Brain research
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Comparative Study
Time-course of changes in firing rates and firing patterns of subthalamic nucleus neuronal activity after 6-OHDA-induced dopamine depletion in rats.
The subthalamic nucleus (STN) plays a key role in motor control. Disorganization of its neuronal activity is implicated in the manifestation of parkinsonian motor symptoms. The aim of the present work was to study the time-course of changes in the firing activity of STN neurons in a rat model of parkinsonism. ⋯ Only 4% exhibited burst activity and 6% had mixed firing patterns. After SNc-lesion, the percentage of cells exhibiting burst and mixed patterns increased progressively from 35% during the first week to 56% at week 4 post-lesion. In sum, these experiments revealed that the firing rate of STN neurons was altered only transiently following nigral lesions, whereas a progressive and stable change in the firing pattern was observed up to 4 weeks post lesion, suggesting that the persistence of bursts firing more closely relates to the motor pathologies of this rat model of parkinsonism.
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The present study investigated the effect of lesions of the anterior cingulate cortex (ACC) on mechanical allodynia/hyperalgesia after L5 ligation or on inflammatory nociceptive responses following formalin injection in the rat. For both the neuropathic and inflammatory pain models, three groups of animals were used. The control groups consisted of a group of sham lesioned animals and a group of animals that had unilateral damage to the ACC or unilateral/bilateral damage to surrounding cortical tissue. ⋯ The difference between the groups was most prevalent in the amount of time spent licking the paw. However, ACC lesions did not significantly attenuate the enhanced mechanical paw withdrawal threshold in the neuropathic nociceptive model. These results suggest a differential role of the ACC in the modulation of different types of pain conditions.
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An acute pain animal model for fMRI study would provide useful spatial and temporal information for studying the supraspinal nociceptive neuronal responses. The aim of the present study was to investigate whether the nociceptive responses in different brain areas can be differentiated by using functional magnetic resonance imaging (fMRI) in anesthetized rats. Functional changes in brain regions activated by noxious or non-noxious stimuli of the sciatic nerve were investigated using fMRI in a 4.7 T MR system in alpha-chloralose anaesthetized rats. ⋯ These four brain areas activated by noxious stimuli were significantly suppressed by prior intravenous injection of morphine (5 mg/kg). The present findings demonstrated that the difference of the innocuous and nociceptive responses in the brain could be detected and localized by an in vivo spatial map using fMRI. Results suggest that fMRI may be an invaluable tool for studying pain in anesthetized animals.