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M S Hooks

Publications and source records attributed to M S Hooks.

7 recordsLinked to original sources
PubMed1992

Individual differences in basal and cocaine-stimulated extracellular dopamine in the nucleus accumbens using quantitative microdialysis.

The current experiment examined the role of nucleus accumbens (NACC) dopamine in individual differences. Subjects were divided into high responders (HR) and low responders (LR) based on their locomotor response to a novel environment. HR rats were subjects which had a locomotor response to novelty in the upper third of the population screened and LR rats in the bottom third of the population. A new method of microdialysis was then used that allowed determination of the extracellular dopamine concentration. This was accomplished by adding various dopamine concentrations (0.0, 5.0 and 20.0 nM) to the perfusate. The concentration of dopamine in the dialysate was subsequently determined. The difference in the dialysate and perfusate dopamine was regressed on the perfusate dopamine. The regression yielded the in vivo recovery and the extracellular concentration. HR rats exhibit a 250% higher basal dopamine concentration (6.45 +/- 1.01 nM, n = 6) than LR rats (2.58 +/- 0.16 nM, n = 7). The in vivo microdialysis recovery was used to estimate the extracellular dopamine following cocaine challenge (15 mg/kg) in the two groups. Following i.p. cocaine administration, HR rats had both a greater locomotor response and increase in absolute dopamine concentration compared to LR rats. The maximum dopamine concentration in the HR group was 23 +/- 2.9 nM, while that in the LR group was only 8.6 +/- 1.1 nM. The maximum in the LR group is comparable to the basal level in the HR group. However, there were no difference in percent change in dopamine following cocaine.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Naloxone reduces amphetamine-induced stimulation of locomotor activity and in vivo dopamine release in the striatum and nucleus accumbens.

This study tested the possibility that naloxone (NX), an opioid antagonist, reduces the behavioral effects of amphetamine (AMPH) in rats by attenuating the dopaminergic response to AMPH. In the first experiment, adult, male rats were injected SC with either NX (5.0 mg/kg) or saline and 30 min later received doses of AMPH (0.0, 0.1, 0.4, 1.6, and 6.4 mg/kg) cumulatively at 30-min intervals. Gross locomotor counts following AMPH administration were significantly lower for rats pretreated with NX than for rats pretreated with saline. In the second experiment, the same drug treatments were given while performing microdialysis in either the striatum (STR) or nucleus accumbens (NACC). STR rats treated with vehicle showed a larger percentage increase in DA levels following AMPH treatment than did NACC rats treated with vehicle. NX pretreatment did not affect dopamine concentrations in either brain region. However, compared to pretreatment with saline pretreatment with NX significantly decreased the dopaminergic response to AMPH in the STR. There was no difference between the two groups in the peak dopaminergic response to AMPH in the NACC, but there was a significant AMPH x treatment x time interaction due to differences between the groups during the later portion of the response to 6.4 mg/kg AMPH. There was also a difference in locomotor activity following AMPH treatment between NX- and saline-treated subjects during dialysis. These findings suggest that a decrease in the dopaminergic response to AMPH is the mechanism by which NX attenuates behavioral stimulant effects of AMPH. In addition, there is a difference between the STR and NACC in dopaminergic responsiveness to AMPH.

Animals↗
PubMed1992

Individual differences in amphetamine sensitization: dose-dependent effects.

Rats were screened for locomotor activity in a novel environment and divided into high (HR) or low (LR) responders based on whether their locomotor score for the first hour was above or below the median. In the first experiment, HR and LR rats were compared for their locomotor response following repeated administration of either 0.0, 0.5, 1.0, or 1.5 mg/kg d-amphetamine sulfate (AMPH). Injections of either 0.5 or 1.0 mg/kg AMPH produced higher locomotor activity in HR rats than in LR rats. Furthermore, there was a correlation between the locomotor response to novelty and the response to either 0.5 or 1.0 mg/kg AMPH. In addition, whereas both groups of rats developed the same degree of sensitization to 0.5 mg/kg AMPH, only the HR rats developed pronounced sensitization to repeated administration of 1.0 mg/kg AMPH. When both HR and LR were considered, there was a significant correlation between response to novelty and the extent of sensitization to the locomotor-stimulating properties of 1.0 mg/kg AMPH. There were no differences in locomotor activity or sensitization between HR and LR rats following the highest dose of AMPH (1.5 mg/kg). In a separate experiment, HR and LR rats were compared for locomotor activity following a series of intracranial infusions of AMPH. There were no overall differences in locomotor activity between the HR and LR groups following AMPH infusions into either the nucleus accumbens (NACC) or the anterior dorsal striatum (ADS). However, the locomotor activity scores in the novel environment significantly correlated with the locomotor response to 3.0 micrograms AMPH infused into either the NACC or ADS.(ABSTRACT TRUNCATED AT 250 WORDS)

Amphetamine↗
PubMed1992

Sensitization and individual differences to IP amphetamine, cocaine, or caffeine following repeated intracranial amphetamine infusions.

Rats that have a high locomotor response to novelty (HR) sensitize more readily to IP-administered amphetamine than rats with a low locomotor response (LR) to novelty. This experiment compared sensitization in HR and LR rats following amphetamine (3.0 micrograms/side for 5 days) infused bilaterally into either the nucleus accumbens (NACC), ventral tegmental area (VTA), or the medial frontal cortex (MFC). The subsequent locomotor response to IP-administered d-amphetamine sulfate (1 mg/kg), cocaine HCl (15 mg/kg), and caffeine benzoate (20 mg/kg) was also examined. No differences were observed between HR and LR rats following amphetamine infusion into either the MFC, NACC, or VTA. However, HR rats showed greater locomotor activity compared to LR rats following either IP amphetamine, cocaine, or caffeine for subjects cannulated in the NACC, MFC, or the VTA. Repeated infusions of amphetamine into the VTA increased the locomotor response to both IP amphetamine and cocaine, but not to IP caffeine, while repeated infusions of amphetamine into the NACC or MFC had no effect on locomotor response to any drug subsequently administered IP. The results support previous findings that changes induced by intra-VTA infusions, but not intra-NACC or MFC infusions, of amphetamine induce sensitization to IP-administered amphetamine and cocaine. Findings from the present experiment indicate the ability of the dopamine cell body region, but not the dopamine terminal fields, to produce locomotor sensitization to amphetamine and cocaine. The results from the present experiment also indicate the lack of localization to one of studied regions of individual differences.(ABSTRACT TRUNCATED AT 250 WORDS)

Amphetamine↗
PubMed1991

Response to novelty predicts the locomotor and nucleus accumbens dopamine response to cocaine.

The relationship between a rat's locomotor response to a novel environment and its behavioral and dopaminergic responses to cocaine was examined. Subjects were divided into two groups based on their locomotor response to a novel environment. Subjects who had a novelty response above the median were classified as high responders (HR), while those with a novelty response below the median were classified as low responders (LR). Following administration of cocaine-HCl (0, 2.5, 5.0, 10.0, or 15.0 mg/kg), HR rats showed a greater locomotor response than LR rats. Moreover, there was a significant correlation between a subject's locomotor response to the novel environment and the locomotor response to either 10.0 (r = 0.65) or 15.0 (r = 0.92) mg/kg cocaine. In a separate experiment, the extracellular concentration of dopamine in the nucleus accumbens (NACC) was monitored using microdialysis procedures. Following cocaine administration (15.0 mg/kg) HR rats showed a larger NACC dopamine response and greater locomotor activity than LR rats. In addition, there was a threefold greater locomotor activity to dopamine ratio in HR rats than in LR rats. A correlation between a subject's locomotor response to a novel environment and the dopaminergic response to cocaine was also evident. These results suggest that differences in the locomotor response to cocaine can, to some degree, be predicted by a rat's locomotor response to a novel environment, and that variations in dopamine-dependent mechanisms of the NACC may underlie these individual differences.

Animals↗
PubMed1991

Individual differences in locomotor activity and sensitization.

Male rats were screened for locomotor activity in a novel environment and divided into high (HR) and low (LR) responders based on whether their locomotor activity score for the first hour was above or below the median locomotor activity for the subject sample. Subsequently, the locomotor response to repeated administration of either amphetamine (AMPH; 0.5 mg/kg), cocaine (10 mg/kg), scopolamine (0.5 mg/kg) or saline was monitored in separate groups of HR and LR rats. HR rats had significantly higher overall activity scores than LR rats for all 3 drugs. Both HR and LR rats developed tolerance at the same rate to repeated scopolamine administration. In contrast, only HR rats showed pronounced sensitization to the locomotor stimulating properties of AMPH and a direct correlation was evident between the locomotor response to novelty and the magnitude of sensitization. These results suggest that an individual's response to a novel environment can, to a certain extent, predict drug-induced locomotor activity and that individual differences in the response to novelty and sensitization to AMPH may result from individual variations in a common neural mechanism.

Amphetamine↗