Fig. 3.

Pharmacology and kinetic characterization of excitatory and inhibitory synaptic events. A, Sample traces of evoked responses to glutamate application on afferent E16 neurons, exhibiting fast- and slow-decaying responses. When the membrane potential was clamped at −40 mV, the slow response was near its reversal potential. At 0 mV, the slow response was fully reversed and was outward, whereas the fast response was at its reversal potential. Right, Illustration of three afferents, stimulated for the same postsynaptic cell. In the top trace, there was no response of the postsynaptic cell, in themiddle trace stimulation of another afferent produced a fast response, and stimulation of yet another afferent,bottom, produced a slow IPSC. The decay time constant of the synaptic responses was determined by a best fit exponent from the peak with a time constant in these examples of 15.8 and 4.8 msec. This is illustrated in A in which the open symbol marks a slowly decaying response, and the closed symbol marks a response with a rapid time constant.B, Differential effects of NT-3 and BDNF on evoked EPSCs and IPSCs. The initial response to a single stimulation was measured, and the percentage of excitatory and inhibitory connections evoked by afferent stimuli were plotted. In control cultures, 86.7% of total PSCs were excitatory and 13.3% were inhibitory. In BDNF plus NT-3-treated cultures, 65.6% were excitatory and 34.4% were inhibitory. In BDNF-treated cultures 53.6% of the PSCs were excitatory and 46.4% were inhibitory. In NT3-treated cultures, 92.4% were excitatory and only 7.6% were inhibitory. Differences between the proportion of excitatory and inhibitory synapses were statistically significant (*p < 0.002, χ² test) in BDNF or NT-3 plus BDNF-treated cultures compared with controls. In NT-3 alone-treated cultures, the proportion of excitatory and inhibitory synapses was not statistically different from controls.