Regional variation and characteristics of GABA-receptors in the mammalian CNS

Neurophysiological, biochemical and histochemical analyses have indicated a heterogeneous distribution of the GABA-ergic system in mammalian brain. The poor correlation between the regional distributions of presynaptic markers and synaptic receptors for GABA suggests that it is impossible to predict the functional importance of this neurotransmitter system in any particular brain region using either pre- or post-synaptic determinations alone. The possibility that the receptor affinity for GABA may vary significantly among different brain regions suggests that this may be another mechanism whereby the brain regulates the activity level of this transmitter system. Thus, in any given brain region, the storage and uptake capacities for GABA, the rates of its synthesis and release, and the number and affinity of GABA receptor recognition sites can all play a role in regulating GABA-ergic tone. Subtle alterations in any one or more of these parameters can lead to dysfunction, whose manifestation will depend upon the brain region involved. Regional distribution studies can also yield insights into the possible mechanisms of action of centrally-active drugs. Thus, a significant correlation between the regional distribution of a neurotransmitter receptor and a particular class of drug provides circumstantial evidence that the drug interacts with this receptor site. Such a situation appears to exist for the benzodiazepines and the GABA-receptor.