy did not appreciably affect the distribution of ChAT-I nerves. These results indicate the presence of cholinergic nerves in cerebral arteries. The distribution pattern of ChAT-I nerves was different from that of vasoactive intestinal polypeptide (VIP)-like-immunoreactive nerves and acetylcholinesterase-positive nerves. The possible coexistence of ChAT and VIP-like substance in the same neuron is discussed.

Extra-hypothalamic afferent inputs to the supraoptic nucleus area of the rat as determined by retrograde and anterograde tracing techniques

To detect neuronal cell bodies whose axon projects to the hypothalamic supraoptic nucleus, small volumes (10-50 nl) of 30% horseradish peroxidase or 2% fast blue solutions were pressure-injected into the area of one supraoptic nucleus of rats. Both dorsal and ventral approaches to the nucleus were used. In animals where the injection site extended beyond the limits of the supraoptic nucleus, retrogradely labelled cell bodies were found in many areas of the brain, mainly in the septum, the nucleus of the diagonal band of Broca and ventral subiculum in the limbic system; the dorsal raphe nucleus, the locus coeruleus, the nucleus of the dorsal tegmentum, the dorsal parabrachial nucleus, the nucleus of the solitary tract and the catecholaminergic A1 region in the brain stem; in the subfornical organ and the organum vasculosum of the lamina terminalis, as well as in the median preoptic nucleus. In contrast, when the site of injection was apparently restricted to the supraoptic nucleus, labelling was only clearcut in the two circumventricular organs, the median preoptic nucleus, the nucleus of the solitary tract and the A1 region. Injections of wheat germ agglutinin coupled with horseradish peroxidase (60-80 nl of a 2.5% solution) made in the septum and in the ventral subiculum anterogradely labelled fibers coursing in an area immediately adjacent to the supraoptic nucleus but not within it. In contrast, labelling within the nucleus was found following anterograde transport of tracer deposited in the A1 region and in an area that includes the nucleus of the solitary tract. Neurones located in the perinuclear area were densely labelled by small injections into the supraoptic nucleus; they may represent a relay station for some afferent inputs to the supraoptic nucleus. These results suggest that the supraoptic nucleus is influenced by the same brain areas which project to its companion within the magnocellular system, the paraventricular nucleus.

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.

Cholinergic and non-cholinergic forebrain projections to the interpeduncular nucleus

A combined fluorescent retrograde tracing and acetylcholinesterase (AChE) histochemical technique was used for the study of some forebrain projections to the interpeduncular nucleus (IPN). After injections of a fluorescent tracer into the IPN, the distribution of AChE-containing and of fluorescent retrogradely labeled neurons was simultaneously studied in the habenular nuclei, medial septum and diagonal band of Broca. In all these regions, the majority of retrogradely labeled neurons also contained AChE: neurons located in the habenular nuclei stained lightly or moderately for the enzyme, while neurons located in the diagonal band and medial septum displayed intense AChE staining and were classified as putatively cholinergic perikarya. In all regions, a minority of labeled neurons did not stain for AChE, and were identified as non-cholinergic neurons projecting to the IPN. The present study shows the existence of a biochemical heterogeneity in the habenulo-interpeduncular and telencephalo-interpeduncular pathways, and indicates that the latter contains putatively cholinergic as well as non-cholinergic fibers.

Cholinergic projections from the midbrain and pons to the thalamus in the rat, identified by combined retrograde tracing and choline acetyltransferase immunohistochemistry

The distribution of cholinergic neurons in the midbrain and pons which project directly to the thalamus was investigated in the rat using a procedure which allows the simultaneous detection of retrogradely transported horseradish peroxidase (HRP) and immunohistochemical demonstration of choline acetyltransferase (ChAT) in the same neurons. HRP injections were placed in the dorsal half of the anterior third of the thalamus on one side which included the anteroventral nucleus as well as portions of the rostral intralaminar and reticular nuclei. These thalamic nuclei showed the highest density of immunohistochemically detectable cholinergic fibers. Neurons containing both HRP and ChAT, which represented cholinergic neurons projecting directly to the thalamus, were found in the midbrain and pons in the lateral tegmental reticular formation, parabrachial region and lateral dorsal tegmental nucleus. Ipsilateral to the injection site over 91% of the HRP labeled neurons in all of these regions were cholinergic, while an average of 60% of the cholinergic neurons had transported HRP. Contralateral to the injection site 5-6% of the cholinergic neurons in these regions were also retrogradely labeled. These findings demonstrate direct cholinergic projections to the thalamus from neurons in several regions in the tegmentum and suggest that tegmental projections to the thalamus are predominantly cholinergic.

Cholinergic and non-cholinergic septohippocampal pathways

Cholinergic innervation of the hippocampus was examined in the rat by immunocytochemical localization of choline acetyltransferase immunoreactivity combined with retrograde transport of horseradish peroxidase-conjugated wheatgerm agglutinin. It was found that at least 50% of hippocampal afferents arising in the septal-diagonal band region consisted of non-cholinergic projection neurons. In addition, scattered choline acetyltransferase-immunoreactive neurons were localized to the hippocampal formation. These results indicate that: (1) the septohippocampal pathway is neither uniformly nor predominantly cholinergic; and (2) confirm that cholinergic innervation of the hippocampal formation of the rat is derived in part from intrinsic neurons.

Simultaneous ultrastructural demonstration of retrogradely transported horseradish peroxidase and choline acetyltransferase immunoreactivity

In order to study the synaptic connections of neurons identified by their projection target and neurotransmitter content, we have adapted a method of combining retrograde tracing of horseradish peroxidase (HRP) and immunocytochemistry at the electron microscopic level. HRP was injected into the rat amygdala. Sections from the rostral forebrain were processed according to the 3,3'-diaminobenzidine/glucose oxidase reaction followed by choline acetyltransferase (ChAT) localization. Neurons in the ventral pallidum which contained both the diffuse immunoperoxidase reaction product (ChAT) and large electron dense bodies characteristic of retrogradely transported HRP were defined as double labeled, i.e. cholinergic neurons that project to the amygdaloid body.

Nerve growth factor increases choline acetyltransferase but not survival or fiber outgrowth of cultured fetal septal cholinergic neurons

Neurons dissociated from the septal area of fetal rat brains were grown in culture. Cholinergic neurons were identified by immunocytochemical visualization of choline acetyltransferase and cytochemical demonstration of acetyl cholinesterase. Choline acetyltransferase immunocytochemistry stained cell bodies and proximal processes while acetylcholinesterase cytochemistry visualized the entire neuron. Choline acetyltransferase-positive neurons could only be identified in cultures grown under conditions that produced the maximal choline acetyltransferase activity, measured biochemically. All of the choline acetyltransferase-positive neurons were double stained for acetylcholinesterase while only 6% of the acetylcholinesterase-positive cells were choline acetyltransferase negative in these cultures. These results indicate that acetylcholinesterase is a reliable marker for cholinergic cells in cultures of dissociated septal neurons. Being the more sensitive method, acetylcholinesterase staining was therefore used to identify cholinergic cells in cultures with choline acetyltransferase levels insufficient for immunocytochemical visualization of this enzyme. Addition of nerve growth factor or antibodies to nerve growth factor to the medium did not affect the number of cholinergic neurons surviving in culture. Furthermore, nerve growth factor and anti-nerve growth factor failed to influence the general morphological appearance and the number of processes of these neurons. However, nerve growth factor elevated the biochemically measured activity of choline acetyltransferase up to two-fold. The nerve growth factor-mediated increase in choline acetyltransferase activity was dose dependent with an ED50 of 10 ng/ml (4 X 10(-10) M). The increase was highly specific for nerve growth factor. It was blocked by anti-nerve growth factor, and epidermal growth factor, insulin and other control proteins failed to exert a similar effect. Nerve growth factor had to be present for at least 3 days in the culture medium to increase choline acetyltransferase activity, suggesting that the increase was due to an elevated choline acetyltransferase synthesis rather than to an activation of the enzyme.

Cholinergic systems in the rat brain: II. Projections to the interpeduncular nucleus

The cholinergic innervation of the interpeduncular nucleus was investigated by use of fluorescent tracer histology in combination with choline-O-acetyltransferase (ChAT) immunohistochemistry and acetylcholinesterase (AChE) pharmacohistochemistry. Following propidium iodide or Evans Blue infusion into the interpeduncular nucleus, brains were processed for co-localization of transported fluorescent label and ChAT and AChE. Control infusions of tracers were made into the ventral tegmental area. In order to delimit the course of putative cholinergic afferents to the interpeduncular nucleus from extra-habenular sources, knife cuts surrounding the habenular nuclei were performed. Somata containing propidium iodide that were highly immunoreactive for ChAT were found primarily in the vertical and horizontal limbs of the diagonal band, the magnocellular preoptic area, and the dorsolateral tegmental nucleus, also referred to as the laterodorsal tegmental nucleus. A few such co-labeled somata were also detected in the medial septal nucleus, substantia innominata, nucleus basalis, and pedunculopontine tegmental nucleus. A good correlation was observed between intensely-staining, AChE-containing and ChAT-positive neurons projecting to the interpeduncular nucleus from the aforementioned structures. Although the medial habenula contained numerous cells demonstrating transported label following interpeduncular infusion of fluorescent tracers, the ChAT-positivity associated with somata in that nucleus was weak compared to ChAT-like immunoreactivity in known cholinergic neurons in the basal forebrain and brainstem. Knife cuts that separated the habenular nuclei from the stria medullaris and neural regions lateral and posterior to those nuclei while leaving the fasciculus retroflexus intact resulted in a reduction of ChAT-like immunoreactivity in the medial habenular nucleus, fasciculus retroflexus, and interpeduncular nucleus. These data suggest (1) that the cholinergic innervation of the interpeduncular nucleus derives primarily from ChAT-positive cells in the basal forebrain and dorsolateral tegmental nucleus and (2) that putative cholinergic fibers having their origin in the medial habenula, if they exist, constitute a minor portion of the cholinergic input to the interpeduncular nucleus.

Ultrastructural evidence of amygdalofugal axons terminating on cholinergic cells of the rostral forebrain

In the present study a double-label ultrastructural procedure was used to study amygdalofugal fibers contacting cholinergic cells of the rostral forebrain. Following horseradish peroxidase (HRP) injections into the basolateral amygdala, anterogradely transported HRP was detected in axon terminals contacting the dendrites of choline acetyltransferase-containing cells in the ventral pallidum.

Choline acetyltransferase-like immunoreactivity in the forebrain of the red-eared pond turtle (Pseudemys scripta elegans)

Choline acetyltransferase (ChAT) immunohistochemistry was used to map the cholinergic neurons in the forebrain of Pseudemys turtles. Cell bodies with ChAT-like immunoreactivity were seen in the septum, the nucleus of the diagonal band, and embedded within the medial and lateral forebrain bundles. The region of the medial and lateral forebrain bundles contained the greatest concentration of ChAT-positive neurons. Virtually no ChAT-like immunoreactivity was seen in the areas composing the reptilian homologue of the mammalian striatum. It is suggested that the turtle basal forebrain cholinergic neurons may represent the evolutionary precursors to the mammalian cholinergic neurons of the basal forebrain and even the striatum.

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)

Regional heterogeneity of choline acetyltransferase activity in primate neocortex

Choline acetyltransferase activity in precentral and temporal regions of primate neocortex is 2.5-fold higher than in occipital cortex. These results suggest large differences in the density of innervation in different regions of primate neocortex by the nucleus basalis of Meynert.

Cholinergic stimulation of vasopressin release in spontaneously hypertensive rats

Plasma vasopressin (VP) concentration is elevated in spontaneously hypertensive rats (SHRs) relative to their normotensive Wistar-Kyoto (WKY) controls. The possibility that this reflects altered responsiveness of the hypothalamo-neurohypophyseal system (HNS) in SHRs was examined by comparing VP release in response to acetylcholine from organ cultured HNS explants obtained from SHR and WKY donors. Explants were prepared from 5-, 8-, and 18-week-old animals. Blood pressure was significantly elevated in the 8- and 18-week-old SHR donors relative to their age-matched WKY donors. VP release was assessed on the 4th day of culture during a control hour and during the subsequent hour in the presence of acetylcholine. Acetylcholine caused a concentration-dependent stimulation of VP release from both types of explants, but the response was significantly greater in the explants from 5- and 8-week-old SHRs than in explants from age-matched WKYs. The explants from 18-week-old SHRs and WKYs demonstrated comparable sensitivity to acetylcholine. Basal VP release was not significantly different in explants from age-matched SHRs and WKYs, but it did increase with donor age in both strains. These studies indicate potential hyperresponsiveness of the HNS to excitatory stimuli in SHRs during the developmental phase of hypertension. The hyperresponsiveness disappears in the chronically hypertensive phase. Thus, increased sensitivity of the HNS during the development of hypertension may contribute to the elevation of plasma VP concentration in SHRs.

Hypertrophy of immunohistochemically identified cholinergic neurons of the basal nucleus of Meynert following ablation of the contralateral cortex in the rat

The effects of unilateral damage of the cortex on cholinergic neurons identified by immunohistochemical demonstration of choline acetyltransferase, were examined in the basal nucleus of the rat. Those cells contralateral to the lesion showed significant hypertrophy as compared with cells in the same nucleus in age- and sex-matched control animals. This enlargement was present by 7 days and persisted after 300 days postoperatively, the longest survival time examined. The age of the animal at operation and the extent of the damage may influence the magnitude of the enlargement. Similar changes were seen in the cholinergic cells of the medial septal nucleus after removal of the contralateral hippocampus.

Choline acetyltransferase-immunoreactive neurons intrinsic to rodent cortex and distinction from acetylcholinesterase-positive neurons

Cholinergic neurons intrinsic to rat cortex were studied using a sensitive method for the localization of choline acetyltransferase immunoreactivity, acetylcholinesterase histochemistry, combined localization of choline acetyltransferase and acetylcholinesterase, and combined localization of choline acetyltransferase and retrogradely transported horseradish peroxidase-wheat germ agglutinin. Choline acetyltransferase immunoreactivity was localized predominantly in small bipolar cortical neurons within the upper layers of isocortex, while small multipolar neurons were the predominantly stained cell type in allocortical regions. Acetylcholinesterase histochemistry demonstrated mainly small polymorphic cells scattered throughout all cellular layers in all cortices. Combined staining for choline acetyltransferase and acetylcholinesterase resulted in localization of the markers in different cell populations; choline acetyltransferase-immunoreactive neurons did not contain detectable acetylcholinesterase and acetylcholinesterase-positive neurons did not contain detectable immunoreactivity to choline acetyltransferase. Some possible connections of the cortical choline acetyltransferase-immunoreactive cells were studied in rats which had received injections of horseradish peroxidase-wheat germ agglutinin into either cortex or brainstem. The choline acetyltransferase-immunoreactive cells were frequently admixed with cells labeled with the retrograde marker; however, no double-labeled cells were observed. It was concluded that cortical cholinergic cells are not visualized by acetylcholinesterase histochemistry, and are likely to be involved in local circuitry.

Chemical anatomy of the brain

The development of sensitive histochemical-neuroanatomical techniques has made it possible to analyze the content of specific compounds in single nerve cells and their processes. In consequence, it has been possible to construct detailed maps of the distribution of various types of neurons on the basis of their transmitter substance. There are now many examples of neurons containing both a classical transmitter and a peptide. In some instances the peptides seem to support the action of the classical transmitters. This interaction may have applications in the prevention and treatment of nervous disease states.

Septo-hippocampal and other medial septum-diagonal band neurons: electrophysiological and pharmacological properties

Neurons located in the medial septum-nucleus of the diagonal band (vertical limb) area and antidromically activated by electrical stimulation of the fimbria were recorded in urethane anesthetized rats. Forty-five percent of these septo-hippocampal neurons (SHNs) discharged rhythmically in short bursts (mean burst frequency, 4 Hz). They were antidromically driven at short latencies from the fimbria. SHNs driven at long latencies (above 5 ms) were never bursting neurons. Fimbria stimulation also had a powerful inhibitory effect on the spontaneous activity of SHNs. The vast majority of the septo-hippocampal neurons were excited by the iontophoretic application of acetylcholine or cholinergic agonists, carbachol being the most effective. The acetylcholine-induced excitations were readily abolished by atropine. In contrast hexamethonium and mecamylamine were less effective. The rhythmic bursting activity could not be consistently altered by the iontophoretic application of cholinergic agonists or antagonists or of divalent cations. SHNs were also sensitive to various other putative neurotransmitters (substance P, GABA) known to play a role in the medial septal area. Bursting neurons and ACh-sensitive neurons were less frequent among unidentified medial septal neurons. The regulation of the septo-hippocampal cholinergic pathway is therefore not likely to be due to a direct feedback inhibition by locally released acetylcholine. However a strong inhibitory feedback could be exerted by the hippocampo-septal pathway impinging directly or indirectly on septo-hippocampal neurons.

Topochemical localization of choline acetyltransferase and acetylcholinesterase in mouse brain

The specific activities of choline acetyltransferase (ChAT) and acetylcholinesterase (AChE) were measured at neuroanatomically identified loci of the C57BL/6J mouse brain. ChAT specific activity was highest in corpus striatum. Areas of the basal forebrain had high to moderate activities, while low activities were seen in hypothalamic areas. AChE specific activity correlated highly with ChAT specific activity in all brain regions. Pronounced rostro-caudal gradients of both ChAT and AChE specific activities were discovered in the diagonal band of Broca. Overall, the regional distribution of cholinergic markers in mouse brain closely resembles that of the rat. Systemic administration of 17 beta-estradiol (E2) had no effect on ChAT or AChE specific activities in any brain region.

Cholinergic synapses in the rat brain: a correlated light and electron microscopic immunohistochemical study employing a monoclonal antibody against choline acetyltransferase

Using a monoclonal antibody to choline acetyltransferase, immunoreactive synaptic boutons were identified in the neostriatum, cingulate cortex, basolateral nucleus of the amygdala, hippocampus and interpeduncular nucleus of the rat. The synapses were generally symmetrical although some asymmetrical membrane specializations were observed. Postsynaptic targets included perikarya, dendritic shafts and dendritic spines.

Behavior alters the uptake of [3H]choline into acetylcholinergic neurons of the nucleus basalis magnocellularis and medial septal area

Behavioral experience changed sodium-dependent high affinity choline uptake (SDHACU) in the hippocampus and frontal cortex. Rats were trained on various behavioral tasks and sacrificed after testing. SDHACU was determined in frontal cortex and hippocampus, areas that receive cholinergic innervation from the nucleus basalis magnocellularis (NBM) and the medial septal area (MSA), respectively. Untrained rats taken directly from their home cages had fairly consistent levels of SDHACU in the hippocampus (1.76 +/- 0.45, X +/- S.E.) and frontal cortex (1.46 +/- 0.37). In the hippocampus of rats performing in a radial maze and T-maze and in rats that surpassed a criterion level in an active avoidance task, SDHACU increased significantly above Cage (untrained) group levels. In the cortex of rats performing the radial maze task, SDHACU decreased slightly. There were no other changes in frontal cortical SDHACU. After behavioral testing ceased, SDHACU in rats performing the radial maze task remained elevated above Control and Treadmill group levels for 20 days, but returned to near control levels 40 days later. Our data demonstrate that a functional differentiation exists between the MSA and NBM cholinergic systems, and that the measurement of SDHACU in central cholinergic neurons is a useful tool to identify the influences of behavior and environment upon changes in neurochemical events and neuronal activity.

Characterization of cholinergic neurons in the rat neostriatum. A combination of choline acetyltransferase immunocytochemistry, Golgi-impregnation and electron microscopy

Immunocytochemistry with a monoclonal antibody against choline acetyltransferase has been used to characterise cholinergic neurons in the rat neostriatum. The light microscopic morphology, ultrastructure and synaptic input of these neurons was compared to that of the three types of large neuron found in Golgi preparations of the striatum. The cholinergic neurons are large and have long infrequently branching dendrites. Two of the immunoreactive neurons were also Golgi-impregnated and showed characteristics of the "classical" large neurons of the striatum. Examination in the electron microscope revealed that the synaptic input to perikarya and proximal dendrites is sparse, thus distinguishing them from another large type of neuron, found in the ventral regions of the striatum, whose dendrites and perikarya are ensheathed in synaptic boutons. It is concluded that one of the three morphologically distinguishable classes of large neuron in the striatum is a cholinergic neuron.

The section-Golgi-impregnation procedure--3. Combination of Golgi-impregnation with enzyme histochemistry and electron microscopy to characterize acetylcholinesterase-containing neurons in the rat neostriatum

Three morphologically distinct types of neuron that contain acetylcholinesterase have been distinguished by Golgi-impregnation of sections of the rat neostriatum that had been incubated to reveal acetylcholinesterase activity. The neuron that stained most intensely for acetylcholinesterase was a large cell, with smooth or sparsely spiny dendrites; the axon of one these neurons was partially impregnated by the Golgi stain and had local axon collaterals (type 1). Another acetylcholinesterase-containing neuron had a small to medium-size cell body with long sparsely spiny dendrites emerging from opposite poles (type 2). The third type of neuron that contained acetylcholinesterase was medium to large size and had many primary, sparsely spiny dendrites that branched frequently (type 3). Examination of the same Golgi-impregnated, acetylcholinesterase-stained neurons that had been studied in the light microscope by electron microscopy allowed us to distinguish several other differences between the three types of neuron. Whereas all three types had acetylcholinesterase reaction product in the endoplasmic reticulum and along the nuclear envelope, only neurons of type 1 displayed reaction product in the Golgi apparatus. All three types of neuron received synaptic input, mainly along their dendrites. It is concluded that the combination of Golgi-impregnation with histochemical procedures that demonstrate endogenous enzyme activity can be applied to reveal the morphological characteristics, synaptic input and local synaptic output of neurons with specific biochemical properties.