Altered serotonergic and cholinergic synaptic markers in Pick's disease

Choline acetyltransferase and acetylcholinesterase activities as well as serotonin and imipramine binding were determined in the hypothalamus, nucleus basalis of Meynert, and frontal and temporal poles of subjects with Pick's disease. Choline acetyltransferase activity was decreased in the hypothalamus and nucleus basalis of Meynert, and acetylcholinesterase activity was decreased in the nucleus basalis of Meynert only. Serotonin binding was decreased in all sites but the nucleus basalis of Meynert, and imipramine binding was altered only in the frontal pole. Comparison with previous reports of Alzheimer's disease indicates that with respect to these synaptic markers, Alzheimer's disease and Pick's disease are not similar.

Transient impairment of recognition memory following ibotenic-acid lesions of the basal forebrain in macaques

To assess the contributions of the basal forebrain cholinergic nuclei to visual recognition memory in macaques, we compared the effects of lesions of (a) the nucleus basalis of Meynert, (b) the medial septal and diagonal band nuclei, and (c) all nuclei combined on performance of delayed nonmatching-to-sample with trial-unique stimuli. Whereas monkeys with the separate lesions did not differ from each other or from normal control animals, those with combined lesions showed a significant impairment. With time and extended practice, however, the performance of the animals with combined lesions recovered to normal levels. During the recovery period, these monkeys showed an initially increased sensitivity to scopolamine that later dissipated, at which time they also failed to show the improvement that follows physostigmine administration in normal animals. Postmortem assessment of cortical choline acetyltransferase activity revealed that only the group with combined lesions had significant depletion of this enzyme. The results suggest that (1) the basal forebrain cholinergic system participates in mnemonic processes in primates and that (2) extensive damage to this system is necessary before impairments in recognition memory, even transient ones, can be observed.

Dopaminergic involvement in locomotion elicited from the ventral pallidum/substantia innominata

Microinjection of the indirect GABAA antagonist, picrotoxin, or the mu opioid agonist, Tyr-D-Ala-Gly-NMe-Phe-Gly-ol (DAGO), into the ventral pallidum and substantia innominata (VP/SI) increases locomotor activity in rats. The VP/SI has direct and indirect projections to the region of the ventral mesencephalon containing dopamine perikarya, and to certain dopamine terminal fields, including the nucleus accumbens. Thus, it is possible that modulation of the mesocorticolimbic dopamine system by pharmacological stimulation in the VP/SI may play a role in the locomotor stimulant response. It was shown that pretreatment with dopamine receptor antagonists, either peripherally or microinjected into the nucleus accumbens significantly attenuated the motor stimulant effect of DAGO or picrotoxin injection into the VP/SI. Injection of either picrotoxin or DAGO into the VP/SI increased the levels of dopamine metabolites in the nucleus accumbens and prefrontal cortex. Thus, the motor stimulant response following pharmacological stimulation of the VP/SI appears to be mediated by increased dopamine neurotransmission via feedback mechanisms to the mesocorticolimbic dopamine system.

Early development of the nucleus basalis-cortical projection but late expression of its cholinergic function

The aim of this study was to examine the development of the basalocortical pathway by using choline acetyltransferase and nerve growth factor receptor immunocytochemistry, acetylcholinesterase histochemistry and retrograde axonal transport. The observations were made in the ferret because in this species brain development occurs over a much more protracted period than in the rat. Staining for choline acetyltransferase immunoreactivity in the brain was minimal before birth. Adult levels of staining for the enzyme were not seen in cell bodies until three weeks after birth and in axons up to six weeks after birth. This, however, did not mean that presumptive cholinergic pathways are absent early in development. There was strong staining for nerve growth factor receptor in basal forebrain neurons from at least two weeks before birth. Positive staining for acetylcholinesterase was found in axons that begin to invade the cerebral cortex a week before birth. The retrograde axonal transport technique showed that the basalocortical pathway has a normal organization in the neonate. The conclusion is that cholinergic pathways form early in the prenatal period in the ferret but express their transmitter function late in postnatal development.

Cortical second messengers after NBM damage: no change in responses to cholinergic agonists

Damage to the nucleus basalis of Meynert (NBM) decreases acetylcholine (ACh) innervation of cortex. We explored transmission of cholinergic messages in cortex 2-3 weeks after such damage. The NBM damage was unilateral and the ipsilateral denervated cortex was compared to the contralateral nondenervated cortex. The response to carbachol, a muscarinic ACh receptor-agonist, was measured by inhibition of forskolin-induced cAMP accumulation in cortical membranes and by formation of inositol phosphate (IP) in cortical slices. No difference was found in the carbachol effects between ipsi- and contralateral cortices. Thus, we find no evidence of either receptor loss or receptor supersensitivity. There was, however, a significant decrease in K(+)-stimulated IP formation in the cortex ipsilateral to the damage which probably reflected loss of cholinergic terminals. When comparing the cortex contralateral to NBM damage with the cortex contralateral to sham damage in control rats, no difference was found in any of the above parameters. When severe cognitive deficits are observed, 2-3 weeks after NBM damage, loss of presynaptic ACh is the main change in cortical cholinergic transmission.

Increase of muscarinic receptor following kainic acid lesions of the nucleus basalis magnocellularis in rat brain: an autoradiographic study

We observed changes in cholinergic markers in rat brain seven days after lesioning the nucleus basalis magnocellularis (nbm) with kainic acid. In histochemical preparations stained for acetylcholinesterase (AChE), there was a marked loss of large AChE reactive neurons within and beneath the nbm on the injected side, and the AChE positive fibers were greatly decreased particularly in the IV-VI layers of the frontal and parietal cortices ipsilateral to the kainate lesion. Using in vitro receptor autoradiography, we found a significant increase (about 25%) in 3H-QNB binding sites in the I-IV layers of the ipsilateral frontal and parietal cortices (p 0.05, Student's t-test). The area with decreased AChE activity and increased density in 3H-QNB binding sites corresponded to the innervation of the cholinergic system arising from the nbm. The increase of density in 3H-QNB binding sites was considered to reflect the postsynaptic denervation supersensitivity.

Adrenergic innervation of the substantia innominata: co-localization of phenylethanolamine N-methyltransferase and tyrosine hydroxylase immunoreactivities within the same axons

Adrenergic input to the rat substantia innominata (SI) was studied by immunocytochemical localization of phenylethanolamine N-methyltransferase (PNMT), the synthetic enzyme for adrenaline. Using primary antibodies derived from different species, we demonstrated in double-immunofluorescence labeling experiments that all PNMT-immunoreactive fibers in SI are also immunoreactive for tyrosine hydroxylase, the synthetic enzyme for dopamine. This result indicates that the PNMT immunoreactive axons in SI are indeed adrenergic fibers.

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

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

Calbindin-immunoreactive cholinergic neurones in the nucleus basalis of Meynert in Alzheimer-type dementia

An antibody to the calcium binding protein, calbindin D28K (CaBP), was used to study the number and size of CaBP-immunoreactive neurones in the nucleus basalis of Meynert (nbM) of postmortem human brains from neurologically normal controls and from patients with neuropathologically diagnosed Alzheimer-type dementia (ATD). In controls, almost all the large neurones and their processes in the nbM were CaBP immunoreactive. Compared to neurologically normal controls the number of CaBP-immunoreactive neurones in the nbM in patients dying with ATD was significantly reduced and there was a clear loss of the majority of CaBP immunoreactive neurones. The few remaining nbM CaBP immunoreactive neurones in the ATD cases were smaller than those in the neurologically normal controls. Double-staining experiments revealed that many of the nbM CaBP-immunoreactive neurones contained choline acetyltransferase immunoreactivity, so that CaBP is an alternative marker for the nbM cholinergic neurones in the human fore-brain. These findings suggest that a disturbance in calcium homeostasis may be a possible factor contributing to the loss of these cholinergic/CaBP-containing neurones.

Calcitonin gene-related peptide (CGRP) in the rat substantia innominata and globus pallidus: a light and electron microscopic immunocytochemical study

The substantia innominata (SI) and the caudal part of the globus pallidus (GP) in the rat are densely innervated by calcitonin gene-related peptide-immunoreactive (CGRP+) axons. Electron microscopic analysis revealed that CGRP+ boutons mainly formed asymmetrical synapses with dendrites in GP and SI.

Changes in cholinergic but not in GABAergic markers in amygdala, piriform cortex, and nucleus basalis of the rat brain following systemic administration of kainic acid

Three days after systemic administration of kainic acid (15 mg/kg, s.c.), selected cholinergic markers (choline acetyltransferase, acetylcholinesterase, muscarinic acetylcholine receptor, and high-affinity choline uptake) and GABAergic parameters [benzodiazepine and gamma-aminobutyric acid (GABA) receptors] were studied in the frontal and piriform cortex, dorsal hippocampus, amygdaloid complex, and nucleus basalis. Kainic acid treatment resulted in a significant reduction of choline acetyltransferase activity in the piriform cortex (by 20%), amygdala (by 19%), and nucleus basalis (by 31%) in comparison with vehicle-injected control rats. A lower activity of acetylcholinesterase was also determined in the piriform cortex following parenteral kainic acid administration. [3H]Quinuclidinyl benzilate binding to muscarinic acetylcholine receptors was significantly decreased in the piriform cortex (by 33%), amygdala (by 39%), and nucleus basalis (by 33%) in the group treated with kainic acid, whereas such binding in the hippocampus and frontal cortex was not affected by kainic acid. Sodium-dependent high-affinity choline uptake into cholinergic nerve terminals was decreased in the piriform cortex (by 25%) and amygdala (by 24%) after kainic acid treatment. In contrast, [3H]flunitrazepam binding to benzodiazepine receptors and [3H]muscimol binding to GABA receptors were not affected 3 days after parenteral kainic acid application in any of the brain regions studied. The data indicate that kainic acid-induced limbic seizures result in a loss of cholinergic cells in the nucleus basalis that is paralleled by degeneration of cholinergic fibers and cholinoceptive structures in the piriform cortex and amygdala, a finding emphasizing the important role of cholinergic mechanisms in generating and/or maintaining seizure activity.

Dopamine in the rat ventral pallidum/substantia innominata: biochemical and electrophysiological studies

Recent anatomical literature suggests that dopaminergic projections ascending from the midbrain terminate within the ventral pallidum/substantia innominata (VP/SI). The present investigation evaluated this possibility using standard biochemical and electrophysiologic approaches. Biochemical studies revealed that dopamine and its major metabolites are present within the rat VP/SI. Concentrations of these compounds were diminished greatly when dopaminergic neurons of the substantia nigra were destroyed. Electrophysiologic studies demonstrated that VP/SI neurons often respond to local applications of dopamine with a decrease in firing rate. These observations support the contention that dopamine regulates neuronal activity within the VP/SI and that cells of origin for at least a portion of this projection lie within the substantia nigra.

Muscarinic receptor plasticity in rats lesioned in the nucleus basalis of Meynert

The present study investigated the effects of chronic treatment with scopolamine (10 mg/kg i.p. for 21 days) on the muscarinic acetylcholine receptors in the frontoparietal cortex of rats, lesioned at the level of the nucleus basalis of Meynert. Ibotenic acid (25 nmol in 0.5 microliters) was injected bilaterally or unilaterally into the area of this nucleus and produced a major impairment of the cortical cholinergic system. These lesions depleted specifically frontoparietal cortical choline acetyltransferase activity. Sham-operated rats were similarly operated but no neurotoxin was injected. The chronic treatment with scopolamine caused a significant increase in the binding of [3H](-)quinuclidinylbenzilate to muscarinic receptors in the frontoparietal cortex of control and sham-operated rats but not in lesioned animals. This increase was due to an up-regulation in the number of muscarinic acetylcholine receptors, without significant change in their affinity. These results suggest that a functional presynaptic cholinergic terminal is necessary for the plasticity of muscarinic receptors in the central nervous system.

Altered lipofuscin pigmentation in the basal nucleus (Meynert) in Parkinson's disease

The basal nucleus (Meynert) and the horizontal limb nucleus of the diagonal band are composed of 3 types of neurons that can be differentiated with the use of Nissl preparations counterstained for the demonstration of lipofuscin pigment. The pattern of pigmentation of these neurons has been investigated in parkinsonian cases and compared with controls. In the parkinsonian cases the number of large multipolar neurons showing pigment granules in a dendritic stem is significantly higher than in controls. Moreover, the degree of pigment penetration is more pronounced in parkinsonian cases. The results show that staining of lipofuscin granules offers an approach to detecting further details of the changes in the basal nucleus in Parkinson's disease.

Suppression of amygdaloid kindled convulsion following unilateral injection of 2-amino-7-phosphonoheptanoic acid (2-APH) into the substantia innominata of rats

The comparative effect of intracerebral injection of 2-APH, a selective antagonist for N-methyl-D-aspartate (NMDA) receptors, into the substantia innominata (SI) and the amygdala (AM) of AM-kindled rats was examined. The intra-SI injection (ipsilateral to the kindled AM) induced a transient incoordination followed by immobility with loss of the rightening reflex, beginning at about 5 min following the injection and lasting for about 3 h. When the animals were stimulated at the previously established generalized seizure triggering threshold (GST) 45 min after the injection, the kindled seizure regressed to earlier stages although the afterdischarge (AD) duration remained unchanged. At 24 h, kindled seizure was readily activated at the GST. When 2-APH was injected into the kindled AM, no behavioural change occurred but AM stimulation at the GST failed to produce AD 45 min after the injection. Kindled seizure could be elicited, however, when the stimulus intensity was increased. This elevation of the GST lasted for 1-18 days. The findings suggest that NMDA receptors in the AM and SI play a differential role in AM seizure initiation and propagation, respectively. They also provide further support to the role presumed to be played by the SI in transforming the limbic seizure into motor seizure.

Stimulation of the nucleus basalis of Meynert increases acetylcholine release in the cerebral cortex in rats

The effect of focal stimulation of the magnocellular nucleus of the basal forebrain (nucleus basalis of Meynert; NBM) on acetylcholine (ACh) release in the cerebral cortex in the parietal lobe was examined in halothane-anesthetized rats. ACh was measured using a microdialysis method. Focal electrical stimulation of the unilateral NBM increased ACh release in the ipsilateral cerebral cortex in stimulus intensity and frequency dependently. Microinjection of L-glutamate (100 nmol) into the unilateral NBM also increased ACh release in the ipsilateral cerebral cortex. The ACh release in the contralateral cerebral cortex was not affected by these unilateral stimulations of the NBM. It was concluded that focal stimulation of the NBM releases ACh from cortical terminals of cholinergic fibers originating in the NBM.

Galanin-like immunoreactivity is present in human substantia innominata and in senile plaques in Alzheimer's disease

Galanin immunoreactivity has been shown to be present in cholinergic magnocellular basal forebrain neurons in both rat and monkey brain. In the present study galanin immunoreactivity in human substantia innominata was found in both the magnocellular neurons of the nucleus basalis of Meynert and in a dorsomedial group of intensely immunoreactive parvocellular neurons. Scattered galanin-immunoreactive fibers, but no immunoreactive neurons, were found in normal human cerebral cortex. Galanin-immunoreactive neurites were found in a small number of senile plaques in the hippocampus and temporal isocortex of Alzheimer's disease patients. The existence of galanin immunoreactivity in human magnocellular basal forebrain neurons which are depleted in Alzheimer's disease suggests that galanin may be similarly affected.

NGF receptor immunoreactivity in aged rat brain

The cellular distribution of nerve growth factor (NGF) receptor (NGFR) immunoreactivity in 3 cholinergic nuclei (medial septal nucleus, nucleus of the diagonal band and nucleus basalis magnocellularis) of the aged rat brain was compared to that of young-adult animals. In young-adult rats, NGFR immunoreactivity was strong in the neuronal body and in the whole dendritic tree. In aged animals, NGFR immunoreactivity was weak in both cell body and dendrites and was practically absent in the dendrite's distal portion. The loss of dendritic NGFR may play a critical role in the decline of neuronal function in the aging brain.

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

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

High density of benzodiazepine binding sites in the substantia innominata of the rat

In order to study the neuronal basis of the pharmacological interactions between benzodiazepine receptor ligands and cortical cholinergic turnover, we examined the regional distribution of specific benzodiazepine binding sites using in vitro autoradiography. In the basal forebrain, the substantia innominata contained a high density of [3H]lormetazepam (LMZ) binding sites (Bmax = 277 fmol/mg tissue; Kd = 0.55 nM). The label could be displaced by diazepam (IC50 = 100 nM), the benzodiazepine receptor antagonist beta-carboline ZK 93426 (45 nM) and the partial inverse agonist beta-carboline FG 7142 (540 nM). It is hypothesized that the amnesic effects of benzodiazepine receptor agonists are exerted through benzodiazepine receptors which are situated on cholinergic neurons in the substantia innominata and are involved in a tonic inhibition of cortical acetylcholine release. The benzodiazepine receptor antagonist ZK 93426 may exert its nootropic effects via benzodiazepine receptors in the substantia innominata and, consequently, by disinhibiting cortical acetylcholine release.

Scopolamine induces up-regulation of nicotinic receptors in intact brain but not in nucleus basalis lesioned rats

The effect of chronic scopolamine treatment on muscarinic and nicotinic receptors in frontoparietal cortex in rats was investigated. Administration of the muscarinic antagonist, scopolamine (10 mg/kg i.p./day) for 21 days, produced a significant increase in the density of both muscarinic and nicotinic receptors by 27.7% and 12.1% respectively as measured by the specific binding of (-)-[3H]quinuclidinylbenzilate and (-)-[3H]-nicotine. There was no modification in the affinities for these ligands. Rats, bilaterally lesioned with ibotenic acid at the level of nucleus basalis of Meynert, which innervates the frontoparietal cortex, showed no up-regulation of cortical nicotinic receptors after chronic scopolamine treatment, suggesting the importance of the synaptic integrity in the regulation mechanism.