Cerebellar nuclear lesions in rats: subsequent avoidance behavior and ascending anatomical connections

Motor Performances of Spontaneous and Genetically Modified Mutants with Cerebellar Atrophy

Chance discovery of spontaneous mutants with atrophy of the cerebellar cortex has unearthed genes involved in optimizing motor coordination. Rotorod, stationary beam, and suspended wire tests are useful in delineating behavioral phenotypes of spontaneous mutants with cerebellar atrophy such as Grid2^Lc, Grid2^ho, Rora^sg, Agtpbp1^pcd, Reln^rl, and Dab1^scm. Likewise, transgenic or null mutants serving as experimental models of spinocerebellar ataxia (SCA) are phenotyped with the same tests. Among experimental models of autosomal dominant SCA, rotorod deficits were reported in SCA1 to 3, SCA5 to 8, SCA14, SCA17, and SCA27 and stationary beam deficits in SCA1 to 3, SCA5, SCA6, SCA13, SCA17, and SCA27. Beam tests are sensitive to experimental therapies of various kinds including molecules affecting glutamate signaling, mesenchymal stem cells, anti-oligomer antibodies, lentiviral vectors carrying genes, interfering RNAs, or neurotrophic factors, and interbreeding with other mutants.

Is there an "antisocial" cerebellum? Evidence from disorders other than autism characterized by abnormal social behaviours

The cerebellum is a hindbrain structure which involvement in functions not related to motor control and planning is being increasingly recognized in the last decades. Studies on Autism Spectrum Disorders (ASD) have reported cerebellar involvement on these conditions characterized by social deficits and repetitive motor behavior patterns. Although such an involvement hints at a possible cerebellar participation in the social domain, the fact that ASD patients present both social and motor deficits impedes drawing any firm conclusion regarding cerebellar involvement in pathological social behaviours, probably influenced by the classical view of the cerebellum as a purely "motor" brain structure. Here, we suggest the cerebellum can be a key node for the production and control of normal and particularly aberrant social behaviours, as indicated by its involvement in other neuropsychiatric disorders which main symptom is deregulated social behaviour. Therefore, in this work, we briefly review cerebellar involvement in social behavior in rodent models, followed by discussing the findings linking the cerebellum to those other psychiatric conditions characterized by defective social behaviours. Finally, possible commonalities between the studies and putative underlying impaired functions will be discussed and experimental approaches both in patients and experimental animals will also be proposed, aimed at stimulating research on the role of the cerebellum in social behaviours and disorders characterized by social impairments, which, if successful, will definitely help reinforcing the proposed cerebellar involvement in the social domain.

The cerebellum in fear and anxiety-related disorders

Fear and anxiety-related disorders are highly prevalent psychiatric conditions characterized by avoidant and fearful reactions towards specific stimuli or situations, which are disproportionate given the real threat such stimuli entail. These conditions comprise the most common mental disorder group. There are a high proportion of patients who fail to achieve remission and the presence of high relapse rates indicate the therapeutic options available are far from being fully efficient. Despite an increased understanding the neural circuits underlying fear and anxiety-related behaviors in the last decades, a factor that could be partially contributing to the lack of adequate therapies may be an insufficient understanding of the core features of the disorders and their associated neurobiology. Interestingly, the cerebellum shows connections with fear and anxiety-related brain areas and functional involvement in such processes, but explanations for its role in anxiety disorders are lacking. Therefore, the aims of this review are to provide an overview of the neural circuitry of fear and anxiety and its connections to the cerebellum, and of the animal studies that directly assess an involvement of the cerebellum in these processes. Then, the studies performed in patients suffering from anxiety disorders that explore the cerebellum will be discussed. Finally, we'll propose a function for the cerebellum in these disorders, which could guide future experimental approaches to the topic and lead to a better understanding of the neurobiology of anxiety-related disorders, ultimately helping to develop more effective treatments for these conditions.

Brain regions and genes affecting postural control

Postural control is integrated in all facets of motor commands. The role of cortico-subcortical pathways underlying postural control, including cerebellum and its afferents (climbing, mossy, and noradrenergic fibers), basal ganglia, motor thalamus, and parieto-frontal neocortex has been identified in animal models, notably through the brain lesion technique in rats and in mice with spontaneous and induced mutations. These studies are complemented by analyses of the factors underlying postural deficiencies in patients with cerebellar atrophy. With the gene deletion technique in mice, specific genes expressed in cerebellum encoding glutamate receptors (Grid2 and Grm1) and other molecules (Prkcc, Cntn6, Klf9, Syt4, and En2) have also been shown to affect postural control. In addition, transgenic mouse models of the synucleinopathies and of Huntington's disease cause deficiencies of motor coordination resembling those of patients with basal ganglia damage.

Effects of early midline cerebellar lesion on cognitive and emotional functions in the rat

Midline lesion of the cerebellum was performed in young 10-day-old DA/HAN strained (pigmented) rats. Once adults, the lesioned animals were subjected to a series of behavioral tests and their performances were compared with those of control (nonlesioned) rats. Compared with controls, the spontaneous motor activity of the lesioned rats was higher, they showed persevering behavior and did not pay attention to environmental distractors. In anxiety and social discrimination tests, disinhibition tendencies were obvious, which suggested that the animals were less dependent on the context. These abnormalities were most likely due to early midline lesion of the cerebellum and not to a deficit in maternal care before weaning, since the dams took care of the lesioned and control pups similarly. From these results, it can be concluded that the cerebellar vermis is involved in motor control, attentional capabilities and emotional behavior. Given that the lesioned rats observed in this study presented obvious autistic-like symptoms, and since a number of autistic subjects have cerebellar deficits and, particularly, a hypoplasia of vermal lobules, our results may strengthen the idea that the cerebellar vermis is involved in autism, as already suggested in the guinea pig (Caston J, et al. Eur J Neurosci 1998;10:2677-2684).

Autonomic and vasomotor regulation

The cerebellum not only modulates the systemic circulation, but also profoundly influences cerebral blood flow (rCBF) and metabolism (rCGU), and initiates long-term protection of the brain from ischemia. Electrical stimulation of the rostral ventral pole of the fastigial nucleus (FN), elevates arterial pressure (AP), releases vasoactive hormones, elicits consummatory behavioral and other autonomic events and site specifically elevates rCBF independently of changes in rCGU. Cerebral vasodilation results from the antidromic excitation of axons of brain stem neurons which innervate cerebellum and, through their collaterals, neurons in the rostral ventrolateral reticular nucleus (RVL). RVL neurons initiate cerebral vasodilation over polysynaptic vasodilator pathways which engage a population of vasodilator neurons in the cerebral cortex. In contrast, intrinsic neurons of FN, when excited, elicit widespread reductions in rCGU and, secondarily, rCBF, along with sympathetic inhibition. Electrical stimulation of FN can reduce the volume of a focal cerebral infarction produced by occlusion of the middle cerebral artery by 50%. This central neurogenic neuroprotection is long lasting (weeks) and is not due to changes in rCBF or rCGU. Rather, it appears to reflect alterations in neuronal excitability and/or downregulation of inflammatory responses in cerebral vessels. The FN, therefore, appears to be involved in widespread autonomic, metabolic, and behavioral control, independent of motor control. The findings imply that the FN receives inputs from neurons, probably widely represented in the central autonomic core, which may provide continuing information processing of autonomic and behavioral states. The cerebellum may also widely modulate the state of cortical reactivity to ischemia, hypoxia, and possibly other neurodegenerative events.

Cerebellar contribution to spatial event processing: right/left discrimination abilities in rats

Recently, we demonstrated the involvement of cerebellar circuits in the procedural components of spatial information processing by testing hemicerebellectomized (HCbed) rats in classical spatial paradigms, such as the Morris Water Maze and the water T-maze. Since procedural components are strongly present in these tests, an impairment also in processing more abstract spatial information, linked to 'where an object is' rather than to 'how to find it', could be hidden by the severe procedural deficits. On this basis, we investigated the influence of cerebellar lesions on spatial abilities strictly reducing procedural variables by employing an active avoidance task, first without and then with a request for right/left discrimination. In the two-way active avoidance task without spatial requests, controls and cerebellar operated rats developed active avoidance responses which were not statistically different, demonstrating that this kind of associative learning is not significantly affected by hemicerebellectomy (HCb). A second experimental group of cerebellar lesioned rats was tested in a modified version of this basic paradigm in which a right/left discrimination request was added. This group displayed severe deficits, which even in the last testing sessions prevented them from performing comparably to the control animals. Reversal of the rewarded choice, even if it affected the performances of both controls and operated rats in the first inversion trials, elicited the lowest number of correct responses in HCbed rats throughout the entire spatial reversal learning, suggesting a severe deficit in the ability to change an initially learned behaviour. These results demonstrate that, beside having a marked impairment in facing procedural components of spatial processing, cerebellar lesioned rats are severely defective also in right/left discrimination tasks, suggesting a role of cerebellar networks also in the discriminative spatial information processing.

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.

Avoidance and classical conditioning of leg flexion in dogs

This study of leg flexion conditioning in dogs, which were trained under both avoidance and classical contingencies consecutively, confirmed and extended the results from the Wahlsten and Cole study (In Classical Conditioning II: Current Research and Theory, Appleton Century-Crofts, New York, 1972). Briefly, dogs were trained to asymptotic behavioral levels under either avoidance or classical contingencies with a CS-US interval of either three (3) or five (5) seconds where the unconditioned stimulus (US) was shock to the foreleg and the conditioned stimulus (CS) was 1000 Hz tone. The dogs were then switched to the other contingency (without any modification in the stimulus situation other than the shock contingency) and trained to asymptotic behavioral levels. The CS remained on for the entire CS-US period and terminated with the end of the scheduled interval. Under the classical contingency, the US occurred as scheduled on every trial regardless of the dog's behavior. Under the avoidance contingency, the US was prevented from occurring if the subject responded with a criterion leg lift during the CS-US interval. The only feedback to the dog of a successful performance was the leg lift itself. The results indicated that there were two different conditioned responses produced, one just after CS onset under the avoidance contingency, and one just before US onset under the classical contingency for both CS-US intervals. The findings were interpreted as supporting a single-factor informational view of learning and a neural model was presented.

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.

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.

Cerebellar contributions to instrumental learning

There is emerging evidence that the cerebellum is involved in spatial and nonspatial instrumental learning tasks. Cerebellar-lesioned animals have deficits in water maze learning tasks that may be explained by two-way interactions with higher order brain regions. There is suggestive evidence that cerebellar modulation extends to shock avoidance and discrimination learning. Although this evidence needs to be confirmed by a wider range of lesion methods and choice of learning tasks, it is in line with the hypothesis that the cerebellum affects cognitive processes and is not strictly concerned with motor control and the acquisition and retention of conditioned reflexes.

Active avoidance behavior using pontine nucleus stimulation as a conditioned stimulus in the rat

Five groups of rats were trained in an active avoidance task in a shuttle box with different conditioned stimuli. Animals with either a light-conditioned stimulus or with electrical stimulation of the ventral pontine nucleus as a conditioned stimulus rapidly learned to avoid an aversive event, while those with no conditioned stimulus, with electrical stimulation of the lateral pontine nucleus or the medial lemniscus did not learn to avoid. Therefore, stimulation of a specific subdivision of the pontine nucleus is as effective as a light-conditioned stimulus to learn an active avoidance task.

Effects of cerebellectomy on motivation-related behavior: a time-course study

The open field behavior and learning capacity of male rats of the Wistar strain was studied 1, 2, and 6 months after cerebellectomy (CBX). The results show a decrease in locomotor activity 1 month after CBX and thereafter a slow recovery. Grooming behavior was still normal after 1 month, but it decreased 2 months after CBX. Learning capacity, as assessed by the shuttle-box test, was remarkably decreased in cerebellectomized animals 1 month after operation. A significant impairment of memory capacity was also observed in rats tested for passive avoidance behavior 2 months after CBX. A partial recovery of this parameter was present 6 months after operation. These results support the hypothesis of a possible influence of cerebellum on motivation-related behaviors, independently of its modulatory role on motricity.

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.

Role of the cerebellum in habituation exploration behavior in the rat

Adult control and cerebellectomized DA/HAN-strained male rats were submitted to habituation of exploration behavior in a test environment consisting of a novel cage in which four objects were displayed. Seven days after the initial session of habituation, retention of the habituation was tested. Within-session habituation was observed in cerebellectomized and control rats. However, retention of habituation was impaired in rats that were cerebellectomized after the initial session but not in those cerebellectomized before the session. These results are consistent with the hypothesis that the cerebellum has a role in memory of habituation to environmental stimuli.

Cerebellum and memory: an experimental study in the rat using a passive avoidance conditioning test

Adult DA/HAN strain rats were submitted to a one-trial passive avoidance conditioning procedure consisting in associating darkness with a nociceptive stimulus. Seven or fourteen days after the one-trial initial experience, they were tested again in order to know whether they had forgotten it or not. The animals were divided into two experimental groups, the rats being either conditioned (COC group) or not (NOC group) before cerebellectomy, and two control groups, the animals being either intact (C group) or sham-operated (SO group). Each group was divided into two subgroups, one being given the retrieval test 7 days and the other 14 days after the initial conditioning. The results show that retention in C, SO and NOC rats was similar whether the animals were tested 7 days or 14 days after the initial one-trial conditioning. Seven days after their initial experience and the cerebellectomy, the retention in COC rats was null while when they were tested 14 days after cerebellar removal these animals had much better scores, significantly higher than 7 days after the lesion. It is concluded that the cerebellum is involved in the consolidation processes of the memory trace but is not the site of memory storage.

Role of the cerebellum in an avoidance conditioning task in the rat

Adult DA/HAN strain male rats were submitted to an avoidance conditioning procedure. They were divided into two experimental groups, the animals being either conditioned (COC group) or not (NOC group) before cerebellectomy, and two control groups, the animals being either intact (C group) or sham-operated (SO group). Although the NOC rats could be conditioned successfully and the cerebellum is not absolutely necessary for the avoidance conditioning achievement, their scores were significantly lower than the preoperative scores of COC rats. Moreover, the scores of NOC rats (postoperative scores) were significantly lower than the postoperative scores of COC animals, suggesting that the preoperative conditioning makes the postoperative conditioning easier. At last, comparing postoperative scores of COC rats with those obtained by C and SO rats when given the retrieval test and comparing preoperative and postoperative scores in COC animals show that retention of the initial (preoperative) conditioning is partly abolished by the cerebellectomy. Histological controls demonstrated that the entire cerebellum except for the flocculus and the nodulus was removed. These results strongly suggest that the cerebellum is involved in the memory processes that sustain the avoidance conditioning.

Effects of cerebellar vermal lesions on species-specific fear responses, neophobia, and taste-aversion learning in rats

The cerebellar vermis has extensive anatomical connections with many brain stem and forebrain structures which have been implicated in emotional or affective behavior. Previous reports indicate that lesions of the vermis in a variety of experimental animals result in altered emotional behavior. The studies reported here attempted to clarify the nature of the change in emotional behavior following vermal lesions in rats by testing the animals in a variety of fear-eliciting situations. As compared with controls, vermal-lesioned rats froze less in the presence of a cat and showed fewer signs of fear in an open field. However, their responses to footshock did not differ fundamentally from controls. They recovered more quickly than controls from the neophobic response to a novel taste but showed robust taste-aversion learning. The results are discussed in terms of the role of the cerebellum in the modulation of fear-related behaviors and in terms of similarities and differences with the effects of amygdala lesions. The results expand the body of data implicating the cerebellum in the modulation of complex motivational behavior.

Cerebellar pathology in schizophrenia--cause or consequence?

Atrophy of the cerebellar vermal cortex has been reported to occur in 10% or more of patients with schizophrenia. Data from studies on experimental animals indicate that a functional relationship between the cerebellum and parts of the forebrain involved in emotion exists, and that the cerebellum may influence some types of behavior. Cerebellar abnormality in schizophrenic patients, although of uncertain cause, could contribute to the symptomatology of the disease.