COOPER, R.L.; VIELE, K.; STROMBERG , A.J.; Dept. Biology, Univ. of Kentucky, Lexington, KY, USA; Dept. Statistics, Univ. of KY; Dept. Statistics, Univ. of KY: Estimating the number of release sites and probability of firing within the nerve terminal by statistical analysis of synaptic charge

Investigating the function of individual synapses is essential to understanding the mechanisms that influence the efficacy of chemical synaptic transmission. The known simplicity of the synaptic structure at the crayfish neuromuscular junction (NMJ) and its quantal nature of release allow an assessment of discrete synapses within the motor nerve terminals. Our goal is to investigate the effect of the stimulation frequency on the number of active release sites (n) and the probability of release (p) at those active sites. Because methods based on direct counts often provide unstable joint estimates of (n) and (p) and underestimate n, we base our analysis on mixture modeling. In particular, the mixture modeling approach is used to estimate (n) and (p) for stimulation frequencies of 1Hz, 2Hz, and 3Hz. Our results indicate that as the stimulation frequency increases, new sites are recruited (thus increasing n) and the probability of release (p) increases. The increase in (n) and (p) are not as well reflected by estimates obtained by direct counting procedures and binomial distributions. Funded by NSF grants IBN-9808631 (RLC), NSF-ILI-DUE 9850907 (RLC), NSF-DMS-9971954 (KV), and NSF-IBN-0131459 (RLC, AJS, KV).