The ascending projections of cholinergic neurons in the laterodorsal tegmental nucleus (TLD) were investigated in the rat by using Phaseolus vulgaris leucoagglutinin (PHA-L) and wheat germ agglutinin-conjugated horseradish peroxidase (WGA-HRP) anterograde tracing techniques. Two ascending pathways were identified after iontophoretic injections of PHA-L into the TLD. A long projection system courses through the dorsomedial tegmentum, caudal diencephalon, medial forebrain bundle, and diagonal band. Different branches of this system innervate the midbrain (superior colliculus, interstitial magnocellular nucleus of the posterior commissure, and anterior pretectal nucleus), the diencephalon (lateral habenular nucleus, parafascicular, anteroventral, anterodorsal, mediodorsal, and intralaminar thalamic nuclei), and the telencephalon (lateral septum and medial prefrontal cortex). The second system is shorter and more diffuse and innervates the median raphe, interpeduncular, and lateral mammillary nuclei. Retrograde tracing with WGA-HRP, combined with choline acetyltransferase immunohistochemistry, revealed that most of the TLD projections to the tectum, pretectum, thalamus, lateral septum, and medial prefrontal cortex are cholinergic. Afferents to the TLD were studied by anterograde and retrograde tracing techniques. Injection of tracers into the TLD retrogradely labelled neurons bilaterally in the midbrain reticular formation, the periaqueductal gray, the medial preoptic nucleus, the anterior hypothalamic nucleus, and the perifornical and lateral hypothalamic areas. Retrogradely labelled cells were also located bilaterally in the premammillary nucleus, paraventricular hypothalamic nucleus, zona incerta, and lateral habenular nucleus. In the telencephalon, the nucleus of the diagonal band and the medial prefrontal cortex contained retrogradely labelled neurons ipsilateral to the TLD injection site. The projections of the medial prefrontal cortex, the bed nucleus of the stria terminalis, and the lateral habenular nucleus to the TLD were confirmed in anterograde tracing studies. These findings indicate that the TLD gives rise to several ascending cholinergic projections that innervate diverse regions of the forebrain. Afferents to the TLD arise in hypothalamic and limbic forebrain regions, some of which appear to have reciprocal connections with the TLD. The latter include the lateral habenular nucleus and medial prefrontal cortex.

No abstract

No abstract

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.

No abstract