Comparison of the effects of 2,5-dimethoxy-4-iodoamphetamine and D-amphetamine on the ability of rats to discriminate the durations and intensities of light stimuli

• Published in: Behavioural pharmacology Vol. 21; no. 1; pp. 11 - 20
• Main Authors: Hampson, CL, Body, S, den Boon, FS, Cheung, THC, Bezzina, G, Langley, R W, Fone, KCF, Bradshaw, C M, Szabadi, E
• Format: Journal Article
• Language: English
• Published: 01-02-2010
• ISSN: 0955-8810
• DOI: 10.1097/FBP.0b0136328334707a

Rats' ability to discriminate durations is disrupted by the monoamine-releasing agent D-amphetamine and the 5-HT2 receptor agonist 2,5-dimethoxy-4-iodoamphetamine (DOI). It is unknown whether this effect is specific for temporal discrimination or reflects general disruption of stimulus control. This experiment addressed this question by comparing the effects of D-amphetamine and DOI on temporal discrimination and discrimination along a nontemporal dimension, light intensity. Twelve rats responded on a schedule in which a light (intensity 22 cd/m super(2)) was presented for t seconds (2.5-47.5 s), after which levers A and B were presented. Responses on A were reinforced when t was less than 25 s, and responses on B were reinforced when t was greater than 25 s. Twelve rats responded on a similar schedule in which a light of intensity i (3.6-128.5 cd/m super(2)) was presented for 25 s. Responses on A were reinforced when i was less than 22 cd/m super(2), and responses on B were reinforced when i was greater than 22 cd/m super(2). Logistic functions were fitted and psychophysical parameters estimated [T sub(50),I sub(50) (central tendency of temporal or light-intensity discrimination); Weber fraction (relative discriminative precision)]. D-Amphetamine (0.2-0.8 mg/kg) increased the Weber fraction for temporal and light-intensity discrimination; DOI (0.625-0.25 mg/kg) increased it for temporal discrimination only. Both drugs increased T sub(50); neither altered I sub(50). D-Amphetamine and DOI have similar effects on temporal discrimination but different effects on light-intensity discrimination. The increase in T sub(50) may reflect the impairment of sustained attention during prolonged stimulus presentation.