Effects of Age and Acute Ethanol on Glutamatergic Neurotransmission in the Medial Prefrontal Cortex of Freely Moving Rats Using Enzyme-Based Microelectrode Amperometry

Ethanol abuse during adolescence may significantly alter development of the prefrontal cortex which continues to undergo structural remodeling into adulthood. Glutamatergic neurotransmission plays an important role during these brain maturation processes and is modulated by ethanol. In this study, we investigated glutamate dynamics in the medial prefrontal cortex of freely moving rats, using enzyme-based microelectrode amperometry. We analyzed the effects of an intraperitoneal ethanol injection (1 g/kg) on cortical glutamate levels in adolescent and adult rats. Notably, basal glutamate levels decreased with age and these levels were found to be significantly different between postnatal day (PND) 28-38 vs PND 44-55 (p<0.05) and PND 28-38 vs adult animals (p<0.001). We also observed spontaneous glutamate release (transients) throughout the recordings. The frequency of transients (per hour) was significantly higher in adolescent rats (PND 28-38 and PND 44-55) compared to those of adults. In adolescent rats, post-ethanol injection, the frequency of glutamate transients decreased within the first hour (p<0.05), it recovered slowly and in the third hour there was a significant rebound increase of the frequency (p<0.05). Our data demonstrate age-dependent differences in extracellular glutamate levels in the medial prefrontal cortex and suggest that acute ethanol injections have both inhibitory and excitatory effects in adolescent rats. These effects of ethanol on the prefrontal cortex may disturb its maturation and possibly limiting individuals´ control over addictive behaviors

The effect of intermittent alcohol vapor or pulsatile heroin on somatic and negative affective indices during spontaneous withdrawal in Wistar rats

RATIONALE: Once dependent on alcohol or opioids, negative affect may accompany withdrawal. Dependent individuals are hypothesized to “self-medicate” in order to cope with withdrawal, which promotes escalated drug or alcohol use. OBJECTIVES: The current study aimed to develop a reliable animal model to assess symptoms that occur during spontaneous alcohol and opioid withdrawal. METHODS: Dependence was induced using intermittent alcohol exposure or pulsatile heroin delivery and assessed for the presence of withdrawal symptoms during acute withdrawal by measuring somatic signs, behavior in the forced swim test (FST) and air-puff induced 22-kHz ultrasonic vocalizations (USVs). Additional animals subjected to eight weeks of alcohol vapor exposure were evaluated for altered somatic signs, operant alcohol self-administration and 22-kHz USV production, as well as performance in the elevated plus-maze (EPM). RESULTS: During spontaneous withdrawal from pulsatile heroin or intermittent alcohol vapor, animals displayed increased somatic withdrawal signs, FST immobility and 22-kHz USV production, but did not show any behavioral change in the EPM unless the duration of exposure was extended to four weeks. Following eight weeks of alcohol vapor exposure, animals displayed somatic withdrawal signs, escalated alcohol self-administration and increased 22-kHz USVs. CONCLUSIONS: These paradigms provide consistent methods to evaluate the behavioral ramifications, and neurobiological substrates, of alcohol and opioid dependence during spontaneous withdrawal. As immobility in the FST and percent open-arm time in the EPM were dissociable, with 22-kHz USVs paralleling immobility in the FST, assessment of air-puff induced 22-kHz USVs could provide an ethologically-valid alternative to the FST