Chronic oral methylphenidate treatment reversibly increases striatal dopamine transporter and dopamine type 1 receptor binding in rats

Abstract

Previously, we created an 8-h limited-access dual bottle drinking paradigm to deliver methylphenidate (MP) to rats at two dosages that result in a pharmacokinetic profile similar to patients treated for attention deficit hyperactivity disorder. Chronic treatment resulted in altered behavior, with some effects persisting beyond treatment. In the current study, adolescent male Sprague-Dawley rats were split into three groups at four weeks of age: control (water), low-dose MP (LD), and high-dose MP (HD). Briefly, 4 mg/kg (low dose; LD) or 30 mg/kg (high dose; HD) MP was consumed during the first hour, and 10 mg/kg (LD) or 60 mg/kg (HD) MP during hours two through eight. Following three months of treatment, half of the rats in each group (n = 8-9/group) were euthanized, and remaining rats went through a 1-month abstinence period, then euthanized. In vitro receptor autoradiography was performed to quantify binding levels of dopamine transporter (DAT), dopamine type 1 (D1R)-like receptors, and dopamine type 2 (D2R)-like receptors using [³H] WIN35,428, [³H] SCH23390, and [³H] Spiperone, respectively. Immediately following treatment, HD MP-treated rats had increased DAT and D1R-like binding in several subregions of the basal ganglia, particularly more caudal portions of the caudate putamen, which correlated with some previously reported behavioral changes. There were no differences between treatment groups in any measure following abstinence. These findings suggest that chronic treatment with a clinically relevant high dose of MP results in reversible changes in dopamine neurochemistry, which may underlie some effects on behavior.

Keywords: Dopamine; Methylphenidate; Psychostimulant; Reward deficiency syndrome, reward, addiction; Transporter.

Fig 1

Adapted schematic of coronal brain sections showing regions of interest analyzed (Paxinos and Watson 2006): 1 dorsolateral prefrontal cortex (dl PFC), 2 medial prefrontal cortex (m PFC), 3 pole of the nucleus accumbens shell (Pole AcbS), 4 pole of the nucleus accumbens core (Pole AcbC), 5 nucleus accumbens core (AcbC), 6 nucleus accumbens shell (AcbS), 7 olfactory tubercle (OT), 8 rostral dorsolateral caudate putamen (rost dl CPu), 9 rostral dorsomedial. caudate putamen (rost dm CPu), 10 rostral ventrolateral caudate putamen (rost vl CPu), 11 rostral ventromedial caudate putamen (rost vm CPu), 12 middle dorsolateral caudate putamen (mid dl CPu), 13 middle dorsomedial caudate putamen (mid dm CPu), 14 middle ventrolateral caudate putamen (mid vl CPu), 15 middle ventromedial caudate putamen (mid vm CPu), 16 ventral pallidum (VP), 17 dorsal tail of the caudate putamen (d CPu tail), 18 ventral tail of the caudate putamen (v CPu tail). Measures on the top left of each section indicates approximate distance from bregma.

Figure 2

Dopamine transporter (DAT) binding following chronic oral methylphenidate treatment (A&C) and abstinence (AB) (B&D). (A) High dose (HD MP) treated rats had increased DAT binding in the middle dorsolateral caudate putamen (mid dl CPu), middle dorsomedial caudate putamen (mid dm CPu), middle ventrolateral caudate putamen (mid vl CPu), middle ventromedial caudate putamen (mid vm CPu), and ventral tail of the caudate putamen (v CPu tail) compared to water treated rats, and in the mid dl CPu, mid dm CPu, mid vl CPu, and mid vm CPu compared to low dose (LD MP) treated rats (p≤0.01 for all). *HD MP vs. water, ∧HD MP vs. LD MP. (B) There were no significant differences in DAT binding between treatment groups in rats euthanized after an abstinence period. (C&D) Autoradiographic images of dopamine transporter binding with [3H] WIN35,428. Images represent brain sections from rats treated with water, low dose methylphenidate (LD MP), and high dose methylphenidate (HD MP) and euthanized immediately following treatment (C) or after an abstinence (AB) period (D). Measures on left show approximate distance from Bregma.

Figure 3

Dopamine type 1-like receptor (D1R) binding following chronic oral methylphenidate treatment (A&C) and abstinence (AB) (B&D). (A) High dose (HD MP) treated rats had increased D1R-like binding in the olfactory tubercle (OT), middle dorsolateral caudate putamen (mid dl CPu), middle dorsomedial caudate putamen (mid dm CPu), middle ventromedial caudate putamen (mid vm CPu), and dorsal tail of the caudate putamen (d CPu tail) compared to water treated rats, and in the OT, vm CPu, and d CPu tail compared to LD MP treated rats (p≤0.01 for all). *HD MP vs. water, ^∧HD MP vs. LD MP. (B) There were no significant differences in D1R-like binding between treatment groups in rats euthanized after an abstinence period. (C&D) Autoradiographic images of dopamine type 1-like receptor binding with [³H] SCH23390. Images represent brain sections from rats treated with water, low dose methylphenidate (LD MP), and high dose methylphenidate (HD MP) and euthanized immediately following treatment (C) or after an abstinence (AB) period (D). Measures on left show approximate distance from Bregma.

Figure 4

Dopamine type 2-like receptor (D1R) binding following chronic oral methylphenidate treatment (A&C) and abstinence (AB) (B&D). There were no significant differences in D2R-like binding between treatment groups in rats euthanized immediately following abstinence or after an abstinence period. (C&D) Autoradiographic images of dopamine type 2-like receptor binding with [3H] Spiperone. Images represent brain sections from rats treated with water, low dose methylphenidate (LD MP), and high dose methylphenidate (HD MP) and euthanized immediately following treatment (C) or after an abstinence (AB) period (D). Measures on left show approximate distance from Bregma.