Stress exposure impairs the cognitive functioning of the prefrontal cortex (PFC). Previous research has examined the dopamine (DA) D1 receptor mechanisms underlying this response. The current study performed a preliminary examination of the role of D4 receptor mechanisms by determining whether the selective D4 receptor antagonist, PNU-101387G, could prevent stress-induced working memory deficits in monkeys. Animals were tested on the delayed response task following treatment with PNU-101387G (0 or 0.1-0.8 mg/kg, 60-min pretreatment), and the pharmacological stressor, FG7142 (0 or 0.2 mg/kg,. Exposure to stress can exacerbate or precipitate neuropsychiatric disorders such as schizophrenia and affective disorders involving deficits in higher cognitive functions (Mazure 1995). Thus, it is important to understand the mechanisms by which stress exposure alters higher cortical function. For years it has been appreciated that even mild stress exposure releases monoamines in the prefrontal cortex (PFC; e.g., Goldstein et al. 1996;Kaneyuki et al. 1991;Thierry et al. 1976). The PFC is critical for guiding behavior using working memory (Goldman-Rakic 1987). Our lab has shown that stress impairs working memory performance in rats and monkeys via excessive stimulation of catecholamine receptors (reviewed in Arnsten and Goldman-Rakic 1998;Birnbaum et al. 1999). A continuing goal of this research is to identify the receptor subtypes underlying stressinduced PFC deficits.
FG7142 significantly impaired delayed response performance relative to vehicle; PNU-101387G pretreatment produced a dose-related reversal of the FG7142 response. PNU-101387G had no significant effects on its own, but there were trends toward improvement at low doses and impairment at higher doses. Further studies in a largerThe effects of stress have been examined using spatial working memory paradigms such as the delayed response task which are tightly linked to PFC function in monkeys (Goldman and Rosvold 1970). Exposure to either loud noise stress or to a pharmacological stressor (the inverse benzodiazepine agonist, FG7142) impaired delayed response performance in monkeys (Arnsten and Goldman-Rakic 1998;Murphy et al. 1996). In con- 23 , NO . 4 trast, these same stressors had no effect on discrimination tasks with similar motor and motivational needs that do not rely on PFC function (Arnsten and Goldman-Rakic 1998;Murphy et al. 1996). A similar pattern has been observed in humans, where loud noise stress impaired performance of tasks associated with the PFC such as the Stroop interference task (Hartley and Adams 1974), but facilitated simple or well-rehearsed tasks (reviewed in Broadbent 1971).Much research to date has focused on the dopamine (DA) mechanisms underlying the stress response, as DA release in the PFC appears to be the most reactive of the monoamines to stress exposure (Goldstein et al. 1996). Several lines of evidence indicate that high levels of DA release in the PFC lead to working memory impairment. Stress-induced working memory defic...