LONG-TERM EFFECTS OF INTERMITTENT VERSUS CONTINUOUS ETHANOL EXPOSURE ON HIPPOCAMPAL SYNAPSES OF THE RAT

The hippocampus is known to be very sensitive to a large spectrum of d ifferent neurotoxins including ethanol. Ethanol administered continuou sly or intermittently may affect the hippocampus in different ways. In termittent administration of ethanol has many features in common with the low level electrical stimulation protocols which lead to the funct ional changes associated with the phenomenon of kindling. In this stud y, the differential effects of intermittent intraperitoneal ethanol in jections (3 g/kg twice daily) and continuously administered ethanol in drinking water (20 %) on hippocampal synapses in the rat were studied using ethanolic phosphotungstic acid staining and electron microscopy . After 1 month of intermittent exposure a significant reduction (18 % ) of synapses was seen in the stratum lucidum of the CA3 region. Conti nuously treated animals showed no significant change over this time de spite a higher total ethanol intake. In the dentate gyrus, a compensat ory increase in supragranular synaptic number was seen only in continu ously treated animals. These findings demonstrate the sensitivity of s ynapses of the hippocampus to the presence of ethanol and the larger e ffects of peaking ethanol concentrations compared to more constant lev els. These results emphasize the need to consider the differential eff ects of various types of ethanol consumption also on the human brain.