Ciliated perikarya, "peptidergic" synapses and supraependymal structures in the guinea pig hypothalamus.

There are numerous nerve cells giving rise to solitary cilia of type 9 x 2 + 0, in the hypothalamic areas studied (medial preoptic nucleus, supraoptic and paraventricular nuclei, anterior periventricular nucleus, wavy paraventricular ependyma, and infundibular wall), further in the precentral gyrus and cerebellar flocculus. In the hypothalamic nuclei, the perikarya contained granular vesicles of varying sizes (800 A to 1800 A in diameter). In the supraoptic nucleus, a second neuron type was described among the lateral optic fibres. These nerve cells differ from the main neurosecretory ones by the size of their granular vesicles and their high number of large axo-somatic synapses formed by myelinated axons. In the paraventricular nucleus, axons may terminate on the basal lamina of vessels. A subependymal neuron group was described near the wavy paraventricular ependyma. The subependymal hypothalamic neuropil is characterized by various kinds of synapses including apparent "peptidergic" ones, and by axo-glial synaptic connections. The latter are also present on the apica surface of the ependyma in various regions of the 3rd ventricle. In addition, intraventricular structures (dendrites, axons, neuronal and non-neuronal perikarya, synapses) were studied by scanning (SEM) and transmission electron microscopy (TEM).