Naloxone’s Effect on Activity-Induced Phase Shifts of Circadian Rhythms

Daniel Janik,Margaret Alvarez Brereton

doi:10.5539/ijb.v9n4p10

Daniel Janik, Margaret Alvarez Brereton

Open Access

https://doi.org/10.5539/ijb.v9n4p10

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Abstract

Vigorous running in a novel exercise wheel by hamsters during the subjective day results in large (about 3 hr) phase advances of their circadian rhythms. We administered the opiate receptor antagonist naloxone at 10 mg/kg and 20 mg/kg (i.p.) and found that at 20 mg/kg it significantly reduced phase shifts. This dose of naloxone also reduced the amount of running shown by hamsters in the novel wheel. At the 20 mg/kg dose, the reduced amount of running resulted in smaller phase shifts. The results are consistent with the hypothesis that nonphotic phase shifts are linked to exercise and arousal in hamsters. However, because high amounts of running were accompanied by phase shifting in animals whose opiate receptors were blocked, the results provide no evidence that the rewarding nature of running in rodents is an important causal factor in nonphotic phase shifting beyond its role in promoting running.

Highlights

Nonphotic phase shifting of circadian rhythms often involves physical activity or arousal associated with physical activity (Reebs & Mrosovsky, 1989a,b; Reebs, Lavery, & Mrosovsky, 1989)
The main exceptions to this generalization were two points [Fig 1(right) -marked with asterisks] that came from one animal who ran vigorously when injected with both saline and naloxone, but failed to show a large shift in either case
When we compared treatment groups for phase-shifting, we found that there was no significant difference between naloxone-treated animals and saline controls at 10 mg/kg (Fig 2A; p=0.82, t-test), but animals treated with 20 mg/kg naloxone showed significantly less phase-shifting than saline-treated animals (Fig 2A; p=.029, t-test)

Summary

Introduction

Nonphotic phase shifting of circadian rhythms often involves physical activity or arousal associated with physical activity (Reebs & Mrosovsky, 1989a,b; Reebs, Lavery, & Mrosovsky, 1989). A number of other stimulus situations can lead to nonphotic-like phase shifts or influence entrainment These include restricted food access (Mistlberger, 1994), opportunity to hoard (Rusak et al, 1988) and interaction with a conspecific (Mrosovsky et al, 1989). When it is restricted to a novel wheel for three hours in the middle of the subjective day - circadian time (CT) 4-7 - and engaged in voluntary running for most of that period, it consistently shows a 3 hr circadian phase advance (Janik and Mrosovsky, 1993; Mrosovsky et al, 1992) This manipulation, termed a pulse, is easy to carry out, making it a good procedure for studying the underlying mechanisms of nonphotic phase shifts

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