Autoradiographic labelling of 5-HT3 receptors in the hemi-parkinsonian rat brain

The anti-dyskinetic effect of the clinic-ready mGluR2 positive allosteric modulator AZD8529 in the 6-OHDA-lesioned rat

L-3,4-dihydroxyphenylalanine (L-DOPA) remains the main treatment for motor symptoms of Parkinson's disease (PD). However, chronic use is associated with the development of complications such as L-DOPA-induced dyskinesia. We previously demonstrated that LY-487,379, a highly selective metabotropic glutamate receptor 2 (mGluR2) positive allosteric modulator (PAM), reduces the severity of L-DOPA-induced abnormal involuntary movements (AIMs) in the 6-hydroxydopamine (6-OHDA)-lesioned rat model of PD, without interfering with the anti-parkinsonian action of L-DOPA. Here, we seek to determine the effect of AZD8529, another highly selective mGluR2 PAM, on L-DOPA-induced AIMs in the 6-OHDA-lesioned rat. Unlike LY-487,379, AZD8529 has previously undergone clinical trials and could therefore be repurposed if proven efficacious in pre-clinical studies. We first determined the pharmacokinetic (PK) profile of AZD8529 to administer doses leading to clinically relevant plasma levels in the behavioural studies. Then, dyskinetic 6-OHDAlesioned rats were administered AZD8529 (0.1, 0.3, and 1 mg/kg) or vehicle in combination with L-DOPA followed by assessment of AIMs severity. The cylinder test was then used to evaluate the effect of AZD8529 on the anti-parkinsonian action of L-DOPA. We found that AZD8529 (0.1, 0.3 and 1 mg/kg) in combination with L-DOPA significantly reduced the severity of AIMs duration (P < 0.05), but not amplitude, when compared to L-DOPA/vehicle. AZD8529 administration did not interfere with L-DOPA anti-parkinsonian action. Our results provide evidence that mGluR2 positive allosteric modulation with AZD8529 may be a viable, yet relatively modest, treatment strategy to alleviate L-DOPA-induced.

Phytoconstituents Targeting the Serotonin 5-HT3 Receptor: Promising Therapeutic Strategies for Neurological Disorders

The 5-hydroxytryptamine-3 receptor (5-HT3R), a subtype of serotonin receptor, is a ligand-gated ion channel crucial in mediating fast synaptic transmission in the central and peripheral nervous systems. This receptor significantly influences various neurological activities, encompassing neurotransmission, mood regulation, and cognitive processing; hence, it may serve as an innovative target for neurological disorders. Multiple studies have revealed promising results regarding the beneficial effects of these phytoconstituents and extracts on conditions such as nausea, vomiting, neuropathic pain depression, anxiety, Alzheimer's disease, cognition, epilepsy, sleep, and dyskinesia via modulation of 5-HT3R in the pathophysiology of neurological disorder. The review delves into a detailed exploration of in silico, in vitro, and in vivo studies and clinical studies that discussed phytoconstituents acting on 5-HT3R and attenuates difficulties in neurological diseases. The diverse mechanisms by which plant-derived phytoconstituents influence 5-HT3R activity offer exciting avenues for developing innovative therapeutic interventions. Besides producing an agonistic or antagonistic effect, some phytoconstituents exert modulatory effects on 5-HT3R activity through multifaceted mechanisms. These include γ-aminobutyric acid and cholinergic neuronal pathways, interactions with neurokinin (NK)-1, NK2, serotonergic, and γ-aminobutyric acid(GABA)ergic systems, dopaminergic influences, and mediation of calcium ions release and inflammatory cascades. Notably, the phytoconstituent's capacity to reduce oxidative stress has also emerged as a significant factor contributing to their modulatory role. Despite the promising implications, there is currently a dearth of exploration needed to understand the effect of phytochemicals on the 5-HT3R. Comprehensive preclinical and clinical research is of the utmost importance to broaden our knowledge of the potential therapeutic benefits associated with these substances.

[3H]-NFPS binding to the glycine transporter 1 in the hemi-parkinsonian rat brain

L-3,4-dihydroxyphenylalanine (L-DOPA) is the main treatment for Parkinson's disease (PD) but with long term administration, motor complications such as dyskinesia are induced. Glycine transporter 1 (GlyT1) inhibition was shown to produce an anti-dyskinetic effect in parkinsonian rats and primates, coupled with an improvement in the anti-parkinsonian action of L-DOPA. The expression of GlyT1 in the brain in the dyskinetic state remains to be investigated. Here, we quantified the levels of GlyT1 across different brain regions using [3H]-NFPS in the presence of Org-25,935. Brain sections were chosen from sham-lesioned rats, L-DOPA-naïve 6-hydroxydopamine (6-OHDA)-lesioned rats and 6-OHDA-lesioned rats exhibiting mild or severe abnormal involuntary movements (AIMs). [3H]-NFPS binding decreased in the ipsilateral and contralateral thalamus, by 28% and 41%, in 6-OHDA-lesioned rats with severe AIMs compared to sham-lesioned animals (P < 0.01 and 0.001). [3H]-NFPS binding increased by 21% in the ipsilateral substantia nigra of 6-OHDA-lesioned rats with severe AIMs compared to 6-OHDA-lesioned rats with mild AIMs (P < 0.05). [3H]-NFPS binding was lower by 19% in the contralateral primary motor cortex and by 20% in the contralateral subthalamic nucleus of 6-OHDA-lesioned rats with mild AIMs animals compared to rats with severe AIMs (both P < 0.05). The severity of AIMs scores positively correlated with [3H]-NFPS binding in the ipsilateral substantia nigra (P < 0.05), ipsilateral entopeduncular nucleus (P < 0.05) and contralateral primary motor cortex (P < 0.05). These data provide an anatomical basis to explain the efficacy of GlyT1 inhibitors in dyskinesia in PD.