Evidence for a dual control, by neurosecretion, of hormone synthesis and hormone release in the pituitary of the dogfish scylliorhinus stellaris

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Abstract
The intrinsic secretory cells of the neuro-intermediate lobes of the pituitary of the elasmobranch fish Scylliorhinus stellaris belong to two main categories (1) central cells which do not demonstrate any marked polarity of their cytoplasmic organelles and show no clear indications of being under neurosecretory control, and (2) peripheral cells which are polarized along an axis from a synthetic pole to a storage and release pole. Neurosecretory fibres make intimate contact with the two poles of these peripheral cells. The neurosecretory fibres may be classed as type A or type B by the size and appearance of the elementary neurosecretory vesicles they contain. These two fibres innervate the synthetic and release poles of the intrinsic cells respectively by direct contact of their terminals to form secretomotor junctions. It seems likely that there is a dual control of synthesis and release of a melanophore-dispersing hormone (MSH). The possibility that type A fibres inhibit MSH synthesis by a peptide substance with oxytocic action, and that MSH release is controlled by amine production by type B fibres is discussed.