The role of CYP2D in rat brain in methamphetamine-induced striatal dopamine and serotonin release and behavioral sensitization

Abstract

Rationale: Cytochrome P450 2D (CYP2D) enzymes metabolize many addictive drugs, including methamphetamine. Variable CYP2D metabolism in the brain may alter CNS drug/metabolite concentrations, consequently affecting addiction liability and neuropsychiatric outcomes; components of these can be modeled by behavioral sensitization in rats.

Methods: To investigate the role of CYP2D in the brain in methamphetamine-induced behavioral sensitization, rats were pretreated centrally with a CYP2D irreversible inhibitor (or vehicle) 20 h prior to each of 7 daily methamphetamine (0.5 mg/kg subcutaneous) injections. In vivo brain microdialysis was used to assess brain drug and metabolite concentrations, and neurotransmitter release.

Results: CYP2D inhibitor (versus vehicle) pretreatment enhanced methamphetamine-induced stereotypy response sensitization. CYP2D inhibitor pretreatment increased brain methamphetamine concentrations and decreased the brain p-hydroxylation metabolic ratio. With microdialysis conducted on days 1 and 7, CYP2D inhibitor pretreatment exacerbated stereotypy sensitization and enhanced dopamine and serotonin release in the dorsal striatum. Day 1 brain methamphetamine and amphetamine concentrations correlated with dopamine and serotonin release, which in turn correlated with the stereotypy response slope across sessions (i.e., day 1 through day 7), used as a measure of sensitization.

Conclusions: CYP2D-mediated methamphetamine metabolism in the brain is sufficient to alter behavioral sensitization, brain drug concentrations, and striatal dopamine and serotonin release. Moreover, day 1 methamphetamine-induced neurotransmitter release may be an important predictor of subsequent behavioral sensitization. This suggests the novel contribution of CYP2D in the brain to methamphetamine-induced behavioral sensitization and suggests that the wide variation in human brain CYP2D6 may contribute to differential methamphetamine responses and chronic effects.

Keywords: Behavioral sensitization; CYP2D; Dopamine; Metabolism; Methamphetamine; Microdialysis; Neuropharmacology; Propranolol; Serotonin; Striatum.

Fig. 1

ICV propranolol (versus vehicle) pretreatment enhanced MAMP-induced stereotypy and rearing responses. Rats were given ICV propranolol (n = 11) or vehicle (n = 12) pretreatment 20 h prior to 7 daily MAMP injections, and stereotypy and rearing responses were recorded daily for 120 min (experiment 1). Stereotypy time on (a) day 1 did not differ between pretreatments and on (b) day 7 was higher in propranolol-pretreated rats. (c) Total stereotypy time increased across MAMP sessions and was higher propranolol-pretreated rats. (d) The slope of stereotypy time across sessions was higher in propranolol-pretreated rats. Rearing events on (e) day 1 were higher in propranolol-pretreated rats and on (f) day 7 did not differ between pretreatments. (g) Total rearing events decreased across MAMP sessions only in propranolol-pretreated rats. (h) The slope of rearing events across sessions did not differ between pretreatments. Main effect of pretreatment: §p < 0.05. Propranolol versus vehicle: *p < 0.05. Day versus day 1: #p < 0.05, ###p < 0.001. Veh, vehicle; Prl, propranolol; SD, standard deviation

Fig. 2

ICV and IST propranolol (versus vehicle) pretreatment increased brain MAMP and decreased the brain OH-MAMP/MAMP ratio. Rats were given propranolol (n = 3 ICV, 3 IST) or vehicle (n = 3 ICV, 3 IST) pretreatment 20 h prior to a single MAMP injection (experiment 2). (a) MAMP concentrations in brain dialysate were higher in propranolol-pretreated rats. While (b) AMP, (c) the AMP/MAMP ratio, and (d) OH-MAMP in brain dialysate did not differ between pretreatments, (e) the OH-MAMP/MAMP ratio was lower in propranolol-pretreated rats. One sample (0–15 min) from n=1 animal was not collected, and no analytes could be reported for the sample; OH-MAMP in three samples (75–120 min) from n=1 animal were omitted due to issues with collection yielding unreliable analyte concentrations (i.e., ~50 times higher than other samples). Main effect of pretreatment: §p < 0.05. SD, standard deviation

Fig. 3

ICV propranolol (versus vehicle) pretreatment enhanced MAMP-induced stereotypy response. Rats were given ICV propranolol (n = 8) or vehicle (n = 8) pretreatment 20 h prior to 7 daily MAMP injections, and stereotypy response was recorded daily from 30 to 50 min after injection (experiment 3). a Total stereotypy time increased across MAMP sessions and was higher in propranolol-pretreated rats. b The slope of stereotypy time across sessions was higher in propranolol-pretreated rats. Main effect of pretreatment: §§p < 0.01. Propranolol versus vehicle: *p < 0.05, **p < 0.01, ***p < 0.001. Day versus day 1: ##p < 0.01, ###p < 0.001. Veh, vehicle; Prl, propranolol; SD, standard deviation

Fig. 4

ICV propranolol (versus vehicle) pretreatment did not significantly alter brain MAMP and metabolite concentrations. Rats were given ICV propranolol or vehicle pretreatment 20 h prior to 7 daily MAMP sessions, and IST microdialysis was conducted on days 1 (top) and 7 (bottom) (experiment 3). a, f MAMP, b, g AMP, c, h the AMP/MAMP ratio, d, i OH-MAMP, and e, j the OH-MAMP/MAMP ratio in brain dialysate did not differ significantly between pretreatments. Day 1: n = 8 propranolol, 7 vehicle. Day 7: n = 6 propranolol, 8 vehicle. SD, standard deviation

Fig. 5

ICV propranolol (versus vehicle) pretreatment enhanced MAMP-induced dopamine and serotonin release. Rats were given ICV propranolol or vehicle pretreatment 20 h prior to 7 daily MAMP sessions, and IST microdialysis was conducted on days 1 and 7 to measure dopamine (top) and serotonin (bottom) (experiment 3). Dopamine release (%baseline) did not differ between pretreatments on (a) day 1 or (b) day 7. (c) Dopamine AUC_0-75 (area under the %baseline-time curve) was higher in propranolol-pretreated rats and trended towards increasing between sessions. Serotonin release (%baseline) did not differ between pretreatments on (d) day 1 or (e) day 7. (f) Serotonin AUC_0-75 (area under the %baseline-time curve) trended towards being higher in propranolol-pretreated rats. Day 1: n = 8 propranolol, 7 vehicle. Day 7: n = 6 propranolol, 8 vehicle. Main effect of pretreatment: §p < 0.05. SD, standard deviation

Fig. 6

Day 1 dopamine and serotonin correlated with brain MAMP and AMP. Rats were given ICV propranolol or vehicle pretreatment 20 h prior to 7 daily MAMP sessions, and IST microdialysis was conducted on days 1 and 7 (experiment 3). Day 1 dopamine AUC_0-75 correlated with day 1 brain (a) MAMP and (b) AMP, but not with (c) OH-MAMP AUC_0-75. Day 1 serotonin AUC_0-75 correlated with day 1 brain (d) MAMP and (e) AMP, but not with (f) OH-MAMP AUC_0-75. Correlations were assessed with pretreatment groups combined (n = 8 propranolol, 7 vehicle). SD, standard deviation

Fig. 7

Stereotypy slope correlated with day 1 brain dopamine, serotonin, and the sum of dopamine and serotonin. Rats were given ICV propranolol or vehicle pretreatment 20 h prior to 7 daily MAMP sessions; stereotypy response was recorded daily from 30 to 50 min after injection, and IST microdialysis was conducted on days 1 and 7 (experiment 3). The slope of stereotypy time across sessions correlated with day 1 (a) dopamine and (b) serotonin AUC_0-75 and with (c) the sum of dopamine and serotonin AUC_0-75. Correlations were assessed with pretreatment groups combined (n = 8 propranolol, 7 vehicle). SD, standard deviation