Distinct forms of Gq-receptor-dependent plasticity of excitatory transmission in the BNST are differentially affected by stress

Abstract

Long-term depression (LTD) is an important synaptic mechanism for limiting excitatory influence over circuits subserving cognitive and emotional behavior. A major means of LTD induction is through the recruitment of signaling via G(q)-linked receptors activated by norepinephrine (NE), acetylcholine, and glutamate. Receptors from these transmitter families have been proposed to converge on a common postsynaptic LTD maintenance mechanism, such that hetero- and homosynaptic induction produce similar alterations in glutamate synapse efficacy. We report that in the dorsolateral and ventrolateral bed nucleus of the stria terminalis (BNST), recruitment of G(q)-linked receptors by glutamate or NE initiates mechanistically distinct forms of postsynaptically maintained LTD and these LTDs are differentially regulated by stress exposure. In particular, we show that although both mGluR5- and alpha(1)-adrenergic receptor (AR)-dependent LTDs involve postsynaptic endocytosis, the alpha(1)-AR-initiated LTD exclusively involves modulation of signaling through calcium-permeable AMPA receptors. Further, alpha(1)-AR- but not mGluR5- dependent LTD is disrupted by restraint stress. alpha(1)-AR LTD is also impaired in mice chronically exposed to ethanol. These data thus suggest that in the BNST, NE- and glutamate-activated G(q)-linked signaling pathways differentially tune glutamate synapse efficacy in response to stress.

Fig. 1.

α₁-AR LTD requires clathrin-dependent endocytosis. (A) Methoxamine (100 μM) produces LTD in control cells (n = 6, ■) but not in cells infused with 2 μM (in patch solution) of the dynamin inhibitory peptide (○, n = 5; P > 0.63). (B) Histogram comparing the EPSCs of the two conditions in A (min 50–55). The black bar is the control, and the white bar is the dynamin inhibitory peptide (*P < 0.03). (C) Coapplication of 20 μM U0126 and 100 μM methoxamine induces LTD (n = 5; P > 0.0001). methox, methoxamine.

Fig. 2.

α₁-AR LTD confers a loss of sensitivity to 100 μM Naspm in the BNST. (A) Ten minutes of 100 μM Naspm produced a depression of EPSCs in naive slices (n = 6; P < 0.002). (B) Following induction of LTD by 100 μM methoxamine (methox), 100 μM Naspm failed to reduce EPSCs further (n = 5; P > 0.83). (C) Following induction of mGluR 5 LTD by 100 μM (RS)-3,5-dihydroxyphenylglycine (DHPG), 100 μM Naspm significantly reduced EPSCs (■, n = 8; P < 0.001), and this depression was significantly different from time-matched control experiments without Naspm (○, n = 7; *P < 0.03). (D) Histogram comparing 100 μM Naspm in naive slices (min 30–35), 100 μM Naspm following 100 μM methoxamine (min 65–70 renormalized), and 100 μM Naspm following 100 μM DHPG (min 55–60 renormalized; *P < 0.05 for one-way ANOVA). n.s., not significant.

Fig. 3.

GluR1 C-terminal peptide attenuates α₁-AR LTD but not mGluR5 LTD. (A) Infusion of a peptide from the C terminus of GluR1 (n = 6) but not GluR2 (n = 5) attenuates the LTD induced by application of 100 μM methoxamine (methox; P < 0.05; GluR1 vs. GluR2). (B) Neither the GluR1 (n = 7) nor GluR2 (n = 4) peptide attenuated the LTD induced by 100 μM (RS)-3,5-dihydroxyphenylglycine (DHPG).

Fig. 4.

Chronic restraint stress occludes α₁-AR LTD but not mGluR5 LTD. The 10-day restraint stress paradigm blocked α₁-AR LTD in the vlBNST (n = 6; P > 0.78) (A) and significantly attenuated α₁-AR LTD in the dlBNST (B) (n = 5 in both conditions; P < 0.05). methox, methoxamine. (C and D) Stress exposure does not manipulate mGluR5 LTD induced by 100 μM (RS)-3,5-dihydroxyphenylglycine (DHPG) in either the dlBNST (n = 5 for both conditions) or vlBNST(stress: n = 7, naive: n = 6). (E and F) Stress paradigm significantly attenuated the function of CP-AMPARs in the vlBNST (min 25–30; n = 8 for both conditions; P < 0.05). n.s., not significant.

Fig. 5.

Chronic exposure to ethanol attenuates α₁-AR LTD in the BNST. (A) Sham mice demonstrated robust LTD when stimulated with 100 μM methoxamine (methox), similar to naive mice (n = 6). (B) Response to 100 μM methoxamine (methox) was attenuated in the BNST in mice that had experienced one withdrawal following CCE (n = 7). (C) Methoxamine (methox; 100 μM) resulted in attenuated LTD following a CIE paradigm (n = 5). (D) Histogram comparing sham, CCE, and CIE conditions: both CCE and CIE conditions are significantly attenuated from control conditions by one-way ANOVA (min 40–45; *P < 0.05 for ANOVA; CIE vs. sham, P < 0.05; CCE vs. sham, P < 0.05).