[Changes in spatio-temporal patterns after long-term potentiation (LTP) in mouse hippocampal slices and effects of trichloroethylene on LTP].

Spatio-temporal patterns of neuronal activity after the induction of long-term potentiation (LTP) in mouse hippocampal slices were studied with the use of a real-time high-resolution optical recording system. The slices were stained with voltage-sensitive dye and then high-frequency pulses (tetanus) were delivered to Schaffer collaterals of CA3 at the stratum radiatum of CA1. Optical signals as well as field potential in response to test pulses were potentiated after tetanus. The area of response measured by optical recording was slightly but significantly enlarged after tetanus, suggesting that the propagation of optical responses from CA1 towards the subiculum was enlarged. It was suggested that a great increase in neuronal activity was elicited at CA1 and the subiculum after LTP. These changes of spatio-temporal patterns of neuronal activity may contribute to learning and memory. The effect of trichloroethylene (TCE) on LTP was studied with the use of both electrical and optical and recording. The hippocampus from mice injected with 300 mg/kg or 1000 mg/kg TCE was sliced 24 hours after TCE-administration. Test pulses were delivered to Schaffer collaterals every 30 sec and the field potential from the stratum pyramidale of CA1 was recorded. At 40 min after the application of tetanus, population spikes (PS) were potentiated in all groups, but the post/pre ratio of PS was smaller in TCE groups than in the control. Optical recording was also carried out in 1000 mg/kg TCE-injected mice. At 40 min after tetanus, the optical signal response to the test pulse was potentiated in both TCE and control groups, but the post/pre ratio of the optical signals was smaller in TCE than in the control. No significant difference was detected in the increase in the neuronal response area between TCE and the control. It was suggested that TCE depressed the LTP, whereas the increase in the area after tetanus meant that a good amount of neuronal activity was still potentiated.