Fluorescence localization of monoamines in crab neurosecretory structures.

There is a growing body of evidence supporting the hypothesis that neurosecretory cells control the release of their own products by the same general mechanisms which operate in other neurones. They integrate inhibitory and excitatory synaptic input, propagate action potentials along their axons, and they release their products as a result of depolarization of their terminals by a calcium-dependent mechanism (review: Bern & Yagi, 1965; and, for example, Douglas & Paisner, 1964 a, b; Haller et al. 1965; Dicker, 1966; Fridberg et al. 1966; Cooke, 1964, 1967; Kater, 1968a; Dyball & Koizumi, 1969). The uncertainty preventing acceptance of this hypothesis results from the presence in a number of neurohaemal structures of other nervous and nonnervous elements. These, on morphological grounds, may be considered for a role in the control of neurosecretory release (e.g. reviews: Bern, 1962; and Knowles, 1967; also, Enemar & Falck, 1965; Odake, 1967; Bjorklund, 1968; Kobayashi, Hirano & Oota, 1965; Knowles & Vollrath, 1966; Scharrer, 1963; Bern, Yagi & Nishioka, 1965; Normann, 1965). Here and in the following paper (Berlind, Cooke & Goldstone, 1970) we take up this problem in crab pericardial organs (Alexandrowicz, 1953). This paper describes monoamine-containing axons and terminals distributed in parallel with neurosecretory axons and terminals (Maynard, 19616; Maynard & Maynard, 1963; Cooke, 1964). The following paper presents experiments designed to test the involvement of monoamines in release of heart-excitatory material from the pericardial organs. A third paper (Berlind & Cooke, 1970) adds new evidence that the heartexcitatory material released is peptide in nature and is not accompanied by detectable protein or enough monoamine to affect the heart. A brief summary of this work has appeared (Cooke, Berlind & Goldstone, 1970). Alexandrowicz (1953), on morphological grounds, proposed a neurohaemal function for pericardial organs, and Alexandrowicz & Carlisle (1953) found that pericardial organ extracts had potent heart-excitatory effects. Cooke (1964) found that heartexcitatory material is released from isolated pericardial organs when stimulation results in a slowly conducted component of the compound action potential as recorded from the trunks of the plexus. There are cells in the ventral (thoracic) ganglion of crabs having the morphological features of neurosecretory cells (Matsumoto, 1958). These contribute axons and terminals to the pericardial organs (Maynard, 1961 a, b) and are