Morphological characteristics of acetylcholinesterase-containing neurons in the CNS of DFP-treated monkeys. Part 2. Diencephalic and medial telencephalic structures.

The distribution and morphological characteristics of neurons containing acetylcholinesterase (AChE, EC 3.1.1.7.) in diencephalic and medial telencephalic structures of the rhesus monkey (Macaca mulatta) were studied by means of a pharmaco-histochemical method that involves staining for AChE (Karnovsky-Roots' procedure) at various times after the administration of di-isopropylfluorophosphate (DFP). At medial telencephalic levels, numerous, mostly multipolar, AChE-containing neurons of medium to large size are present in the bed nucleus of the anterior commissure, in the ascending division of the nucleus of the diagonal band of Broca, and in the so-called "substantia innominata". This last structure is composed of medial and lateral AChE cell groups that extend caudad, beneath the lenticular nucleus, for a considerable distance. The AChE neurons lying within the substantia innominata correspond, at least in part, to the basal nucleus of Meynert. Most neurons of the olfactory tubercle are devoid of AChE but lie within a lightly-stained AChE background. In addition, clusters of amorphous and highly reactive AChE material are found within the islands of Cajella and along the ventromedial edge of the olfactory tubercle. At the level of the thalamus, the strongest AChE staining is seen in the periokarya of the anterior dorsal nucleus and of most nuclei located within the fibrous or lamellar thalamic structures--i.e., the reticular nucleus, the intralaminar nuclei, and the midline nuclei except nuclei parataenialis and reuniens. In most of these nuclei the neuronal somata are of medium size and stain moderately for AChE. Their proximal processes are either lightly stained or devoid of AChE. At the level of the hypothalamus of the monkey, intense AChE staining can be seen within the neuronal somata of the supraoptic and paraventrivular nuclei. In the paraventricular necleus, the AChE-positive perikarya are of medium size and have numerous AChE-containing processes. Moderately reactive AChE neurons of smaller size with unstained processes are also present in the paraventricular nucleus. Most perikarya of the main rostral portion of the supraoptic nucleus are moderately stained for AChE, are closely packed, and their processes are difficult to discern. The main cellular aggregate of the supraoptic nucleus extends caudad and is composed of a large group of moderately to intensely stained neurons lying along the optic tract and which constitute the caudal, or infundibular, portion of the supraoptic nucleus. Other moderately to intensely stained AChE neurons were found in the lateral and perifornical areas and most particularly in the dorsal hypothalamic area. These neurons are of medium size and mostly multipolar. Moderately stained AChE neurons were also observed in the supramammillary nucleus, as well as those of the acruate nucleus, however, are only weakly reactive. The median eminence and most neurons of the ventromedial nucleus of the monkey hypothalamus are virtually devoid of AChE...