[Experimental changes of GABA receptor binding in the central nervous system (author's transl)]

The effects of etazolate and cartazolate, two pyrazolopyridine derivatives with anxiolytic actions, on the receptor binding of gamma-aminobutyric acid (GABA) was studied in vitro using membrane fractions prepared from rat brain. Both compounds increased the specific GABA receptor binding. This effect was markedly enhanced in the presence of several anions, predominantly halide ions. Pyrazolopyridines appear to modulate the binding properties of GABA receptors by acting on a site closely related to the chloride ion channel of the membrane. These results indicate that activation of the GABA system is a possible mechanism of action of pyrazolopyridines. In the second part of the study binding experiments were used to provide evidence for the presynaptic localisation of GABA receptors on primary afferent terminals in the dorsal horn of the rat spinal cord. Capsaicin-induced degeneration of primary afferent fibres significantly reduced the number of GABA receptors in the dorsal spinal cord, whereas the number of benzodiazepine and glycine receptors remained unchanged. The results support the role of GABA as transmitter involved in presynaptic inhibition in the spinal cord.