Figure 4. Enkephalin evokes outward currents in CA1 parvalbumin (PV) interneurons through both mu and delta opioid receptors.

(A) Schematic of whole-cell voltage clamp recording configuration from PV interneurons with peptide uncaging. (B) Average outward currents evoked by photoactivation of N-MNVOC-LE (6 μM) with an 84 mW light flash in the absence (black, artificial cerebrospinal fluid [ACSF], n = 9 cells from five mice) and presence of mu and delta opioid receptor antagonists (red, CTOP, n = 10 cells from six mice; blue, TIPP-Psi, n = 11 cells from six mice; purple, CTOP+ TIPP-Psi, n = 5 cells from three mice). Scale bar: x = 5 s, y = 20 pA. (C) Summary of peak current amplitudes shown in B. (D) Linear optical power-response curve of peak current as a function of light intensity, in the absence (ACSF, black, n = 9 cells per laser intensity) and presence of either CTOP (red, n = 10 cells) or TIPP-Psi (blue, n = 11 cells). (E) Logarithmic optical power-response curves of the data in D normalized to the maximal peak current observed in each condition. (F) Rising phase of the average peak-normalized outward currents evoked by photoactivation of CYLE (6 μM) with an 84 mW light flash in the absence (black, ACSF, n = 11 cells from four mice) and presence of mu and delta opioid receptor antagonists (red, CTOP, n = 10 cells from four mice; blue, TIPP-Psi, n = 12 cells from four mice). (G) Time constants of current activation in response to photoactivation of CYLE from F. (H) Schematic of viral Cre-dependent mu opioid receptor over-expression in CA1 of PV-Cre mice. (I) Average outward currents evoked by photoactivation of CYLE by an 84 mW light flash in the presence of TIPP-Psi in either PV-Cre; tdTom mice (blue, data from B) or PV-Cre mice overexpressing the mu opioid receptor (purple, n = 8 cells from three mice). Scale bar: x = 10 s, y = 20 pA. (J) Summary of current amplitudes shown in I. (K) Time constants of current activation in response to photoactivation of CYLE.

Figure 4—figure supplement 1. Sensitivity of somato-dendritic currents to the G protein-coupled inward rectifier K⁺ (GIRK) blocker Ba²⁺ and mu opioid receptor expression level.

(A) Average outward currents evoked by photoactivation of CYLE with a 84 mW light flash in the absence (black, artificial cerebrospinal fluid [ACSF], n = 13 cells from seven mice) and presence of mu and delta opioid receptor antagonists (red, CTOP, n = 14 cells from 10 mice; TIPP-Psi, n = 13 cells from nine mice), as well as Ba²⁺ (1 mM) (gray, ACSF + Ba²⁺, n = 8 cells from two mice; light red, CTOP + Ba²⁺, n = 10 cells from four mice; light blue, TIPP-Psi + Ba²⁺, n = 10 cells from four mice), and the hyperpolarization-gated cyclic nucleotide (HCN) blocker ZD7288 (lightest red, CTOP + Ba²⁺, ZD7288, n = 9 cells from three mice), as indicated. Scale bar: x = 5 s, y = 25% of current without Ba²⁺ or ZD7288. (B) Summary of the percentage of the average peak current amplitude that is blocked in each condition shown in A. (C) Peak amplitude of the MOR current in Pvalb^Cre neurons expressing mCh-2A-hMOR vs. red fluorescence in the recorded cell, as well as the Pearson’s correlation coefficient. For this comparison, all cells were used regardless of fluorescence level. Meanwhile, in Figure 4I–K, only cells that had fluorescence >250 were included. (D) Time constant of MOR-current activation in Pvalb^Cre neurons expressing mCh-2A-hMOR vs. red fluorescence in the recorded cell, as well as the Pearson’s correlation coefficient.