Changes in Tyrosine Hydroxylase Activity and Dopamine Synthesis in the Nigrostriatal System of Mice in an Acute Model of Parkinson's Disease as a Manifestation of Neurodegeneration and Neuroplasticity

Abstract

The progressive degradation of the nigrostriatal system leads to the development of Parkinson's disease (PD). The synthesis of dopamine, the neurotransmitter of the nigrostriatal system, depends on the rate-limiting enzyme, tyrosine hydroxylase (TH). In this study, we evaluated the synthesis of dopamine during periods of neurodegradation and neuroplasticity in the nigrostriatal system on a model of the early clinical stage of PD. It was shown that the concentration of dopamine correlated with activity of TH, while TH activity did not depend on total protein content either in the SN or in the striatum. Both during the period of neurodegeneration and neuroplasticity, TH activity in SN was determined by the content of P19-TH, and in the striatum it was determined by P31-TH and P40-TH (to a lesser extent). The data obtained indicate a difference in the regulation of dopamine synthesis between DA-neuron bodies and their axons, which must be considered for the further development of symptomatic pharmacotherapy aimed at increasing TH activity.

Keywords: MPTP model; Parkinson’s disease; mice; neurodegeneration; neuroplasticity; phosphorylation; tyrosine hydroxylase.

Figure 1

The scheme of the experiments for assessing: (A) the concentration of DA in the striatum as well as the content of TH and its phosphorylated forms at serine at positions P19-, P31-, and P40-TH and (B) the activity of TH during inhibition of DAA in the striatum and substantia nigra during the period of neurodegeneration (from −2 h to 6 h after MPTP injections) and neuroplasticity (24 h) in the nigrostriatal system in an early clinical PD model. DA—dopamine, HPLC-ED—high-performance liquid chromatography with electrochemical detection; L-DOPA—L-3,4-dihydroxyphenylalanine; MPTP—1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine; NSD-1015—3-hydroxybenzylhydrazine; TH—tyrosine hydroxylase; SN—substantia nigra, WB—Western blot.

Figure 2

The concentration of DA (A), DOPAC (B), HVA (C), and 3MT (D) in the striatum of the control and 2 h after 2 × 12 mg/kg of MPTP and 3, 6, and 24 h after 4 × 12 mg/kg of MPTP. The results are presented as percentages of those of the control (100%). * p < 0.05 compared with the control (saline). ** p < 0.05 compared with selected MPTP groups.

Figure 3

The DA turnover calculated by DOPAC/DA (A), HVA/DA (B), and 3MT/DA (C) in the striatum of the control and 2 h after 2 × 12 mg/kg of MPTP and 3, 6, and 24 h after 4 × 12 mg/kg of MPTP. The results are presented as percentages of those in the control (100%). * p < 0.05 compared with the control (saline). ** p < 0.05 compared with selected MPTP groups.

Figure 4

(A) The concentration of L-DOPA in the striatum upon inhibition of AADC by NSD-1015 (100 mg/kg 30 min before decapitation) of the control and 2 h after 2 × 12 mg/kg of MPTP and 3, 6, and 24 h after 4 × 12 mg/kg of MPTP. (B) The content of L-DOPA in the SN upon inhibition of AADC by NSD-1015 (100 mg/kg 30 min before decapitation) of the control and 3, 6, 24 h after 4 × 12 mg/kg of MPTP. The results are presented as percentages of those in the control (100%). * p < 0.05 compared with the control (saline). ** p < 0.05 compared with selected MPTP groups.

Figure 5

(A) Western blot representation of TH, P31-TH, P40-TH, and P19-TH immunoreactivity in the striatum of the control and 2 h after 2 × 12 mg/kg of MPTP and 3, 6, and 24 h after 4 × 12 mg/kg of MPTP. (B–E) Bar graph representation of TH (B), P31-TH (C), P40-TH (D), and P19-TH (E) in the striatum of the control (saline) and 2 h after 2 × 12 mg/kg of MPTP and 3, 6, and 24 h after 4 × 12 mg/kg of MPTP. The results are presented as percentages of those in the control (100%). * p < 0.05 compared with the control (saline). ** p < 0.05 compared with selected MPTP groups.

Figure 6

(A) Western blot representation of TH, P31-TH, P40-TH, and P19-TH immunoreactivity in the SN of the control and 3, 6, and 24 h after 4 × 12 mg/kg of MPTP. (B–E) Bar graph representation of TH (B), P31-TH (C), P40-TH (D), and P19-TH (E) in the SN of the control (saline) and 3, 6, and 24 h after 4 × 12 mg/kg of MPTP. The results are presented as percentages of those in the control (100%). * p < 0.05 compared with the control (saline). ** p < 0.05 compared with selected MPTP groups.

Figure 7

The quantity of DA neuron cell bodies and content of DA in the SN, the quantity of terminals of DA axons and DA concentration in the striatum in the control (saline) and during 24 h after 4 × 12 mg/kg of MPTP (the data adapted with permission from Ref. [29]). The figure was created using Biorender (www.biorender.com, the date of last access to the link is 14 June 2022).