Effect of cerebellar granule cell depletion on spatial learning and memory and in an avoidance conditioning task: studies in postnatally X-irradiated rats.

Rats of the DA/HAN strain (pigmented rats) were submitted to two experimental tasks consisting in spatial learning (water escape experiment) and in passive avoidance conditioning. These rats were either totally or partially deprived of their granule cells using two different schedules of postnatal X-irradiation of the cerebellum. When they were 3 months old, the animals were submitted to an initial learning session, followed by a retrieval test seven days later. The scores of the rats which were partially deprived of granule cells appeared similar to those of controls, except for a mild deficiency of spatial learning. The learning and retrieval scores of the rats totally deprived of granule cells were similar to those of controls at the passive avoidance conditioning task, but these animals were unable to accurately learn a spatial task and showed memory impairments relative to controls. These results are discussed in terms of cognitive defects.

Effect of cerebellar granule cell depletion on learning of the equilibrium behaviour: study in postnatally X-irradiated rats.

To assess the role of the mossy fibre-granule cell pathway in learning, the cerebellum of young DA/HAN strain rats was irradiated to make the cortex completely or partially agranular. The X-rays were delivered according to two different schedules, between 5-14 postnatal days (early group) and between 10-14 postnatal days (late group). Histological controls at 35 days showed a mean loss of granule cells of 96 +/- 1% in the early group and of 61 +/- 3% in the late group. The irradiated animals were subjected, from day 23 to day 35, to daily sensorimotor training on a rotorod. The scores and the strategy used (walking or hanging) by the rats were noted. The results demonstrate that a partial loss of granule cells due to a late X-irradiation schedule induced mild motor disabilities but no learning deficit, the only problem being difficulty in elaborating rapidly an efficient strategy to solve a novel problem. A sub-total loss of the granule cells, due to an early X-irradiation schedule, induced gross motor disabilities and the animals used hanging > 90% of the time. Due to the discrepancy between the learning abilities, which were preserved at least in part, and the gross motor impairments, the animals elaborated a novel strategy (jumping from the beam), allowing them to escape the experimental situation. This avoidance behaviour may be due to a decrease of anxiety, a lack of behavioural inhibition and/or attentional deficits that have been already observed in several other examples of cerebellar abnormalities.

Role of preoperative and postoperative sensorimotor training on restoration of the equilibrium behavior in adult mice following cerebellectomy.

The equilibrium behavior of cerebellectomized C57/BL6 adult mice was studied on a rota rod rotating at 20 revolutions per minute and the influence of preoperative or/and postoperative training on restoration of equilibrium capabilities investigated. The duration of the preoperative training was either short (1 day) or long (7 days). The postoperative training began either the day after cerebellectomy or was delayed by 7 days. The results demonstrate that postoperative training was efficient in restoring the equilibrium behavior in all cases, except for the animals which were trained for a long period (7 days) before the lesion. Preoperative training was also efficient providing it was long enough (7 days), except for the animals which postoperative training began the day after cerebellectomy. It can be stated that both preoperative and postoperative trainings influence the restoration of the equilibrium following a cerebellectomy and that, in some instances, preoperative training can be as efficient as postoperative.

Effects of lesion of the inferior olivary complex in learning of the equilibrium behavior in the young rat during ontogenesis. I. Total lesion of the inferior olive by 3-acetylpyridine.

Young DA/HAN strain rats were submitted to an equilibrium test consisting in maintaining equilibrium upon a rotorod rotating at 10 or 20 rpm. They were either intact or lesioned, the lesion consisting in destruction of the inferior olivary complex (IOC) by 50-95 mg/kg i.p. administration of 3-acetylpyridine (3-AP) at day 15, followed, 2 to 4 h later, by i.p. injection of niacinamide (300 mg/kg). All the 3-AP-treated animals included in this study were completely lesioned, the extent of the lesion being estimated by both the response of the rats to harmaline and histological controls at the end of the experiments. The IOC lesioned rats were either naive (tested at one given day) or trained every day (10 trials per day); among the latters, some were trained before and after the lesion, the others being trained either before or only after. Control rats were submitted to the same training schedule. Both quantitative (time during which the animals maintained the equilibrium upon the rotating rod) and behavioral data (strategy used by the animals to maintain equilibrium) were obtained. The results demonstrate that, compared to those of controls rats, the quantitative and behavioral scores of the IOC lesioned animals were altered. Comparison of naive and trained animals shows that the impairment of the equilibrium behavior is not only due to the ataxia provoked by the IOC lesion but is also due to cognitive deficits. However, prelesion training facilitates the acquisition of a more efficient postlesion equilibrium behavior. From these results, it can be concluded that the olivo-cerebellar pathway is involved in the adaptation of motor behavior to the environmental conditions.

Differential roles of cerebellar cortex and deep cerebellar nuclei in the learning of the equilibrium behavior: studies in intact and cerebellectomized lurcher mutant mice.

Three- to 6-month-old lurcher mutant mice (+/lc), which exhibit a massive loss of neurons in the cerebellar cortex and in the inferior olivary nucleus but whose deep cerebellar nuclei are essentially intact, were trained daily, for 9 days, to maintain their equilibrium upon a rota rod rotating at 20 or 30 revolutions per minute (rpm). Their scores were measured and their behavior upon the rotating rod quantified in comparison to those of matched control (+/+) mice. Lurcher mice were able to learn to maintain their equilibrium efficiently when rotated at 20 rpm but were not when rotated at 30 rpm. After cerebellectomy, the equilibrium capabilities of the animals were much altered, especially in +/lc. These results show that the deep cerebellar nuclei are sufficient for motor learning, provided the task is not too difficult (20 rpm), but that the cerebellar cortex is required when the task is more difficult (30 rpm). Therefore, it can be concluded that the adaptive motor capabilities of lurcher mice are less developed than those of control animals.

Effect of administration of 3-acetylpyridine followed by niacinamide injection on survival, extent of the inferior olivary complex lesion, and response to harmaline in the young rat.

In the 15 day-old DA/HAN strained rat, i.p. injection of 3-acetylpyridine (3-AP) 50, 65 or 95 mg.kg-1 was followed 2 to 4 hours later by administration of niacinamide (300 mg.kg-1). The percentage of survival and the extent of the inferior olivary complex (IOC) lesion, determined histologically, were correlated with both the dose of 3-AP administered and the time delay between 3-AP and niacinamide injections. Moreover, the tremor elicited by harmaline was also correlated with the extent of the IOC lesion. The results show that it is more advantageous to administer 95 mg.kg-1 3-AP and to delay niacinamide injection by 2h30 or less to get the higher percentage of survival (about 90%) and a reasonably high percentage of totally IOC lesioned rats (more than 30%). They also demonstrate that the harmaline test is not sufficient to acutely judge of the extent of the IOC lesion and that, in all cases, histological controls have to be done. The results are discussed in terms of interrelationships of the variable studied.

Effects of inhibition of the GABAergic systems by picrotoxin on retention of a nociceptive experience in the rat, with special reference to the influence of cerebellar cortex output.

Adult cerebellectomized and noncerebellectomized DA/HAN strain (pigmented) female rats were submitted to a one-trial passive avoidance conditioning procedure consisting in associating darkness with a nociceptive stimulus. Seven days later, they were tested again to assess the retention stage. The results demonstrate that in noncerebellectomized rats, picrotoxin, whatever the dose, administered prior to the retention test, does not significantly impair retrieval. On the contrary, when administered just prior to the initial conditioning, impairments of the initial single nociceptive experience were evident (the greater the picrotoxin dose, the greater the impairments). In animals that were cerebellectomized 1 week before the experiment, picrotoxin administered at a low dose before the initial experience elicited memory impairments that were similar to those induced in noncerebellectomized rats but that were greater than those elicited in cerebellectomized, nontreated animals. However, in cerebellectomized rats, picrotoxin administered at a low dose elicited memory impairments that were weaker than in noncerebellectomized animals injected with a high dose of the drug. Considering that a low dose of picrotoxin administered to cerebellectomized animals had effects that were similar to those of a high dose injected to noncerebellectomized rats, and given that it has previously been demonstrated that a cerebellectomy performed after a single nociceptive experience impairs its memory, it is tempting to suggest that the two different doses of the drug administered to cerebellectomized and noncerebellectomized rats have similar effects on memory. If such an interpretation is valid, the information would have to leave the cerebellar cortex to be stored for long.

Effects of lesion of the inferior olivary complex by 3-acetylpyridine on learning and memory in the rat.

DA/HAN-strained male rats (pigmented rats) were submitted to two experimental tasks consisting of spatial learning (water-escape) and a passive avoidance conditioning. Both these tasks were performed by different animals. In order to destroy the inferior olivary complex, the animals were injected with 3-acetylpyridine either 9 days prior to the initial learning session or 24 h after completion of the learning task. They were retested (retrieval test) 10 days after the initial learning was achieved. Learning and retention were compared to those noted in control rats. Administration of 3-acetylpyridine before the initial learning did not prevent the spatial learning but the scores were greatly altered and the number of trials needed to reach the fixed learning criterion was much greater than in controls. However, 10 days later the animals had memorized their initial experience. Injection of 3-acetylpyridine after the initial learning session impaired memory: the animals had completely forgotten their initial learning. It can therefore be concluded that lesion of the afferent climbing fibres to the cerebellar cortex alters learning and retention of a spatial task. Such a lesion does not interfere with learning and retention of a passive avoidance conditioning, since in this condition the experimental animals injected with 3-acetylpyridine either before or after the initial learning behave similarly to controls. The effects of the inferior olivary complex lesion are obviously different according to the task to be learnt, suggesting that these two tasks do not require the integrity of the same nervous structures.

Role of the cerebellum in spatial orientation in the rat.

Adult DA/HAN strain rats were submitted to a spatial orientation task consisting of finding a reward in an open field. They were first submitted to an initial learning session and 10 days later to a retrieval test. The animals were divided into four groups of five rats each: animals that were cerebellectomized before the initial learning session or after the initial learning session, sham-operated rats, and control (intact) animals. Different parameters that characterize the spatiotemporal organization of the rat's exploratory behavior were quantified. From the results, it can be concluded that the cerebellum is not absolutely necessary in the processes that sustain spatial learning but that it is involved in the mechanisms sustaining focused spatial memory and in the cognitive processes of the motor program elaboration and not only in the regulation of the movement being done.

Horizontal optokinetic nystagmus in unilaterally enucleated pigmented rats: role of the pretectal commissural fibers.

Monocular enucleation reduces the asymmetry of horizontal optokinetic nystagmus (H-OKN) in afoveate mammals by increasing responses to naso-temporal visual stimulation. The origin of these larger responses was investigated in adult pigmented rats monocularly enucleated as neonates or as adults by analyzing retinal and commissural projections to the deafferented nucleus of the optic tract (NOT) and the functional role of this nucleus before and after section of the posterior commissure. Anatomically, monocular enucleation reduces the volume of the contralateral deafferented NOT. Anterograde tracers injected in the intact eye reveal a crossed projection of the retina to the NOT and to the dorsal (DTN) and medial (MTN) terminal nuclei of the accessory optic system as in normal rats. In addition, there is an uncrossed projection to the MTN in the rats enucleated as neonates. Retrograde tracer injected in the deafferented NOT confirms the absence of an uncrossed retinal projection but reveals connections between both NOT via the posterior commissure as in normal rats. Electrophysiologically, the larger naso-temporal optokinetic responses in monocularly enucleated rats return to normal after posterior commissurotomy. This study demonstrates that no anatomical remodelling takes place to increase naso-temporal responses in monocularly enucleated rats. The larger responses must then result from functional changes. The role of exclusive contralateral projections of the retina to the NOT and of the commissural connections in mediating the asymmetry of the optokinetic nystagmus in afoveate mammals is discussed.

Effects of cerebellectomy at day 15 on the ontogenesis of the equilibrium behavior in the rat.

Young cerebellectomized and control (sham-operated) DA/HAN strained rats, 1 day to 1 month old, were submitted to an equilibrium test consisting for the animals in maintaining their equilibrium when placed on a horizontal mast rotating around its longitudinal axis at 10 or 20 rpm (slow and fast rotation rates, respectively). Cerebellectomized animals, operated when 15 days old, were either naive (tested at one given day) or trained; these last ones were trained before and after the operation, or only before, or only after, according to a slow or a fast rotation rate. Control rats were also either naive or trained in conditions similar to those given to operated animals. Relevant comparisons show that: (1) rats cerebellectomized at day 15 which have not been trained before the operation are unable to learn a given motor pattern. (2) When trained before the operation, the animals learn the motor patterns that they use to maintain their equilibrium upon the rotating mast as well as controls. (3) Postoperative training is inefficient in the acquisition of the equilibrium behavior whether the animals were trained preoperatively or not. (4) Compared to the slow rotation rate (10 rpm), the evolution of the equilibrium behavior in cerebellectomized rats is not altered when the rotation rate is increased to 20 rpm, that is when the task is more difficult.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of the cerebellum in the ontogenesis of the equilibrium behavior in the young rat: a behavioral study.

Young cerebellectomized and control DA/HAN strained rats, one day to 1 month old, were submitted to an equilibrium test. Cerebellectomized animals, operated when 10-, 20- or 24-day-old, were either trained-operated-trained (trained every day before and after cerebellectomy), naïve-operated-trained (cerebellectomized while naïve and trained every day after the operation), or naïve-operated-naïve (tested at one given day after the operation). Control rats were either trained-controls (trained every day) or naïve-controls (tested at a given day). Relevant comparisons show that (1) in control rats, the maturation of the equilibrium behavior does not depend on a specific training, at least to a great extent; however, training increases the rate of acquisition of the maximal score. (2) Rats cerebellectomized at day 10 and trained after cerebellectomy only are not able to learn a given motor pattern, while rats cerebellectomized by the 20th or 24th day are; however, their scores are always lower than those of control animals trained from the same age. Cerebellectomy alters the ontogenesis of the equilibrium behavior more especially as the operation is early. (3) Impairments of the equilibrium behavior after cerebellectomy can be explained by both motor disorders and learning processes deficiency. (4) Preoperative training counterbalances the effects of cerebellectomy in improving postoperative scores only when the cerebellum is removed at day 24. From these results it can be concluded that, in the rat, the cerebellum is involved in the learning processes that sustain the ontogenesis of the equilibrium behavior as it is in other motor learning mechanisms.

Detection of stable isotopes of lithium or boron with the help of A (n,alpha) nuclear reaction. Application to the use of 6Li as a tracer for unidirectional flux measurements and to the microlocalization of lithium in animal histologic preparations.

In the particular case of boron and lithium we examine the possibilities of using stable isotopes for experiments of isotopic labelling and microlocalization, as no radioisotopes exist. The detection is made with the help of a specific nuclear reaction, using homogeneous detectors. The first experimental applications are given: transepithelial fluxes of lithium (frog skin) have shown Liefflux values larger than the influx ones. Detailed microlocalization of lithium have been made on histological preparations of mice having received lithium treatment: particularly important contents are found in the hypophysis, the salivary glands, the bladder, the kidney (especially the pelvis), the intestinal system and certain parts of the brain (particularly the hippocampus); the liver, however remains very poor in lithium. Physiological implications are examined.

[Oscillations in the transepithelial electric potential and current under the influence of lithium]. / Oscillations de potentiel et de courant électriques transépithéliaux sous l'effet du lithium

One can induce sustained oscillations of the spontaneous potential of the frog epithelium by replacing whole or part of the sodium of the external medium with lithium; in the same conditions, the electric current at imposed potential gives damped oscillations. The shape of the oscillations varies much according to the external medium. In the case of the quasi-sinusoidal oscillations, The period is always about 10 mn. We suggest formulating this phenomenon within the framework of the dissipative structurations in non-equilibrium thermodynamics.