Dissecting the mesopontine tegmentum: Contributions of a specific neuronal population to sensory and motor processing
Russell, Ashley Lynn
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The MPT contains many nuclei, two of which are the PPTg and LDTg. These two nuclei are composed of cholinergic, glutamatergic and GABAergic neuronal subpopulations, each with a unique projection pattern and complexity. Previous research has shown a role for the PPTg and LDTg in motoric behaviors and sensorimotor gating. However, there are still wide gaps in our understanding of fundamental aspects of PPTg and LDTg function. Of the different neuronal subpopulations it is not known to what extent, and in which ways, they are involved in sensory and/or motor behaviors. To investigate this, cholinergic specific neuronal lesions (using Dtx-UII) or non-specific neuronal lesions (using Ibotenic acid [IBO]) were performed on male Sprague Dawley rats. Rats with PPTg, LDTg and sham lesions were subjected to a battery of behavioral tests to compare motor behaviors. Rotarod testing at an accelerating speed showed significant deficits at a time period post-surgery for both IBO and Dtx-UII PPTg lesion rats but no significant deficits at fixed speeds. By using the Vermicelli Handling Test it was found that IBO PPTg lesioned rats had preserved ability to perform fine movements, but increases in the frequency of abnormal adjustments possibly due to deficits in motor sequencing and control. Based on these results, deficits post PPTg or LDTg lesion do not appear to be in gross motor behaviors, rather fine motoric sequencing behaviors, perhaps alluding to a new role of the PPTg in behavioral functioning. By beginning to understand a functional role of the PPTg and LDTg in behavioral control, it will help to better understand the role of the MPT in disease, specifically, its role in Parkinson's disease.