Fig. 6

Substance P reduces the rate of information transmission (A) Synaptic events in the morning before (pink) and after (blue) antagonizing NK1Rs. Note the spontaneous events in absence of stimulus (green boxes) and variability of responses to different cycles of the stimulus. (B) Signal-to-noise ratio (SNR) as a function of contrast around C1/2 in the morning, before (pink) and after (blue) injection of L-733,060 (p < 10−5; KS test). Each point shows the mean ± SEM. (C) As (B) but in the afternoon, before (green) and after (black) injection of substance P (p < 10−5; KS test). (D) Average SNR across a 20% range of contrasts under the four conditions shown in (B) and (C). (E) Specific information in bits for synaptic events containing different numbers of quanta in the morning. L-733,060 (blue) reduced the information carried by both univesicular and multivesicular events (n = 11 synapses; p < 10−6, KS test). (F) As (D), but in the afternoon. Injection of substance P increased the information carried by multivesicular events (n = 12 synapses; p < 10−4, KS test). (G) Mutual information (bits s−1 with stimulus presentation at 5 Hz) in four conditions: morning (AM, n = 24 synapses); morning after injection of the antagonist L-733,060 (AM + L733, n = 11); afternoon (PM, n = 12 synapses), and afternoon after injection of substance P (PM + SP, n =12 synapses). All pair-wise comparisons were significantly different at p < 10−4 (KS test) except for “AM + L733” versus “PM + SP” (p = 0.7). See also Figures S4 and S5.