703 – Methylphenidate abuse among icelandic i.v. substance abusers

Prescription Stimulant Misuse and ADHD Symptomatology Among College Students in Iceland

Objective: Misuse of prescription stimulant medication is a prevalent problem on American college campuses; however, few studies have been conducted beyond the United States. Although Iceland has the highest methylphenidate prescription rates in the world, prevalence of stimulant misuse within the Icelandic college student population remains to be investigated. Method: We examined the prevalence of prescription stimulant misuse among N = 521 college students in Iceland, using an online survey. Results: Overall prevalence of lifetime stimulant misuse was approximately 13%; 11% among participants without a prescription for stimulant medication, and 42% among participants holding a prescription. The primary reported reason for misuse was academic enhancement; risk factors included male sex, anxiety symptoms, and ADHD symptomatology. Conclusion: The present findings have implications for public health policy in Iceland, particularly as it relates to the college population. Prevention and intervention programs that provide college students with safer strategies to manage academic demands are warranted.

Glutaminergic signaling in the caudate nucleus is required for behavioral sensitization to methylphenidate

Methylphenidate (MPD) is a widely prescribed psychostimulant for the treatment of attention deficit hyperactivity disorder, and is growing in use as a recreational drug and academic enhancer. MPD acts on the reward/motive and motor circuits of the CNS to produce its effects on behavior. The caudate nucleus (CN) is known to be a part of these circuits, so a lesion study was designed to elucidate the role of the CN in response to acute and chronic MPD exposure. Five groups of n = 8 rats were used: control, sham CN lesions, non-specific electrolytic CN lesions, dopaminergic-specific (6-OHDA toxin) CN lesion, and glutaminergic-specific (ibotenic acid toxin) CN lesions. On experimental day (ED) 1, all groups received saline injections. On ED 2, surgeries took place, followed by a 5-day recovery period (ED 3-7). Groups then received six daily MPD 2.5 mg/kg injections (ED 9-14), 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 (ED 18). Locomotive activity was recorded for 60 min after each injection by a computerized animal activity monitor. The electrolytic CN lesion group responded to the MPD acute and chronic exposures similarly to the control and sham groups, showing an increase in locomotive activity, i.e. sensitization. The dopaminergic-specific CN lesion group failed to respond to MPD exposure both acute and chronically. The glutaminergic-specific CN lesion group responded to MPD exposure acutely but failed to manifest chronic effects. This confirms the CN's dopaminergic system is necessary for MPD to manifest its acute and chronic effects on behavior, and demonstrates that the CN's glutaminergic system is necessary for the chronic effects of MPD such as sensitization. Thus, the dopaminergic and glutaminergic components of the CN play a significant role in differentially modulating the acute and chronic effects of MPD respectively.