Marisol Lamprea

Effects of reversible inactivation of the medial septum on rat exploratory behavior in the elevated plus-maze using a test-retest paradigm.

The effect of intraseptal injections of lidocaine before a first or a second session in the elevated plus-maze, in a test-retest paradigm, was investigated. In addition to gross session analyses, a minute-by-minute analysis of the sessions was used to evaluate both anxiety and memory. Lidocaine injections before the test session produced increases in the frequency of entries, time spent and distance run in the open arms without affecting activity occurring in the closed arms. During the retest session, saline- and lidocaine-treated rats exhibited increased indices of anxiety and lidocaine-treated rats exhibited decreased closed-arm entries. The minute-by-minute analysis showed a faster decrease in anxiety-related behaviors during the test session by saline- than by lidocaine-treated rats and a significant decrease in closed-arm exploration by saline-treated rats, but not by lidocaine-treated ones. Lidocaine injection before the retest session produced increases in the frequency of entries, time spent and distance run in the open arms in the second session when compared with saline-treated rats. Minute-by-minute analysis showed an increase in the time spent in the open arms by lidocaine animals at the beginning of the retest session in comparison to saline animals and a significant decrease in closed-arm exploration by both groups. These results suggest that inactivation of the medial septum by lidocaine affects the expression of unconditioned and conditioned forms of anxiety in the elevated plus-maze and, in a lesser way, the acquisition and retention of spatial information.

Characterizing spatial extinction in an abbreviated version of the Barnes maze

Adult male Wistar rats were trained to find an escape box in the Barnes maze in order to characterize the extinction process of a learned spatial preference. To do so, once they had fully acquired the spatial task, they were repeatedly exposed to the maze without the escape box. Multiple behavioral measurements (grouped into motor skill and spatial preference indicators) were followed up throughout the complete training process. Animals gained efficiency in finding the escape box during acquisition, as indicated by the reduction in the time spent escaping from the maze, the number of errors, the length of the traveled path, and by the increase in exploration accuracy and execution speed. When their retention and preference were tested 24h later, all the subjects retained their enhanced performance efficiency and accuracy and displayed a clear-cut preference for the escape hole and its adjacent holes. Almost all motor skill indicators followed an inverse, though not monotonic, pattern during the extinction training, returning to basal levels after three trials without escape box, displaying a transient relapse during the fifth extinction trial. Preference indicators also followed a reverse pattern; however, it took seven trials for them to return to basal levels, relapsing during the eighth extinction trial. The abbreviated Barnes maze acquisition, evaluation, and extinction procedures described herein are useful tools for evaluating the effects of behavioral and/or pharmacological treatment on different stages of spatial memory, and could also be used for studying the neurophysiological and neurobiological underpinnings of this kind of memory.

Vibrissal paralysis unveils a preference for textural rather than positional novelty in the one-trial object recognition task in rats

In order to explore the role of active whisking in object novelty detection, the performance of rats having bilateral vibrissal paralysis was compared to that of non-lesioned animals in three modified versions of the one-trial object recognition task performed in the dark. Vibrissal paralysis was induced by crushing the buccal and mandibular branches of the facial nerve. Lesioned animals were not different from non-lesioned ones in terms of weight-gain, locomotive activity, motivation to explore, and ability to become habituated to a given environment. Only lesioned animals were unable to discriminate a change in object texture as novelty cue in the first task, designed to test textural novelty detection. In the second task, designed to test positional novelty detection, both lesioned and non-lesioned subjects were able to discriminate a change in object position as novelty cue. In the third task, designed to force the subjects to choose between two conflicting novelty cues (texture and position), non-lesioned subjects displayed a clear-cut preference for textural novelty while subjects having bilateral vibrissal paralysis preferred positional novelty. According to these results, active whisking is necessary for textural, but not for positional novelty detection. Moreover, these results indicate that textural novelty in non-lesioned animals seems to overcome positional novelty if these are in competition in an object recognition memory task.

Thermal stress decreases general motor activity of rats in the elevated plus-maze but does not alter aversion to the open arms

Environmental temperature is known to affect a variety of biological processes ranging from simple chemical reactions up to ecological distribution of animal species. To our knowledge, however, there are no studies relating environmental temperature and exploration in the elevated plus-maze. The present study was aimed at investigating the influence of animal house temperature on the exploration of an elevated plus-maze. Fifty-seven male Wistar-derived rats were divided into five groups which were kept for 96-h in an animal house with different temperatures (18, 22, 26, 30 or 34 degrees C) and then tested in the elevated plus-maze. Results showed that the animals submitted to the higher temperatures decreased body weight, frequency of entries into both the open and closed arm, time spent in the open arm extremities, distance run in the closed arms and frequency of rearing while increasing the mean duration of each entry into both the open and closed arms. There were no significant effects on the time spent in the open arms and the percentage of entries into the open arms. These effect are probably due to thermal stress and do not relate to emotional changes but rather to modifications in general activity. The frequency of stretching and head-dipping exhibited different profile reactions to temperature when compared to the above measures. These behavioral modifications are also consistent with the effects of thermal stress rather than alterations in emotionality.

Vibrissal paralysis produces increased corticosterone levels and impairment of spatial memory retrieval

Graphical abstract Figure. No Caption available. HighlightsVibrissal paralysis was induced by bilateral facial nerve lesion in rats.Injured and control rats were trained and tested in a spatial memory task.Vibrissal paralysis induced retrieval but not acquisition impairment.Corticosterone response to training or testing was higher in injured rats.Paralysis‐induced stress response potentiation may cause retrieval impairment. ABSTRACT This research was aimed at establishing how the absence of active whisking in rats affects acquisition and recovery of spatial memory. The mystacial vibrissae were irreversibly paralyzed by cutting the facial nerve’s mandibular and buccal branches bilaterally in the facial nerve lesion group (N = 14); control animals were submitted to sham‐surgery (N = 15). Sham‐operated (N = 11) and facial nerve‐lesioned (N = 10) animals were trained (one session, eight acquisition trials) and tested 24 h later in a circular Barnes maze. It was found that facial nerve lesioned‐animals adequately acquired the spatial task, but had impaired recovery of it when tested 24 h after training as compared to control ones. Plasma corticosterone levels were measured after memory testing in four randomly chosen animals of each trained group and after a single training trial in the maze in additional facial nerve‐lesioned (N = 4) and sham‐operated animals (N = 4). Significant differences respecting the elevation of corticosterone concentration after either a single training trial or memory testing indicated that stress response was enhanced in facial nerve‐lesioned animals as compared to control ones. Increased corticosterone levels during training and testing might have elicited the observed whisker paralysis‐induced spatial memory retrieval impairment.

Overtraining modifies spatial memory susceptibility to corticosterone administration

HighlightsMale rats were either trained or overtrained in a spatial memory task in Barnes maze.Memory test and extinction were done after corticosterone or vehicle administration.Overtraining enhanced memory retrieval and made it resistant to corticosterone.Neither training intensity nor corticosterone affected extinction acquisition.Training intensity and corticosterone have opposite effects on extinction retrieval. ABSTRACT Even though the effects of overtraining and glucocorticoids on different phases of spatial memory are known, the interaction between these factors on the retrieval and extinction of spatial memory has not yet been described. Adult male Wistar rats received eight training trials per day in the Barnes maze for either one or two days. Twenty‐four hours after the last training trial they were randomly assigned for receiving an intraperitoneal vehicle or corticosterone injection (0.125 or 0.5 mg/kg) and ten minutes later they were given a memory test, followed by seven extinction trials. Extinction retention was evaluated twenty‐four hours after extinction. The second training session did not provoke significant changes regarding escape latency nor weighted errors, thereby showing that overtraining had been obtained. The overtrained animals performed better than the trained ones during the retrieval test. Corticosterone administration did not affect the overtrained animals’ performance; by contrast, only the lower dose impaired trained animals’ retrieval. Overtrained subjects acquired extinction more rapidly than those which received just one session, but corticosterone did not significantly modify extinction. However, whilst the spatial task remained extinguished in trained animals during the extinction retrieval test, spontaneous recovery occurred in overtrained animals. Such training intensity effects on extinction retrieval were reverted by corticosterone. Overall, these results suggested that overtraining modified the susceptibility of spatial memory’s trace to the effects of corticosterone on retrieval and extinction.