Temel, Y. | Search bioRxiv

bioRxiv2019

Serotonergic treatment normalizes midbrain dopaminergic neuron increase after periaqueductal gray stimulation-induced anticipatory fear in a rat model

BackgroundElectrical stimulation of the dorsolateral periaqueductal gray (dlPAG) in rats has been shown to elicit panic-like behaviour and can be a useful tool for modelling anticipatory fear and agoraphobia.\n\nMethodsIn this study, we further analysed our previous data on the effects of escitalopram (a selective serotonin reuptake inhibitor, SSRI) and buspirone (a 5-HT1A receptor partial agonist) on dlPAG-induced anticipatory fear behaviour in a rat model using freezing as a measure. We then used tyrosine hydroxylase (TH) immunohistochemistry to probe the effects on dopaminergic neurons.\n\nResultsAlthough acute treatment of escitalopram, but not buspirone, was effective in reducing anticipatory freezing behaviour, chronic administrations of both drugs were comparably effective. We found that the number of dopaminergic neurons in the ventral tegmental area (VTA) was lowered in both chronic buspirone and escitalopram groups. We showed a strong correlation between the number of dopaminergic neurons and freezing in the VTA. We further showed positive correlations between dopaminergic neurons in the VTA and substantia nigra pars compacta in escitalopram and buspirone groups, respectively.\n\nLimitationsAlthough our data strongly hint to a role of dopaminergic mechanisms in the dlPAG induced fear response, more in-depth studies with larger sample sizes are needed to understand the neuronal mechanisms underlying the interactions between serotonergic drugs and dopaminergic cell number and fear behavior.\n\nConclusionChronic treatment with an SSRI and a 5-HT1A agonist decrease the number of dopaminergic neurons in the VTA. These effects seem to be associated with reduced dlPAG-induced anticipatory freezing behaviour.\n\nKey PointsO_LIChronic treatment of escitalopram and buspirone was effective in reducing dlPAG induced anticipatory freezing behaviour.\nC_LIO_LIThe number of dopaminergic neurons in the ventral tegmental area (VTA) was lowered in both chronic buspirone and escitalopram groups and was correlated to freezing.\nC_LIO_LIWe found positive correlations between dopaminergic neurons in the VTA and substantia nigra pars compacta in escitalopram and buspirone groups, respectively.\nC_LI

neuroscience↗

bioRxiv2019

Cortico-basal white matter alterations occurring in Parkinson’s disease

Magnetic resonance imaging studies typically use standard anatomical atlases for identification and analyses of (patho-)physiological effects on specific brain areas; these atlases often fail to incorporate neuroanatomical alterations that may occur with both age and disease. The present study utilizes Parkinsons disease and age-specific anatomical atlases of the subthalamic nucleus for diffusion tractography, assessing tracts that run between the subthalamic nucleus and a-priori defined cortical areas known to be affected by Parkinsons disease. The results show that the strength of white matter fiber tracts appear to remain structurally unaffected by disease. Contrary to that, Fractional Anisotropy values were shown to decrease in Parkinsons disease patients for connections between the subthalamic nucleus and the pars opercularis of the inferior frontal gyrus, anterior cingulate cortex, the dorsolateral prefrontal cortex and the pre-supplementary motor, collectively involved in preparatory motor control, decision making and task monitoring. While the biological underpinnings of fractional anisotropy alterations remain elusive, they may nonetheless be used as an index of Parkinsons disease. Moreover, we find that failing to account for structural changes occurring in the subthalamic nucleus with age and disease reduce the accuracy and influence the results of tractography, highlighting the importance of using appropriate atlases for tractography.

neuroscience↗