Differential effects of chronic adolescent glucocorticoid or methamphetamine on drug-induced locomotor hyperactivity and disruption of prepulse inhibition in adulthood in mice

Enhanced methamphetamine sensitisation in a rat model of the brain-derived neurotrophic factor Val66Met variant: Sex differences and dopamine receptor gene expression

Brain-derived neurotrophic factor (BDNF) and the Val66Met polymorphism may play a role in the development of psychosis and schizophrenia. The aim of this study was to investigate long-term effects of methamphetamine (Meth) on psychosis-like behaviour and dopamine receptor and dopamine transporter gene expression in a novel rat model of the BDNF Val66Met polymorphism. At the end of a 7-day subchronic Meth treatment, female rats with the Met/Met genotype selectively showed locomotor hyperactivity sensitisation to the acute effect of Meth. Male rats showed tolerance to Meth irrespective of Val66Met genotype. Two weeks later, female Met/Met rats showed increased locomotor activity following both saline treatment or a low dose of Meth, a hyperactivity which was not observed in other genotypes or in males. Baseline PPI did not differ between the groups but the disruption of PPI by acute treatment with apomorphine was absent in Meth-pretreated Met/Met rats. Female Met/Met rats selectively showed down-regulation of dopamine D2 receptor gene expression in striatum. Behavioural effects of MK-801 or its locomotor sensitisation by prior Meth pretreatment were not influenced by genotype. These data suggest a selective vulnerability of female Met/Met rats to short-term and long-term effects of Meth, which could model increased vulnerability to psychosis development associated with the BDNF Val66Met polymorphism.

Methamphetamine-induced locomotor sensitization in mice is not associated with deficits in a range of cognitive, affective and social behaviours: interaction with brain-derived neurotrophic factor Val66Met genotype

Chronic methamphetamine (Meth) abuse may induce psychosis similar to that observed in schizophrenia. Brain-derived neurotrophic factor (BDNF) has been implicated in the development of psychosis. We have previously shown long-term protein expression changes in mice treated chronically with Meth depending on BDNF Val66Met genotype. The aim of this study was to investigate if these protein expression changes were associated with differential changes in a range of behavioural paradigms for cognition, anxiety, social and other behaviours. Male and female Val/Val, Val/Met and Met/Met mice were treated with an escalating Meth dose protocol from 6 to 9 weeks of age, with controls receiving saline injections. Several overlapping cohorts were tested in the Y-maze for short-term spatial memory, novel-object recognition test, context and cued fear conditioning, sociability and social preference, elevated plus maze for anxiety-like behaviour and prepulse inhibition (PPI) of acoustic startle. Finally, the animals were assessed for spontaneous exploratory locomotor activity and acute Meth-induced locomotor hyperactivity. Acute Meth caused significantly greater locomotor hyperactivity in mice previously treated with the drug than in saline-pretreated controls. Meth-pretreated female mice showed a mild increase in spontaneous locomotor activity. There were no Meth-induced deficits in any of the other behavioural tests. Val/Met mice showed higher overall social investigation time and lower PPI compared with the Val/Val genotype independent of pretreatment. These results show limited long-term effects of chronic Meth on a range of cognitive, affective and social behaviours despite marked drug-induced locomotor sensitization in mice. There was no interaction with BDNF Val66Met genotype.

Differential Effects of Chronic Methamphetamine Treatment on High-Frequency Oscillations and Responses to Acute Methamphetamine and NMDA Receptor Blockade in Conscious Mice

Dysregulation of high-frequency neuronal oscillations has been implicated in the pathophysiology of schizophrenia. Chronic methamphetamine (METH) use can induce psychosis similar to paranoid schizophrenia. The current study in mice aimed to determine the effect of chronic METH treatment on ongoing and evoked neuronal oscillations. C57BL/6 mice were treated with METH or vehicle control for three weeks and implanted with extradural recording electrodes. Two weeks after the last METH injection, mice underwent three EEG recording sessions to measure ongoing and auditory-evoked gamma and beta oscillatory power in response to an acute challenge with METH (2 mg/kg), the NMDA receptor antagonist MK-801 (0.3 mg/kg), or saline control. A separate group of mice pretreated with METH showed significantly greater locomotor hyperactivity to an acute METH challenge, confirming long-term sensitisation. Chronic METH did not affect ongoing or evoked gamma or beta power. Acute MK-801 challenge reduced ongoing beta power whereas acute METH challenge significantly increased ongoing gamma power. Both MK-801 and METH challenge suppressed evoked gamma power. Chronic METH treatment did not modulate these acute drug effects. There were minor effects of chronic METH and acute METH and MK-801 on selected components of event-related potential (ERP) waves. In conclusion, chronic METH treatment did not exert neuroplastic effects on the regulation of cortical gamma oscillations in a manner consistent with schizophrenia, despite causing behavioural sensitisation.