Neurodegeneration and behavioural effect of ketamine and methamphetamine in rats

Abstract

Ketamine and methamphetamine (METH) are increasingly becoming a popular choice of drugs among drug abusers. The abuse has reached epidemic proportion worldwide. Prolong exposure to these drugs is thought to cause neurodegeneration resulting in loss of hippocampal neurons and functions. This study examined the neurodegenerative effect of ketamine and METH on adult rats` hippocampus, its relation to exploratory behaviour in different doses and duration of exposure and correlation between neuron CAl and CA3. Fifty-five Sprague-Dawley rats (male, 4 weeks old, and 150-200g) were divided into acute (1 day) and chronic (5 days) drug treatment groups. The acute treatment groups were treated with different doses of ketamine (10 mg!kg, 20 mg!kg and 50 mg!kg, n=5 per subgroup) and methamphetamine (5 mg!kg and 10 mg!kg, n=5 per subgroup) for 4 injections at 2- hour intervals. The same protocol was repeated for 5 consecutive days in the chronic regimen. Behavioural test was performed using hole-board maze (16 holes, 40 em x 40 em, flexiglass) under well controlled condition for 5 minutes at well-define time points. The rats were sacrificed 12 hours after the last exposure to the drugs. Viable neuronal cell count was performed in CAl and CA3 regions of the hippocampus on cresyl violet stained sections (Image J Software; 0.48 mm2 areas). Correlation between the number of CAl neurons and CA3 neurons was analyzed using Pearson correlation coefficient test. Linear regression was used to analyze the causality effect of CA3 to CAl neurons. The result showed that the acute and chronic ketarnine did not show significant neuronal reduction in CAl region. Acute METH treatment groups, 5mg!kg and 10 mfkg with mean value 80 cells± 5.10 per 0.48 mm2 and 78 cells ± 6.20 per 0.48 mm respectively caused significant CAl region neuronal loss. Similar reduction was observed in chronic METH reynnen, with mean value for 5mg!kg and !Omg!kg were 66 cells± 6.18 per 0.48 mm and 61 cells± 5.63 per 0.48 mm2 respectively. CA3 region neuronal count was significantly reduced in acute ketamine (50 mg!kg; 153 cells± 5.59 per 0.48 mm2 ) and acute METH (5 mg!kg; 120 cells± 7.18 per 0.48 mm2 , 10 mg!kg; 107 ± 7.79 per 0.48 mm2) treatment groups. All treatment groups for the chronic regimen demonstrated significant CA3 region neuronal count reduction. For exploratory behaviour, head dipping data was considered as unreliable. Statistical analysis was done with ANOV A with post-hoc analysis and the differences are significant at p < 0.05. A positive correlation was observed between CAl and CA3 region neuron counts in chronic Ketamine (F=8.341, p=O.OIO), acute (F=95.076, p=O.OOO) and chronic METH (F=288.434, p=O.OOO) regimen. These data demonstrated that only high dose of acute 50 mg!kg and chronic doses of ketamine caused neurodegeneration in CA3 region with no significant results for both regimens in CAl region while both METH regimens exhibited significant neuronal degeneration in CAl and CA3 regions of hippocampus.