Long-term potentiation as a function of test pulse intensity: a study using input/output profiles.

Input/output profiles of the population responses in CA1 were recorded in the rat hippocampal slice in vitro following stimulation of the Schaffer collaterals before and after theta-frequency patterned primed-bursts (PBs). The most robust potentiation was found for the population spike amplitude, which reached > 200% at low intensity test pulses, but decreased at high intensity. The latency of the population spike was more consistently decreased at high than low stimulus intensities. The enhancement of the population dendritic EPSPs was larger at low than high intensity. Intracellular recordings from CA1 neurons indicated that the intracellular and population EPSPs showed a similar saturation with stimulus intensity, while all single neurons fired at 60 microA intensity when the population spike only reached a mean 70% of its maximal amplitude, suggesting that population spike increase at > 60 microA intensity or following potentiation was caused by increased firing synchrony among neurons. It is suggested that input/output profiles are necessary for the standardization of the degree of long-term potentiation among different laboratories.

Blood pressure effects of lower abdominal aortic surgery with particular reference to the use of morphine and droperidol in modifying the responses.

Hypertensive responses during operations on the abdominal aorta are common. We have shown that hypertensive changes occur before cross-clamping of the aorta. We have also shown that droperidol modifies the hypertensive changes in operations on the lower aorta. Although further studies are required, our preliminary results show a higher rise of serum epinephrine and norepinephrine levels in one patient receiving morphine, as compared to one patient receiving the same dose per unit body weight of morphine plus droperidol. With maintenance of adequate pre-operative hydration and intra-operative fluid and blood replacement, declamping hypotension was transient in both groups of our patients.