Chlorpheniramine facilitates inhibitory avoidance in teleosts submitted to telencephalic ablation

The present study investigated the involvement of H(1) histaminegic receptor on the acquisition of inhibitory avoidance in Carassius auratus submitted to telencephalic ablation. The fish were submitted to telencephalic ablation 5 days before the experiment. The inhibitory avoidance procedure included 1 day for habituation, 3 days for training composed of 3 trials each (1st day: T1, T2, T3; 2nd day: 2T1, 2T2, 2T3; 3rd day: 3T1, 3T2, 3T3) and 1 day for test. On training days, the fish were placed in a white compartment, after 30 s the door was opened. When the fish crossed to a black compartment, a weight was dropped (aversive stimuli). Immediately after the third trial, on training days, the fish received, intraperitoneally, one of the pharmacological treatments (saline (N = 20), 8 (N = 12) or 16 (N = 13) µg/g chlorpheniramine, CPA). On the test day, the time to cross to the black compartment was determined. The latency of the saline group increased significantly only on the 3rd trial of the 2nd training day (mean ± SEM, T1 (50.40 ± 11.69), 2T3 (226.05 ± 25.01); ANOVA: P = 0.0249, Dunn test: P < 0.05). The group that received 8 µg/g CPA showed increased latencies from the 2nd training day until the test day (T1 (53.08 ± 17.17), 2T2 (197.75 ± 35.02), test (220.08 ± 30.98); ANOVA: P = 0.0022, Dunn test: P < 0.05)). These results indicate that CPA had a facilitating effect on memory. We suggest that the fish submitted to telencephalic ablation were able to learn due to the local circuits of the mesencephalon and/or diencephalon and that CPA interferes in these circuits, probably due an anxiolytic-like effect.

Matching salt intake to physiological need in rats using foraging protocols

Several studies of the quantitative relationship between sodium need and sodium intake in rats are reviewed. Using acute diuretic treatment 24 h beforehand, intake matches need fairly accurately when intake is spread out in time by using a hypotonic solution of NaCl. In contrast, using a hypertonic solution, intake is typically double the need. Using the same diuretic treatment, although the natriuresis occurs within ~1 h, the appetite appears only slowly over 24 h. Increased plasma levels of aldosterone parallel the increased intake; however, treatment with metyrapone blocks the rise in aldosterone but has no effect on appetite. Satiation of sodium appetite was studied in rats using sodium loss induced by chronic diuretic treatment and daily salt consumption sessions. When a simulated foraging cost was imposed on NaCl access in the form of a progressive ratio lever press task, rats showed satiation for NaCl (break point) after consuming an amount close to their estimated deficit. The chronic diuretic regimen produced hypovolemia and large increases in plasma aldosterone concentration and renin activity. These parameters were reversed to or toward non-depleted control values at the time of behavioral satiation in the progressive ratio protocol. Satiation mechanisms for sodium appetite thus do appear to exist. However, they do not operate quantitatively when concentrated salt is available at no effort, but instead allow overconsumption. There are reasons to believe that such a bias toward overconsumption may have been beneficial over evolutionary time, but such biasing for salt and other commodities is maladaptive in a resource-rich environment.

The role of dopamine D3 receptor in the amphetamine-induced conditioned place preference in mice / 法医学杂志

OBJECTIVE@#To study the role of dopamine D3 receptor involved in the amphetamine-induced conditioned place preference (CPP) in mice.@*METHODS@#The CPP was observed in D3 receptor knock-out (D3RKO) mice and C57BL/6 wild-type control mice after administration of amphetamine. The data were analyzed with a two-way ANOVA using the SPSS 13.0 software.@*RESULTS@#D3RKO mice showed a significant amphetamine-induced CPP (P<0.001), compared with the ones administered with saline in C57BL/6 control mice.@*CONCLUSION@#The results indicate that amphetamine can produce significant CPP in dopamine D3 receptor knock-out mice, suggesting that amphetamine-induced addiction can be inhibited by dopamine D3 receptor.

Clitoria ternatea (Linn) root extract treatment during growth spurt period enhances learning and memory in rats.

Neonatal rat pups (7 days old) were intubated with either 50 mg/kg body weight or 100 mg/kg body weight of aqueous root extract of Clitoria ternatea (CTR) for 30 days. These rats were then subjected to open field, two compartment passive avoidance and spatial learning (T-Maze) tests (i) immediately after the treatment and (ii) 30 days after the treatment, along with age matched normal and saline control rats. Results showed no change in open field behaviour, but showed improved retention and spatial learning performance at both time points of behavioural tests, indicating the memory enhancing property of CTR which implicates a permanent change in the brain of CTR treated rats.

2, 4-dichloro phenoxy acetic acid alters monoamine levels, acetylcholinesterase activity & operant learning in rats.

2, 4-Dichloro phenoxy acetic acid (2, 4-D) was given at 100 mg/kg body weight per day by oral intubation from postnatal days 2 to 25 to assess its effect on the levels of norepinephrine (NE), dopamine (DA) and 5-hydroxytryptamine (5-HT) in olfactory bulb (OB), hippocampus (HI), visual cortex (VC), cerebellum (CB) and brainstem (BS). NE levels were increased in OB, HI, VC and BS at 10 days of age. However, by 25 days, NE levels were decreased in OB, HI and VC. DA levels were also increased in OB, HI, VC and CB at 10 days of age and again decreased by 25 days in OB, HI and VC. 5-HT levels were increased in HI, CB and BS at 10 days and in VC and CB at 25 days of age. Reduced acetylcholinesterase (AChE) activity in OB and HI and monoamines in different brain regions at 25 days of age might be responsible for the observed deficits in both acquisition and rate of pedal press response when animals were exposed chronically to 2, 4-D during postnatal brain development.

Success of autonomic operant conditioning of heart rate without involving contractions of somatic skeletal muscles.

In conscious Wistar rats neuromuscularly paralysed by gallamine, operantly conditioned reduction of heart rate was achieved under both negative and positive reinforcement schedules using the tail shock avoidance or the rewarding brain-stimulations in 20-min test sessions. The primary aim was to assess whether it would be possible to achieve operant conditioning of the heart rate, evoked not as a secondary reflex response of any voluntary skeletal muscular contractions of trunk but as a conditioned voluntary function of the central autonomic regulation of a visceral organ, since this entire subject was peculiarly left in confusion by Miller (5, 8) who wanted that others should independently study it. This study revealed interestingly that not every subject might be able to achieve the visceral learning in a given set of conditions, and suggested that this type of a special learning might be dependent on individual predisposition in the central nervous system. In the present study, 15 showed the learning, out of the 58 subjects assessed. It was also observed that there was a variation in the magnitude of the learning response among different learners, and, also, in the same subject in different sessions conducted on different days. This is considered as an indication that this type of conditioned autonomic function is probably not easily recruited into the long-term memory mechanisms. The overall average of the operant lowering of the heart rate progressively achieved by the end part of the learning session was about 10.5% from the basal average rate, and the score of reinforcement (per cent of painful tail shocks avoided, or of increase in number of brain shocks achieved) was over 80%. The extinction test confirmed the learning. Control experiments revealed that the conditioned heart rate changes were not due to any unconditioned stimulus effects. The learning observed under the brain-stimulation reinforcement was confirmed by losing the learning response after lesioning the site of the rewarding stimulation. The visceral operant learning occurring in state of somatomotor paralysis under both negative and positive types of reinforcement was blocked by haloperidol. Morphine delayed the onset of the pain avoidance operant learning, whereas it speeded up the hedonic brain-stimulation operant learning. The results, considered from all the above angles, dispell the doubt previously expressed about the occurrence of the operant conditioning of heart rate under a visceral learning paradigm.

Effect of cyproheptadine on bar-pressing for food reward in rats.

Lever pressing rate under a continuous reinforcement schedule for food reward in rats was reduced significantly by cyproheptadine in the dose of 5 and 10 mg/kg body weight. Under fixed ratio schedule of reinforcement, the responding was also suppressed significantly by 5 and 10 mg/kg body weight doses of cyproheptadine. However, high dose (20 mg/kg) of cyproheptadine administered subsequent to the low doses, failed to inhibit the bar pressing rate under either continuous or fixed ratio schedules.

Neuropharmacological actions of labetalol.

Labetalol, an alpha- and beta- adrenoceptor antagonist was investigated for its central nervous system effects in rats and mice. A marked reduction in the spontaneous motor activity with no concomittant muscle weakness was produced. The drug caused closure of eyelids in rats. Labetalol caused hypothermia and prolonged the pentobarbitone-induced hyposis. In animals trained for conditioned avoidance response the drug blocked the SCR in all the animals and CAR in a few number of animals. The drug did not protect the animals against electroshock convulsions. From the results it appears that labetalol is a central nervous system depressant.