Methamphetamine-induced stereotypy correlates negatively with patch-enhanced prodynorphin and arc mRNA expression in the rat caudate putamen: the role of mu opioid receptor activation

Abstract

Amphetamines induce stereotypy, which correlates with patch-enhanced c-Fos expression the patch compartment of caudate putamen (CPu). Methamphetamine (METH) treatment also induces patch-enhanced expression of prodynorphin (PD), arc and zif/268 in the CPu. Whether patch-enhanced activation of any of these genes correlates with METH-induced stereotypy is unknown, and the factors that contribute to this pattern of expression are poorly understood. Activation of mu opioid receptors, which are expressed by the neurons of the patch compartment, may underlie METH-induced patch-enhanced gene expression and stereotypy. The current study examined whether striatal mu opioid receptor blockade altered METH-induced stereotypy and patch-enhanced gene expression, and if there was a correlation between the two responses. Animals were intrastriatally infused with the mu antagonist CTAP (10 microg/microl), treated with METH (7.5 mg/kg, s.c.), placed in activity chambers for 3h, and then sacrificed. CTAP pretreatment attenuated METH-induced increases in PD, arc and zif/268 mRNA expression and significantly reduced METH-induced stereotypy. Patch-enhanced PD and arc mRNA expression in the dorsolateral CPu correlated negatively with METH-induced stereotypy. These data indicate that mu opioid receptor activation contributes to METH-induced gene expression in the CPu and stereotypy, and that patch-enhanced PD and arc expression may be a homeostatic response to METH treatment.

Figure 1

Schematic diagram of the four sub-regions in rostral (AP+ 1.68) CPu used for autoradiogram analysis of mRNA expression in the patch and matrix compartments (A) and the approximate locations of the microinjection needle tips (B). The numbers indicate the millimeters anterior to bregma (Paxinos and Watson, 2005). DL, dorsolateral, DM, dorsomedial, VL, ventrolateral, VM, ventromedial (Adapted from Adams et al., 2001 and Gonzalez-Nicolini et al., 2003).

Figure 2

Effects of CTAP pretreatment on METH-induced PD mRNA expression in the rostral CPu. In situ hybridization film autoradiograms showing PD (A) and mu opioid receptor immunohistochemical staining in adjacent sections (B) and quantitative analysis of PD mRNA expression in the patch and matrix compartments of DL (C), DM (D), VM (E) and VL (F) CPu, from rats intrastriatally infused with vehicle or CTAP (10 μg/μl), 15 min prior to METH or saline treatment. Arrows indicate patches of mu opioid receptor labeling and corresponding patches of intense PD mRNA expression. Note the decrease in PD expression in METH-treated animals pretreated with CTAP. Quantitative values are average gray values (arbitrary units; ±S.E.M., n=5–8 animals/group) obtained from densitometric analysis of film autoradiograms. *Significantly different from saline-pretreated control group, P<0.05; +Significantly different from respective saline-pretreated group, P<0.05. There was a not significant main effect of treatment in the VL CPu, but a significant effect of pretreatment and a significant pretreatment-treatment interaction.

Figure 3

Effects of CTAP pretreatment on METH-induced arc mRNA expression in the rostral CPu. In situ hybridization film autoradiograms showing arc (A) and mu opioid receptor immunohistochemical staining in adjacent sections (B) and quantitative analysis of arc mRNA expression in the patch and matrix compartments of DL (C), DM (D), VM (E) and VL (F) CPu, from rats intrastriatally infused with vehicle or CTAP (10 μg/μl), 15 min prior to METH or saline treatment. Arrows indicate patches of mu opioid receptor labeling and corresponding patches of intense arc mRNA expression. Note the decrease in arc expression in METH-treated animals pretreated with CTAP. Quantitative values are average gray values (arbitrary units; ±S.E.M., n=5–8 animals/group) obtained from densitometric analysis of film autoradiograms. *Significantly different from saline-pretreated control group, P<0.05; +Significantly different from respective saline-pretreated group, P<0.05.

Figure 4

Effects of CTAP pretreatment on METH-induced zif/268 mRNA expression in the rostral CPu. In situ hybridization film autoradiograms showing zif/268 (A) and mu opioid receptor immunohistochemical staining in adjacent sections (B) and quantitative analysis of PD mRNA expression in the patch and matrix compartments of DL (C), DM (D), VM (E) and VL (F) CPu, from rats intrastriatally infused with vehicle or CTAP (10 μg/μl), 15 min prior to METH or saline treatment. Arrows indicate patches of mu opioid receptor labeling and corresponding patches of zif/268 mRNA expression. Note the decrease in zif/2678 expression in METH-treated animals pretreated with CTAP. Quantitative values are average gray values (arbitrary units; ±S.E.M., n=5–8 animals/group) obtained from densitometric analysis of film autoradiograms. *Significantly different from saline-pretreated control group, P<0.05; +Significantly different from respective saline-pretreated group, P<0.05. There was not a significant main effect of METH treatment in the VL CPu.

Figure 5

Effects of intrastriatal infusion of CTAP (10 μg/μl) and acute METH treatment (7.5 mg/kg) on stereotyped behavior (A) and spatial distribution scores (B). Values are expression as the mean ±SEM. AUC values are in parentheses. *Significantly different from respective control group, P<0.005; +Significantly different from vehicle-pretreated METH group, P<0.005. Acute METH treatment increased stereotypy and spatial distribution scores, both of which were reduced by pretreatment with CTAP.

Figure 6

Patch-enhanced gene expression in the DL CPu, and the correlation between cumulative stereotypy scores and the ratio of patch-to-matrix mRNA in the DL CPu. Acute METH treatment significantly increased the ratio of patch-to-matrix PD mRNA expression (A, inset) and arc mRNA expression (B, inset) only in the DL CPu an effect that was blocked by pretreatment with CTAP, for PD, but not arc mRNA expression. There was a significant negative correlation between the cumulative stereotypy scores and the ratio of patch-to-matrix expression of PD (A) and arc (B) mRNA expression, which was disrupted in both cases by mu striatal opioid receptor blockade. *Significantly different from saline-pretreated control group, P<0.05; +Significantly different from respective saline-pretreated group, P<0.05. There was an overall main effect of treatment for the patch-to-matrix ratio of arc mRNA expression.