Unit activity of the septum and hippocampus transplanted alone or together into the anterior chamber of the rat eye

Abstract

Unit activity of grafts of the septum and hippocampus, developing for 3–6 months in the anterior chamber of the eye was investigated in acute experiments on curarized orcerveau isole rats. Whereas neurons in the transplanted septum had spontaneous activity of irregular, regular, or rhythmic bursting type, activity was absent in hippocampal grafts or consisted of very infrequent synchronized population sites. If grafts of the septum and hippocampus developed together and contact was established between them, the same types of activity developed in the hippocampus as in the septum. In many paired grafts spontaneous epileptic phenomena were observed; they were easily provoked also by electrical stimulation of one of the grafts. Superfusion with medium with a high Mg++ concentration and low Ca++ concentration abolished spontaneous activity in most neurons of hippocampal but not septal grafts, and also suppressed some of the epileptic phenomena, evidence of the leading role of the septum in the organization of spontaneous hippocampal unit activity.