Vertebrate GABA receptors

Events Occurring in the Axotomized Facial Nucleus

Transection of the rat facial nerve leads to a variety of alterations not only in motoneurons, but also in glial cells and inhibitory neurons in the ipsilateral facial nucleus. In injured motoneurons, the levels of energy metabolism-related molecules are elevated, while those of neurofunction-related molecules are decreased. In tandem with these motoneuron changes, microglia are activated and start to proliferate around injured motoneurons, and astrocytes become activated for a long period without mitosis. Inhibitory GABAergic neurons reduce the levels of neurofunction-related molecules. These facts indicate that injured motoneurons somehow closely interact with glial cells and inhibitory neurons. At the same time, these events allow us to predict the occurrence of tissue remodeling in the axotomized facial nucleus. This review summarizes the events occurring in the axotomized facial nucleus and the cellular and molecular mechanisms associated with each event.

Chloride ions preferentially mask high-affinity GABA binding sites

Chloride ions (Cl-) act to regulate the appearance of gamma-aminobutyric acid (GABA) binding sites in synaptic membranes from bovine retinas. Scatchard analysis indicates that the presence of Cl- results in a preferential decrease (85%) in the number of high-affinity binding sites, with no statistically significant change in the affinity (KD) of either the high- or low-affinity sites. The finding that the appearance of this binding site is altered by the presence of Cl- may indicate that Cl- acts, either directly or indirectly, to regulate the appearance, and hence function, of the high-affinity GABA receptor.

GABA binding processes in rat brain and liver

Although these studies have provided some further insight into GABA binding processes associated with transport and receptor-activation, such attempts remain limited due to the lack of specificity of the ligands used to displace these components. Thus, BMI appeared to interact with both transport and synaptic receptor sites for GABA. Perhaps certain GABA-agonists (e.g., muscimol, isoguvacine) will be shown to interact more specifically with synaptic GABA-receptors? So-called "specific" binding of GABA and its analogues, or antagonists might not be the issue to be kept in focus in this type of experiment, especially since it cannot be separated into presynaptic, postsynaptic and non-synaptic components. The specificity of an interaction of ligand with membrane site may be determined by other requirements of the particular system concerned. In any case, it seems essential to examine the binding sites, themselves, in order to define more clearly which of these are involved in receptor-activation and in uptake. An approach involving the isolation and purification of GABA-receptors should provide evidence for specific binding of GABA to its postsynaptic receptors.