M.V. Sofroniew

Persistence of cholinergic neurons in the basal nucleus in a brain with senile dementia of the Alzheimer's type demonstrated by immunohistochemical staining for choline acetyltransferase

Immunohistochemically identified cholinergic neurons in the basal nucleus of Meynert in a brain with SDAT have been compared with those in two age- and sex-matched normal brains. The numbers of such cells at carefully matched levels are not significantly lower, but the cells in SDAT are substantially smaller than in the normal basal nucleus. The persistence of shrunken cholinergic neurons in the basal nucleus in the diseased brain is similar to that seen in an experimental study of retrograde cellular degeneration in the nucleus following damage of the cortex.

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.

The anatomy of the CNS cholinergic neurons

Convincing biochemical and pharmacological evidence of the transmitter role of acetylcholine (ACh) in the CNS has been available for some years, but it is only in recent times that unequivocal tools have been obtained for the demonstration of cellular localization of CNS cholinergic neurons. In this report we summarize aspects of the neuroanatomy of the cholinergic neurons gained through the immunohistochemical application of antibodies against the ACh biosynthetic enzyme (choline acetyltransferase).

Retrograde changes in cholinergic neurons in the basal forebrain of the rat following cortical damage.

The effects of unilateral cortical damage on immunohistochemically identified cholinergic neurons of the basal nucleus have been examined in the rat. In the first 2 weeks after operation, the cells were swollen and their nuclei became eccentric, these changes being closely similar to those seen in the cholinergic oculomotor nuclei of the same animals following removal of the extraocular muscles. During the third week these acute changes were replaced by shrinkage of the cholinergic cell bodies and their dendrites. At longer survival times the appearance of the neurons did not alter, and all the cholinergic cells persisted in their shrunken form after 120 days, the longest survival time examined.

The cholinergic nuclei of the basal forebrain of the rat: normal structure, development and experimentally induced degeneration

The normal morphology and distribution of the cholinergic neurones of the basal forebrain of the rat have been studied qualitatively and quantitatively after staining immunohistochemically with a monoclonal antibody to choline acetyl transferase (ChAT). This was done in order to provide an adequate control for the changes found in these cells on both sides of the brain in the experimental investigation of the reaction of the cells to damage of their axons. The cholinergic cells form a more or less continuous anteroposterior band, but they can be subdivided into distinct nuclear groups on the basis of the size and form of the cell bodies and dendrites, their position and arrangement. these nuclei conform closely to previous descriptions of Nissl-stained material: the medial septal nucleus, the vertical and horizontal nuclei of the diagonal band and the basal nucleus. Quantitative measurements of the cross-sectional areas of the cells in the different nuclei confirmed the conclusions drawn from the qualitative examination. Measurements of the ChAT cells at different ages showed that in all nuclei they are significantly larger in size in infancy than in the adult, and they shrink to the mature size by 46 days. The cells in the various cholinergic nuclei show distinctly different reactions to damage of their terminal axonal fields. After removal of a large part of the neocortex by removal of the overlying pia-arachnoid mater the cells in the basal nucleus in the operated hemisphere underwent retrograde cellular degeneration, being swollen and paler-staining up to 14 days, and thereafter shrinking by 20-30% (as compared with those in the brains of age- and sex-matched littermate controls). The degree of shrinkage was appreciably greater when the animals were operated upon at the neonate stage. No cell loss was found, qualitatively or quantitatively, in the basal nucleus. After removal of the hippocampus there is marked loss of cholinergic neurones in the medial septal nucleus and in the vertical nucleus of the diagonal band, and with severe shrinkage of the remaining cells. Removal of the olfactory bulb results in only slight shrinkage of the cells, and no cell loss, in the horizontal nucleus of the diagonal band.(ABSTRACT TRUNCATED AT 400 WORDS)

Vasopressin and oxytocin in the mammalian brain and spinal cord

Abstract The application of immunohistochemical and radioimmunoassay techniques to the study of the distribution of the neurohypophyseal peptides vasopressin and oxytocin has revealed the presence of both peptides throughout the mammalian CNS. Other studies have shown that these peptides exert potent effects on specific central neurons and may be involved in a variety of complex central functions. Recent advances in the concepts surrounding the distribution and possible functions of central vasopressin and oxytocin are summarized in this article.

Inputs to motoneurones in the hypoglossal nucleus of the rat: Light and electron microscopic immunocytochemistry for choline acetyltransferase, substance P and enkephalins using monoclonal antibodies

Light and electron microscopic peroxidase-antiperoxidase immunocytochemistry has been used to localize choline acetyltransferase, substance P and enkephalin in the hypoglossal nucleus of the rat. Choline acetyltransferase immunoreactivity was observed in motoneurone cell bodies and proximal dendrites, in large varicosities in the surrounding neuropil and in nerve terminals in synaptic contact with immunostained motoneurones. Most choline acetyltransferase immunostained terminals which made synaptic contact with motoneurone cell bodies and proximal dendrites possessed prominent subsynaptic cisterns and belong to the terminal type referred to in the literature as C or L. Substance P and enkephalin immunoreactivity did not occur in motoneurones but was seen in fibres and synaptic terminals. Substance P immunoreactive fibres made multiple axosomatic contacts while enkephalin immunoreactive terminals made synaptic contact mainly with large and small dendrites. C terminals were not stained for either substance P or enkephalin. This study provides immunocytochemical support for the classic identification of hypoglossal motoneurones as cholinergic and in addition shows that these neurones are innervated by a number of morphologically and chemically distinct terminal types. C terminals have previously been shown to contain cholinesterase and our demonstration that these terminals contain choline acetyltransferase thus provides additional evidence for their cholinergic nature and for a cholinergic innervation of hypoglossal motoneurones. The origin of the immunoreactive terminals was not identified in this study but possible candidates include the raphe nuclei for substance P. and propriobulbar interneurones for choline acetyltransferase.

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.

Effect of Unilateral Decortication on Choline Acetyltransferase Activity in the Nucleus Basalis and Other Areas of the Rat Brain

Abstract: 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.

Parenterally administered GM1 ganglioside prevents retrograde degeneration of cholinergic cells of the rat basal forebrain.

The effect of daily intraperitoneal injections of GM1 ganglioside on retrograde degeneration in the basal forebrain has been examined, using a monoclonal antibody directed against choline acetyltransferase to identify the cholinergic neurones. Rats underwent extensive damage of the cerebral cortex and underlying hippocampus. From the day of operation on, they received daily injections of ganglioside. After a survival of 30 days, the animals were killed and the cholinergic cells of the basal forebrain were examined. These were compared with material treated in the same way from animals who had received the injections of ganglioside but no lesion, animals who had been operated upon but without the ganglioside treatment, and normal animals. Intraperitoneal ganglioside administration markedly reduces the retrograde death of the cholinergic neurones of the medial septal nucleus and abolishes the shrinkage of the remaining neurones following hippocampal damage.