Effect of TPMPA (GABA_C receptor antagonist) on neuronal response properties in rat barrel cortex

GABA_C receptors are ligand-gated chloride channels and have important roles in some neurological functions like vision. Recent investigations demonstrated that these receptors are also expressed in the somatosensory cortex. In this study, we investigated the effect of (1,2,5,6-tetrahydropyridin-4-yl)methylphosphinic acid (TPMPA) (GABA_C receptor antagonist) on the properties of the neuronal response to natural stimuli (whisker deflection) in deep layers of rat barrel cortex. Twenty-eight male Wistar rats, weighing 230-260 g, were used in this study. TPMPA (100 μmol/rat) was administered intracerebroventricularly (ICV). Neuronal responses to deflection of principal (PW) and adjacent (AW) whiskers were recorded in barrel cortex using tungsten microelectrodes. A computer-controlled mechanical displacement was used to deflect whiskers individually or in combination at 30 ms inter-stimulus intervals. ON and OFF responses for PW and AW deflections were measured. A condition-test ratio (CTR) was computed to quantify neuronal responses to whisker interactions. Our data suggest that ICV administration of TPMPA increased neuronal spontaneous activity, ON and OFF responses to PW, and/or AW deflections. However, CTR for neither ON nor OFF responses changed following TPMPA administration. The results of this study demonstrated that inhibition of GABA_C receptors by TPMPA can modulate neuronal response properties in rat barrel cortex.