Regulation of group I metabotropic glutamate receptor expression in the rat striatum and prefrontal cortex in response to amphetamine in vivo

Abstract

G protein-coupled metabotropic glutamate receptors (mGluRs) are expressed in widespread regions of the mammalian brain and are involved in the regulation of a variety of neuronal and synaptic activities. Group I mGluRs (mGluR1 and mGluR5 subtypes) are expressed in striatal medium spiny output neurons and are believed to play an important role in the modulation of cellular responses to dopamine stimulation with psychostimulants. In this study, we investigated the effect of a single dose of the psychostimulant amphetamine on mGluR1/5 protein expression in the rat forebrain in vivo. We found that acute systemic injection of amphetamine at a behaviorally active dose (5 mg/kg) was able to reduce mGluR5 protein levels in a confined biochemical fraction of synaptosomal plasma membranes enriched from the striatum. In contrast to the striatum, amphetamine increased mGluR5 protein levels in the medial prefrontal cortex. These changes in mGluR5 expression in both the striatum and the medial prefrontal cortex were transient and reversible. In addition, protein levels of mGluR1 in the enriched synaptosomal fraction from both the striatum and the medial prefrontal cortex remained stable in response to acute amphetamine. Similarly, Homer1b/c proteins, which are prominent anchoring proteins of mGluR1/5 and are highly expressed in the striatum and the medial prefrontal cortex, showed no change in their protein abundance in striatal and cortical synaptosomes after amphetamine administration. These data demonstrate differential sensitivity of mGluR1 and mGluR5 expression to amphetamine. Acute amphetamine injection is able to alter mGluR5 protein levels at synaptic sites in a subtype- and region-specific manner.

Fig. 1

Effects of acute AMPH administration on mGluR5 expression. (A) Schematic illustration of biochemical fractionation procedures for enriching synaptic membrane-bound proteins. (B) A representative immunoblot showing mGluR5 monomers and dimers in the striatum. (C and D) Effects of acute AMPH administration on mGluR5 protein levels in the striatum (C) and mPFC (D). Representative immunoblots of mGluR5 and actin are shown left to the quantification of immunoblot results. Arrows indicate the bands quantified. Rats were injected with a single dose of saline (1 ml/kg, i.p.) or AMPH (5 mg/kg, i.p.). They were sacrificed 1 h after the drug injection. Data are expressed as means ± S.E.M. (n = 4-5 per group). *p < 0.05 versus saline.

Fig. 2

Effects of acute AMPH administration on mGluR1 expression. (A) A representative immunoblot showing mGluR1 monomers and dimers in the striatum. (B and C) Effects of acute AMPH administration on mGluR1 protein levels in the striatum (B) and mPFC (C). Representative immunoblots of mGluR1 and actin are shown left to the quantification of dimers in immunoblot results. Rats were injected with a single dose of saline (1 ml/kg, i.p.) or AMPH (5 mg/kg, i.p.). They were sacrificed 1 h after the drug injection. Data are expressed as means ± S.E.M. (n = 4-5 per group).

Fig. 3

Effects of acute AMPH administration on Homer1b/c expression. (A) A representative immunoblot showing Homer1b/c in the striatum. (B and C) Effects of acute AMPH administration on Homer1b/c protein levels in the striatum (B) and mPFC (C). Representative immunoblots of Homer1b/c and actin are shown left to the quantification of immunoblot results. Rats were injected with a single dose of saline (1 ml/kg, i.p.) or AMPH (5 mg/kg, i.p.). They were sacrificed 1 h after the drug injection. Data are expressed as means ± S.E.M. (n = 4-5 per group).

Fig. 4

The time-dependent effect of AMPH on mGluR1, mGluR5, and Homer1b/c expression. (A and B) Time-dependent changes in mGluR5 protein levels in the striatum (A) and mPFC (B) following acute injection of AMPH. (C and D) Effects of AMPH on mGluR1 expression in the striatum (C) and mPFC (D). (E and F) Effects of AMPH on Homer1b/c expression in the striatum (E) and mPFC (F). Rats were subject to a single dose of AMPH (5mg/kg) or saline (1 ml/kg, i.p.). They were sacrificed at different time points (15 min, 1 h, or 5 h after drug injection). Data are expressed as means ± S.E.M. (n = 4–5 per group). *P < 0.05 versus saline at the same time point.

Fig. 5

Effects of acute injection of amphetamine on behavioral activity. Rats were given a single dose of amphetamine (5 mg/kg, i.p.) or saline (1 ml/kg, i.p). The data are expressed as means ± S.E.M. (n = 4-8 per group).