Fig. 3: Glutamatergic inputs to the LHb from the LPO are inhibited by MOR activation.

a Schematic diagram of AAV2-hSyn-hChR2(H134R)-mCherry injection targets which project to the LHb. b Proportions of LHb neurons receiving functional synaptic connections from six input regions measured with optogenetic stimulation of terminals expressing ChR2. c Among connected neurons (n = 17–58), venn diagrams depict the numbers of LHb cells receiving optically stimulated glutamatergic and/or GABAergic synaptic input. d (Left) Experiment design: DAMGO (500 nM) was applied during optical synaptic stimulation experiments to probe for functional MOR presynaptic control of glutamate release from specific inputs. (Right) Change from baseline amplitude of optically-evoked EPSCs during DAMGO application. EPSCs from LPO terminal stimulation were most strongly inhibited by MOR activation: One-way ANOVA, df = 4, F = 4.11, p = 0.0057 followed by Tukey HSD pairwise comparisons. Data are expressed as mean with 25th and 75th percentiles e, (Left) Representative traces of optically-evoked EPSCs in an LHb neuron from a rat with ChR2 expressed in inputs from the LPO. DAMGO decreased the amplitude of light-evoked EPSC, which was partially reversed by the selective MOR antagonist CTAP (500 nM). Rise time was <2 ms, indicative of a monosynaptic response. (Right) Summary time course of the DAMGO inhibition across all optically-evoked LPO-LHb EPSCs (n = 12 cells/9 rats), indicated as the mean (circle) ± SEM. f LPO inputs to the LHb in female rats (left) had a similar overall connectivity rate but (middle) more GABAergic connections than glutamate connections. (Right) DAMGO inhibited light-evoked glutamatergic synaptic inputs from the LPO to the LHb in female rats as well. Means represented by horizontal lines with 25th and 75th percentiles. Tests are two-tailed. *p < 0.05, **p < 0.01.