A comparison of escape and avoidance conditioning in wild and domesticated rats

In the first of two experiments, three cotton rats (Sigmodon hispidus) and three albino rats were exposed to instrumental escape, unsignaled avoidance, and signaled avoidance, in that order. All subjects learned the escape procedure quickly, with the albino rats having generally shorter latencies, higher response rates, and requiring fewer sessions to reach the criterion. When the avoidance contingency was introduced, the cotton rats continued to respond almost entirely in the presence of the shock, whereas the albino rats responded in its absence, thus displaying effective avoidance behavior. Introduction of a pre-aversive stimulus did not improve the performance of the cotton rats. In the second experiment, five cotton rats and four albino rats were exposed to a free-operant (Sidman) avoidance procedure with a shock-shock interval of 3 sec and a response-shock interval of 20 sec. The cotton rats initiated responding at lower shock intensities than the albino rats, but their asymptotic avoidance responding was far less effective.     

Neocortex and feeding behavior in the rat.

Consummatory behavior and weight-regulation capacity were measured in 12 normal rats and in 43 rats that survived complete (C), sequential unilateral (U), anterolateral (A), or posterior (P) neocortical ablations. Groups C and A displayed aphagia and adipsia followed by a sequence of recovery stages gualitatively identical to, but shorter than, recovery typically seen following lateral hypothalamic lesions. After recovery, Group C displayed long-term effects of finickiness and pradial drinking. These effects as well as a measure of recovery of body-weight-regulation capacity were significantly intercorrelated with lesion size, and body-weight set point remained significantly lower than normal. Group U was relatively unaffected by the first unilateral ablation and showed, relative the second ablation but displayed the long-term effects. Group P, though significantly affected by the lesion, did not display the pattern or intensity of effects described for the other bilaterally ablated groups.     

Ingestive behavior in rat pups is modified by maternal sodium depletion

Developmental programming by maternal stress during pregnancy is found to influence behavioral development in the offspring. The main objective of this study was to investigate the effect of maternal sodium depletion in rats during pregnancy on the development of thirst mechanisms in the offspring. Pregnant rats underwent 3 episodes of saline depletion, induced by injecting sc 10 mg of Furosemide in saline (0.5 ml). The treatment, given on the 14th, 17th and 20th days post-conception, is thought to induce acute sodium depletion on dams. The offspring were tested for their drinking responses to Isoproterenol (500 μg/kg sc). In accordance to the known sequence of ontogenic development of drinking mechanisms, all groups of pups drunk after being stimulated with Isoproterenol at 6 days of age. The offspring from Furosemide-treated dams drank significantly less than the control group after Isoproterenol (p<0.001). Nevertheless, basal intake (water drunk after vehicle-saline only) was also significantly lower in these pups (p<0.001). In conclusion, offspring exposed to saline depletion in utero, modify their thirst responses at 6 day of age. This confirms that in utero conditions determine thirst responses in the offspring and they could provide adaptive advantages.     

The prolonged effects of naloxone on play behavior and feeding in the rat

The effects of naloxone on social play and feeding behaviors of postweanling and adult Long-Evans hooded rats were studied. Administration of 1.0, 5.0, or 10.0 mg/kg naloxone reduced play in a dose-related fashion. The effects of a 5.0-mg/kg dose of naloxone could be detected at least 3 h after administration, in terms of both a decrease in social behavior and decreased food consumption, indicating that the behavioral time course of naloxone effects is greater than some reports in the pharmacokinetic literature suggest.     

Functional organization of the rat amygdala with respect to avoidance behavior.

Bilateral electrolytic lesions in the periamygdaloid piriform cortex of female albino rats produced marked disruptive effects on the acquisition of active avoidance responses in a 1-way as well as a 2-way test situation, significantly impaired passive avoidance behavior, and inhibited feeding in a novel environment. Lesions in each of the 6 major subdivisions of the amygdala (cortical, medial, central, intercalated, lateral, and basolateral nuclei) consistently produced facilitatory effects on active avoidance behavior in 1-way as 2-way situations. Passive avoidance behavior was impaired in animals with lesions in the central, intercalated, and basolateral nuclei. Damage to the anterior amygdaloid area or the the nuclei of the lateral olfactory tract did not reliably affect active or passive avoidance behavior.     

Some effects of methylphenidate on stimulus control of ratio avoidance behavior in the rat

After exposure to an avoidance schedule which included a warning signal, a rat was placed on a multiple schedule in which the first component was the same as before, i.e., a single response reset the response-shock interval, delaying shock, and the second component differed only in that four bar-presses were required to postpone shock. A fixed ratio requirement of four responses (FR 4) generated behavior resembling a fixed ratio requirement of one response (FR 1) since responding was controlled by the warning signal but more shocks were received. At a dosage of 2 mg/kg, methylphenidate given intraperitoneally decreased shock frequency during FR 4 periods while FR 1 behavior was not affected; at 4 mg/kg, stimulus control of avoidance responding was impaired during both components. Results at 4 mg/kg were partially confirmed by two animals exposed to an FR 4 avoidance schedule which included a warning signal but with different parameters. Response distributions showed that methylphenidate increased response rates in the absence of the warning signal, i.e., stimulus control of ratio-avoidance behavior was impaired although the increased response rates reduced shock frequency. One hour later responses again occurred more frequently during the signal than in its absence but shocks were less frequent than during control (non-drug) periods.