LONG-TERM ADRENALECTOMY REDUCES HIPPOCAMPAL GRANULE CELL EXCITABILITYIN-VIVO

Ten days after bilateral adrenalectomy (ADX), neural transmission betw een the perforant path and hippocampal dentate granule cells was sever ely impaired in the anaesthetized rat, in that the slope of the stimul us-response curve was reduced to less than half the value in sham cont rols, the stimulation current necessary to elicit a standard populatio n spike (PS) field potential was increased approximately threefold, th e amplitude of PS and its ratio to the slope of the field excitatory p ostsynaptic potential (EPSP) were reduced, and high-frequency tetaniza tion (TET) of the perforant path resulted in potentiated PS with small er amplitude and higher onset latency in ADX rats than in sham control s. However, the fractional increase of PS amplitude and its decay foll owing TET were similar in 10 day-ADX and sham groups, from which it is inferred that long-term ADX entails a general decrease of dentate gra nule cell excitability, particularly at somatic membrane level, withou t specifically affecting the mechanism of long-term potentiation. None of the above changes occurred 24 after ADX.