Acute ethanol disrupts photic and serotonergic circadian clock phase-resetting in the mouse

Abstract

Background: Alcohol dependence is associated with impaired circadian rhythms and sleep. Ethanol administration disrupts circadian clock phase-resetting, suggesting a mode for the disruptive effect of alcohol dependence on the circadian timing system. In this study, we extend previous work in C57BL/6J mice to: (i) characterize the suprachiasmatic nucleus (SCN) pharmacokinetics of acute systemic ethanol administration, (ii) explore the effects of acute ethanol on photic and nonphotic phase-resetting, and (iii) determine if the SCN is a direct target for photic effects.

Methods: First, microdialysis was used to characterize the pharmacokinetics of acute intraperitoneal (i.p.) injections of 3 doses of ethanol (0.5, 1.0, and 2.0 g/kg) in the mouse SCN circadian clock. Second, the effects of acute i.p. ethanol administration on photic phase delays and serotonergic ([+]8-OH-DPAT-induced) phase advances of the circadian activity rhythm were assessed. Third, the effects of reverse-microdialysis ethanol perfusion of the SCN on photic phase-resetting were characterized.

Results: Peak ethanol levels from the 3 doses of ethanol in the SCN occurred within 20 to 40 minutes postinjection with half-lives for clearance ranging from 0.6 to 1.8 hours. Systemic ethanol treatment dose-dependently attenuated photic and serotonergic phase-resetting. This treatment also did not affect basal SCN neuronal activity as assessed by Fos expression. Intra-SCN perfusion with ethanol markedly reduced photic phase delays.

Conclusions: These results confirm that acute ethanol attenuates photic phase-delay shifts and serotonergic phase-advance shifts in the mouse. This dual effect could disrupt photic and nonphotic entrainment mechanisms governing circadian clock timing. It is also significant that the SCN clock is a direct target for disruptive effects of ethanol on photic shifting. Such actions by ethanol could underlie the disruptive effects of alcohol abuse on behavioral, physiological, and endocrine rhythms associated with alcoholism.

Figure 1

Pharmacokinetic profiles of ethanol in the SCN following i.p. injections of three doses of ethanol. For each dose, peak levels occurred within 20–40 min of injection. Clearance rate was dose-dependent. Time points are the means ± S.E.

Figure 2

Dose-dependent inhibition of phase-delay responses to a light pulse delivered at ZT 16 (top) and phase-advance responses to i.p. injection of (±)8-OH-DPAT delivered during the middle of the light-phase (ZT 6; bottom). Bars with different letters are significantly different (p<0.05). Bars represent means ± S.E.

Figure 3

Representative double-plotted actograms of general locomotor activity showing ethanol attenuation of photic phase-delay responses to a 30 min light pulse delivered at ZT 16 and phase-advance responses to an i.p. (±)8-OH-DPAT injection delivered at ZT 6. A, ethanol (2 g/kg) + light; B, saline + light; C, ethanol (2 g/kg) + 8-OH-DPAT; D, saline + 8-OH-DPAT. Asterisks denote the time of ethanol injection and subsequent light pulse or (+)8-OH-DPAT injection.

Figure 4

Inhibition of phase-delay responses to a light pulse delivered at ZT 14 by direct reverse-microdialysis perfusion of ethanol to the SCN. The ethanol and artificial cerebrospinal (ACSF) perfusions had no phase-resetting effect in the absence of a light pulse. For all treatments, bars with different letters are significantly different (pπ.05). Bars represent means ± S.E.

Figure 5

Representative double-plotted actograms of general locomotor activity showing the inhibition by reverse-microdialysis perfusion of ethanol to the SCN of photic phase-delays induced by a light pulse delivered at ZT 14. A, vehicle (artificial cerebrospinal fluid); B, ethanol; C, vehicle/no light pulse; D, ethanol/no light pulse. Asterisks denote onset of the perfusions and subsequent light pulse (or no pulse).

Figure 6

Photomicrographs and graph illustrating the lack of effect of i.p. ethanol injection (2 g/kg) on immunoreactive Fos expression in the SCN at midday (ZT 6; A, ethanol; B, saline) . 3V, third ventricle; OC, optic chiasm. Bars represent means ± S.E.