DETECTION OF VISUAL SIGNALS BY RATS - EFFECTS OF CHLORDIAZEPOXIDE ANDCHOLINERGIC AND ADRENERGIC-DRUGS ON SUSTAINED ATTENTION

Central cholinergic and adrenergic pathways support the attentional pr ocesses necessary for detecting and reporting temporally unpredictable stimuli. To assess the functional effects of pharmacological manipula tions of these pathways, male Long-Evans rats performed a two-choice: discrete-trial signal-detection task in which food was provided for pr essing one lever after presentation of a signal (a 300-ms light flash) , and for pressing a second lever at the end of a trial lacking a sign al. Seven signal intensities were presented during each I-h session in a pseudo-random order across three 100-trial blocks. After acquisitio n of a stable performance baseline, the acute effects of chlordiazepox ide (0, 3, 5, 8 mg/kg IP), pilocarpine (0, 1.0, 1.8, 3.0 mg/kg SC), sc opolamine (0, 0.030, 0.056, 0.100 mg/kg SC), nicotine (0, 0.08, 0.25, 0.75 mg/kg SC), mecamylamine (0, 1.8, 3.0: 5.6 mg/kg IP), clonidine (0 , 0.003, 0.010, 0.030 mg/kg SC), and idazoxan (0, 1, 3, 10 mg/kg SC) w ere assessed. Five measures of performance were analyzed: response fai lures; the proportion of ''hits'' [P(hit): the proportion of correct r esponses on signal trials]; the proportion of ''false-alarms'' [P(fa): the proportion of incorrect responses on non-signal trials]; and resp onse times (RT) for hits and for correct rejections. All drugs which s lowed responding affected RT for hits and correct rejections equivalen tly, suggesting little or no influence of motor slowing on choice accu racy. Chlordiazepoxide reduced P(hit) at low signal intensities only, without affecting P(fa) or RT, consistent with sensory impairment (red uced visual sensitivity). All other drugs except nicotine reduced P(hi t) at high signal intensities preferentially, suggesting a non-visual source of the impairment. Scopolamine, mecamylamine and clonidine affe cted both P(hit) and P(fa); pilocarpine and idazoxan reduced P(hit) wi thout affecting: P(fa). Nicotine at 0.75 mg/kg decreased P(hit) in the first block of trials; at 0.08 mg/kg it increased P(hit) in the secon d block; no dose affected P(fa). RTs were increased by pilocarpine, sc opolamine, mecamylamine and clonidine, but not by nicotine or idazoxan . The data suggest that drugs which reduce cholinergic or adrenergic t one (scopolamine, mecamylamine and clonidine) impair sustained attenti on by decreasing the detection of signals and by increasing the false alarm rate, whereas drugs which elevate cholinergic or adrenergic tone (pilocarpine, nicotine and idazoxan) decrease attention by impairing detection of signals without affecting the false alarm rate. In contra st, the GABA-facilitating drug chlordiazepoxide appeared to affect vis ual thresholds rather than attention.