Behavioral and neural biology最新文献

The NMDA receptor blockers CGP 37849 (competitive) and MK 801 (noncompetitive) improve retention performance in the step-down passive avoidance situation but impair it in the step-through dark avoidance. It is suggested that the drugs in the two tasks act on different underlying processes. Whereas the memory facilitating effects of both drugs can be suppressed by pretreatment with either aldosterone or corticosterone, their negative effects on retention were steroid-insensitive. This set of results suggests that the mechanisms by which NMDA blockers improve memory are different from the mechanisms by which they block memory.

Five experiments were performed to investigate the effects of amlodipine, a calcium channel antagonist of the 1,4-dihydropyridine class, on consolidation and retrieval of memory in mice. In a single-trial passive avoidance task, amlodipine was administered pretraining, post-training, or pretesting. Results of temporal and dose—response studies showed that memory enhancement (significant increase in step-through latency) occurred when amlodipine (5, 7, 9, 15, and 30 mg/kg) was given either immediately post-training or (15 mg/kg) 15 min pretesting. Using a conditioned emotional response task, tone was paired with shock using Pavlovian conditioning procedures. Strength of conditioning was assessed by measuring suppression of drinking in the presence of a tone. Amlodipine (7 mg/kg) given immediately following both high- and low-intensity shock significantly enhanced conditioned suppression. In the third experiment thirsty mice were trained on a spatial discrimination task in a linear maze. Correct choices were reinforced with liquid reinforcement. Amlodipine (10 mg/kg) injected immediately after the training session produced a significant enhancement of discrimination performance on a 24-h retention test. In the fourth experiment mice were given 25 training trials in a two-way active avoidance task and were treated with either amlodipine (10 mg/kg) or saline after training. Amlodipine-treated mice made significantly more avoidances on the test session than control animals. The final experiment demonstrated that the deficit in approach-avoidance behavior seen in 18-month-old mice could be reversed by amlodipine treatment after the training session. These studies suggest that amlodipine can facilitate memory consolidation and retrieval.

This study was conducted to determine whether juvenile squirrel monkeys exposed to a snake for a 60-min episode during the preweaning period display behavioral and physiological responses to a snake similar to those displayed by feral-born adult monkeys. Juvenile male monkeys born to feral mothers in the lab were either exposed to a live snake during infancy or were snake-naive. Simultaneously tested were adult feral-born and adult lab-born (snake-naive) males. Juveniles exposed as infants to a snake displayed behavioral responses and plasma cortisol elevations following exposure to the snake that were similar to those of feral-born adults. In contrast, the snake-naive monkeys, regardless of age, rarely vocalized at the snake and displayed lower plasma cortisol elevations. These behavioral and physiological responses did not appear to be elicited by a moving animate stimulus per se, insofar as exposure to a moving fish elicited minimal behavioral changes and no cortisol elevations. In contrast to previous findings, these studies indicate that lab-born snake-naive squirrel monkeys are responsive to snakes, but that experience with snakes in infancy produces behavioral and physiological responses more similar to those observed in feral-born monkeys.

Following observations in the literature that sensory cortex ablations prevent extinction of conditioned fear, the present experiments tested the generality of this finding by examining whether visual cortex ablations would prevent extinction of conditioned fear as assessed by fearpotentiated startle using a visual conditioned stimulus. Consistent with previous reports, visual cortex ablations did not prevent the acquisition or expression of fear-potentiated startle to a visual conditioned stimulus. More importantly, visual cortex ablations did not prevent extinction of fear-potentiated startle to a visual conditioned stimulus, nor did they reverse preoperatively established extinction, indicating that sensory cortex is not required for extinction of conditioned fear in all situations.

The effects of reduced somatosensory feedback from the penis and/or the preputial region upon the male rat's copulatory thrusting patterns and sexual behavior were analyzed. Copulatory thrusting was recorded with an accelerometric technique allowing for the determination of duration and frequency of the thrusting trains. Section of the dorsal penile nerves (denervation) or lidocaine applied to the distal part of the penis reduced the number of intromissions and the intromission ratio. These treatments had no effect on copulatory thrusting patterns. Lidocaine injected into the preputial region also reduced the number of intromissions and the intromission ratio. Moreover, the number of disorganized mounts, as revealed by the accelerometric record, was much increased by this treatment. In addition, the duration of the thrusting trains associated with mount and intromission was increased. No effect was found on thrusting frequency. These data suggest that somatosensory feedback from the penis is critical for the achievement of intromission, whereas feedback from the preputial region is important for the execution of copulatory thrusting. Furthermore, it is possible that the strong sensory stimulation of the prepuce associated with penile insertion participates in the termination of thrusting and penile withdrawal.

Immediate post-training intraperitoneal administration of α-d[+]-glucose (10–300 mg/kg) significantly enhanced retention of male Swiss mice tested 24 h after training in an inhibitory avoidance task. The dose—response curve was an inverted U in this range of dose. However, of the doses tested, only 30 mg/kg was effective. Glucose did not affect response latencies in mice not given the footshock on the training trial, suggesting that the actions of glucose on retention performance were not due to nonspecific effects on response latencies. The influence of glucose (30 mg/kg) was time-dependent, which suggests that glucose facilitated memory consolidation processes. Administration of glucose (30 mg/kg) 2 or 10 min prior to the retention test did not affect the retention performance of mice given post-training injections of either saline or glucose (30 mg/kg). These findings indicate that the memory-enhancing effects of post-training administration of glucose are not state-dependent and are consistent with the view that the behavioral effects of glucose are mediated through an interaction with the neural or neurohumoral processes underlying the storage of acquired information.

The intent of this study was to perform a detailed analysis of behavioral asymmetries (turning behavior) exhibited by animals which had sustained a unilateral lesion of the substantia nigra (SN). Rats were tested for behavior asymmetries over 16 days, once before, and 7 times after 6-OHDA had been injected into one SN. On the basis of the number of narrow diameter ipsiversive half turns produced during testing, they were then assigned to one of three groups: (a) those which showed an initial asymmetry from which they recovered, (b) those which were asymmetrical throughout testing, and (c) those in which the asymmetry only emerged during the testing period. We examined several different aspects of turning behavior. Recovery from asymmetry was associated with an increase in the number of contraversive, as well as a decrease in the number of ipsiversive narrowangle turns. The average diameter of these ipsiversive turns also increased. Animals which recovered showed a contraversive asymmetry for wide-diameter turns which increased during testing. Narrow-diameter contraversive turns decreased during testing in the two nonrecovery groups. Both nonrecovery groups showed a contraversive asymmetry for wide-diameter turns. Asymmetry was attributable to a tendency to circle and move ipsiversively in the two nonrecovery groups, whereas it was due to circling behavior in animals which showed recovery. Additionally, more cells, labeled by HRP injected into the ipsilateral caudate putamen, were found in the damaged SN of animals which recovered.

Although the CS preexposure effect in CTA was once viewed exclusively as an acquisition failure, recent studies have suggested that the latent inhibition phenomenon is the result of retrieval impairment. This interpretive challenge is based on the unexpected finding that recovery of the aversion occurs over a long retention interval following conditioning (Kraemer, Lariviere, & Spear, Animal Learning and Behavior, 16, 185–190, 1988; Bakner, Strohen, Nordeen, & Riccio, Physiology & Behavior, 50, 1269–1272, 1991). This study examined whether a similar recovery occurs after US prexposure. Following preexposure to the US (LiCl), rats received a sucrose—illness pairing and were subsequently tested after either short or long training-to-test intervals. In contrast to the findings with the CS preexposure effect, US-preexposed subjects did not show a spontaneous increase in CTA following the long retention interval.

The present report investigates the effects of lead exposure during the pre- and postnatal period on the latent learning ability in a maze. Rats were submitted to lead acetate intoxication by giving their dams 0.5, 1.0, or 4.0 mM lead acetate or deionized water. Rats were weaned at 21 days, and the treatment was continued by giving the same solution of lead acetate in the drinking water until behavioral testing. Under a nonappetitive condition, rats were exposed either to an open field or to a maze apparatus. They were thereafter deprived of food and tested in the maze apparatus. Lead treatment induced an increase in locomotor activity in the open field during training sessions, and animals failed to habituate to the environment. Nevertheless, both lead-treated and control rats that had been previously exposed to the maze performed better than those exposed to the open field. These results suggest that rats intoxicated with lead are able to learn about the environment when no immediate reinforcement is involved.