Cortical and thalamic effects of local application of pentazocine to the rat somatosensory cortex.

Cortical and thalamic somatosensory evoked activity was studied following local application of 3% pentazocine to the primary somatosensory SI area (PSA) or to the parietal association area (PAA) of the rat cerebral cortex. At cortical level pentazocine affected the responsiveness of the two cortical areas in a way at least in part opposite. In PSA it essentially depresses the negative wave of the responses, whereas in PAA it increases both the positive and the negative components of the evoked potentials. The changes observed were restricted to the cortical region on which the drug was applied. At thalamic level, administration of pentazocine to the PSA or the PAA did not modify the bioelectrical activity recorded from the center median-parafascicular complex. It is concluded that pentazocine has a direct influence on cortical neurons involved in somatosensory processes. The failure of pentazocine-induced cortical changes to modulate neuronal activity at thalamic level is discussed.