Urocortin Arrests the Development of Parkinsonian-like Features in Rat via CRF-R1 Receptors

Amjad Abuirmeileh1, Alex Harkavyi1, Rebecca Lever1, Christopher Biggs2, Peter Whitton1. 1The School of Pharmacy, London, United Kingdom, 2University of Westminster, London, United Kingdom.

Evidence suggests that the corticotrophin releasing factor (CRF) related peptide urocortin (UCN) confers neuroprotection in two distinct rat paradigms of Parkinson’s disease (PD) induced by intraceebral lipopolysaccharide (LPS) or 6-hydroxydopamine (6-OHDA; Abuirmeileh et al., 2007). These protective effects seem to be mediated via CRF receptors (CRF-R1 and/or CRF-R2) since they are prevented by the non-selective CRF receptor antagonist α-helical CRF. NBI-27914, is a CRF-R1 selective antagonist which we have now used in conjunction with UCN to determine its receptor selectivity in 6-OHDA lesioned rats. This was investigated by evaluating the integrity of the nigrostriatal system as indicated by striatal DA content and loss of the tyrosine hydroxylase (TH) positive neurons in the substantia nigra (SN).

Male Wistar rats (230-260g) were administered pargyline (50mg kg-1) and desmethylimipramine (25mg kg-1, i.p) in order to protect non-DA neurons prior to intracerebral 6-OHDA injection. Rats were injected with 8μg of 6-OHDA or vehicle into the left medial forebrain bundle and 7 days later were given intranigral UCN, NBI-27914 and/or vehicle ipsilaterally in the left SN. Rats were all decapitated 14 days after initial treatment. Brains were rapidly removed and processed for DA determination as previously described (Biggs et al., 2006). The rest of the brains were then sliced (12 μm thickness) at the level of the SN for immunohistochemical visualization of TH+ cells. Data were statistically analysed using one way ANOVA followed by post hoc Dunnet’s t-test where appropriate (n = 6 per group).

In 6-OHDA treated rats striatal DA level was reduced by 91 ± 7 % in comparison to shams but only 26 ± 5 % after UCN co-administration. The CRF-R1 specific antagonist NBI-27914 reversed the preservation of DA content by UCN (84 ± 8 % reduction). Given alone NBI-27914 caused no apparent reduction in striatal DA compared with shams. Immunohistochemical studies revealed very clear and substantial changes in the numbers of nigral TH+ cells. Thus, 6-OHDA alone caused a reduction such that no TH+ cells were readily apparent compared with extensive staining in sham treated animals. UCN, given 7 days after 6-OHDA, led to a substantial preservation or possible de novo genesis of TH+ cells in lesioned rats to a level comparable to shams but this effect was entirely reversed by co-treatment with NBI-27914. NBI-27914 alone had no apparent effect on TH+ cell numbers in the nigra.

In accord with our previous findings UCN prevented or reversed key features of intranigral 6-OHDA neurotoxicity. Our current data clearly suggest that this is a receptor specific effect, mediated via the CRF-R1 subtype. The finding that NBI-27914 had no effect alone suggests that there is unlikely to be a tonic effect of UCN in intact animals. These findings may be significant for the development of new therapies in PD treatment.

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