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Neural cell adhesion molecules (NCAMs) can undergo post-translational modifications, such as the addition of polysialic acid chains, thus generating PSA-NCAMs, which are expressed mainly during development. Since polysialylation considerably modifies NCAM adhesivity, expression of NCAMs and PSA-NCAMs has been investigated in the developing hypophysis by immunohistochemistry. At embryonic day 13 (E13), an antibody against NCAM outlined all cellular profiles in the entire Rathke's pouch; this labelling persisted until adulthood. NCAM expression increased in all lobes during development and concerned all pituitary cell types. In contrast, at E13, PSA-NCAMs were only detected in the neural lobe, solely constituted of pituicytes at this stage, and the tuberal lobe, the only lobe expressing hormonal mRNA at the same stage. PSA-NCAMs expression increased in the neural lobe at E17 with the arrival of the neurosecretory fibres and persisted into adulthood. In the anterior lobe, PSA-NCAMs appeared at E15 where their distribution was similar to that of the differentiating corticotrophic cells; at subsequent stages, their expression extended to the whole anterior lobe. Only two cell types, corticotrophic and somatotrophic cells, remained labelled in the adult gland. In the intermediate lobe, melanotrophic cells never expressed PSA-NCAMs but these were expressed on folliculo-stellate cells at birth, preceding the onset of innervation. These results suggest that NCAMs and PSA-NCAMs play a role in pituitary histogenesis, cell differentiation and neurointermediate lobe innervation.

The peptidergic nature of most of the fibres of the neurosecretory system of Scyliorhinus caniculus has been demonstrated with the oxidation method of Naumann and Sterba (1976). Some of the fibres of this peptidergic system terminate on capillaries in the hypothalamic floor, some on neurointermediate cells. The evolutionary aspects of these observations are discussed.

Fluorescent (aminergic) fibers were demonstrated by the Falck-Hillarp technique in all parts of the neurohypophysis (NH) in the roach (Leuciscus rutilus). The fibers are very thin and few in number in the rostral (RNH) and proximal neurohypophysis (PNH) but slightly more numerous in the NH adjacent to the pars intermedia (PI). The fibers occur in normal fish as well as in specimens pre-treated with gamma-methyl-noradrenaline. It is proposed that all parts of the adenohypophysis have a very sparse aminergic innervation. There is no correlation between the number of type "B' fibers and fluorescent fibers in the roach NH. The technical difficulties in obtaining good and reliable results in teleost material are discussed.

The dopaminergic innervation of the goldfish pituitary gland was studied by immunocytochemistry at the electron-microscope level using highly specific antibodies against dopamine coupled to bovine serum albumin with glutaraldehyde. A satisfactory preservation of the tissue was achieved after immersion in 5% glutaraldehyde in phosphate buffer containing sodium metabisulfite to prevent oxidation of the endogenous dopamine. The immunocytochemical procedure was performed on Vibratome sections using the preembedding method. Immunoreactivity was restricted to part of the neurosecretory type-B fibers (diameter of the secretory vesicles lower than 100 nm) in which it was found to occupy the whole cytoplasm. Labeled fibers were observed within the neurohypophysis in the different parts of the gland and in the adenohypophyseal tissue where immunoreactive profiles were detected in close apposition to the different cell types. These data are in agreement with previous results obtained by means of radioautography and further support a role for dopamine in the neuroendocrine regulation of pituitary functions in teleosts.

The neurointermediate lobe of the hypophysis in the Chameleon (Chamaeleo dilepis) was examined with light and electron microscopic methods, with special reference to the cytology of the pars intermedia (PI). The PI is the largest lobe of the hypophysis consisting of (1) dark cells with secretory granules ranging from 200-600 nm; (2) light cells, far fewer in number, containing granules 150-300 nm in diameter; (3) stellate, non-secretory cells. The secretory cells abut onto the perivascular basal lamina of the capillary sinusoids while their apical part borders an intercellular space. This surface of the cells often bears a cilium. The granules arise from the Golgi cisternae while small detached vesicles are found between circumscribed sites of the cell membrane and the Golgi apparatus. No nervous elements were found in the pars intermedia and it is assumed that the regulation of this lobe is purely humoral. This is supported by the presence of three types of nerve terminals in the pars nervosa: (a) terminals with large secretory granules and small vesicles; (b) terminals with dense-core vesicles and small vesicles; (c) terminals with small vesicles only. All of these are secretory as indicated by the presence of the synaptic semidesmosomes formed with the perivascular basal lamina.

In the pars distalis of the hypophysis of adult Rana temporaria, three types of nerve-fiber profiles were found at two distinct sites, in both lateral parts of the bordering regions of the anterior lobe with the intermediate lobe of the hypophysis. The first type of nerve-fiber profile consists of bundles of very fine axonal elements (diameter: less than 0.7 micron). The second type is formed by larger nerve fibers (diameter up to 4 microns) containing a few neurosecretory granules of approximately 100 nm. The third type of nerve-fiber profile resembles the second type but these nerve fibers make synaptoid contacts on at least two different types of glandular cells. The possible functional significance of these nerve fibers in the pars distalis is discussed. No nerve fibers were found in the central part of the bordering region of the pars distalis with the intermediate lobe, at the bordering region with the median eminence and with the neurohypophysial stalk, and in all other parts of the pars distalis.

The pars intermedia of the pituitary in the rabbit and hare is abundantly innervated by axons reacting selectively with antibodies against oxytocin. These axons contain dense secretory vesicles about 140 nm in diameter, i.e., smaller than those in the neurosecretory axons of the neural lobe. No fiber elements staining for other peptides (vasopressin, somatostatin, substance P) were observed in the pars intermedia, except rare leu-enkephalin axons restricted to the rostral zone of the gland. Dopaminergic innervation appears to be completely absent from the intermediate lobe. This was shown by the lack of reaction with an antibody against tyrosine-hydroxylase, which did reveal a well-developed tubero-infundibular system of nerve fibers. Axons reacting with an antibody against serotonin were irregularly distributed in the pars intermedia. In the absence of dopaminergic axons, the extensive oxytocin-like innervation may play a major role in regulating the melanotrophic cell activity in the Leporidae.

The horseradish-peroxidase (HRP) technique was used to visualize the cell bodies of axons projecting to the goldfish pituitary. Following intravenous injections of HRP, HRP reaction products were observed in axons of the rostral pars distalis, proximal pars distalis, neurointermediate lobe, pituitary stalk and in axons coursing from the pituitary into the hypothalamus. HRP-labelled cells in the brain were localized in two regions only - the nucleus preopticus (NPO) pars magnocellularis and pars parvocellularis, and the nucleus lateralis tuberis (NLT) of the hypothalamus. These observations suggest that the NPO and NLT are the source of the neurosecretory innervation of the goldfish pituitary.

Eels were adapted to black- or white-coloured backgrounds and the pituitary glands were prepared for light and electron microscopy. Immunocytochemical staining was used to study the distribution of the neurohypophysial melanin-concentrating hormone in the neurointermediate lobe. The hormone was located in small, elliptical, electron-opaque neurosecretory granules, measuring approximately 120 x 90 nm. The neurones terminated on blood vessels in the centre of the neurohypophysis and on the basement membrane separating neural and intermediate lobe tissues. The results of both light and electron immunocytochemistry and of radioimmunoassay are consistent with a higher rate of hormone release from eels adapted to white backgrounds than from those adapted to black backgrounds. In addition to this, when fish that had been adapted to white tanks were transferred to black tanks, there was an accumulation of irMCH in the gland and an increased numerical density of secretory granules at nerve terminals. These results reinforce the proposal that MCH is released during adaptation to a white background, to cause melanin concentration and to inhibit MSH release, and that its release is halted in black-adapted fish.