Antifacilitation and facilitation in the cardiac ganglion of the spiny lobsterPanulirus interruptus

SummaryAntifacilitation and facilitation of synaptic transmission between cell 6 and the large cells were studied in the spiny lobster cardiac ganglion. Two-impulse experiments invariably produced antifacilitation in the second large-cell PSP at all inter-pulse intervals (10 msec to 10 sec) (Fig. 2). When conditioning trains with 2–4 impulses preceded the test impulse, the test PSP was antifacilitated at intervals of less than 100 msec and usually facilitated at intervals greater than 100 msec (Fig. 3). At intervals shorter than 50 msec the test PSP amplitude was nearly independent of the number of conditioning impulses. At greater intervals, the test PSP amplitude was a linear function of the number of impulses in the conditioning train (Fig. 4 and 5). A model was constructed based on the assumption thatF (defined asVT/V0, whereV0 andVT are the control and test PSP amplitudes, respectively) is the sum of antifacilitation (F−) and facilitation (F+) (Fig. 9).F− depends only on the separation between the last conditioning impulse and the test impulse and is described by the equation: $$F^ - = 1.0 - A_1 e^{{{ - t} \mathord{\left/ {\vphantom {{ - t} {\tau _1 }}} \right. \kern-\nulldelimiterspace} {\tau _1 }}} - A_2 e^{{{ - t} \mathord{\left/ {\vphantom {{ - t} {\tau _2 }}} \right. \kern-\nulldelimiterspace} {\tau _2 }}} $$ , wheret is the conditioning-to-test interval in seconds,A1=0.26,A2=0.74,τ1=0.02 sec, andτ2=4.1 sec.F+ is described by the equationN C $$(1 - e^{{{ - t} \mathord{\left/ {\vphantom {{ - t} {\tau _4 }}} \right. \kern-\nulldelimiterspace} {\tau _4 }}} )^2 \cdot e^{{{ - t} \mathord{\left/ {\vphantom {{ - t} {\tau _3 }}} \right. \kern-\nulldelimiterspace} {\tau _3 }}} $$ , whereN is the number of conditioning impulses,t is the interval between the end of the conditioning train and the test impulses,τ3=3.6 sec,τ4=0.08 sec, andC is a constant.