Figure 9: Inhibition of endogenous PK2 signalling by a receptor blocker exacerbates MPTP-induced toxicity in mice.

Mice were intraperitoneally injected with 18 mg kg⁻¹ MPTP or equal volumes of saline (vehicle), once daily for three consecutive days. PKRA7 (20 mg kg⁻¹ per day) was given i.p. 24 h before MPTP treatment and continued once daily for 10 consecutive days until euthanization. (a) TH-DAB immunostaining in the substantia nigra (SN) and striatum (× 2 magnification). Scale bar, 200 μm. (b,c) Stereological counts of TH-positive (b) and Nissl-positive (c) neurons in the SN of ventral midbrain. (d) Integrated density quantification of DAB immunostaining in the striatum. Data represented by group mean±s.e.m. of three mice per group using one-way ANOVA with Bonferroni post-test comparison and n=3 (^**P<0.01 and ^***P<0.001, relative to relevant control or MPTP-treatment groups). (e) Western blot analysis of SN samples probed for TH and its quantification (right panel) show reduced TH levels when PKRA7 is administered along with MPTP. Data represented by group mean±s.e.m. using one-way ANOVA with Bonferroni post-test comparison and five to seven mice per group (*P<0.05, ^**P<0.01 and ^***P<0.001, relative to control or MPTP-treated groups). (f) Compared with MPTP-alone, PKRA7 treatment significantly reduced striatal dopamine levels, as measured using high-performance liquid chromatography (HPLC). Data represented by group mean±s.e.m. using Student’s t-test with n=2–3 mice per group (*P<0.05, ^**P<0.01, and ^***P<0.001, relative to relevant control or MPTP-treatment groups). (g–i) Mice were tested for motor activities 7 days after the last dose of MPTP. (i) Representative movement tracks of mice are shown. Behaviour analysis showing horizontal activity (g) (Student’s t-test with n=7) and number of movements (h). Data represented as the mean±s.e.m. using one-way ANOVA with Bonferroni post-test comparison and n=7–8 mice per group (*P<0.05, ^**P<0.01).