| Abstract: | We have carried out an electron microscopic investigation of retrogradely HRP-labeled nonpyramidal neurons in layers V and VI of the primary auditory cortex (AI), which are sources of transcallosal projections. We have established that on average 15.8±1.7% of the perikaryon surface of these cells is occupied by axo-somatic synapses. We detected in ultrathin sections from two to nine synapses on the profiles of the perikaryon of callosal neurons. All of these axo-somatic synapses are formed by axon terminals containing small flat synaptic vesicles and are characterized by symmetrical contacts. The length of the cross section of the contacts was on average 1.6±0.1 µm. The axon terminals of callosal fibers, antegradely labeled by the enzyme, form in the deep layers of the cortex asymmetrical synapses on the spines and stems of the dendrites. A possible functional significance of the axo-somatic synapses in the production of the impulse activity of callosal neurons in the deep layers of the AI region, is discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 23, No. 5, pp. 549–556, May, 1991. |
