GABAergic characteristics of transcallosal activity of cat motor cortical neurons

GABAergic characteristics of transcallosal activity of cat pyramidal tract neurons (PTNs) and non-PTNs (nPTNs) were studied with stressing on GABAB receptors. PTNs and nPTNs were further classified into group 1 (< 10 ms) and group 2 (> 10 ms) based on the latency upon transcallosal stimulation. However, mainly the results of group 1 neurons were presented here, due to the small number of group 2 neurons. GABA, bicuculline, CGP 35348 and phaclofen were iontophoretically applied. The spike number to 20 trials of transcallosal stimulation was 8.9 +/- 4.3 (mean +/- S.D.) for group 1 PTNs (n = 14) and 10.4 +/- 4.5 for group 1 nPTNs (n = 38) under the control conditions. CGP 35348, phaclofen and bicuculline significantly increased the spike numbers in both cases. The increase was greater for nPTNs than for PTNs. GABA decreased them. The transcallosal latency was 3.9 +/- 1.1 ms for PTNs under the control conditions. CGP 35348, phaclofen and bicuculline significantly shortened the latency, and GABA elongated it. The transcallosal latency for nPTNs under the control conditions was 2.7 +/- 1.2 ms. This was significantly shortened by application of CGP 35348, phaclofen or bicuculline. GABA restored it. In conclusion, CGP 35348, phaclofen and bicuculline increased spike discharge and shortened the latency upon transcallosal stimulation for both group 1 PTNs and nPTNs.