Systemic Rotenone Administration Causes Extra-Nigral Alterations in C57BL/6 Mice

Abstract

Systemic administration of rotenone replicates several pathogenic and behavioural features of Parkinson’s disease (PD), some of which cannot be explained by deficits of the nigrostriatal pathway. In this study, we provide a comprehensive analysis of several neurochemical alterations triggered by systemic rotenone administration in the CNS of C57BL/6 mice. Mice injected with either 1, 3 or 10 mg/kg rotenone daily via intraperitoneal route for 21 days were assessed weekly for changes in locomotor and exploratory behaviour. Rotenone treatment caused significant locomotor and exploratory impairment at dosages of 3 or 10 mg/kg. Molecular analyses showed reductions of both TH and DAT expression in the midbrain, striatum and spinal cord, accompanied by altered expression of dopamine receptors and brain-derived neurotrophic factor (BDNF). Rotenone also triggered midbrain-restricted inflammatory responses with heightened expression of glial markers, which was not seen in extra-nigral regions. However, widespread alterations of mitochondrial function and increased signatures of oxidative stress were identified in both nigral and extra-nigral regions, along with disruptions of neuroprotective peptides, such as pituitary adenylate cyclase-activating polypeptide (PACAP), vasoactive intestinal peptide (VIP) and activity-dependent neuroprotective protein (ADNP). Altogether, this study shows that systemic rotenone intoxication, similarly to PD, causes a series of neurochemical alterations that extend at multiple CNS levels, reinforcing the suitability of this pre-clinical model for the study extra-nigral defects of PD.

Downregulation of PACAP and the PAC1 Receptor in the Basal Ganglia, Substantia Nigra and Centrally Projecting Edinger–Westphal Nucleus in the Rotenone model of Parkinson’s Disease

“…We assume this corresponds to a true cell loss because the lower cell counts cannot be explained by lower intensity PAC1R immunoreactivity, as PAC1R SSD values did not show significant changes. The counting of dopaminergic neurons also proved the cell loss in the SNpc, which further supported the validity of the model [17,31,44,45,72]. Indeed, systemic [23] intracerebroventricular [59] or intra-SNpc [32,33] PACAP administration has a neuroprotective effect via upregulation of its receptors [58,73].…”

“…When studying our results, one may come to the idea that the rotenone exposure induced a brain-wide decrease in the mRNA expression. Our results do not support this, because a nearly significant (p = 0.053) elevation of Adcyap1 mRNA expression occurred in the insular cortex that fits well with the observations of Broome et al [31] in the prefrontal cortex. Similarly, the count of Adcyap1 mRNA-expressing cells even increased in the neurons of SNpc that did not express TH, while the magnitude of expression was reduced in the dopaminergic neurons.…”

“…The approval of this awaits further experimentation, but similar mechanisms were demonstrated in cerebellar granular [68], PC12 [69] and brain microvascular endothelial cells [70]. In line with this, a large body of evidence in multiple species suggests the cytoprotective action of PACAP in various toxic models of PD including 6-OHDA [25,32], salsolinol [26], MPTP [27,28,71] or rotenone [29][30][31][32]; for reviews see [8,23].…”

“…The beneficial role of PACAP/PAC1R signaling in various models of neurodegenerative states including PD has been proven [6,23,24]. For example, toxicity studies on dopaminergic cell cultures revealed that the deleterious effect of 6-hydroxydopamine (6-OHDA) [25], salsolinol [26]; 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) [27,28], or rotenone [29][30][31] may be reversed by PACAP treatment (for a review see [8,23]). In vivo experiments further supported the evolutionarily conserved neuroprotective action of PACAP in various models of PD.…”