FIGURE 4.

Efferent synapses of chemogenetically silenced neurons are functionally unaltered. (A) Experimental design. (B) Recordings from cultures chronically treated with DREADD agonist (right) and cultures to which no agonist was applied (control, left). Illumination with blue light (1 ms duration, blue bars) either evoked synaptic currents with short latency (<6.5 ms, dark gray area in sample traces), and low jitter (putative monosynaptic connections, top row), synaptic currents with longer latencies (>6.5 ms) and larger jitter (putative polysynaptic, i.e., indirect connections, middle row), or no responses at all (bottom row). (C) In recordings from 26 untreated and 28 agonist-treated cultures, there was no significant difference in the fraction of monosynaptic, polysynaptic or unconnected neurons between control and DREADD agonist-treated cultures [Chi square test: X²(2, n = 54) = 0.35, p = 0.84]. Monosynaptic GABAergic connections (two in control cultures, one in DREADD agonist-treated cultures) were excluded from the analysis. (D) Post-synaptic current amplitudes observed within 8 ms after stimulus onset (complete gray area in B) in control cultures (median 13.7 pA) and cultures treated with DREADD agonist (median 14.4 pA) were not significantly different (Mann Whitney U rank sum test: U = 361.5, p = 0.97). Medians of the distributions are indicated by large black bars, means by small black bars, first and third quartiles by box boundaries and 5th and 95th percentiles by whiskers. Circles represent recordings from individual neurons.