Modification by Environmental Enrichment of Acute Caffeine's Behavioral Effects on Male and Female Rats

Abstract

Background:

Although there are many reports of caffeine's effects on rodent behavior, little is known of their modification by environmental enrichment.

Methods:

Newly weaned hooded rats were group-housed for 3 months in standard (n=32) or environmentally enriched cages (n=32), and then observed in an open field and Y-maze following intraperitoneal injection of saline or acute caffeine (30 mg/kg). Each test was separated by 1 week, and the sequence differed for each rat. Injections occurred before the open-field trial, and between an acquisition and retention trial in the Y-maze when each rat encountered two black arms, one of which had changed from white. Ambulation, rearing, self-grooming, defecation, and location were recorded in the open field, along with choices of the changed (novel) Y-maze arm. The caffeine×sex×cage design yielded an n of 8 per cell for the open field, and 5–8 for the Y-maze.

Results:

Caffeine increased open-field ambulation (p<0.001) and center occupancy (p<0.05), decreased defecation (p<0.05) and habituation of ambulation (p<0.001), and, for rats from enriched cages, increased rearing (p<0.05). Novel Y-maze arm entries were increased for rats from standard cages (p<0.05), while time in this arm was decreased for enriched rats (p<0.05).

Conclusions:

Caffeine increased activity and may have been mildly anxiolytic. It may have also impaired habituation-associated memory in the open field, and attenuated enrichment-induced enhancement of consolidation in the Y-maze.