Spatial signal detection in rats is differentially disrupted by delta-9-tetrahydrocannabinol, scopolamine, and MK-801

Cannabinoid receptors have been implicated as having important roles in human cognitive processes, especially memory and attention. While some work has studied the effects of the active ingredient in marijuana, delta-9-tetrahydrocannabinol (THC), on short-term memory, no work has examined the involvement of these receptors in mediating attention. Therefore, the present study compared the effects of THC on the performance by rats of an operant spatial signal detection task with those of cholinergic muscarinic antagonist scopolamine and glutamatergic NMDA antagonist MK-801, both compounds known to influence attention and other cognitive processes in rats. These experiments were conducted in a two lever operant chamber in which a cue lamp was mounted over each lever. The rats were pretrained to respond rapidly on the corresponding lever following a rapid presentation of the cue lamp above it. The stimulus was presented in a random order of three durations (100, 300 or 1000 ms) to measure detectability of the stimulus under saline, THC (1.0 or 2.0 mg/kg i.p.), scopolamine (0.06-0.25 mg/kg i.p.), or MK-801 (0.06-0.25 mg/kg i.p.). THC significantly and selectively disrupted stimulus detection accuracy at the 100 ms stimulus duration, but did not influence response bias or the rate of responding. Scopolamine and MK-801 both produced alteration in errors of omission and position bias. These data suggest that THC produces an impairment in visual attention and that the nature of this impairment is qualitatively different from that produced by muscarinic-receptor or NMDA-receptor antagonism.