Topical application of penicillin into hippocampal in vitro slices: A methodological study using benzyl (14C) penicillin

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Abstract
A gas pressure system is employed for topical application of pico/nanoliter volumes of 9 mmol/l benzyl (14C) penicillin into guinea pig in vitro transverse hippocampal slices. Control of pressure pulse parameters enables ejectates, computed after liquid scintillation, from 10 .mu.m, 5.mu.m and 2 .mu.m pipettes with high reliability of ejection. Ejection performance of 5 .mu.m and 2 .mu.m pipettes was studied. For the 5 .mu.m tips, with the chosen ejection parameters, feeding pressure=0.5 MPA[mega-pascal], feeding pulse duration 50 ms, a 99% ejection incidence was obtained (n [number] = 200). The mean volumes ejected were 0.12 and 0.5 nl (n = 50) for 1 and 4 pulses delivered, respectively. Corresponding ejectate means obtained from five 2 .mu.m pipettes given a feeding pressure of 1.5 MPa, and a feeding pulse duration of 70 ms, were 0.04 and 0.13 nl. Statistical evaluation of the individual pipette ejection performances gave characteristic regression slopes within each pipette group. A comparison between visually controlled injection into oil and injection into slice showed a close correspondence. Applicability of the ejection method is discussed in relation to functional studies on the conversion of single neurons into epileptic ones.