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Recent molecular studies have noted the affinity among cephalochordates and vertebrates. In particular, a cluster of vertebrate-like homeobox genes regulates the development of the lancelet Branchiostoma lanceolatum. A previous study has outlined the expression pattern of the pituitary-specific transcription factor Pit-1 in adult lancelets. Pit-1 belongs to the POU family of transcription factors, which, like homeotic proteins, are members of the helix-turn-helix superfamily of proteins. POU is an acronym for Pit-1, Oct-1 and Oct-2, and Unc-86. In the present work, we investigated the head region of premetamorphic larvae of B. lanceolatum, by means of scanning electron microscopy, wholemount and tissue sections immunocytochemistry, and Western blotting assay, to verify the presence and distribution of Pit-1. Immunoreactive Pit-1 protein was detected in the rostral nerves and in a cluster of photoreceptor cells of the frontal eye. At the same time, an electrophoretic band of 33 kDa was shown from extracts of premetamorphic larvae and recognized by a monoclonal antibody to rat Pit-1. On the basis of the immunocytochemical and electrophoretic results, we can assume that Pit-1 may play a neuromodulatory role in the larval central nervous system. Moreover, the spatial and temporal distribution of Pit-1 protein in larva and adult lancelets agrees only in part with that described in embryonic and adult mice, suggesting different molecular controls of regional identity in the nervous system of cephalochordates and vertebrates.

The diencephalon of nonmammalian vertebrates contains aminergic perikarya situated beneath the ependyma lining the third ventricle, known as the paraventricular organ (PVO). Catecholamines were visualized in the goldfish forebrain by formaldehyde-glutaraldehyde-induced fluorescence. Neuronal somata containing catecholamines were found in three paraventricular nuclei--the nucleus recessus posterioris (NRP), the nucleus recessus lateralis (NRL), and the nucleus posterioris paraventricularis (NPPv)--which may be considered to constitute the PVO of the goldfish. Lesion-degeneration investigations were conducted to determine whether the PVO contributes to the innervation of the goldfish pituitary. Following electrothermic lesions of the NRP, degenerating axons and nerve terminals were observed in the rostral pars distalis and in the proximal pars distalis, but not in the neuro-intermediate lobe of the pituitary. Following lesions of the NRL or of the NPPv, degenerating axons and nerve terminals were observed in the rostral pars distalis, the proximal pars distalis, and in the neurointermediate lobe. These observations demonstrate that the PVO is a source of pituitary afferents in the goldfish and suggest that the PVO is a source of the catecholaminergic innervation of the teleost pituitary.

With the aid of lesion experiments and the Falck-Hillarp fluorescence technique, it is shown that the aminergic nerves of the hypophysis, including pars distalis, originate in the caudal hypothalamus and reach the gland via a fibre tract in the floor of tuber cinereum. However, some contribution to the eminentia mediana from the preoptic area could not be excluded. A vasomotor function of the pars distalis nerves is unlikely. Based on a comparative survey the hypothesis is put forward, that the pars distalis nerves, which disappear during the metamorphic climax, are remnants of an aminergic innervation existing together with a hypophyseal portal system as a functional link between brain and pituitary in the fish-like ancestor of amphibians. Aspects are given on the problem of why a direct pars distalis innervation has neither been retained nor evolved during evolution of tetrapods.

The distribution of immunoreactive substance P (IR-SP) neurons was examined in the hypothalamus and pituitary gland of the rhesus monkey by using the peroxidase-antiperoxidase immunocytochemical technique. Immunoreactive SP cell bodies were observed in the arcuate nucleus, in the region lateral to the arcuate nucleus, and in the median eminence (ME). Immunoreactive SP cells were also seen in the periventricular area of the dorsal tuberal region. A rich network of SP fibers was concentrated in the arcuate region, and the fiber stain was particularly dense in the external zone of the median eminence and in the external layer of the infundibular stalk. Also, substance P fibers were seen in the internal layer of the pituitary stalk and in the neural lobe of the pituitary gland. Outside the hypothalamus a dense network of IR-SP fibers was observed in the globus pallidus.

Experiments using two retrogradely transported fluorescent dyes (bisbenzimide-true blue, and Evans blue-granular blue) were performed in order to determine whether the same or different populations of neurons of the paraventricular nucleus of the hypothalamus (PVH) project to the pituitary gland, dorsal vagal complex, and spinal cord in the rat. The results suggest that cells projecting to the pituitary gland are concentrated in the magnocellular core of the nucleus, while the descending connections arise primarily from the surrounding parvocellular division. The occurrence of neurons double-labeled with both dyes further indicate that at lease 10-15% of the labeled cells in the parvocellular division send divergent axon collaterals to the dorsal vagal complex and to the spinal cord. Cell counts suggest that at least 1,500 cells in the PVH project to the medulla and/or spinal cord. These results, combined with a cytoarchitectonic analysis, show that the PVH consists of eight distinct subdivisions, three magnocellular and five parvocellular. The lateral hypothalamic area and zona incerta also contain a large number of cells projecting to the dorsomedial medulla and spinal cord; approximately 15% of such cells are the double-labeled following injections of separate tracers into these two regions of the same animal.