Figure 1. Norepinephrine Regulation of CRH Neurons via Local Synaptic Circuits.

(A) Loose-seal patch clamp recordings of the spiking responses of CRH neurons to bath application of norepinephrine (100 μM) in control aCSF and in GABA_A (PTX) and ionotropic glutamate receptor blockers (DNQX/APV).

(B) Time series of changes in spike frequency prior to (−5 to 0 min), during (0–5 min), and after norepinephrine application (100 μM) in control solution, PTX, and DNQX/APV (n = 9–14 cells/group).

(C) Mean spike frequency responses to norepinephrine without (control) and with the GABA_A (PTX) and glutamate receptor antagonists (DNQX/APV) (n = 9–14 cells/group).

(D) Whole-cell recording of the effect of norepinephrine (100 μM) on sEPSCs in a CRH neuron recorded in picrotoxin to block sIPSCs.

(E) Time plot of the norepinephrine-induced increase in the frequency of sEPSCs (n = 17 cells).

(F) Concentration dependence of the norepinephrine-induced increase in sEPSC frequency (n = 5–17 cells/group).

(G) The norepinephrine-induced increase in sEPSC frequency was blocked by TTX (n = 10 cells), suggesting action potential dependence.

(H) Whole-cell recording of the norepinephrine (100 μM) effect on sIPSCs in a CRH neuron recorded in DNQX/APV to block sEPSCs. Norepinephrine caused an increase in sIPSCs in some cells (1) and a decrease in sIPSCs in others (2).

(I) Time plots of the normalized increase and decrease in mean sIPSC frequency in response to norepinephrine in different cohorts of CRH neurons (n = 11 and 9 cells, respectively).

(J) Mean norepinephrine-induced increase (NE (+)) and decrease (NE (−) in sIPSC frequency relative to baseline (n = 9 and 8 cells, respectively). The norepinephrine-induced increase, but not decrease, in sIPSC frequency was blocked by TTX (n = 8 cells), suggesting the facilitation (NE (+)), but not the suppression (NE (−)), of sIPSCs by norepinephrine was spike dependent.

(K) Norepinephrine concentration dependence showing that the two sIPSC responses to norepinephrine had different concentration dependencies. The norepinephrine-induced suppression of sIPSCs (open circles) was dominant at lower concentrations, whereas the norepinephrine-induced facilitation of sIPSCs (closed circles) was seen in some but not all recorded cells at higher concentrations (n = 7–9 cells [suppression] and 2–11 cells [facilitation]). *p < 0.05; **p < 0.01.