Noradrenergic synaptic function in the bed nucleus of the stria terminalis varies in animal models of anxiety and addiction

Abstract

Lewis rats show increased anxiety-like behaviors and drug consumption compared with Sprague-Dawley rats. Prior work suggests norepinephrine (NE) signaling in the bed nucleus of the stria terminalis (BNST) could have a role in mediating these phenotypes. Here, we investigated NE content and dynamics in the ventral BNST (vBNST) using fast-scan cyclic voltammetry in these two rat strains. We found that NE release evoked by electrical stimulus and its subsequent uptake was dysregulated in the more anxious Lewis rats. Because addiction is a multifaceted disease influenced by both genetic and environmental factors, we hypothesized NE dynamics would vary in these strains after the induction of a physical dependence on morphine. Following naloxone-precipitated morphine withdrawal, NE release and uptake dynamics were not changed in Lewis rats but were significantly altered in Sprague-Dawley rats. The alterations in Sprague-Dawley rats were accompanied by an increase in anxiety-like behavior in those animals as measured with the elevated plus maze. These studies suggest novel mechanisms involved in the development of affective disorders, and highlight the noradrenergic system in the vBNST as a common substrate for the manifestation of pathological anxiety and addiction.

Figure 1

Fast-Scan Cyclic Voltammetry of norepinephrine (NE) in the bed nucleus of the stria terminalis (BNST). (a–c) Tissue content analysis of catecholamines in the BNST and nucleus accumbens (NAc). (d) Representative histology of recording electrode placement in the ventral BNST (vBNST) (black dashed circle) and area excised for tissue content analysis (red dashed line; LV, lateral ventricle; AC, anterior commissure). (e) Representative cyclic voltammogram of NE at [NE]_max. (f) Representative color plots demonstrating NE release and uptake in baseline conditions, following 2 mg/kg raclopride, or 5 mg/kg idazoxan.

Figure 2

Comparison of norepinephrine (NE) dynamics in naïve Lewis (L) and Sprague-Dawley (SD) rats. (a) Representative concentration traces demonstrating NE release and uptake in the ventral bed nucleus of the stria terminalis (vBNST) of both SD and L rats (scale bar, 100 nM; gray box =stimulation, 60 pulses, 60 Hz). (b) Input–output curve of [NE]_max at 20, 40, 60, 80, 100 and 120 pulses in SD and L rats. (c) Histogram of mean clearance half-life of NE following 60 Hz, 60 pulse stimulation in both SD and L rats.

Figure 3

Effect of idazoxan (IDA) and morphine on norepinephrine release in the ventral bed nucleus of the stria terminalis (vBNST). (a and b) Representative concentration traces of Sprague-Dawley (SD) and Lewis (L) rats, respectively. Solid line—evoked norepinephrine (NE) concentration with 60 Hz, 60 pulses stimulation; dashed line—evoked NE concentration following 5 mg/kg IDA with the same electrical stimulus. (c) Average [NE]_max following 5 mg/kg IDA relative to pre-drug stimulated release. (d) Change in [NE]_max as percent of pre-drug baseline in both Sprague-Dawley (closed squares) and Lewis (open circles) rats, plotted vs log concentration of IDA (n=3 each strain). (e) Average [NE]_max to acute 5 mg/kg morphine relative to pre-drug stimulated release. (f) Average clearance half-life following acute 5 mg/kg morphine relative to pre-drug stimulated release.

Figure 4

Morphine dependence in Sprague-Dawley (SD) and Lewis (L) rats. (a) Model of drug administration paradigm. (b) Global withdrawal scores, (c) pre-withdrawal body weight (as % of day 1), and (d) fecal boli weight in SD morphine/naloxone (SD-MN) and L-MN rats following withdrawal, compared with control SD saline/naloxone (SD-SN) and L-SN rats. Time spent in (e) open arms (f), center or (g) closed arms of the elevated plus maze as a fraction of total time in the maze in SD-MN, SD-SN, L-MN, and L-SN rats.

Figure 5

Clearance half-life and change in response following idazoxan (IDA) administration in morphine/naloxone (MN) animals vs saline controls. (a) t_1/2 and (b) change in [NE]_max as percent of pre-drug baseline in MN Sprague-Dawley (SD) rats vs saline controls (P<0.05). (c) t_1/2 and (d) change in [NE]_max as percent of pre-drug baseline in MN Lewis (L) rats vs saline controls (n.s.). SN, saline/naloxone.