Methylphenidate (MPD) is a psychostimulant that is widely used to treat attention deficit hyperactivity disorder, and is being increasingly misused as a recreational drug and cognitive enhancer. MPD acts on the reward system of the CNS through specific signaling pathways to produce its effects on behavior, including tolerance, withdrawal, and sensitization. The nucleus accumbens (NAc) is one of the predominant components of this system, however the role of the NAc’s glutaminergic system in the behavioral response to MPD has not been studied. The objective of this study was to assess the role of glutaminergic signaling and the response to acute and chronic MPD exposure as measured by three different locomotive behaviors following selective bilateral lesions. Three groups of n=8 rats were used: control, sham NAc lesions, and glutaminergic-specific (ibotenic acid toxin) NAc lesions. On experimental day (ED) 1, all groups received saline injections to establish a baseline. On ED 2, NAc surgeries took place, followed by a 5-day recovery period (ED 3-7). On ED 8 saline was given to obtain a post-surgical baseline. Groups then received six daily MPD 2.5 mg/kg injections (ED 9-14) to produce a chronic effect, behavioral sensitization in this study, then three days of washout with no injection (ED 15-17), followed by a re-challenge with the previous 2.5 mg/kg MPD dose on ED 18. Locomotive activity was recorded for 60 minutes after each injection by a computerized animal activity monitoring system. All groups showed an increase in behavioral activity following acute MPD exposure, and developed behavioral sensitization following chronic MPD exposure that was maintained after three days of MPD washout. Compared to controls and sham lesions, the horizontal activity response was significantly (P<0.05) attenuated both acutely and chronically following glutaminergic selective ibotenic acid lesions to the NAc however the other indices showed no change. This indicates that glutaminergic signaling in the NAc plays a role in modulating the response to acute and chronic MPD.
Methylphenidate, Ritalin, Nucleus accumbens, Lesion, Sensitization, Glutamate