THE STRUCTURE AND COMPARATIVE ANATOMY OF THE NUCLEUS BASALIS MEYNERT OF DELPHINUS DELPHIS LINNAEUS (MAMMALIA, CETACEA, DELPHINIDAE)

The cholinergic system in the basal forebrain of the Atlantic white-sided dolphin (Lagenorhynchus acutus)

The basal forebrain (BFB) cholinergic neurotransmitter system is important in a number of brain functions including attention, memory, and the sleep-wake cycle. The size of this region has been linked to the increase in encephalization of the brain in a number of species. Cetaceans, particularly those belonging to the family Delphinidae, have a relatively large brain compared to its body size and it is expected that the cholinergic BFB in the dolphin would be a prominent feature. However, this has not yet been explored in detail. This study examines and maps the neuroanatomy and cholinergic chemoarchitecture of the BFB in the Atlantic white-sided dolphin (Lagenorhynchus acutus). As in some other mammals, the BFB in this species is a prominent structure along the medioventral surface of the brain. The parcellation and distribution of cholinergic neural elements of the dolphin BFB was comparable to that observed in other mammals in that it has a medial septal nucleus, a nucleus of the vertical limb of the diagonal band of Broca, a nucleus of the horizontal limb of the diagonal band of Broca, and a nucleus basalis of Meynert. The observed BFB cholinergic system of this dolphin is consistent with evolutionarily conserved and important functions for survival.

Organization of the basal forebrain in the cat: localization of L-enkephalin, substance P, and choline acetyltransferase immunoreactivity

The present study uses immunocytochemical techniques to determine whether cholinergic basal forebrain neurons in the cat are in a position to receive a homogeneous pattern of inputs, or if specific immunocytochemically defined afferent systems are localized to only selected regions of the basal forebrain. Monoclonal antibodies against choline acetyltransferase (ChAT) were used to identify the location of putative cholinergic neurons which are known to project to the cerebral cortex. In addition, polyclonal antibodies against substance P (SP) or enkephalin (Enk) were used on either adjacent or on the same histological sections reacted for ChAT to identify the neuropeptide plexuses that provide input to the basal forebrain. ChAT-immunoreactive (ChAT-IR) perikarya were located throughout the vertical limb, genu and horizontal limb of the diagonal band of Broca. ChAT-IR neurons also were located within the substantia innominata (SI), within the peripallidal zone around the globus pallidus, and were intercalated within the internal capsule. Enk-IR and SP-IR were used to determine the distribution of putative peptidergic terminals within the basal forebrain. Extensive Enk-IR and SP-IR terminal label was localized within the globus pallidus and the surrounding peripallidal zones, as well as within the SI, whereas the components of the diagonal band of Broca demonstrated negligible Enk-IR and SP-IR label. These data predict that the subdivisions of the cholinergic basal forebrain in the cat do not share a uniform afferent system, and only selective portions of this cholinergic system are in an anatomical position to receive a major direct input from the identified subcortical peptidergic afferents. The segregation of afferents has important consequences in the selective control of cortical function by the cholinergic basalocortical pathway.

Basal nucleus of Meynert. A neuropathological study in Alzheimer's disease, simple senile dementia, Pick's disease and Huntington's chorea

The basal nucleus of Meynert (bnM) was examined in 9 patients with Alzheimer's disease--4 presenile and 5 senile cases--in 3 patients with simple senile dementia, 5 with Pick's disease, 5 with Huntington's chorea and 5 non-demented controls. The histopathological study was followed by a quantitative analysis of the magnocellular population of neurons and by the determination of their nucleolar volume. In Alzheimer's disease there was a neuronal loss ranging from 44 to 76%, which was negatively correlated with both the age at onset and age at death of the patients. Numerous surviving cells showed neurofibrillary tangles, and in 3 cases senile plaques were present. The nucleolar volume of the large neurons was significantly reduced and the percentage reduction correlated with the percentage loss of cells. In contrast, the bnM was relatively unaffected in the other disorders considered. The involvement of bnM in Alzheimer's disease confirms the previous neuropathological observations, providing further evidence that it constitutes a constant anatomical feature of this disorder. The extent of the damage is age-dependent. The sparing of the bnM in simple senile dementia suggests that it may be a different nosological entity from late onset Alzheimer's disease and this may constitute a simple criterion for distinguishing between the two forms of dementia on an anatomical basis.

Neuronal loss in the basal nucleus of Meynert in progressive supranuclear palsy

A morphometric study of the basal nucleus of Meynert (bnM) has been performed in a 70-year-old man with a 4-year history of pathologically confirmed progressive supranuclear palsy (PSP). An important neuronal loss (52%) was demonstrated in the bnM. This finding has not been previously documented with morphometric methods in PSP, but the involvement of the bnM is well known in other related conditions, i.e., Parkinson's disease, Alzheimer's disease, and Parkinson-dementia complex of Guam. Our findings yield support to the view that the involvement of the bnM, a nucleus with complex connections with various subcortical structures and diffuse cholinergic projections on the neocortex, could play an important role in the physiopatholog of subcortical dementia.

Cholinergic projections from magnocellular nuclei of the basal forebrain to cortical areas in rats

Acetylcholinesterase (AChE) and choline acetyltransferase (CHAc) activities were studied by quantitative histochemical (AChE) as well as biochemical methods (AChE, ChAc) in certain cortical brain areas in rats after stereotaxic lesions had been placed in several structures of the basal forebrain. After lesioning the magnocellular nuclei of the substantia innominata (nuc. basalis Meynert, NBM) the activities of AChE and ChAc decreased to moderate or low residual values in the ipsilateral cortical areas. This indicated that cholinergic pathways were directly linked to frontal, sensory-motor, auditory and visual cortex. After lesions of the globus pallidus the decrease in cortical AChE activity was less pronounced. Lesions of the caudate, accumbens or entopeduncular nucleus did not influence the cortical AChE activities. The results are discussed with respect to the similarity of the organization of the cholinergic projection to the cortex arising from NBM cells and the monoaminergic system which innervates the cortex. It is suggested that both neurotransmitter systems by their interaction might modulate and control cortical information processing and behavior in a manner analogous to the control of peripheral activity by the sympathetic and parasympathetic system.

Midbrain, diencephalic and cortical relationships of the basal nucleus of Meynert and associated structures in primates

The structure and connectivity of the basal nucleus of Meynert, the substantia innominata in which it lies, and certain related areas have been examined in New World and Old World Monkeys, using retrograde and anterograde axonal transport methods. Experiments using the retrograde, horseradish peroxidase method confirm the observations of Kievet and Kuypers ('75) that the basal nucleus and substantia innominata project directly, heavily and with a somewhat crude topography upon the neocortex. Experiments involving the anterograde, autoradiographic method show that the basal nucleus and substantia innominata form part of a complex pathway that links them together with the lateral hypothalamus, certain parts of the amygdala and the peripeduncular nucleus of the midbrain. The peripeduncular nucleus is often regarded as a part of the central auditory pathway; it gives rise to a fiber bundle of considerable size that ascends on the dorsal surface of the ipsilateral optic tract and terminates ultimately in the lateral hypothalamic area of both sides. As well as distributing fibers to the basal nucleus, substantia innominata and lateral hypothalamus, this pathway provides a heavy projection to a cytoarchitectonically distinct posterior part of the lateral nucleus of the amygdala, the medial and intercalated nuclei of the amygdala and a less dense projection to the bed nucleus of the stria terminalis. Certain parts of the hypothalamus and possibly the preoptic areas give rise to a complementary descending pathway that distributes fibers to the ipsilateral basal nucleus, substantia innominata and amygdala, and ends in the peripeduncular nuclei of both sides. Decussating fibers in both the ascending and descending pathways cross in the ventral supraoptic commissure. It is concluded that the basal nucleus should include most of the aggregated and unaggregated large cells that lie in the substantia innominata and which in places intrude upon the preoptic regions and the nucleus of the diagnonal band of Broca. Together, these may form a complex that receives inputs from a variety of brainstem sources, and projects widely and diffusely upon all cortical structures of the telencephalon.