Local Changes in Neurosteroid Levels in the Substantia Nigra Reticulata and the Ventral Tegmental Area Alter Chronic Ethanol Withdrawal Severity in Male Withdrawal Seizure‐Prone Mice

Abstract

Background Allopregnanolone (ALLO) is a potent positive modulator of γ-aminobutyric acidA receptors (GABAARs) that affects ethanol withdrawal. Finasteride (FIN), a 5α-reductase inhibitor that blocks the formation of ALLO and other GABAergic neurosteroids, alters ethanol sensitivity. Recently, we found that Withdrawal Seizure-Prone mice from the first genetic replicate (WSP-1) exhibited behavioral tolerance to the anticonvulsant effect of intra-hippocampal ALLO during ethanol withdrawal and that intra-hippocampal FIN significantly increased ethanol withdrawal severity. The purpose of the present study was to determine whether neurosteroid manipulations in the substantia nigra reticulata (SNR) and ventral tegmental area (VTA) produced effects during ethanol withdrawal comparable to those seen with intra-hippocampal ALLO and FIN. Methods Male WSP-1 mice were surgically implanted with bilateral guide cannulae aimed at the SNR or VTA at two weeks prior to ethanol vapor or air exposure for 72 hrs. Initial studies examined the anticonvulsant effect of a single ALLO infusion (0, 100 or 400 ng/side) at a time corresponding to peak withdrawal in the air- and ethanol-exposed mice. Separate studies examined the effect of four FIN infusions (0 or 10 µg/side/day) during the development of physical dependence on the expression of ethanol withdrawal. Results ALLO infusion exerted a potent anticonvulsant effect in ethanol-naïve mice, but a diminished anticonvulsant effect during ethanol withdrawal. Administration of FIN into the SNR exerted a delayed proconvulsant effect in ethanol-naïve mice, whereas infusion into the VTA increased ethanol withdrawal duration. Conclusions Activation of local GABAARs in the SNR and VTA via ALLO infusion is sufficient to exert an anticonvulsant effect in naïve mice and to produce behavioral tolerance to the anticonvulsant effect of ALLO infusion during ethanol withdrawal. Thus, ethanol withdrawal reduced sensitivity of GABAARs to GABAergic neurosteroids in two neuroanatomical substrates within the basal ganglia in WSP-1 male mice.

Sex Differences in Ethanol’s Anxiolytic Effect and Chronic Ethanol Withdrawal Severity in Mice with a Null Mutation of the 5α-Reductase Type 1 Gene

“…Another potential explanation for the lack of genotype difference in chronic withdrawal is that the presence of 5α-reductase-2 in the KO mice compensated for any impact of Srd5a1 deletion on ethanol withdrawal severity. We have found that microinjection of finasteride into discrete brain regions, which would only inhibit Srd5a1 , was required to significantly increase chronic ethanol withdrawal severity (Gililland-Kaufman et al, 2008; Tanchuck et al, 2013), whereas systemic finasteride did not significantly alter chronic ethanol withdrawal severity in male and female C57BL/6J mice (Finn et al, 2004b). Future studies could pharmacologically inhibit the type 2 enzyme in the Srd5a1 mutants or test the double mutants that have been developed (mice lacking Srd5a1 and Srd5a2 ; Mahendroo et al, 2001) and determine the impact on chronic ethanol withdrawal severity.…”

“…The withdrawal-induced decrease in endogenous ALLO levels was accompanied by a significant reduction in activity and expression of 5α-reductase and 3α-HSD (Cagetti et al, 2004; Finn et al, 2004a; Tanchuck et al, 2009), and separate studies determined that administration of finasteride increased chronic ethanol withdrawal (Gililland-Kaufman et al, 2008; Tanchuck et al, 2013). These preclinical findings are consistent with results in small cohorts of alcoholic patients in which a decrease in plasma ALLO and THDOC levels corresponded to an increase in the subjective ratings of anxiety and depression during the early withdrawal phase (Romeo et al, 1996).…”

Chronic Intermittent Ethanol Exposure and Withdrawal Alters (3α,5α)‐3‐Hydroxy‐Pregnan‐20‐One Immunostaining in Cortical and Limbic Brain Regions of C57BL/6J Mice

“…GABAergic neurons within the VTA have interconnectivity with cortical and limbic regions (Diana et al., ), and the VTA appears to be sensitive to endogenous modulation of 3 α ,5 α ‐THP levels (Frye and Rhodes, ). Recently, it was shown that microinjection of 3 α ,5 α ‐THP directly into the VTA produced an anticonvulsant effect in air‐exposed WSP mice (Tanchuck et al., ). Following CIE exposure, GABAergic modulation of dopamine VTA neurons was decreased during acute withdrawal (Diana et al., ).…”

Quantification of ten neuroactive steroids in plasma in Withdrawal Seizure-Prone and -Resistant mice during chronic ethanol withdrawal

“…However, basal levels of 5 neuroactive steroids were lower in WSP-1 versus WSR-1 mice, so a withdrawal-induced decrease in WSP-1 mice may have a greater physiological consequence versus a similar decrease in WSR-1 mice (e.g., 3α,5α- and 3α,5β-androstanediols). Additionally, it should be considered that ethanol withdrawal renders WSP mice (but not WSR) from both genetic replicates tolerant to the anticonvulsant effects of exogenous ALLO administration (e.g., Finn et al, 2006; Gililland-Kaufman et al, 2008; Tanchuck et al, 2013). This behavioral tolerance corresponded to a rightward shift in the ability of ALLO to potentiate GABA-stimulated chloride flux in forebrain microsacs (Finn et al, 2006), consistent with a reduction in GABA A R sensitivity to GABA A R-active neuroactive steroids during ethanol withdrawal in WSP mice.…”