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Gangli della base e comportamento: funzioni dei neuroni striatali nei meccanismi di motivazione e ricompensa
No full textParticipation of the pedunculopontine tegmental nucleus in arousal-demanding functions
Full text linkThe temporal context of certainty-uncertainty modulates the subthalamic nucleus-mediated anticipatory responding
No full text"Lesions of the subthalamic nucleus (STN) in the rat are known to induce anticipatory responses in the. preparatory period preceding conditioned movements. This study aimed to investigate how the temporal. context in which a stimulus is presented affects the anticipatory responding caused by a unilateral STN. lesion. A reaction-time task was employed in which a trigger signal starting a bar-pressing movement. was presented at either side of the head in two temporal contexts. In the first, the trigger was presented. at a fixed delay (FD paradigm) of 1 s following an instruction signal. In the second, the 1 s delay was. randomly distributed (RD paradigm) among other delays. Reaction time was faster in the FD paradigm. with respect to the RD paradigm. An increased readiness to move was observed in animals engaged in. the RD paradigm as the delay period shortened, and this function was not abolished by the STN lesion.. Anticipatory responding in general was less pronounced than in other paradigms previously reported. in the literature, and predominated in the RD paradigm with respect to the FD paradigm. The destruction. of the STN worsened the anticipatory responding only in the FD paradigm. A major consequence of the. STN lesion was an increase of unconditioned responses to the instruction signal starting each trial. This. attention deficit was more pronounced in the RD paradigm with respect to the FD paradigm, and was. subsequently worsened by the lesion in both paradigms.. The results suggest that the anticipatory responding may depend on the level of uncertainty implicit in. each behavioural paradigm whereas inappropriate responding to the behavioural cue starting a trial may. be independent from this factor, and highlight the importance of the behavioural paradigms employed. when dealing with STN functions.
Continuous stimulation of the pedunculopontine tegmental nucleus at 40Hz affects preparative and executive control in a delayed sensorimotor task and reduces rotational movements induced by apomorphine in the 6-OHDA parkinsonian rat
No full textLow-frequency pedunculopontine nucleus stimulation affects sensorimotor performance and reduces rotational movements induced by dopaminergic drugs in a parkinsonian rat model
No full textCholinergic input from the pedunculopontine nucleus to the cerebellum: implications for deep brain stimulation in Parkinson′s disease
Full text linkUnilateral lesions of the pedunculopontine nucleus do not alleviate subthalamic nucleus-mediated anticipatory responding in a delayed sensorimotor task in the rat
No full textLesions of the subthalamic nucleus (STN) in the rat are known to cause anticipated movements in behavioral tasks requiring a preparatory period before the execution of externally cued conditioned movements. In the present study, we describe the effects of lesions of the pedunculopontine nucleus (PPN), a structure located on the outflow of the STN to lower brainstem and spinal motor nuclei, on the anticipatory responding caused by a unilateral lesion of the STN in a delayed sensorimotor task. Rats were instructed to keep a lever pressed down by the presentation of a composite visual and acoustic signal, and were required to hold the lever pressed until a trigger stimulus occurred after an unpredictable delay. The trigger stimulus required the animals to release the lever and to press a second lever for food reinforcement. The task was evaluated according to analysis of movement parameters and errors made by the animals during the preparative and executive phases of the conditioned movement. An ibotenate lesion was placed into the STN in either side of the brain. This lesion was followed 3 weeks later by an ibotenate lesion of the PPN ipsilaterally to the STN previously lesioned. The results indicate that the anticipatory responding induced by the STN lesion was not alleviated by the subsequent PPN lesion. However, the animals bearing the combined lesion were severely impaired in conditioned responding to salient stimuli involved in the paradigm and showed side-specific lengthening of reaction and movement times without global motor impairments. The results suggest that the anticipatory responses caused by STN lesions do not require the intervention of the PPN and that the disruption of the dopaminergic nigrostriatal pathway following the combined lesion may be responsible for impairments observed
The pedunculopontine nucleus projection to the parafascicular nucleus of the thalamus: an electrophysiological investigation in the rat
No full textExtracellular electrophysiological recordings of neurons of the parafascicular nucleus of the thalamus were done in normal rats and in rats bearing lesions of either the cerebellar nuclei or the entopeduncular nucleus to investigate the functional control of the pedunculopontine nucleus on the parafascicular nucleus. A total of 97 neurons were recorded in the parafascicular nucleus in intact rats, 83 in rats bearing a chronic electrolytic lesion of the ipsilateral deep cerebellar nuclei, and 69 in rats bearing an ibotenate lesion of the ipsilateral entopeduncular nucleus. Lesions of the cerebellar nuclei or the entopeduncular nucleus were made to evaluate the participation of cerebellothalamic fibers or of polysynaptic basal ganglia circuits in the responses recorded in parafascicular neurons following electrical microstimulation of the ipsilateral pedunculopontine nucleus. Two types of excitation and one type of inhibition were the main responses observed in neurons of the parafascicular nucleus following stimulation of the pedunculopontine nucleus. The first type of excitation, observed in 49.5% of neurons recorded in normal rats, had an onset of 1.8 +/- 0.6 ms, lasted 9.2 +/- 0.8 ms and was able to follow high frequency stimulation over 300 Hz. The second type of excitation, observed in a smaller percentage of neurons recorded (3.1%), was a long-latency (8.3 +/- 0.7 ms) activation lasting 19.0 +/- 4.5 ms. It did not follow stimulation frequencies higher than 50-100 Hz. The inhibitory response was observed in 17.5% of the neurons recorded. The latency of this inhibition was 4.5 +/- 1.8 ms and the duration 41.9 +/- 6.8 ms. In rats bearing a lesion of the deep cerebellar nuclei or of the entopeduncular nucleus, the short-latency activation was still present in 24.1% and 31.9% of neurons recorded, respectively. However, the occurrence of the long-latency excitation rats bearing lesions of either the cerebellum or the entopeduncular nucleus increased to 12.1% and to 17.4%, respectively, while the occurrence of the inhibition rose to 22.9% and to 28.9%. These results show that an excitatory influence on the parafascicular nucleus is exerted by the pedunculopontine nucleus irrespectively of the presence of cerebellofugal fibers. This influence appears to be also independent from the integrity of basal ganglia circuits having a relay at the level of the entopeduncular nucleus. However, the variety of responses recorded suggests that the influences of the pedunculopontine nucleus on the parafascicular nucleus are by far more complex than those exerted on its basal ganglia targets such as the substantia nigra. The results are discussed according to a model of functioning of pedunculopontine fibers directed to thalamic and basal ganglia nucle
Recovery of the focusing action of nigral dopamine on corticostriatal transmission in the reinnervated striatum of the rat
No full textThe function of the pedunculopontine nucleus in the preparation and execution of an externally-cued bar pressing task in the rat
No full textIn the present study the role of the pedunculopontine nucleus (PPN) in the preparation and execution of an externally-cued rewarded motor act was investigated. Animals were instructed to press down a lever at the presentation of a combined visual and acoustic signal and were required to hold down the lever until a trigger stimulus occurred after an unpredictable delay ranging from 2 to 4 s. The trigger stimulus required animals to release the lever and to press a second lever for food reinforcement. The time between instruction and trigger signals represented the preparation phase preceding movement. Unilateral ibotenic acid-induced focal degeneration of pedunculopontine neurons did not influence either reaction and movement times, or capacity of the animals to correctly respond to presentation of stimuli of behavioral significance. On the contrary, bilateral lesions increased both reaction and movement times, and dramatically reduced the percentage of correct responses. The analysis of incorrect responses suggested that the most striking deficit exhibited by the animals following the bilateral lesion was a lack of conditioned response to the signal initiating each trial. However, the animals retained the capability to respond correctly in some trials, and were able to collect the reward when delivered outside the behavioral context. Histological analysis of lesions showed that in addition to loss of neurons within the pedunculopontine region, reduction of tyrosine-hydroxylase positive neurons had occurred in the pars compacta of the substantia nigra. The data suggest that the PPN is involved in the preparation and execution of externally-cued movements, and demonstrate that its destruction mimics the main effects produced by the dopaminergic denervation of the dorsal striatum
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