Neuronal activity in suspension transplants of the neocortex

The characteristics of suspension (ST) and tissue (TT) transplants of the embryonal neocortex, transplanted into adult rats into the neocortical region of the representation of the vibrissae, were compared. The degree of taking of the ST and the TT did not differ significantly (89.5 and 95%, respectively). Transplants completely isolated from the brain were not found in the ST on the basis of histological and electrophysiological indices. The reactivity of ST neurons during electrical stimulation of the brain structures of the recipient and sensory stimulation, like the latent periods of the on-responses, did not differ significantly in the ST and the TT; however, the per cent of neurons responding with on-responses, was nearly twice as low in the ST as in the TT. At the same time, there were substantially more neurons in the ST responding to tactile stimulation with inhibition of discharges. It is hypothesized that the disruption in the primary cytoarchitectonics of the ST which takes place inevitably in the preparation of the suspensions is a cause of the differences indicated between the ST and the TT.