Time-Dependent Bidirectional Effects of Chronic Caffeine on Functional Recovery of the Dorsal Light Reflex After Hemilabyrinthectomy in the Goldfish Carassius auratus

Caffeine works through a variety of complex mechanisms to exert an often bidirectional set of functional and structural neurological changes in vertebrates. We investigated the effects of chronic caffeine exposure on functional recovery of the dorsal light reflex (DLR) in hemilabyrinthectomized common goldfish, Carassius auratus. In this lesion model, the unilateral removal of the vestibular organs results in a temporary loss of gravitationally modulated postural control which is quantifiable via the DLR. We compared the functional recovery over 24 days of post-surgery goldfish continuously held in a caffeine solution of 2.5 mg/L (n = 10), 5.0 mg/L (n = 10), 10.0 mg/L (n = 11), or 0.0 mg/L control (n = 9). Comparison to a sham surgery group (n = 11) indicated statistically significant changes in the DLR of all hemilabyrinthectomized fish on day 1. The control group recovered over the study period and approached, but did not reach sham surgery DLR. Although the caffeine-treated fishes appeared to initiate some postural recovery within the first 2 weeks, beginning on day 10, all caffeine groups diverged from the control group with a deterioration of postural control. All three caffeine groups were significantly deficient in comparison with the control on days 10–24. These results suggest that caffeine exposure can at first be benign, but that high dosage or prolonged exposure hinders functional recovery