ABSTRACT
Chemical characteristics of callosal neurons in the frontal and occipital cortex of Wistar rat were studied by means of combined method of HRP retrograde tracing andimmunocytochemistry of glutamate (Glu) and ?-aminobutyric acid (GABA). Glutamate containing callosal neurons were large or medium sized pyramidal cells and mainly localized in layers Ⅱ/Ⅲ, Ⅴ and Ⅵ. They tended to appear in clusters. GABA containing callosal neurons were also found. They were medium sized nonpyramidal cells with round, elliptic, or fusiform soma and were mostly localized in layers Ⅴ and Ⅵ. They also tended to appear in clusters. The percentage of GABA containing callosal neurons (about 8% and 10% in frontal and occipital cortex respectively)was much less than that of glutamate containing callosal neurons (about 17% and 29% in frontal and occipital cortex respectively). These results further confirmed that part of callosal cells used glutamate as an excitatory transmitter and firstly confirmed that some callosal neurons contained an inhibitory transmitter GABA morphologically. In view of the existence of GABA containing callosal neurons, it also suggested that at least in rat cerebral cortex,some GABA containing neurons had longer projections than local circuit neurons. According to the results of ours and other authors, we suggested that callosal system was the one that contained different kinds of neurotransmitters, and that diversification of the transmitters and their interaction in the callosal system was one of the neuroanatomical bases of the complicated and advanced functions of the callosal neurons.