Amphetamine sensitization and cross-sensitization with acute restraint stress: impact of prenatal alcohol exposure in male and female rats

Abstract

Rationale: Individuals with fetal alcohol spectrum disorder (FASD) are at increased risk for substance use disorders (SUD). In typically developing individuals, susceptibility to SUD is associated with alterations in dopamine and hypothalamic-pituitary-adrenal (HPA) systems, and their interactions. Prenatal alcohol exposure (PAE) alters dopamine and HPA systems, yet effects of PAE on dopamine-HPA interactions are unknown. Amphetamine-stress cross-sensitization paradigms were utilized to investigate sensitivity of dopamine and stress (HPA) systems, and their interactions following PAE.

Methods: Adult Sprague-Dawley offspring from PAE, pair-fed, and ad libitum-fed control groups were assigned to amphetamine-(1-2 mg/kg) or saline-treated conditions, with injections every other day for 15 days. Fourteen days later, all animals received an amphetamine challenge (1 mg/kg) and 5 days later, hormones were measured under basal or acute stress conditions. Amphetamine sensitization (augmented locomotion, days 1-29) and cross-sensitization with acute restraint stress (increased stress hormones, day 34) were assessed.

Results: PAE rats exhibited a lower threshold for amphetamine sensitization compared to controls, suggesting enhanced sensitivity of dopaminergic systems to stimulant-induced changes. Cross-sensitization between amphetamine (dopamine) and stress (HPA hormone) systems was evident in PAE, but not in control rats. PAE males exhibited increased dopamine receptor expression (medial prefrontal cortex (mPFC)) compared to controls.

Conclusions: PAE alters induction and expression of sensitization/cross-sensitization, as reflected in locomotor, neural, and endocrine changes, in a manner consistent with increased sensitivity of dopamine and stress systems. These results provide insight into possible mechanisms that could underlie increased prevalence of SUD, as well as the impact of widely prescribed stimulant medications among adolescents with FASD.

Figure 1. Experimental Timeline

All experimental procedures are charted above beginning with the pre-injection period. During the first 15 days of the experiment, all subjects received a total of 8 injections (intraperitoneal, i.p.), 1 injection every other day for 15 days. During these 15 days, AMPH-treated rats received 1 mg/kg AMPH for the first 4 injections and 2 mg/kg AMPH for the last 4 injections, while the saline-treated rats received only saline injections. Rats then remained undisturbed for a 14 day washout period, and on Day 29 all subjects (both AMPH- and saline-pretreated) received a single injection of AMPH (1 mg/kg, i.p.). On Day 34, blood was collected under either basal or stress conditions to assess HPA sensitization.

Figure 2. Sensitization of ‘typical’ behaviors

Mean±SEM ; n=18–20/group. Sensitization of ‘typical’ behaviors assessed by distance travelled during 80 min sessions in an open field on test days 1, 15 and 29 [behavior analyzed in 5 min bins, but presented in 10 min bins]. AMPH-treated rats received 1 mg/kg AMPH for the first 4 injections and 2 mg/kg AMPH for the last 4 injections, while saline-treated rats only received saline-injections during this time (Days 1–15 every other day). On Day 29, after a 14 day washout period, all subjects (both AMPH- and saline-pretreated) received a single injection of AMPH (1 mg/kg, i.p.) to examine sensitization. A) Males: Saline-treated (left): ^cPAE>C; ^dPAE>PF. AMPH-treated (right): ^aPAE>C; ^bPAE>PF. B) Females: Saline-treated (left): ^dPAE>C; ^ePAE>PF. AMPH-treated (right): ^aPAE>C; ^bPAE>PF; ^cPF>C. Time of injection indicated by dashed line. Both saline- and AMPH-pretreated groups received 1mg/kg AMPH on Day 29.

Figure 3. Sensitization of ‘atypical’ behaviors

Mean±SEM; n=18–20/group. Sensitization of ‘atypical’ behaviors assessed by number of 360° rotations during 80 min sessions inside an open field on test days: 1, 15 and 29 [behavior analyzed in 5 min bins, but presented in 10 min bins]. AMPH-treated rats received 1 mg/kg AMPH for the first 4 injections and 2 mg/kg AMPH for the last 4 injections, while saline-treated rats only received saline-injections during this time. On Day 29, after a 14 day washout period, all subjects (both AMPH- and saline-pretreated) received a single injection of AMPH (1 mg/kg, i.p.) to examine sensitization. A) Males: Saline-treated (left): ^dPAE>C; ^ePAE>PF. AMPH-treated (right): ^aPAE>C; ^bPAE>PF; ^cPF<C. B) Females: Saline-treated (left): ^cPAE>C; ^dPAE>PF. AMPH-treated (right): ^aPAE>C; ^bPAE>PF. Time of injection indicated by dashed line. Both saline- and AMPH-pretreated groups received 1mg/kg AMPH on Day 29.