Water deprivation associated with operant conditioning inhibits hypertensive disease in young spontaneously hypertensive rats

The development of high blood pressure in young spontaneously hypertensive rats (SHR) is inhibited by operant conditioning motivated by chronic water deprivation. The present study showed that the inhibition of hypertension was not due to the operant conditioning,per se, but was a result of chronic water deprivation (23.5 hr schedule) imposed on the rats from five through 12 weeks of age. Blood pressures were measured directly using a carotid artery cannula and light enflurane anesthesia. The behaviorally conditioned SHR and the water-deprived SHR controls had equal blood pressures and were significantly less hypertensive than untreated or enriched environment SHR groups. The antihypertensive action of water deprivation was not detected by weekly indirect blood pressure measurements made in the awake state. Nonetheless, the chronicity of the deprivation-induced inhibition of hypertension was confirmed by a lesser degree of left ventricular hypertrophy in the deprived SHR relative to the nondeprived SHR. Our behavioral results again demonstrated hyperreactivity in the SHR relative to the Wistar Kyoto (WKY). This behavioral hyperreactivity in the SHR may explain the exaggerated increase in drinking in the deprived SHR groups when returned toad lib conditions. The data of this study and our previous work suggest that arousal differences between SHR and WKY strains are more reliably differentiated by fixed interval schedules of reinforcement than by a fixed ratio schedule. Hyperarousal may precede hypertension in the SHR, but it is undetermined whether hypertension can be found in the absence of hyperarousal in these rats.     

Passive-avoidance behavior of spontaneously hypertensive rats

Spontaneously hypertensive rate (SHR) generally exhibit higher performance in avoidance tasks than Wistar-Kyoto control rats (WKY) do. The SHR are more active than the WKY after transfer to a novel environment and after electric footshocks. The present study examined the performance, behavior, and plasma corticosterone of young male SHR and WKY in a passive-avoidance task in which high levels of locomotor activity do not facilitate performance. The effects of three levels of discriminability of the safe area were studied. Passive-avoidance performance was statistically significantly lower in the SHR, but the difference was small. There was no difference between the SHR and the WKY in post-test plasma-corticosterone levels, and there was no relationship between ambulation and plasma-corticosterone levels. The behavioral differences between the SHR and the WKY varied as a function of the discriminability of the safe area. Specifically, in the low-discriminability condition, ambulation, but not rearings, was equally suppressed in the SHR as in the WKY and there was no difference in immobility. In the high-discriminability condition the SHR exhibited more ambulation, more rearing, and less immobility than the WKY. These data confirm that the SHR exhibit an increased tendency for facilitation of locomotor activity during activation compared to the WKY. Because the passive-avoidance performance of the SHR was lower than that of the WKY, these data suggest that previous reports of superior avoidance learning in the SHR reflect their elevated level of locomotor activity rather than an improved ability to acquire conditioned responses. Ability to discriminate stimuli seems to be normal in the SHR since ambulation was modified according to stimulus parameters.     

Residential-maze behavior of spontaneously hypertensive rats

Spontaneously hypertensive rats (SHR) exhibit elevated levels of ambulation after transfer to a novel environment compared to the Wistar-Kyoto rat (NR). The present experiment compared long-term activity of SHR and NR in a residential maze to determine whether the SHR exhibit elevated levels of locomotor activity under undisturbed, baseline conditions in addition to enhanced reactivity to stimuli. The SHR were much more active visiting more arms of the maze than the NR during the initial hours following transfer to the maze, and during hours around dark onset and light onset. However, the SHR also exhibited higher levels of activity than the NR under baseline conditions. While the NR visited the arm containing food more frequently than other arms, the SHR exhibited no such preference. These data show that both stimulus-induced and basal levels of ambulation are increased in the SHR compared to its normotensive genetical counterpart.     

Effect of voluntary exercise on open-field behavior and on aggression in the spontaneously hypertensive rat (SHR)

In the present study we investigated the influence of voluntary exercise on exploratory behavior and on aggression in the spontaneously hypertensive rat (SHR). Twenty-four SHR (8 weeks old) were randomly assigned to either an exercise group or a sedentary control group. The animals in the exercise group exhibited a spontaneous wheel running activity of 5-6 km/day during 6 weeks. The characteristic hyperexploratory behavior of SHR was lowered in the exercise group (p less than .001) as compared to the control group. The runners also showed a tendency for less aggression. In the postexercise period, when the runners' wheels were locked, the exercise group had a significant rise in aggression (p less than .01) vs the controls. The exploratory behavior returned immediately to the level of the controls, but we found no further increase in any of the parameters measured. However, the runners showed a type of displaced aggression exhibited as digging and biting in the test cage. This evidence suggests that voluntary exercise lowers the hyperexploratory behavior and aggression in the SHR and that an abrupt stop in exercise gives an "abstinence" reaction.     

Aggression as a reinforcer: operant behavior in the mouse-killing rat

Two experiments examined mouse killing as a reinforcer of key pressing by rats that killed mice. In Experiment I, mouse-killing rats performed the key-pressing response when each press was reinforced with presentation of a mouse. Offered a choice between a key that yielded presentation of mice and one that did not, the rats preferred the key that yielded mice. When the contingency was reversed, the rats preferred the other key and continued to kill mice. In Experiment II, mouse-killing rats that did not kill rat pups performed a key-pressing response reinforced with presentation of mice on a variable-interval schedule. In tests for responding reinforced on that schedule with presentation of normal mice, anesthetized mice, dead mice, or rat pups, these rats that killed mice but not rat pups exhibited a decline in response rate when rat pups were the reinforcer. Altering the condition of the mice did not significantly affect performance.     

Behavioral hyperreactivity in the spontaneously hypertensive rat compared to its normotensive progenitor

The spontaneously hypertensive rat (SHR) is an excellent model of essential hypertensive disease. Hyperreactivity has been postulated as a contributing factor in the development of high blood pressure in the SHR and in man. In the maturing organism recurring hypertensive stress responses may promote permanent vascular changes and result in a fixed hypertension. Simple behavioral activity and emotionality rating scales were used to compare a large number of SHR with equally large groups of closely-related and distantly-related normotensive rats. As predicted, the SHR were clearly more active and emotional than their ancestral Wistar Kyoto (WKY) strain. However, the distantly-related normotensive Wistars did not differ from the SHR in either activity or emotionality. These results indicate that behavior and hypertension are not necessarily related in the rat. Nonetheless, the behavioral differences between the SHR and their closest genetic match, the WKY, suggest that arousal and blood pressure levels may be causally linked in this case of naturally occurring hypertension.     

The spontaneously hypertensive rat as an animal model of attention-deficit hyperactivity disorder: effects of methylphenidate on exploratory behavior

Spontaneously hypertensive rats (SHR) show a pervasive hyperactivity in several paradigms. Thus, these rats may be used as an animal model of childhood hyperactivity also called Attention-Deficit Hyperactivity Disorder. This disorder is frequently treated with psychomotor stimulant drugs, but little is known about the effects of such drugs on behavior. The present study investigated the behavioral effects of 1-24 mg/kg methylphenidate (Ritalin) on the exploratory behavior of male SHR and Wistar-Kyoto control rats (WKY) in a two-compartment free-exploration open field. Except following very high doses. SHR spent most of the session time in the field while WKY stayed in the home cage. Low and medium doses were followed by increased activity in the field for SHR and increased activity in the cage for WKY. The response-stimulatory effects of low to medium doses of methylphenidate are less in SHR than in WKY. Starting at medium doses, activity decreased and stereotyped behavior increased progressively by increasing dose. Locomotor activity in the field decreased following lower doses than locomotor activity in the cage, and vertical activity (rearing) was reduced by lower doses than horizontal activity (crossing). The following conclusions were drawn. (i) There is no "paradoxical" inhibition of SHR hyperactivity following methylphenidate. On the contrary, SHR activity is in fact stimulated, albeit to a lesser degree than that of WKY. (ii) The stimulatory effects of low to medium doses are, in general, most pronounced for the kind of exploratory behavior most frequently used by the rat during baseline conditions. (iii) Rearing might be more susceptible to adverse effects of methylphenidate than ambulation.     

Behavioral studies in spontaneously hypertensive rats

In the present study we examined some behavioral patterns in spontaneously hypertensive (SHR) male rats as compared with Wistar (W) rats. The following methods were employed: open field test, two-way active avoidance, passive avoidance, shock-induced fighting, shock-induced suppression of drinking (conflict test), and dominant-subordinate behavior in rats competing for water. Spontaneously hypertensive rats showed higher level of locomotor activity, lower emotionality, lower anxiety level, increased acquisition of avoidance tasks, and enhanced dominance behavior. In addition, hypertensive rats were less aggressive in shock-induced fighting test. It is concluded, that spontaneously hypertensive rats seem to be hyperactive in terms of locomotor activity while their emotionality appears to be paradoxically reduced.     

Opioid-reinforced operant behavior: selective suppression by alpha-methyl-para-tyrosine.

Morphine-addicted rats performed operant responses for opioid or milk rewards. When rats were then denied access to opioids, abstinence symptoms developed. Responding under extinction conditions 2 wk. after opioid withdrawal provided a measure of the "relapse" tendency. Systemic administration of DL-alpha-methyl-para-tyrosine, an inhibitor of catecholamine synthesis, suppressed these responses if they had been reinforced by an opioid but not if they had been established with milk reinforcement. This indicates that the integrity of the catecholamine systems is vital for relapse to occur.     

Open-field behavior of spontaneously hypertensive and Wistar-Kyoto normotensive rats: effects of reciprocal cross-fostering

The influence of the maternal environment on the development of open-field behavior in spontaneously hypertensive (SHR) rats was investigated using the technique of reciprocal cross-fostering. Entire litters of SHR and Wistar-Kyoto (WKY) normotensive rats were either reared by their natural mothers, in-fostered to dams of the same strain, or cross-fostered to dams of the opposite strain on the day after birth. Open-field behavior was assessed in male and female rats from the six groups (2 strains x 3 rearing conditions) at 30, 60, 90, and 120 days of age. Animals were observed in the open-field during a 5-min test period and the number of squares entered and hindlimb rears were recorded. At all ages tested, SHR rats were more active in the open field, entering more squares and rearing more frequently than WKYs. SHR females were more active than age-matched SHR males, while no sex differences were apparent in the WKY strain. At each age, open-field behavior was similar across WKY rearing groups. SHR control and in-fostered animals responded similarly in the open field; however, SHR cross-fostered rats (particularly females) tended to be more active than controls. Although cross-fostering has profound effects on cardiovascular development and functioning in the SHR, it appears that altering the early maternal environment experienced by SHR pups does not grossly affect the development of open-field behavior.     

Stress ulcer and open-field behavior of spontaneously hypertensive,normotensive, and Wistar rats

Spontaneously hypertensive rats (SHRs) and the normotensive Wistar/Kyoto (WKY) rat were observed, along with Wistar rats (which represent the parent strain), on various open-field behaviors. All three strains were subsequently exposed to the activity-stress (A-S) ulcerogenic procedure. SHR and Wistar rats were very active in most open-field measures as compared with WKY rats, but only SHRs were active during the A-S treatment. WKY rats were very ulcer prone and had significantly more ulcers than SHRs, which in turn had more ulcers than Wistar rats. It was anticipated that Wistar rats would resemble the WKY rats, but in most measures the Wistars resembled the SHRs. The study suggests that although WKY rats function as an appropriate control for hypertension studies, these rats may be inappropriate as controls for other physiological and behavioral studies.     

Visual-reinforcer color-and operant behavior in Siamese fighting fish

Male Siamese Fighting Fish (Betta splendens) were conditioned to emit an operant response sequence reinforced by presentation of a model of a male Siamese Fighting Fish in aggressive display. Operant response rate varied as a function of the color of the model with respect to the color of the subject.