Effect of clonidine on consummatory negative contrast and on novelty-induced stress

Effect of serotonergic drugs on negative contrast in consummatory behavior

The effect of acute and chronic administration of the 5-HT1A agonist buspirone on successive negative contrast was investigated in Experiments 1-6. Contrast in consummatory behavior was induced by shifting rats from a 32% to a 4% sucrose solution. Experiments 1-5 showed that buspirone (0.125, 0.25, 0.5, 1.0, 2.0, 15.0 mg/kg) was ineffective in alleviating contrast or in facilitating recovery from contrast. The 15 mg/kg dose substantially decreased consummatory responding. Experiment 6 showed that the chronic (24 days) administration of buspirone (0.5, 2.0 mg/kg) also did not alleviate contrast. The chronic, but not the acute administration of the 2.0 mg/kg dose decreased consummatory behavior. In Experiment 7 the 5-HT1A agonist gepirone (2.5, 5.0 and 10.0 mg/kg) was also found to be ineffective in reducing contrast but, at the higher doses, decreased overall sucrose intake. Experiments 8 and 9 found that the 5-HT2 antagonists ketanserin (2.0 and 8.0 mg/kg) and ritanserin (0.63 and 2.5 mg/kg) also did not alleviate contrast. Midazolam (1.0 mg/kg), included as a positive control, eliminated contrast. These data suggest that serotonergic mechanisms are not involved in negative contrast.

Effect of anxiolytics and antidepressants on extinction and negative contrast

Anxiolytics, particularly the benzodiazepines and barbiturates tend to retard, but not prevent, extinction, promote recovery from negative contrast, and elevate S- responding in discrimination training. Anxiolytics, administered during acquisition, tend to eliminate the partial reinforcement extinction effect, but this result is substantially influenced by parametric considerations. Behaviors that are energized in extinction may have a different pharmacological profile than behaviors that decline. Conclusions regarding the effects of antidepressants must be more tentative but, in general, acutely administered antidepressants are relatively ineffective in all of these paradigms. However, antidepressants may enhance the efficiency of responding on DRL schedules whereas anxiolytics tend to disrupt such behavior.

Rats (Rattus norvegicus) selectively bred to differ in avoidance behavior also differ in response to novelty stress, in glycemic conditioning, and in reward contrast

The behavior of the Syracuse high avoidance (SHA) and Syracuse low avoidance (SLA) rats, selectively bred by Brush (F. R. Brush, J. C. Froehlich, & P. Sakellaris, 1979, Behavior Genetics, 9, 309-316) to differ in avoidance behavior, was examined in several different tasks. The SLA rats showed a greater elevation in plasma glucose when exposed to a novel environment; after 7 days of exposure to this environment there was evidence of habituation in the SHA rats but not in the SLA rats; the SHA rats showed a hyperglycemic conditioned response in a glycemic conditioning procedure, the SLA rats showed no evidence of conditioning but had higher overall levels of plasma glucose; both strains showed reliable successive negative contrast effects in consummatory behavior when shifted from 32 to 4% sucrose, but the contrast was larger in the SLA rats; the administration of chlordiazepoxide eliminated negative contrast in the SLA rats but had no effect on contrast in the SHA rats; and the SLA rats were reliably heavier than the SHA rats. The behavioral differences were considered in the context of differences in emotional reactivity between the two strains.

Effect of clonidine on sucrose intake and water intake varies as a function of dose, deprivation state, and duration of exposure

Lick frequency was monitored in five-minute intervals over a one-hour period in rats given access to 8% sucrose (Experiment 1) or water (Experiment 2). Prior to the session, the rats were administered either isotonic saline or clonidine (6.24, 12.5, or 25 micrograms/kg). In deprived rats (82%) clonidine led to a dose-related increase in consummatory behavior. Water intake in deprived rats was depressed by clonidine. In rats maintained on a free-feeding schedule, the higher clonidine doses led to a decrement in sucrose intake over the first 15 minutes of access; whereas the 6.25 micrograms/kg dose stimulated consummatory behavior, but only during the first five minutes of access. There were no reliable effects of clonidine on sucrose intake late in the access period for the free-feeding rats. Water intake in free-feeding rats tended to be enhanced by the low dose of clonidine, particularly late in the access period. In general, deprivation enhanced sucrose intake and depressed water intake and clonidine exaggerated both of these trends.