<i>Vitamin</i> D₃ Receptor Activation Rescued Corticostriatal Neural Activity and Improved Motor-Cognitive Function in -D₂R Parkinsonian Mice Model

Abstract

Background: fourth generation antipsychotics have been implicated in the blockade of calcium signalling through inhibition of dopamine receptive sites on dopaminergic D 2 Receptor (D 3 R). As a result of the abnormal calcium signalling associated with D 2 R inhibition, changes occur in the motor and memory neural axis leading to the observed behavioural deficits after prolonged haloperidol. Thus, Vitamin D 3 receptor (VD 3 R), a calcium controlling receptor in the striatum can be targeted to relief the neurological symptoms associated with haloperidol (-D 2 R) induced PD. Aim: This study sets to investigate the role of VD3R activation in vitro and in vivo after haloperidol-induced Dopaminergic (D 2 R) blockade. In addition, we examined the associated neural activity and behavioural changes in parkinsonian and VDRA intervention mice. Methods: Dopaminergic D 2 R 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 VD 3 . 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 (-D 2 ) 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 (-D 2 /+VDR) when compared with the parkinsonian mice (-D 2 ). These animals (-D 2 /+VDR) also recorded an improvement in spatial working memory and motor function versus the Parkinsonian mice (-D 2 ). 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 (-D 2 /+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.