Two mechanisms involved in transmission at a ganglionic synapse will be studied: 1) the function of presynaptic autoreceptors, and 2) the release of transmitter by the neuronal cellbody. Both could be involved in modulating ACh secretion and action. These experiments will be done in the avian ciliary ganglion. The co-existence of substance P and enkephalines in this ganglion also provides the opportunity to analyze the postulated role of these peptides in neurotransmission. The interesting possibility of interaction between opiates and ACh autoreceptors in regulating ACh release will be examined. Neuronal soma release is a new concept in synaptic physiology. It may provide feedback regulation of presynaptic release or it may serve as a sefl-biasing device in regulating membrane excitability. Since these mechanisms involve ionically and chemically activated channels, a study with the membrane patch clamp technique will be initiated. One issue of particular interest will be the investigation of the stability of cholinergic channels in neurons and how this property is dependent upon the interaction of the neuron with its synaptic target and its synaptic input. Cholinergic neurons in the CNS are directly involved in movement, memory, learning, etc. Understanding ACh dynamics could be of importance in revealing mechanisms involved in these fundamental CNS functions, and this subject is indeed of clinical relevance because of the recent discovery that dysfunction and eventual death of a group of cholinergic neurons in the human brain may well be the primary cause of ALzheimer's Disease. The patch clamp technique is best used on a preparation where neuronal elements can be visualized, therefore a new "in vitro" preparation will be used. The presynaptic cell forming the bird's accessory nucleus will be grown in culture and caused to synapse with dissociated ciliary cells added to the culture. These preparations will open new avenues of inquiry such as direct study of calcium channels in presynaptic terminals and how they are regulated by neurotransmitters, membrane potentials, and second messengers.