THE EFFECTS OF LINDANE AND LONG-TERM POTENTIATION (LTP) ON PYRAMIDAL CELL EXCITABILITY IN THE RAT HIPPOCAMPAL SLICE

An in vitro orthodromic stimulation technique was used to examine the effects of lindane and long-term potentiation (LTP) inducing stimuli, alone or in combination, on the excitatory afferent terminal of CA1 py ramidal cells and on recurrent collateral evoked inhibition using the rat hippocampal slice model. Hippocampal slices of 400 mu m thickness were perfused with oxygenated artificial cerebrospinal fluid. Stimulat ion of Schaffer collateral/commissural fibers produced extracellular e xcitatory postsynaptic potential (EPSP) and/or population spike (PS) r esponses recorded from electrodes in the CAI region. A paired-pulse te chnique was used to measure gamma-aminobutyric acid (GABA(A))-mediated recurrent inhibition before and after treatments. After both lindane and LTP, larger PS amplitudes for a given stimulus intensity were seen . The resulting leftward shift in the curve of the PS amplitude versus stimulus intensity was larger after LTP than after 25 mu M lindane. B oth lindane and LTP treatments reduced PS thresholds and reduced or el iminated recurrent inhibition as measured by paired-pulse stimulation at the 15 msec interval. The reduction of recurrent inhibition after b oth treatments was more pronounced at lower stimulus intensities. When LTP stimuli were applied after lindane exposure a further large shift to the left was seen in the PS amplitude versus stimulus intensity cu rve. A smaller shift to the left was seen in the PS amplitude versus s timulus intensify curve only at the higher stimuli when lindane exposu re occurred after LTP. Only at low stimulus intensities were further a rgumentations seen in PS amplitudes when the ITP stimuli was followed by a second LTP stimuli. Previous exposure to 25 mu M lindane stimuli does not block the development of a further robust LTP in this in vitr o model. (C) 1997 Intox Press, Inc.