Functional interaction between the associative parietal cortex and hippocampal place cell firing in the rat.

The hippocampus and associative parietal cortex (APC) both contribute to spatial memory but the nature of their functional interaction remains unknown. To address this issue, we investigated the effects of APC lesions on hippocampal place cell firing in freely moving rats. Place cells were recorded from APC-lesioned and control rats as they performed a pellet-chasing task in a circular arena containing three object cues.

Differential effect of thalamic and cortical lesions on memory systems in the rat.

The behavioral effects of lesions of anterior thalamic and medio-dorsal thalamic nuclei, posterior cingulate (retrosplenial) and posterior parietal associative cortex were studied in rats performing a eight-arm radial maze, in which three/eight arms were baited. Lesions were made after rats reached a training criterion. Rats were tested 2 weeks later, in the same experimental apparatus.

Antibody to day-old chick brain glycoprotein produces amnesia in adult rats.

Polyclonal antibody R-1, raised against a chick synaptic membrane glycoprotein fraction whose synthesis is enhanced following training on a passive avoidance task, produces amnesia when injected into chick forebrain 5.5 h posttraining. The amnestic IgG fraction specifically recognizes a low sialylated isoform of NCAM (Mileusnic Rose, Lancashire, & Bullock, 1995).

Locus coeruleus neurons in monkey are selectively activated by attended cues in a vigilance task.

Impulse activity was recorded extracellularly from noradrenergic neurons in the nucleus locus coeruleus (LC; 47 single-cell and 126 multicell recordings) of four cynomolgus monkeys performing an oddball visual discrimination task. For juice reward, the subjects were required to release a lever rapidly in response to an infrequent (10-20% of trials) target cue (CS+) that was randomly intermixed with nontarget (CS-) stimuli presented on a video display. All LC neurons examined were phasically and selectively activated by target cues in this task.

Food-restriction interacts with vasopressin modulation of activity.

The effects of peripheral injection of various doses of lysine-vasopressin (LVP), administered 30 min before a 5-min session in a hole-board apparatus, were compared as a function of food restriction. Comparison of performance for various indices of general activity clearly showed that the food-restricted rats were more active and exhibited less photophobia than normally fed ones. The differences between the two groups were maintained in a second session 24 hours later.

Discharge of noradrenergic locus coeruleus neurons in behaving rats and monkeys suggests a role in vigilance.

Recordings from noradrenergic locus coeruleus (LC) neurons in behaving rats and monkeys revealed that these cells decrease tonic discharge during sleep and also during certain high arousal behaviors (grooming and consumption) when attention (vigilance) was low. Sensory stimuli of many modalities phasically activated LC neurons. Response magnitudes varied with vigilance, similar to results for tonic activity.

Long-term spontaneous improvement of performance is related to the strength of the initial training: theoretical implications.

In a recent study we established that following a partial acquisition of a brightness discrimination escape task (15 trials), Sprague-Dawley albino rats exhibited a long-term spontaneous improvement of performance (LTSI) after 7 to 14 days. Some evidence suggests a relation between the strength of the initial training and the delay of the optimal retention performance. This study investigates such a possibility in studying performance of rats (number of trials needed to reach a criterion of 10 errorless trials) following nine different retention intervals: 10 min, and 1, 3, 5, 7, 10, 14, 21, and 28 days, after a strengthened initial training (25 trials).

Vasopressin injections impair working memory in a delayed matching to sample task in rats.

Effects of vasopressin were measured in a nonspatial working memory task: food-reinforced, delayed matching to sample. Subcutaneous injections of 0.2 microgram of lysine vasopressin (LVP) or saline were alternately administered to Sprague-Dawley rats after the presentation of the sample and compared to the effect of the same treatments given to a yoked control group of rats.

Repeated post trial administration of vasopressin impairs subsequent Differential Reinforcement of Low rates (DRL) performance.

Twenty-six male rats, maintained on a 23-h food deprivation regime, were trained on a DRL learning schedule. During pretraining (CRF) rats were placed in two groups according to speed in obtaining the criterion (good and poor learners). The performance of good and poor learners, injected with lysine vasopressin (LVP) immediately after each training session, was compared with that of control good and poor learners injected with saline.

Effects of posttrial vasopressin injections on appetitively motivated learning in rats.

Sixty male rats, maintained on 23-hr food deprivation were trained on two types of appetitive tasks: bar pressure responding under a CRF schedule, and under a differentially reinforced (light+, dark-) schedule. Performance of rats treated with lysing vasopressin, injected immediately after each training session, was compared to that of control animals injected with saline. In the CRF stage, treated animals reached learning criterion significantly later than did control rats, and made significantly fewer bar presses.

[Aversive effects of halothane anesthesia in the rat, using extinction of tasks by positive reinforcement].

Immediate posttrial halothane anaesthesia accelerates the extinction of two previously acquired operant tasks--barpress learning or modified K-maze learning. This acceleration is not due to any motor impairment. These results are not consistent with the hypothesis of amnestic effects of halothane anaesthesia; they are interpreted in terms of aversive effects.