Postural changes after lesions of the substantia nigra pars reticulata in hemiparkinsonian monkeys

Naringin Exhibits Neuroprotection Against Rotenone-Induced Neurotoxicity in Experimental Rodents

Parkinson's disease (PD) is a neurodegenerative disease that is accompanied with the loss of dopaminergic neurons in the substantia nigra pars compacta which subsequently leads to a reduction in the dopamine level in the striatum. The flavonoids are gaining critical attention in the management of PD due to the toxic effects of the synthetic drugs. Naringin, a potent flavonoid, exerts neuroprotective activity against experimental animal models of PD. It also exhibits protective activity against rotenone-induced neurotoxicity in cell line studies. Therefore, the present study was designed to evaluate the therapeutic potential of naringin against rotenone-induced animal model of PD. The rotenone was injected through intracerebroventricular route into substantia nigra pars compacta (SNpc) to induce PD-like manifestations in the male rats. The behavioral deficits of the animals due to dopaminergic toxicity were evaluated in actophotometer, OFT, bar catalepsy, narrow beam walk, rota-rod, grip strength and foot print analysis. Naringin-attenuated rotenone-induced behavioral abnormalities in the experimental rats. Further, naringin reduced the rotenone-induced dopaminergic toxicity in striatum and SNpc the animals. At the sub-cellular level, naringin attenuated the rotenone-induced decrease in the mitochondrial function, integrity and bioenergetics in the SNpc of the animals. Furthermore, naringin reduced the rotenone-induced mitochondria-dependent apoptosis in the rat SNpc. However, Trigonelline significantly abolished the therapeutic effects of naringin on behavioral, biochemical and molecular observations in rotenone-induced PD-like animals. These observations indicate that naringin may exert neuroprotective activity against rotenone-induced toxicity in the animals possibly through Nrf2-mediated pathway. Thus, it can be presumed that naringin could be an alternative option in the management of PD.

Comparative Analysis of the Effects of Neurotrophic Factors CDNF and GDNF in a Nonhuman Primate Model of Parkinson's Disease

Cerebral dopamine neurotrophic factor (CDNF) belongs to a newly discovered family of evolutionarily conserved neurotrophic factors. We demonstrate for the first time a therapeutic effect of CDNF in a unilateral 6-hydroxydopamine (6-OHDA) lesion model of Parkinson’s disease in marmoset monkeys. Furthermore, we tested the impact of high chronic doses of human recombinant CDNF on unlesioned monkeys and analyzed the amino acid sequence of marmoset CDNF. The severity of 6-OHDA lesions and treatment effects were monitored in vivo using ¹²³I-FP-CIT (DaTSCAN) SPECT. Quantitative analysis of ¹²³I-FP-CIT SPECT showed a significant increase of dopamine transporter binding activity in lesioned animals treated with CDNF. Glial cell line-derived neurotrophic factor (GDNF), a well-characterized and potent neurotrophic factor for dopamine neurons, served as a control in a parallel comparison with CDNF. By contrast with CDNF, only single animals responded to the treatment with GDNF, but no statistical difference was observed in the GDNF group. However, increased numbers of tyrosine hydroxylase immunoreactive neurons, observed within the lesioned caudate nucleus of GDNF-treated animals, indicate a strong bioactive potential of GDNF.

Modeling Parkinson's disease in the common marmoset (Callithrix jacchus): overview of models, methods, and animal care

The common marmoset (Callithrix jacchus) is a small-bodied, popular New World monkey and is used widely in reproductive biology, neuroscience, and drug development, due to its comparative ease of handling, high reproductive efficiency, and its unique behavioral characters. In this review, we discuss the marmoset models in Parkinson's disease (PD), which is a neurological movement disorder primarily resulting from a degeneration of dopaminergic neurons with clinical features of tremor, rigidity, postural instability, and akinesia. The most common PD models involve the administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) or 6-hydroxydopamine to study the pathogenesis and to evaluate novel therapies. Following the systemic or local administration of these neurotoxins, the marmosets with very severe Parkinson's symptoms are recommended to be placed in an intensive care unit with artificial feeding to increase survival rate. All procedures with MPTP should be conducted in a special room with enclosed cages under negative-pressure by trained researchers with personal protection. Behavioral tests are conducted to provide an external measure of the brain pathology. Along with several biomarkers, including α-synuclein and DJ-1, non-invasive neuroimaging techniques such as positron emission tomography and magnetic resonance imaging are used to evaluate the functional changes associated with PD. With the recent growing interest in potential and novel therapies such as stem cell and gene therapy for PD in Korea, the marmoset can be considered as a suitable non-human primate model in PD research to bridge the gap between rodent studies and clinical applications.

Molecular, Neurochemical, and Behavioral Hallmarks of Reserpine as a Model for Parkinson's Disease: New Perspectives to a Long-Standing Model

The administration of reserpine to rodents was one of the first models used to investigate the pathophysiology and screening for potential treatments of Parkinson's disease (PD). The reserpine model was critical to the understanding of the role of monoamine system in the regulation of motor and affective disorders, as well as the efficacy of current PD treatments, such as L-DOPA and dopamine agonists. Nevertheless, with the introduction of toxin-induced and genetic models of PD, reserpine became underused. The main rationale to this drawback was the supposed absence of reserpine construct validity with PD. Here, we highlight classical and recent experimental findings that support the face, pharmacological, and construct validity of reserpine PD model and reason against the current rationale for its underuse. We also aim to shed a new perspective upon the model by discussing the main challenges and potentials for the reserpine model of PD.

Monoamine reuptake inhibitors in Parkinson's disease

The motor manifestations of Parkinson's disease (PD) are secondary to a dopamine deficiency in the striatum. However, the degenerative process in PD is not limited to the dopaminergic system and also affects serotonergic and noradrenergic neurons. Because they can increase monoamine levels throughout the brain, monoamine reuptake inhibitors (MAUIs) represent potential therapeutic agents in PD. However, they are seldom used in clinical practice other than as antidepressants and wake-promoting agents. This review article summarises all of the available literature on use of 50 MAUIs in PD. The compounds are divided according to their relative potency for each of the monoamine transporters. Despite wide discrepancy in the methodology of the studies reviewed, the following conclusions can be drawn: (1) selective serotonin transporter (SERT), selective noradrenaline transporter (NET), and dual SERT/NET inhibitors are effective against PD depression; (2) selective dopamine transporter (DAT) and dual DAT/NET inhibitors exert an anti-Parkinsonian effect when administered as monotherapy but do not enhance the anti-Parkinsonian actions of L-3,4-dihydroxyphenylalanine (L-DOPA); (3) dual DAT/SERT inhibitors might enhance the anti-Parkinsonian actions of L-DOPA without worsening dyskinesia; (4) triple DAT/NET/SERT inhibitors might exert an anti-Parkinsonian action as monotherapy and might enhance the anti-Parkinsonian effects of L-DOPA, though at the expense of worsening dyskinesia.

Potentiation of response to low doses of levodopa in MPTP-injected monkeys by chemical unilateral subthalamotomy

Object

Subthalamotomy is a stereotactic surgery performed in patients with disabling dyskinesias due to Parkinson disease. The authors set out to model this human condition in MPTP monkeys and determine if subthalamotomy allowed a reduction of levodopa for similar benefit.

Methods

The authors performed unilateral subthalamotomy in 4 parkinsonian dyskinetic monkeys by stereotactic injection of ibotenic acid. An optimal dose, defined as the highest dose of levodopa improving parkinsonian motor symptoms while inducing low or no dyskinesias, was established in these animals. Each monkey was scored for the antiparkinsonian and dyskinetic effects of the optimal dose of levodopa, as well as suboptimal and dyskinesia-inducing doses (60% and 140% of the optimal dose, respectively), and these scores were compared with those obtained at baseline before and after subthalamotomy. Bradykinesia was assessed by a prehension task.

Results

Unilateral subthalamotomy had a positive effect on the antiparkinsonian response for all doses of levodopa as well as the baseline. There were no differences in the antiparkinsonian response between the suboptimal dose postsurgery and the optimal dose presurgery. Dyskinesias were increased at the suboptimal and the optimal doses. After surgery, the duration of response to levodopa increased between 20% and 25% in the suboptimal dose, whereas it remained unchanged with higher doses. Bradykinesia was significantly reduced after surgery only at the suboptimal dose.

Conclusions

Subthalamotomy potentiated the response to suboptimal doses of levodopa. Thus, levodopa can be reduced by 40% after surgery for similar beneficial antiparkinsonian response and less dyskinesia than with an optimal dose before surgery.

Deep brain stimulation of the substantia nigra pars reticulata improves forelimb akinesia in the hemiparkinsonian rat

Deep brain stimulation (DBS) employing high-frequency stimulation (HFS) is commonly used in the globus pallidus interna (GPi) and the subthalamic nucleus (STN) for treating motor symptoms of patients with Parkinson's disease (PD). Although DBS improves motor function in most PD patients, disease progression and stimulation-induced nonmotor complications limit DBS in these areas. In this study, we assessed whether stimulation of the substantia nigra pars reticulata (SNr) improved motor function. Hemiparkinsonian rats predominantly touched with their unimpaired forepaw >90% of the time in the stepping and limb-use asymmetry tests. After SNr-HFS (150 Hz), rats touched equally with both forepaws, similar to naive and sham-lesioned rats. In vivo, SNr-HFS decreased beta oscillations (12-30 Hz) in the SNr of freely moving hemiparkinsonian rats and decreased SNr neuronal spiking activity from 28 ± 1.9 Hz before stimulation to 0.8 ± 1.9 Hz during DBS in anesthetized animals; also, neuronal spiking activity increased from 7 ± 1.6 to 18 ± 1.6 Hz in the ventromedial portion of the thalamus (VM), the primary SNr efferent. In addition, HFS of the SNr in brain slices from normal and reserpine-treated rat pups resulted in a depolarization block of SNr neuronal activity. We demonstrate improvement of forelimb akinesia with SNr-HFS and suggest that this motor effect may have resulted from the attenuation of SNr neuronal activity, decreased SNr beta oscillations, and increased activity of VM thalamic neurons, suggesting that the SNr may be a plausible DBS target for treating motor symptoms of DBS.

The significance of neuronal lateralisation in Parkinson's disease

The destruction of the dopaminergic neurons in the substantia nigra (SN) and consequent depletion of striatal dopamine elicits the main movement deficits related to Parkinson's disease (PD). In the early stages of the illness, the motor symptoms are often exhibited asymmetrically. Thus, the onset of PD features starts on either the right or left side. The side of onset appears to determine the prognosis of the disorder and other features, such as right-side tremor dominance has a better prognosis in contrast to left-side dominant bradykinesia-rigidity. In addition, left-side onset of motor features is associated with cognitive decline. Therefore, an intricate relation appears to exist between the side of disease onset and progression/severity and other non-motor symptoms. Unilateral PD in turn corresponds to neuronal nigrostriatal degeneration in the contralateral hemisphere. Indeed positron emission tomography has demonstrated a positive correlation between symptom asymmetry and brain function (Hoorn et al. Parkinsonism Relat Disord 17:58-60, 2011), which corresponds to a unilateral pattern of degeneration. This phenomenon appears to be exclusive to PD. Additionally, the variation in motor symptom(s) dominance exhibited in the disorder conforms to the notion that PD is a spectrum disease with many sub-groups. Thus, clinical and post mortem studies on "lateralisation" may serve as a vital tool in understanding the mechanism(s) eliciting the characteristic destruction of the SN neurons. Additionally, it may be employed as a predictive indicator for the symptomology and prognosis of the illness thus allowing selective treatment strategies targeted at the pronounced hemispheric degeneration.

The neurotoxicity of DOPAL: behavioral and stereological evidence for its role in Parkinson disease pathogenesis

BACKGROUND

The etiology of Parkinson disease (PD) has yet to be fully elucidated. We examined the consequences of injections of 3,4-dihydroxyphenylacetaldehyde (DOPAL), a toxic metabolite of dopamine, into the substantia nigra of rats on motor behavior and neuronal survival.

METHODS/PRINCIPAL FINDINGS

A total of 800 nl/rat of DOPAL (1 µg/200 nl) was injected stereotaxically into the substantia nigra over three sites while control animals received similar injections of phosphate buffered saline. Rotational behavior of these rats was analyzed, optical density of striatal tyrosine hydroxylase was calculated, and unbiased stereological counts of the substantia nigra were made. The rats showed significant rotational asymmetry ipsilateral to the lesion, supporting disruption of dopaminergic nigrostriatal projections. Such disruption was verified since the density of striatal tyrosine hydroxylase decreased significantly (p<0.001) on the side ipsilateral to the DOPAL injections when compared to the non-injected side. Stereological counts of neurons stained for Nissl in pars compacta of the substantia nigra significantly decreased (p<0.001) from control values, while counts of those in pars reticulata were unchanged after DOPAL injections. Counts of neurons immunostained for tyrosine hydroxylase also showed a significant (p=0.032) loss of dopaminergic neurons. In spite of significant loss of dopaminergic neurons, DOPAL injections did not induce significant glial reaction in the substantia nigra.

CONCLUSIONS

The present study provides the first in vivo quantification of substantia nigra pars compacta neuronal loss after injection of the endogenous toxin DOPAL. The results demonstrate that injections of DOPAL selectively kills SN DA neurons, suggests loss of striatal DA terminals, spares non-dopaminergic neurons of the pars reticulata, and triggers a behavioral phenotype (rotational asymmetry) consistent with other PD animal models. This study supports the "catecholaldehyde hypothesis" as an important link for the etiology of sporadic PD.

Targeting the progression of Parkinson's disease

By the time a patient first presents with symptoms of Parkinson's disease at the clinic, a significant proportion (50-70%) of the cells in the substantia nigra (SN) has already been destroyed. This degeneration progresses until, within a few years, most of the cells have died. Except for rare cases of familial PD, the initial trigger for cell loss is unknown. However, we do have some clues as to why the damage, once initiated, progresses unabated. It would represent a major advance in therapy to arrest cell loss at the stage when the patient first presents at the clinic. Current therapies for Parkinson's disease focus on relieving the motor symptoms of the disease, these unfortunately lose their effectiveness as the neurodegeneration and symptoms progress. Many experimental approaches are currently being investigated attempting to alter the progression of the disease. These range from replacement of the lost neurons to neuroprotective therapies; each of these will be briefly discussed in this review. The main thrust of this review is to explore the interactions between dopamine, alpha synuclein and redox-active metals. There is abundant evidence suggesting that destruction of SN cells occurs as a result of a self-propagating series of reactions involving dopamine, alpha synuclein and redox-active metals. A potent reducing agent, the neurotransmitter dopamine has a central role in this scheme, acting through redox metallo-chemistry to catalyze the formation of toxic oligomers of alpha-synuclein and neurotoxic metabolites including 6-hydroxydopamine. It has been hypothesized that these feed the cycle of neurodegeneration by generating further oxidative stress. The goal of dissecting and understanding the observed pathological changes is to identify therapeutic targets to mitigate the progression of this debilitating disease.

Beta frequency synchronization in basal ganglia output during rest and walk in a hemiparkinsonian rat

Synchronized oscillatory neuronal activity in the beta frequency range has been observed in the basal ganglia of Parkinson's disease patients and hypothesized to be antikinetic. The unilaterally lesioned rat model of Parkinson's disease allows examination of this hypothesis by direct comparison of beta activity in basal ganglia output in non-lesioned and dopamine cell lesioned hemispheres during motor activity. Bilateral substantia nigra pars reticulata (SNpr) recordings of units and local field potentials (LFP) were obtained with EMG activity from the scapularis muscle in control and unilaterally nigrostriatal lesioned rats trained to walk on a rotary treadmill. After left hemispheric lesion, rats had difficulty walking contraversive on the treadmill but could walk in the ipsiversive direction. During inattentive rest, SNpr LFP power in the 12-25 Hz range (low beta) was significantly greater in the dopamine-depleted hemisphere than in non-lesioned and control hemispheres. During walking, low beta power was reduced in all hemispheres, while 25-40 Hz (high beta) activity was selectively increased in the lesioned hemisphere. High beta power increases were reduced by l-DOPA administration. SNpr spiking was significantly more synchronized with SNpr low beta LFP oscillations during rest and high beta LFP oscillations during walking in the dopamine-depleted hemispheres compared with non-lesioned hemispheres. Data show that dopamine loss is associated with opposing changes in low and high beta range SNpr activity during rest and walk and suggest that increased synchronization of high beta activity in SNpr output from the lesioned hemisphere during walking may contribute to gait impairment in the hemiparkinsonian rat.

Quantitative assessment of stereotyped and challenged locomotion after lesion of the striatum: a 3D kinematic study in rats

BACKGROUND

Although the striatum is in position to regulate motor function, the role of the structure in locomotor behaviour is poorly understood. Therefore, a detailed analysis of locomotion- and obstacle avoidance-related parameters was performed after unilateral lesion of the striatum in rats.

METHODS AND RESULTS

Using the three dimensional motion capture technology, kinematics of walking and clearing obstacles, head and body orientation were analyzed before and up to 60 days after the lesion. Recordings were performed in treadmill running rats with or without obstacles attached to the treadmill belt. The lesion, which was induced by the direct injection of the mitochondrial toxin malonate into the left caudoputamen resulted in the complete destruction of the dorsal striatum. During the first three days following the lesion, rats were unable to run on the treadmill. Thereafter, rats showed normal looking locomotion, yet the contralesional limbs exhibited changes in length and timing parameters, and were overflexed. Moreover, the head of lesioned rats was orientated towards the side of the lesion, and their postural vertical shifted towards the contralesional side. During obstructed running, the contralesional limbs when they were leading the crossing manoeuvre stepped on the obstacle rather than to overcome obstacle without touching it, yet more frequently with the forelimb than the hindlimb. Unsuccessful crossings appeared to be due to a paw placement farther away from the front of the obstacles, and not to an inappropriate limb elevation. Importantly, deficit in locomotor behaviour did not regress over the time.

CONCLUSION

Our results argue that the striatum of one hemisphere controls kinematics of contralateral limbs during stereotyped locomotion and plays a prominent role in the selection of the right motor program so that these limbs successfully cross over obstacle.

Kainic acid lesion-induced spatial memory deficits of rats

The effects of lesioning the ventral tegmental area (VTA) or substantia nigra (SN) neurons by means of bilateral stereotaxic microinjections of kainic acid (KA) (0.4 mM) were investigated to clarify the role of the VTA and the SN neurons in learning and memory processes. The present study demonstrates that KA in the SN and the VTA lesioned rats significantly decreased spontaneous alternation in Y-maze task, working memory and reference memory in radial 8 arm-maze task, suggesting effects on spatial memory performance. Our findings provide further support for the role of the VTA and the SN neurons in processing and storage of information.

Effects of nigral stimulation on locomotion and postural stability in patients with Parkinson's disease

The physiopathology of gait and balance disorders in Parkinson's disease patients is still poorly understood. Levodopa treatment and subthalamic nucleus (STN) stimulation improve step length and walking speed, with less effect on postural instability. These disorders have been linked to dysfunction of the descending basal ganglia outputs to brainstem structures. In this study, we evaluated the effects of stimulation of the substantia nigra pars reticulata (SNr), on locomotion and balance in Parkinson's disease patients. Biomechanical parameters and leg muscle activity were recorded during gait initiation in seven selected patients operated for bilateral STN stimulation, out of 204 stimulated patients, with one contact of each electrode located within the SNr. Step length, anteroposterior and vertical velocities of the centre of gravity were studied, with special reference to the subjects' ability to brake the centre of gravity fall before foot-contact, and compared to seven controls. In Parkinson's disease patients, five treatment conditions were tested: (i) no treatment, (ii) levodopa treatment, (iii) STN stimulation, (iv) SNr stimulation and (v) combined levodopa treatment and STN stimulation. The effects of these treatments on motor parkinsonian disability were assessed with the UPDRS III scale, separated into 'axial' (rising from chair, posture, postural stability and gait) and 'distal' scores. Whereas levodopa and/or STN stimulation improved 'axial' and 'distal' motor symptoms, SNr stimulation improved only the 'axial' symptoms. Compared to controls, untreated Parkinson's disease patients showed reduced step length and velocity, and poor braking just prior to foot-contact, with a decrease in both soleus (S) and anterior tibialis (AT) muscle activity. Step length and velocity significantly increased with levodopa treatment alone or in combination with STN stimulation in both natural and fast gait conditions, and with STN stimulation alone in the fast gait condition. Conversely, SNr stimulation had no significant effect on these measures in either condition. In the natural gait condition, no fall in the centre of gravity occurred as step length was low and active braking was unnecessary. In the fast gait condition, braking was improved with STN or SNr stimulation but not with levodopa treatment, with an increase in the stance leg S muscle activity. These results suggest that anteroposterior (length and velocity) and vertical (braking capacity) gait parameters are controlled by two distinct systems within the basal ganglia circuitry, representing respectively locomotion and balance. The SNr, a major basal ganglia output known to project to pontomesencephalic structures, is postulated as being particularly involved in balance control during gait.

New hypotheses about postural control support the notion that all dystonias are manifestations of excessive brain postural function

This paper postulates that all forms of the neurological movement disorder, dystonia, can be argued to reflect excessive function of one or more components of the brain postural system. This is based on four central arguments. First, because some forms of postural control are already known to be dynamic, rather than static, it is suggested that hyperkinetic dystonias reflect excessive function of dynamic postures, rather than abnormal movements. Second, the range of functional roles served by the postural system is hypothesized to include direct control of movement, suggesting a postural basis for task-specific dystonias. Third, by defining posture as a neural system that maintains body stabilization, it can be shown that the range of mechanical means of implementing stabilization, including co-contraction of antagonistic muscles, matches the range of presentations of dystonia. Fourth, it is shown that the above premises are able to account for previously unexplained observations in dystonia. Based on the inhibitory influence that stabilizing mechanisms exert on movement, it is suggested that the broad functional role that is here referred to as posture may be the function served by the indirect pathway of the basal ganglia. Specifically, it is proposed that this pathway centrally coordinates function of the distributed network of brain regions controlling posture and, in conjunction with the direct pathway, coordinates posture and movement.

Effects of pallidotomy on motor symptoms in an animal model of Parkinson's disease

The present study was designed to evaluate the motor effects of lesioning the internal globus pallidus in an animal model of Parkinson's disease. Fourty rats were divided into four groups (each of 10 rats) which received either unilateral 6-hydroxydopamine (6-OHDA) lesions of the medial forebrain bundle (mfb) plus sham surgery to the pallidum, sham surgery of mfb plus N-methyl-D-aspartate (NMDA) induced pallidal lesions, combined 6-OHDA mfb + NMDA pallidal lesions or sham surgery to both structures. Animals with 6-OHDA lesions developed significant ipsilateral biases in head position, body axis and circling after amphetamine challenge (all P < 0.05). Prominent contralateral deficits were present in sensorimotor response latency and contralateral circling was induced by apomorphine challenge (both P < 0.05). The addition of an NMDA pallidal lesion, improved the head position and body axis biases, as well as dopamine-agonist induced rotation and contralateral reaction time in a sensorimotor task (all P < 0.05). There was, however, a slight worsening of sensorimotor response on the ipsilateral side (P < 0.05). Pallidal lesions in the absence of 6-OHDA lesions produced contralateral head position and body axis biases (both P < 0.05). These data indicate that pallidotomy improves some, but not all aspects of parkinsonian motor dysfunction in an animal model of Parkinson's disease (PD).

Marmoset monkey models of Parkinson's disease: which model, when and why?

Parkinson's disease (PD) is a debilitating neurodegenerative disease, with clinical features of tremor, muscular rigidity and akinesia, occurring as a result of midbrain dopamine loss. The search for treatments has relied heavily on animal models of the disorder. The use of monkey models of PD plays a distinct role in the development and assessment of novel treatments. The common marmoset (Callithrix jacchus) is a popular New World monkey used in the search for new treatments. These monkeys are easy to handle and survive well in captivity. This review examines the advantages of using marmoset monkeys in PD research and examines the different models available with reference to their use in pre-clinical assessment for novel therapeutic treatments. The most common models involve the administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) or 6-hydroxydopamine (6-OHDA). Recently, selective cerebral transgenic over-expression of alpha-synuclein has also been attempted in marmosets as a potential model for PD. Each model has its advantages. The MPTP-based model in marmosets resembles the disease with regards to the neuroanatomy of neurotransmitter loss; the unilateral application of 6-OHDA allows for the assessment of more complex sensorimotor deficits due to the presence of an intact 'control' side; the over-expression of alpha-synuclein in the midbrain results in the slow onset of behavioural symptoms allowing for a pre-symptomatic time window. The appropriateness of each of these marmoset models for the assessment of treatments depends on several factors including the experimental aim of the study and whether emphasis is placed on the analysis of behavioural deficits.