Neurotransmitters as Regulators of Hypothalamic Function

Abstract

Neurons of the hypothalamus, like those of the entire central nervous system (CNS), are organized into circuits and networks with the communication between neurons involving either electrical synapses (which are a form of specialized gap junctions) or chemical synapses. When a gap junction is open, it allows free bidirectional migration of molecules and ions from the cytoplasm of one neuron directly into the cytoplasm of the other neuron. In electrical synapses, alternating opening and closing of gap junctions between two neurons creates a regulatory situation similar to that observed for gated ion channels imbedded in the plasma membrane (PM) of individual neurons. Although such bidirectional interneuronal communication via electrical synapses is not fully understood, it presumably allows two or more neurons to act together as a functional unit with very rapid information transfer. In contrast to the incomplete understanding of electrical synapses, there is abundant information about the widespread interneuronal signaling via chemical synapses, and this chapter will present that information in detail. Neuron-to-neuron communication via chemical synapses involves the release of chemicals from one neuron and their specific action on an adjacent neuron to alter its excitability. Neuron-derived compounds that alter the excitability of another neuron or a muscle fiber are defined as a neurotransmitter (NT), and the molecule structures of the many different NT exhibit great diversity.