Effects of stimulus salience and methamphetamine on choice reaction time in the rat: central tendency versus distribution skew.

Stimulants decrease reaction time in humans as well as laboratory rats. This effect is seen as a decrease in average reaction time or a shift in the distribution peak towards shorter reaction times. However, response-time distributions are typically skewed, exhibiting a positive tail. Our goal for this project was to develop a method of analyzing reaction-time distributions in the rat which will allow us to study systematically measures of central tendency and distribution skew. This analysis subdivided reaction time into initiation time and movement time, and also subdivided the response time distributions into distribution mode and distribution skew. Rats were trained on a two-choice visual reaction-time task. We then evaluated the effects of stimulus salience and methamphetamine (METH) treatment (vehicle, 0.25, 0.5, 1.0, and 1.5 mg/kg) on measures of distribution mode and skew. Stimulus salience decreased initiation time mode, initiation time skew and movement time skew, but had no effect on movement time mode. METH had a greater effect on skew for the initiation time distribution and a greater effect on mode for the movement time distribution. This analysis will serve as a useful method of determining whether initiation time and movement time, as well as distribution mode and distribution skew, represent different behavioral processes in the rat.

Anxiolytic effects of kava extract and kavalactones in the chick social separation-stress paradigm.

RATIONALE: Piper methysticum extract (kava kava) possesses numerous therapeutic properties, but it is unknown which of its principle constituents (kavalactones) subserve such effects. OBJECTIVES: This experiment sought to characterize the putative anxiolytic properties of P. methysticum extract and its six principle kavalactones in the chick social separation-stress paradigm. METHODS: Eight-day-old chicks received intraperitoneal injections of either vehicle, chlordiazepoxide (5.0 mg/ml per kg), P. methysticum extract (containing 30% kavalactones), kavain, dihydrokavain, methysticin, dihydromethysticin, yangonin, or desmethoxyyangonin (30 mg/ml per kg for kava compounds) 30 min prior to being tested in the presence of two conspecifics or in isolation for a 3-min observation period. Latency to adopt a ventral recumbent posture to index sedation, number of vocalizations to index separation distress, and a composite pain score (in response to 50 microliters 0.10% formalin injection into the plantar surface of the foot) to index stress-induced analgesia served as dependent measures. RESULTS: Both chlordiazepoxide and P. methysticum extract attenuated separation-induced distress vocalizations and stress-induced analgesia. Dihydrokavain attenuated separation-induced distress vocalizations. CONCLUSIONS: These findings suggest that the anxiolytic effects of P. methysticum extract may be mediated, in part, by dihydrokavain.

Long-term effects of a high-dose methamphetamine regimen on subsequent methamphetamine-induced dopamine release in vivo.

Rats were treated with a high-dose methamphetamine (METH) regimen (40 mg/kg/injection, four times at 2-h intervals) or a saline regimen (four injections at 2-h intervals). Temperature related measures taken during the high-dose METH treatment were maximum core temperature and minimum chamber temperature. Fourteen rats (METH N=7; Saline N=7) were implanted with in-vivo dialysis probes 4-7 weeks post-regimen (average=6 weeks). The next day, they received a challenge dose of METH (4.0 mg/kg) and dopamine release was measured. Results showed a significant decrease in challenge-induced dopamine release in rats previously treated with the high-dose METH regimen. These findings demonstrate a functional deficit in the dopamine system 6 weeks after high-dose METH treatment. Temperature-related measures taken during the high-dose regimen were not correlated with METH-induced dopamine release 6 weeks later. An additional group of rats were sacrificed 6 weeks after the high-dose regimen (METH N=12; Saline N=10), and their brains was analyzed for dopamine and serotonin concentrations. Tissue concentrations of dopamine were significantly depleted in striatum and nucleus accumbens/olfactory tubercle, but not septum, hypothalamus, or ventral mid-brain 6 weeks after the high-dose regimen. Tissue concentrations of serotonin were also significantly depleted in striatum, nucleus accumbens/olfactory tubercle, hippocampus, somatosensory cortex, but not septum, hypothalamus or ventral mid-brain. Significant correlations between the temperature-related measures and post-mortem neurotransmitter tissue concentrations were region and transmitter dependent.

Anxiolytic properties of botanical extracts in the chick social separation-stress procedure.

RATIONALE: The recent growth in sales of natural products labeled as dietary supplements in the United States has renewed scientific interest in the study of the therapeutic effects of multi-component botanical products. OBJECTIVES: This study sought to determine whether botanical extracts derived from the Rutaceae family, Acori graminei, the Magnoliaceae family, Alchemilla vulgaris and Primula veris, which had previously been identified in bioassays as having potential anxiolytic activity, were active in the chick social separation-stress procedure. METHODS: Eight-day-old chicks received IP injections of test articles 30 min before being tested in the presence of two social companions or in isolation for a 3-min observation period. Dependent measures were: a) latency to adopt a ventral recumbent posture to index sedation, b) number of vocalizations to index separation-distress and c) a composite pain score (comprised of footlift frequency and footlift duration in response to 50 microl of 0.10% formalin injected into the plantar surface of the foot) to index stress-induced analgesia. RESULTS: Proprietal extracts NPS00033 from the Rutaceae plant family and NPS00039 (Relora) from the Magnoliaceae plant family screened positive in this chick model without causing sedation. CONCLUSIONS: These results suggest that botanical extracts Relora and NPS00033 may be useful in modulating anxiety states.