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

Abstract

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.

Validated multi‐step approach for in vivo recording and analysis of optogenetically evoked glutamate in the mouse globus pallidus

“…, ; Mishra et al . ). Prior to the experiment, the microelectrode was calibrated in vitro with ascorbic acid, increasing concentrations of glutamate followed by dopamine and H 2 O 2 (Fig.…”

“…; Mishra et al . ). As the peak concentration of evoked glutamate in our study is in the lower physiological range and we furthermore used a low output power for our optogenetic stimulation, we see room for further increasing illumination strength and pulse length of the stimulation in future studies to evoke higher extracellular glutamate concentrations.…”

“…, ; Mishra et al . ). The electroplating was performed in 0.05 M nitrogen‐saturated phosphate‐buffered saline (PBS, 40 mL, pH 7.4) at 20°C, using the FAST‐16 electroplating tool (Quanteon; LLC, Nicholasville, KY, USA), peak‐to‐peak amplitude of +0.25 V at 0.05 Hz for 22 min.…”

“…, ; Mishra et al . ). Enzyme‐coated microelectrodes were allowed to cure for at least 48 h at 20°C before any further use.…”

“…No randomization was performed to determine the virus injected for each individual mouse to avoid cross-infection between individual mice injected with different constructs (Reuter et al 2012). Sample size for each group was determined based on that of previous studies utilizing in vivo amperometry with enzyme-coated microelectrodes (Day et al 2006;Konradsson-Geuken et al 2009Mishra et al 2015). No sample size calculations were performed.…”