Effects of adolescent intermittent ethanol on hippocampal expression of glutamate homeostasis and astrocyte‐neuronal tethering proteins in male and female rats

Abstract

Adolescent alcohol drinking is widely recognized as a significant public health problem, and evidence is accumulating that sufficient levels of consumption during this critical period of brain development have an enduring impact on neural and behavioral function. Recent studies have indicated that adolescent intermittent ethanol (AIE) exposure alters astrocyte function, astrocyte-neuronal interactions, and related synaptic regulation and activity. However, few of those studies have included female animals, and a broader assessment of AIE effects on the proteins mediating astrocyte-mediated glutamate dynamics and synaptic function is needed. We measured synaptic membrane expression of several such proteins in the dorsal and ventral regions of the hippocampal formation (DH, VH) from male and female rats exposed to AIE or adolescent intermittent water. In the DH, AIE caused elevated expression of glutamate transporter 1 (GLT-1) in both males and females, elevated postsynaptic density 95 expression in females only, and diminished NMDA receptor subunit 2A expression in males only. AIE and sex interactively altered ephrin receptor A4 (EphA4) expression in the DH. In the VH, AIE elevated expression of the cystine/glutamate antiporter and the glutamate aspartate transporter 1 (GLAST) in males only.Compared to males, female animals expressed lower levels of GLT-1 in the DH and greater levels of ephrin receptor B6 (EphB6) in the VH, in the absence of AIE effects.These results support the growing literature indicating that adolescent alcohol exposure produces long-lasting effects on astrocyte function and astrocyte-neuronal interactions. The sex and subregion specificity of these effects have mechanistic implications for our understanding of AIE effects generally.

Ethanol-induced conditioned taste aversion and associated neural activation in male rats: Impact of age and adolescent intermittent ethanol exposure

“…In Experiment 2, the IL was the only brain region in which a difference in β-gal expression between AIE and water-exposed subjects occurred, with a significantly greater number of β-gal+ cells in the AIE exposed rats relative to their water exposed counterparts when collapsed across ethanol doses. It is likely that greater β-gal expression in the IL of AIE-exposed males is associated with elevated levels of anxiety in these animals, given that AIE exposure results in enhanced anxiety-like behavioral alterations [ 69 ] and the imbalance between excitation and inhibition toward excitation [ 70 , 71 ], as activation of pyramidal neurons in the IL enhances anxiety responding by shifting the balance to excitation [ 72 ], Significant effects of ethanol were evident in the IL and AIV, with ethanol decreasing β-gal expression when collapsed across adolescent condition. These findings were rather unexpected, since adult non-manipulated subjects demonstrated greater β-gal expression in these ROIs following conditioning with the 1.5 g/kg ethanol dose.…”

Ethanol-induced conditioned taste aversion and associated neural activation in male rats: Impact of age and adolescent intermittent ethanol exposure

“…In Experiment 2, the IL was the only brain region in which a difference in β-gal expression between AIE and water-exposed subjects occurred, with a significantly greater number of β-gal+ cells in the AIE exposed rats relative to their water exposed counterparts when collapsed across EtOH doses. It is likely that greater β-gal expression in the IL of AIE-exposed males is associated with elevated levels of anxiety in these animals, given that AIE exposure results in enhanced anxiety-like behavioral alterations (reviewed in Towner & Varlinskaya, 2020) and the imbalance between excitation and inhibition toward excitation (Healey et al, 2021; Swartzwelder et al, 2017), as activation of pyramidal neurons in the IL enhances anxiety responding by shifting the balance to excitation (Berg et al, 2019), Significant effects of ethanol were evident in the IL and AIV, with ethanol decreasing β-gal expression when collapsed across adolescent condition. These findings were rather unexpected, since adult non-manipulated subjects demonstrated greater β-gal expression in these ROIs following conditioning with the 1.5 g/kg ethanol dose.…”

Adolescent intermittent ethanol exposure reduces astrocyte-synaptic proximity in the adult medial prefrontal cortex in rats: Reversal by gabapentin

“…Recently, it has become apparent that AIE-induced alterations are not just neuronal but also glial. Adult dorsal hippocampal astrocytes, in animals with a history of AIE, exhibited reduced proximity with excitatory glutamatergic synapses, but no change in astrocyte morphology [ 20 ], and elevated expression of astrocytic glutamatergic homeostatic machinery [ 19 ]. Of note, we previously reported no differences in hippocampal astrocyte surface area, volume, or synaptic proximity between pre-adolescence (PND 24), early-adolescence (PND 30), late-adolescence (PND 44-47) or adulthood (PND 70) [ 53 ].…”

“…It interacts with the astrocytic glutamate transporter, GLT-1, α 2 δ 1 subunits of voltage-gated Ca 2+ channels, and presynaptic GABA B receptors [ 12 , 30 , 49 , 52 ]. All of these targets have been found to be altered by AIE in the hippocampus by our laboratory [ 7 , 19 , 39 ],including an AIE elevation of thrombospondins (TSPs), which gabapentin is an inhibitor of the VGCC α 2 δ 1 subunit which is activated by TSPs [ 12 , 30 ].…”