Moderate adolescent chronic intermittent ethanol exposure sex-dependently disrupts synaptic transmission and kappa opioid receptor function in the basolateral amygdala of adult rats

Abstract

Adolescent alcohol exposure is associated with many negative outcomes that persist into adulthood, including altered affective and reward-related behaviors. However, the long-term neurological disruptions underlying these behavioral states are not fully understood. The basolateral amygdala (BLA) plays a critical role in many of these behaviors, and shifts in the excitatory/inhibitory balance in this area are capable of directly modulating their expression.While changes to BLA physiology have been demonstrated during the acute withdrawal phase following adolescent ethanol exposure, no studies to date have examined whether these persist long-term. The kappa opioid receptor (KOR) system is a neuromodulatory system that acts as a prominent mediator of negative affective behaviors, and alterations of this system have been implicated in the behavioral profile caused by chronic alcohol exposure in adulthood. Notably, in the BLA, the KOR system undergoes functional changes between adolescence and adulthood, but whether BLA KORs are functionally disrupted by adolescent ethanol exposure has not been examined. In this study, we exposed male and female Sprague-Dawley rats to a vapor inhalation model of moderate adolescent chronic intermittent ethanol (aCIE) and examined the long-term effects on GABAergic and glutamatergic neurotransmission within the adult BLA using whole-cell patch-clamp electrophysiology. We also assessed how KOR activation modulated these neurotransmitter systems in aCIE versus control rats using the selective KOR agonist, U69593. This investigation revealed that aCIE exposure disrupted basal glutamate transmission in females by increasing spontaneous excitatory postsynaptic current (sEPSC) frequency, while having no effects on glutamate transmission in males or GABA transmission in either sex.Interestingly, we also found that aCIE exposure unmasked a KOR-mediated suppression of spontaneous inhibitory postsynaptic current (sIPSC) frequency and sEPSC amplitude only in males, with no effects of aCIE exposure on KOR function in females. Together, these data suggest that moderate-level adolescent ethanol exposure produces long-term changes to BLA physiology and BLA KOR function, and that these changes are sex-dependent. This is the first study to examine persistent adaptations to both BLA physiology and KOR function following adolescent alcohol exposure, and opens a broad avenue for future investigation into other neurobiological and behavioral consequences of adolescent ethanol exposure-induced disruptions of these systems.

Sex differences in α‐adrenergic receptor function contribute to impaired hypothalamic metaplasticity following chronic intermittent ethanol exposure

“…Our findings of sex differences in CIE effects on PNCs are in agreement with previously identified sex differences in CIE vapor exposure, such as females being relatively resilient to higher blood EtOH concentrations (BECs) (Glover et al, 2021), which may be due to accelerated clearance kinetics (Marsland et al, 2021). The fact that female PNCs maintained synaptic flexibility despite consistently higher BECs (due to lower body weights; Figure S1) is consistent with previous data showing that female rats following CIE vapor appear resistant to both CIE‐induced changes to biochemical physiology (Henricks et al, 2017; Kirson et al, 2021; Przybysz et al, 2021) and behavioral escalation of voluntary intake (Morales et al, 2015). Certain sex differences, such as prevention of EtOH‐induced changes in endocannabinoid signaling, appear to be mediated through ovarian hormones (Henricks et al, 2017), which may have contributed to the variability in female data displayed in Figure 2 and Figure S3.…”

“…Our findings of sex differences in CIE effects on PNCs are in agreement with previously identified sex differences in CIE vapor exposure, such as females being relatively resilient to higher blood EtOH concentrations (BECs) (Glover et al, 2021), which may be due to accelerated clearance kinetics (Marsland et al, 2021). The fact that female PNCs maintained synaptic flexibility despite consistently (Henricks et al, 2017;Kirson et al, 2021;Przybysz et al, 2021) and behavioral escalation of voluntary intake (Morales et al, 2015).…”

“…Female noradrenergic neurons within the locus coeruleus are more sensitive to CRF‐induced firing increases (Bangasser et al, 2016) and females are more sensitive to alcohol reinstatement following α2AR antagonism (Bertholomey et al, 2016). On the contrary, males may be particularly vulnerable to CIE‐induced effects in limbic regions, including alterations in endocannabinoid (Henricks et al, 2017) and κ‐opioid signaling (Przybysz et al, 2021) in the basolateral amygdala, and inhibitory current kinetics in the central amygdala (Kirson et al, 2021). Together, this suggests subtle sex differences in noradrenergic mechanisms that are important to consider when targeting the NE system in the context of AUD.…”