Relative expression of mRNA for the somatostatin receptors in the caudate putamen of C57BL/6J and 129P3/J mice: strain and heroin effects

Abstract

Using real time qPCR, we examined the expression of mRNAs for the five somatostatin receptors (SSTRs) in the caudate putamen of male C57BL/6J and 129P3/J mice. Animals were exposed to multiple injections of heroin, or saline, in the setting of a conditioned place preference study. The relative expression levels of the five SSTR mRNAs differed between the two strains. In both strains, SSTR-1 mRNA was expressed at the highest levels and SSTR-5 at the lowest. Interestingly, in 129P3/J mice SSTR-3 mRNA was not detected in the caudate putamen. We confirmed this finding in the frontal cortex, hypothalamus, nucleus accumbens and a region containing the substantia nigra and ventral tegmental area. We also found strain differences in the mRNA levels of SSTR-2 and -4. Intermittent heroin administration had a dose-dependent effect on the levels of SSTR-1 and -3 mRNAs. These results demonstrate strain differences in the expression of specific mRNAs and a heroin-induced dose-dependent elevation of SSTR-1 and -3 mRNAs in the mouse caudate putamen.

Fig. 1

Relative expression levels of all five SSTR mRNAs in the CPu of C57BL/6J and 129P3/J mice. Levels of SSTR-2 and -4 mRNA were higher in the CPu of 129P3/Jmice than in C57BL/6J animals (p<0.0001 and 0.01 respectively). SSTR-3 was not detectable in the CPu of 129P3/Jmice.

Fig. 2

SSTR-3 mRNA was abundant in the hypothalamus, frontal cortex, nucleus accumbens and substantia nigra/ventral tegmental area of C57BL/6J mice but was below the limits of detection in these brain regions from 129P3/J animals.

Fig. 3

Heroin effects on mRNA levels of specific SSTRs. Heroin dose dependently elevated SSTR-1 (A) and SSTR-3 (C) mRNAs. The highest dose of heroin (20 mg/kg) significantly elevated the levels of SSTR-1 (p<0.005) and SSTR-3 (p<0.005) relative to saline controls. Heroin did not significantly affect the expression of SSTR-2 (B), SSTR-4 (D) or SSTR-5 (E) relative to saline controls. Note: Y-axis scale differs in all graphs.