Sedative and Motor Incoordination Effects of Ethanol in Mice Lacking CD14, TLR2, TLR4, or MyD88

Abstract

Background In our companion article, we examined the role of MyD88-dependent signaling in ethanol consumption in mice lacking key components of this inflammatory pathway and observed differential effects on drinking. Here we studied the role of these same signaling components in the acute sedative, intoxicating, and physiological effects of ethanol. TLR4 has been reported to strongly reduce the duration of ethanol-induced sedation, though most studies do not support its direct involvement in ethanol consumption. We examined TLR4 and other MyD88 pathway molecules to determine signaling specificity in acute ethanol-related behaviors. We also studied other GABAergic sedatives to gauge the ethanol specificity and potential role for GABA in ethanol’s sedative and intoxicating effects in the mutant mice. Methods Loss of righting reflex (LORR) and recovery from motor incoordination were studied following acute injection of ethanol or other sedative drugs in male and female control C57BL/6J mice vs. mice lacking CD14, TLR2, TLR4 (C57BL/10ScN), or MyD88. We also examined ethanol-induced hypothermia and blood ethanol clearance in these mice. Results Male and female mice lacking TLR4 or MyD88 showed reduced duration of ethanol-induced LORR and faster recovery from ethanol-induced motor incoordination. MyD88 KO mice had slightly faster recovery from ethanol-induced hypothermia compared to control mice. None of the mutants differed from control mice in the rate of blood ethanol clearance. There were no genotype differences in the duration of gaboxadol-induced LORR, and only mice lacking TLR4 were less sensitive to the sedative effects of pentobarbital. Faster recovery from diazepam-induced motor incoordination was observed in CD14, TLR4, and MyD88 null mice of both sexes. Conclusions TLR4 and MyD88 were key mediators of the sedative and intoxicating effects of ethanol and GABAergic sedatives, indicating a strong influence of TLR4-MyD88 signaling on GABAergic function. Despite the involvement of TLR4 in ethanol’s acute behaviors, it did not regulate ethanol consumption in any drinking model as shown in our companion article. Collectively, our studies demonstrate differential effects of TLR-MyD88 components in the acute vs. chronic actions of ethanol.

Ethanol Consumption in Mice Lacking CD14, TLR2, TLR4, or MyD88

“…A study of TLR4 KO adolescent mice showed slightly reduced EtOH preference following intermittent intraperitoneal EtOH treatment (Montesinos et al., ). Despite the limited evidence for its role in voluntary EtOH drinking, there is consistent evidence that TLR4 mediates the sedative effects of EtOH in mice (Corrigan et al., ; Wu et al., ) (also see our companion study in Blednov et al., ) and rats (Harris et al., ), as well as a role for the Toll innate immune pathway in EtOH‐induced resistance to sedation in Drosophila (Troutwine et al., ).…”

Role of MyD88 in IL-1β and Ethanol Modulation of GABAergic Transmission in the Central Amygdala

“…At the behavioral level, the roles of specific innate immune elements of TLR4 and IL-1 system in the ethanol-related behaviors vary. While TLR4, IL-1R1, IL-1ra, and MyD88 play an important role in acute ethanol-induced sedation and motor impairment, CD14 does not [12,18,51]. Similar specificity is observed with ethanol drinking, where CD14, IL-1ra, and MyD88 (only in males) play significant roles [17,51], while TLR4, IL-1R1, and MyD88 (in females) are not involved in the regulation of ethanol consumption [12,16,17].…”

“…Based on behavioral studies showing a regulatory role of MyD88 on GABAergic transmission [18], here, we assessed the role of MyD88 in the GABAergic effects of IL-1β and ethanol in the CeA. Our findings indicate that IL-1β and ethanol regulation of GABAergic signaling does not require MyD88, but MyD88 can modulate (attenuate) the GABAergic effects of IL-1β and high ethanol concentrations in the CeA.…”

“…Most notably, genomic studies in mice [5], rats [6], and humans [3,7,8] have identified several members of the Toll-like receptors (TLR) and interleukin-1/interleukin18 (IL-1/IL-18) receptor pathways in AUD [9,10]. Moreover, pharmacological [11][12][13], viral [14,15], or transgenic [2,9,11,[16][17][18][19][20] manipulation of the innate immune system leads to alterations of the ethanol-related behaviors in rodents. Collectively, this growing literature on innate immune responses critically contributing to the neurobiology of AUD [21][22][23] suggests that these pathways have high potential as targets for the development of new AUD therapeutic strategies [16,[24][25][26].…”

Toll-like receptor 3 activation increases voluntary alcohol intake in C57BL/6J male mice

“…Figure 4A). Pretreatment with poly(I:C) did not increase ethanol consumption [Figure 4B, F treatment(1,20)=1.584, p=0.22; F time (4,80)=1.024, p=0.40; F treatment x time (4,80)=1.02, p=0.4], although there was a slight initial increase in ethanol preference [Figure 4C,F treatment x time (4,80)=3.015, p=0.02], suggesting that poly(I:C) pretreatment changed the pattern of escalation compared with saline-pretreated mice. Total fluid intake was unaffected by poly(I:C) pretreatment [Figure 4D, F treatment (1,20)=0.01, p=0.9; F time (4,80)=1.01, p=0.42; F treatment x time (4,80)=1.65, p=0.17].…”