Department of Integrative Biology

1. The heart of the nudibranch mollusc Archidoris monterey-ensis is uniquely responsive to regulation by identifiable cardiac motor neurons. The neurotransmitters mediating the strong excitatory and inhibitory actions of the neurons are unknown. 2. In this study we developed an infused, in vitro preparation of the Archidoris heart to determine which of several cardioactive transmitters described in mollusks could affect changes in the rate, amplitude, or tonus of cardiac contractions. Several neurotransmitters we tested increased the rate and amplitude of heart contractions, including serotonin (threshold