Effects of a selective Y2R antagonist, JNJ-31020028, on nicotine abstinence-related social anxiety-like behavior, neuropeptide Y and corticotropin releasing factor mRNA levels in the novelty-seeking phenotype

Abstract

An outbred rat model of novelty-seeking phenotype has predictive value for the expression of locomotor sensitization to nicotine. When experimentally naïve rats are exposed to a novel environment, some display high rates of locomotor reactivity (HRs, scores ranking at top 1/3rd of the population), whereas some display low rates (LRs, scores ranking at bottom 1/3rd of the population). Basally, HRs display lower anxiety-like behavior compared to LRs along with higher neuropeptide Y (NPY) mRNA in the amygdala and the hippocampus. Following an intermittent behavioral sensitization to nicotine regimen and 1 wk of abstinence, HRs show increased social anxiety-like behavior in the social interaction test and robust expression of locomotor sensitization to a low dose nicotine challenge. These effects are accompanied by a deficit in NPY mRNA levels in the medial nucleus of the amygdala and the CA3 field of the hippocampus, and increases in Y2R mRNA levels in the CA3 field and corticotropin releasing factor (CRF) mRNA levels in the central nucleus of the amygdala. Systemic and daily injections of a Y2R antagonist, JNJ-31020028, during abstinence fully reverse nicotine-induced social anxiety-like behavior, the expression of locomotor sensitization to nicotine challenge, the deficit in the NPY mRNA levels in the amygdala and the hippocampus, as well as result an increase in Y2R mRNA levels in the hippocampus and the CRF mRNA levels in the amygdala in HRs. These findings implicate central Y2R in neuropeptidergic regulation of social anxiety in a behavioral sensitization to nicotine regimen in the LRHR rats.

Figure 1

Baseline phenotype differences in NPY mRNA expression in the hippocampus (A, B) and the amygdala (C, D), Y1R mRNA expression in the hippocampus (E, F), and baseline phenotype differences in anxiety-like behavior in the social interaction (G) and the light/dark box (H) tests. Panels A, C and E show images of representative coronal hemisections of the dorsal hippocampus that were radioactively labeled with antisense cRNA probes against NPY (A, C) and Y1R (E) mRNA and exposed on x-ray films in LRHR rats. Panel B shows NPY mRNA integrated density in the CA1 (Top) and the CA3 fields (Bottom) of the hippocampus between LRHR rats. Panel D shows NPY mRNA integrated density in the MeA (Top) and the BLA (Bottom) between LRHR rats. Panel F shows Y1R mRNA integrated density in the CA1 (Top) and the CA3 fields (Bottom) of the hippocampus between LRHR rats. Panel G shows percent time spent in social interaction between LRHR rats. Panel H shows percent time spent in the light compartment of the light/dark box between LRHR rats. Means of quantification results for integrated density as well as behavioral measures ± SEMs are plotted with bar graphs (*: p ≤ 0.05). Scale bar = 250 μm.

Figure 2

Total locomotor reactivity to four intermittent nicotine (0.35 mg/kg, s.c.) or saline (1.0 ml/kg, s.c.) training injections (A), total locomotor reactivity to a low dose nicotine (0.1 mg/kg, s.c.) or saline (1.0 ml/kg, s.c.) challenge (B), percent time spent interacting with the resident rat in the SI test (C), and plasma CORT concentrations in response to a 5 min SI or EPM test (D) are shown. Group means± SEMs are plotted in line (A, D) and bar (B, C) graphs. In panel A, * represents significant effects in total locomotor reactivity to nicotine in HRs compared to saline-injected controls, whereas # represents significant effects in nicotine-injected LRs compared to saline-injected controls. In Panel D, * represents a significant effect at 60 min time point in plasma CORT levels induced by a 5 min EPM exposure in HRs compared to LRs. Significance is set at p = 0.005.

Figure 3

NPY mRNA expression in the hippocampus of a representative HR rat that is pre-trained with saline, treated with vehicle and challenged with nicotine (A), HR rat that is pre-trained with nicotine, treated with vehicle and challenged with nicotine (B) and HR rat that is pre-trained with nicotine, treated with Y2R antagonist and challenged with nicotine (C). Panels A, B and C show images of coronal hemisections of the hippocampus that were radioactively labeled with an antisense cRNA probe against NPY and exposed on an x-ray film. Means of quantification results for integrated density ± SEMs are plotted with the bar graph (D; *: p ≤ 0.0004). Scale bar = 250 μm.

Figure 4

NPY mRNA expression in the MeA and BLA of a representative HR rat that is pre-trained with saline, treated with vehicle and challenged with nicotine (A), HR rat that is pre-trained with nicotine, treated with vehicle and challenged with nicotine (B) and HR rat that is pre-trained with nicotine, treated with Y2R antagonist and challenged with nicotine (C). Panels A, B and C show images of coronal hemisections of the MeA and the BLA that were radioactively labeled with an antisense cRNA probe against NPY and exposed on an x-ray film. Means of quantification results for integrated density ± SEMs are plotted with the bar graph for MeA (D; *: p ≤ 0.0004). Scale bar = 250 μm.

Figure 5

Y2R mRNA expression in the hippocampal CA3 field of a representative HR rat that is pre-trained with saline, treated with vehicle and challenged with nicotine (A), HR rat that is pre-trained with nicotine, treated with vehicle and challenged with nicotine (B) and HR rat that is pre-trained with nicotine, treated with Y2R antagonist and challenged with nicotine (C). Panels A, B and C show images of coronal hemisections of the hippocampus that were radioactively labeled with an antisense cRNA probe against Y2R mRNA, and exposed on an x-ray film. Means of quantification results for integrated density ± SEMs are plotted with the bar graph (D; *: p ≤ 0.0004). Scale bar = 250 μm.

Figure 6

CRF mRNA expression in the CeA of a representative HR rat that is pre-trained with saline, treated with vehicle and challenged with nicotine (A), HR rat that is pre-trained with nicotine, treated with vehicle and challenged with nicotine (B) and HR rat that is pre-trained with nicotine, treated with Y2R antagonist and challenged with nicotine (C). Panels A, B and C show images of coronal hemisections of the CeA that were radioactively labeled with an antisense cRNA probe against CRF mRNA, and exposed on an x-ray film. Means of quantification results for integrated density ± SEMs are plotted with the bar graph (B, *: p ≤ 0.0004). Scale bar = 250 μm.