J. Delacour

A new one-trial test for neurobiological studies of memory in rats. II: Effects of piracetam and pramiracetam.

The effects of the nootropic drugs Piracetam (Pir) and Pramiracetam (Pram) were evaluated on recognition-memory of rats in a new one-trial test. This test is based on spontaneous exploratory activity and does not involve rule learning or reinforcement. Recognition is measured by the time spent by rats in exploring two different objects, one familiar (the sample), the other new. When the retention interval is 1 min, normal rats spend more time exploring the new object which demonstrates that they recognize the familiar one, but they do not discriminate between the two objects after a 24-h interval. Three doses of Pram (15, 30 and 60 mg/kg) and Pir (100, 200 and 400 mg/kg) were administered i.p. 30 min before the acquisition trial. The doses of 30 mg/kg of Pram and of 400 mg/kg of Pir produced a significant improvement in retention when the intertrial interval was 24 h. This effect was not associated with a change in overall exploratory behavior. This study shows that the new object-recognition test may be a useful tool for pharmacological studies of memory in rats.

Effects of medial thalamic lesions in the rat a review and an interpretation

Abstract The results of a systematic study on the effects of medial thalamic lesions in the rat are summarized and interpreted. Within the medial thalamus, the centrum-medianum-parafascicularis complex (CM-Pf) seems to be a critical zone. Its lesion produces rather specific and poorly reversible deficits. These effects seem to depend at the same time on the structure of the test and the type of motivation. They particularly affect active avoidance responses. The data are interpreted either in terms of the activation concept or the notion of response competition. A role of inhibitory control is ascribed to the CM-Pf complex. This interpretation is described in light of anato-physiological data.

Spatial but not object recognition is impaired by aging in rats.

Four groups of male Wistar rats (4, 8, 18, and 24 months) were submitted to object recognition and spatial recognition tests. Object recognition was not significantly affected by aging even at a longer retention interval. On the contrary, spatial recognition was significantly impaired in 18- and 24-month groups. The existence of two dissociable neural systems, respectively involved in object and spatial recognition, is discussed.

Experimental dissociation between wakefulness and paradoxical sleep hippocampal theta.

Abstract The effects of electrolytic lesions of the septum on the theta activity of the dorsal hippocampus were studied in the chronically implanted rat during both wakefulness and paradoxical sleep. The experimental results show that depending on their localization, septal lesions can either: (1) eliminate the wakefulness theta rhythm without suppressing that of paraoxical sleep; (2) eliminate the paradoxical sleep theta rhythm without suppressing that of wakefulness. These results suggest that there are two kinds of theta activity having different anatomophysiological bases and a different functional significance: one associated with wakefulness and the other, with paradoxical sleep.

Selective fimbria and thalamic lesions differentially impair forms of working memory in rats.

Several series of experiments were designed to compare the effects of selective lesions of the fimbria or of thalamic nuclei on three different tasks involving working memory in rats: object recognition, place recognition, and the radial arm maze test. The main effects of fimbria lesions were as follows: they produced deficits in the radial maze; object recognition was spared or even facilitated, whereas place recognition was impaired. Electrolytic lesions of either centromedian-parafascicularis (CM-Pf) or dorsomedialis (DM) nuclei produced highly significant deficits in the radial maze test but spared object and place recognition. Ibotenate lesions of the CM-Pf had no effect on any test, which means that the critical structure in the effects of the electrolytic lesions of the CM-Pf was the fasciculus retroflexus (FR). These data may contribute two main points to animal models of hippocampal and thalamic amnesia: (1) different forms of working memory in rats might have different neural bases and (2) the FR may be involved in learning and memory processes.

Effects of selective lesions of Fimbria-Fornix on learning set in the rat

The effects of selective partial lesions of the Fimbria-Fornix (FiFx) on reversal and place learning sets were investigated in rats by using a T-maze and a semi-circular multiple discrimination apparatus. Lesions restricted to the Fimbria (Fi) produced a significant deficit in reversal and place learning set, whereas lesions to the Fornix (Fx) only disturbed the learning set based on a reversal procedure. Combined Fi + Fx lesions resulted in impairment in the retention of spatial discrimination tested in the two mazes. Ventral Hippocampal Commissure (vhc) had no significant effect on reversal learning set. These results confirm previous data that the hippocampal formation is involved in learning transfer, and suggest that the Fi and the Fx may play a role in learning set. Our data also confirm previous demonstrations of the ability of rats to rapidly acquire place learning set.

Effect of combined or separate administration of piracetam and choline on learning and memory in the rat

Different groups of rats received combined or separate administration of different doses of piracetam (P1:100, P2:200, and P4:400 mg/kg) and choline (C1:100 and C2:200 mg/kg). Compared to control treatment, C1 significantly improved performance in a delayed alternation (DA) task, while P1, P2, P4 or P1C1 had no effect. Moreover, rats receiving P2C1 and P4C1 were significantly inferior in acquiring DA to rats receiving the vehicle or separate administration of P1, P2 or C1. The different treatments with combined or separate administration of P and C had no effect on spontaneous locomotor activity and two-way avoidance conditioning. In a recognition-task only groups C1 and P4 were able to discriminate between familiar and new objects. The combined or separate administration of P1 and C1 on NA, DA, DOPAC, 5-HT, 5-HIAA levels, CAT activity and choline uptake were measured in frontal cortex and hippocampus: the only significant effect was a 5-HT increase in the hippocampus of rats treated with C1.

An introduction to the biology of consciousness.

This paper summarizes the main steps in a scientific study of consciousness. From a survey of the recent literature, it appears that: (1) there is a clear tendency to consider consciousness as a scientific object; (2) consistent subjective and objective descriptions of consciousness are possible; an intentional-modeling structure accounts for its main features; (3) from the evolutionary biology standpoint, conscious cognitive activities, as based on models of the self, the world and the alter-ego, have a functional value; (4) the material basis of consciousness can be clarified without recourse to new properties of the matter or to quantum physics. Current neurobiology, based on classical macrophysics, appears able to handle the problem. In this scope, the neurobiology of sleep-wakefulness and attention, and neuropsychology, have already achieved substantial advances.

d-Amphetamine enhanced memory performance in rats with damage to the fimbria

Rats were preoperatively trained on a 5-unit linear maze and were then subjected to fimbria lesions. The animals were then retested on the same task with one group of rats with fimbria lesions and a control group being injected daily with 0.5 mg/kg d-amphetamine sulfate prior to testing. Lesions significantly impaired postoperative performance of the task, while amphetamine facilitated performance in fimbria lesioned rats. Due to an optimal learning of the task, performance of control animals was not significantly facilitated. These results raise several important issues including the mechanisms of functional recovery after brain lesions and the role of the hippocampal formation in learning and memory.

The Roman strains of rats as a psychogenetic tool for pharmacological investigation of working memory: example with RU 41656.

This study examined the effects of RU 41656, a dopaminergic D2 agonist, on the differential working memory performances and on the differential activities of the neurochemical systems of the Roman high (RHA) and Roman low (RLA) avoidance strains of rats. Compared with RLA, RHA performed worse in three tests of working memory (spontaneous alternation, radial maze and object recognition) and had higher levels of exploratory locomotor activity. Hippocampal and frontal cortex choline acetyltransferase (ChAT) activities were loer in RHA. Frontal cortex DA and DOPAC levels, hippocampal and striatal 5-HT and NA levels were higher in RHA. RU 41656 induced a significant improvement in working memory performance of RHA, whereas in RLA it had no effect. It decreased exploratory locomotor activity in both strains. ChAT activity in hippocampus was not affected by RU 41656 in either strain, whereas in frontal cortex it was increased in RHA but not in RLA. Hippocampal NA levels were decreased by RU 41656 in RHA but not in RLA. These results confirm previous data concerning the promnesic effect of RU 41656 and extend the finding that the Roman strains are a psychogenetic model for the behavioural, neurochemical and psychopharmacological study of the working memory in rats.