Ultrastructural observations of the cholinergic neuron in the rat striatum as identified by acetylcholinesterase pharmacohistochemistry

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.

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.

Aspiny neurons and their local axons in the neostriatum of the rat: a correlated light and electron microscopic study of Golgi-impregnated material

Three types of neuron with smooth (aspiny) dendrites could be distinguished in the Golgi-impregnated rat neostriatum. Examples of each type of aspiny neuron were found with local axon collaterals within the neostriatum and these were selected for gold- toning and examination in the electron microscope. One type of aspiny neuron had an elongated, usually spindle-shaped, medium-size soma with two, or rarely three, primary dendrites originating from opposite poles of the cell; one example of this type of neuron had two separate axons. The second type of aspiny neuron had a nearly round, medium-size soma with four primary dendrites that branched profusely quite close to the cell body. A third type of aspiny neuron had a very large polygonal-shaped cell body. Afferent axon terminals were found in synaptic contact with the dendrites and cell bodies of all three types of aspiny neuron. Axon collaterals of each type of neuron displayed varicosities which, when examined in the electron microscope, were frequently found to be boutons making synaptic contact. All such synaptic contacts had symmetrical membrane specializations and the most common postsynaptic targets were dendritic shafts, sometimes spine-bearing. Dendritic spines themselves also received synapses from each type of neuron. No axosomatic synapses involving boutons of identified axons were found. One example of a synapse between an axon collateral of an aspiny neuron and one of the same neuron's dendrites (an ' autapse ') was demonstrated by electron microscopy. It is concluded that the synaptic terminals of at least four types of neuron, the three aspiny types described here and the medium-size densely spiny neuron, participate in local circuit interactions in the neostriatum.