The purpose of this application is to request continued support for a laboratory devoted to the experimental analysis of neurobiological mechanisms, mainly at the cellular level, by means of ultrastructural, electrophysiological and pharmacological techniques. The Laboratory of Neurobiology, open to graduate students and visiting scientists, is equipped with collecting and holding facilities necessary to take full advantage of the rich marine fauna which inhabits the littoral waters of Puerto Rico, as well as the terrestrial species found in the tropical rain forests of the island. Among the problem currently being investigated are: mechanisms of induction of excitability in crustacean muscle by chemical modification of membrane proteins; characteristics of channels induced by antigens in the membrane of denervated, immunized mammalian muscle fibers; activation of cholinergic endplate receptors and excitating-contraction coupling in vertebrate muscle.