Long-term ionic plasticity of GABAergic signalling in the hypothalamus.

The hypothalamus contains a number of nuclei that subserve a variety of functions, including generation of circadian rhythms, regulation of hormone secretion and maintenance of homeostatic levels for a variety of physiological parameters. Within the hypothalamus, γ-amino-butyric acid (GABA) is one of the major neurotransmitters responsible for cellular communication. Although GABA most commonly serves as an inhibitory neurotransmitter, a growing body of evidence indicates that it can evoke post-synaptic excitation as a result of the active regulation of intracellular chloride concentration. In this review, we consider the evidence for this ionic plasticity of GABAergic synaptic transmission in five distinct cases in hypothalamic cell populations. We argue that this plasticity serves as part of the functional response to or is at least associated with dehydration, lactation, hypertension and stress. As such, GABA excitation should be considered as part of the core homeostatic mechanisms of the hypothalamus.