<i>Vitamin</i>D₃Receptor Activation Rescued Corticostriatal Neural Activity and Improved Motor-Cognitive Function in -D₂R Parkinsonian Mice Model

Background: fourth generation antipsychotics have been implicated in the blockade of calcium signalling through inhibition of dopamine receptive sites on dopaminergic D2 Receptor (D3R). As a result of the abnormal calcium signalling associated with D2R inhibition, changes occur in the motor and memory neural axis leading to the observed behavioural deficits after prolonged haloperidol. Thus, Vitamin D3 receptor (VD3R), a calcium controlling receptor in the striatum can be targeted to relief the neurological symptoms associated with haloperidol (-D2R) induced PD. Aim: This study sets to investigate the role of VD3R activation in vitro and in vivo after haloperidol-induced Dopaminergic (D2R) blockade. In addition, we examined the associated neural activity and behavioural changes in parkinsonian and VDRA intervention mice. Methods: Dopaminergic D2R inhibition was investigated in vitro using Melanocytes isolated from the scale of a Tilapia. In four separate set ups, the cells were cultured in calcium free Ringer’s solution as follows;300 μM haloperidol, 100 μM VD3, 100 mM calcium chloride and a combination of 300 μM haloperidol and 100 μM VD3. Subsequently, dopaminergic vesicle accumulation and calcium signalling were observed in bright field microscopy using blue and green fluorescence probes. In the second phase, PD was induced in adult BALB/c mice (-D2;n = 8) after 14 days of intraperitoneal haloperidol treatment (10 mg/Kg). A set of n = 4 mice were untreated (-D2) while the other group (n = 4) received 100 mg/Kg of VD3 for 7 days (-D2/+VDR). The control groups (n = 4 each) were treated with normal saline (NS) and VD3 (+VDR) for 14 days. At the end of the treatment phase, the animals were assessed in Rotarod, parallel bar-, cylinder-, Y-Maze-, one trial place recognition- and novel object recognition-(NOR) tests. Neural activity was measured using chronic electrode implants placed in the M1 (motor cortex), CPu (striatum), CA1 (hippocampus) and PFC (prefrontal cortex). Neural activity was compared with the outcomes of behavioural tests for memory and motor functions and data was expressed as mean ± SEM (analysed using ANOVA with Tukey post-hoc test, significant level was set at 0.05). Results/Discussion: in vitro outcomes show that VDR increase calcium signalling and reverses the effect of haloperidol;specifically by reducing dopaminergic vesicle accumulation in the cell body. Similarly, in vivo neural recordings suggest an increase in calcium hyperpolarization currents in the CPu and PFC of intervention mice (-D2/+VDR) when compared with the parkinsonian mice (-D2). These animals (-D2/+VDR) also recorded an improvement in spatial working memory and motor function versus the Parkinsonian mice (-D2). These outcomes suggest the role of CPu-PFC corticostriatal outputs in the motor-cognitive decline seen in parkinsonian mice. Similarly, VDRA reduced the neural deficits through restoration of calcium currents (burst activities) in the intervention mice (-D2/+VDR). Conclusion: VDRA treatment reduced the motor-cognitive defects observed in haloperidol induced PD. Our findings suggest the role of VDRA in restoration of calcium currents associated with PFC and CPu corticostriatal outputs seen as burst frequencies in in vivo neural recording.

Vitamin D₃Receptor Activation Rescued Corticostriatal Neural Activity and Improved Motor Function in –D₂R Tardive Dyskinesia Mice Model

Haloperidol-induced dyskinesia has been linked to a reduction in dopamine activity characterized by the inhibition of dopamine receptive sites on D2-receptor (D2R). As a result of D2R inhibition, calcium-linked neural activity is affected and seen as a decline in mo-tor-cognitive function after prolonged haloperidol use in the treatment of psychotic disorders. In this study, we have elucidated the relationship between haloperidol-induced tardive dyskinesia and the neural activity in motor cortex (M1), basal nucleus (CPu), prefrontal cortex (PFC) and hippocampus (CA1). Also, we explored the role of Vitamin D3 receptor (VD3R) activation as a therapeutic target in improving motor-cognitive functions in dyskinetic mice. Dyskinesia was induced in adult BALB/c mice after 28 days of haloperidol treatment (10 mg/Kg;intraperitoneal). We established the presence of abnormal involuntary movements (AIMs) in the haloperidol treated mice (-D2) through assessment of the threshold and amplitude of abnormal involuntary movements (AIMs) for the Limbs (Li) and Orolingual (Ol) area (Li and Ol AIMs). As a confirmatory test, the dyskinetic mice (-D2) showed high global AIMs score when compared with the VD3RA intervention group (-D2/+VDR) for Li and Ol AIMs. Furthermore, in the behavioral tests, the dyskinetic mice exhibited a decrease in latency of fall (LOF;Rotarod-P 2/+VDR), 100 mg/Kg for 7 days, CPu-CA1 burst activity was restored leading to a decrease in abnormal movement, and an increase in motor function. Ultimately, we deduced that VD3RA activation reduced the threshold of abnormal movement in haloperidol induced dyskinesia.