Methylphenidate inhibits gene expression for brain-derived neurotophic factor in hippocampus of young rats

Partha.S.Banerjee & Tyra.S.C.Zetterström. Leicester School of Pharmacy, Faculty of Health & Life Sciences, De Montfort University, Leicester – LE1 9BH, UK.

The central stimulant methylphenidate (MPH) is commonly prescribed for the treatment of attention-deficit hyperactivity disorder (ADHD) in young children (Bolanos et al. 2003). However, serious concerns about the drug’s long-term effects on the developing brain have recently been raised (Volkow and Insel 2003) and indeed few studies have investigated the effect of MPH in the young brain. In the present investigation, we have studied the effect of MPH in the juvenile rat hippocampus on gene expression for brain-derived neurotrophic factor (BDNF), a protein crucial for normal brain development.

Separate groups of 20 days old male Sprague-Dawley rats (85-100g) were injected (i.p.) with doses of MPH (1 mg/kg, 2 mg/kg, 4mg/kg) or saline 1ml/kg. The general behaviour patterns of the animals were monitored for 2 hours after the injection. The rats were then killed, their brains isolated, frozen in isopentane, cut on a cryostat into 20 μm sections and pre-treated using standard protocols. BDNF mRNA levels were analysed by in situ hybridisation histochemistry with 35S-dATP labelled oligonucleotide probe detecting all types of rat BDNF transcripts (Zetterström et al. 1998; Khundakar and Zetterström, 2006). Relative abundance of BDNF mRNA in hippocampus was determined by densitometric analysis of autoradiograms using MCID basicTM software.

All three doses of MPH decreased BNDF mRNA expression significantly in hippocampal brain regions. The decrease was most pronounced in the CA3 where the lowest dose (1mg/kg) decreased BDNF mRNA level by 37% while the highest dose (4mg/kg) produced a substantial decrease of 52%. The effect was less pronounced, albeit significant, in CA1 and dentate gyrus (DG) reaching reductions of: 17% (1mg/kg), 32% (4mg/kg) for the CA1, and 14% (1mg/kg), 26% (4mg/kg) for the DG (see table 1 for details).

Table 1: The effect of MPH on BDNF mRNA expression in juvenile rat hippocampus.

Data (nCi/g) expressed as mean value ±SEM (n=6). *P<0.05 vs. saline; **P<0.001 vs. saline. (Newman-Keuls post-hoc test following two-way ANOVA)

In conclusion, acute administration of MPH at clinically relevant doses induces a dose dependant reduction in BDNF gene expression in the hippocampus of juvenile rats.

Bolanos , C.A.et al. (2003). Biological Psychiatry., 54, 1317-1329.
Khundakar, A.A. & Zetterström, T.S.C. (2006). Brain Research., 1106(1), 12-20.
Volkow , N.D. & Insel, T.R. (2003). Biological Psychiatry., 54, 1307-1309.
Zetterström, T.S.C. et al. (1998). Molecular Brain Research., 57, 106-110.