MPTP Mouse Model
Mice that receive acute, chronic or subchronic administration of the pyridine toxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) selectively lose significant numbers of dopaminergic neurons in two midbrain structures, the substantia nigra (SN) and the ventral tegmental area (VTA). Loss of dopamine cells in the SN mimics the clinical condition of Parkinson’s disease and leads to motor dysfunction.
The dopaminergic loss in mouse VTA is of unknown relevance to Parkinson’s disease but may contribute to the cognitive deficits of Parkinson’s disease because of these neurons’ projections to the frontal cortex.
MPTP-treated mice are a suitable model to study motor deficits and the loss of dopaminergic neurons as well as possible influences of drugs on these parameters.
Figure 1: Open Field test. Animals were injected with 4 x 20 mg/kg MPTP or vehicle at one day. Two days after treatment, animals were tested in the Open field test for activity. n = 9-10 per group; unpaired t-test; Mean + SEM. ***p<0.001.
Figure 2. Tyrosine hydroxylase (TH) quantification in the substantia nigra after MPTP lesion. Animals were injected with 4 x 20 mg/kg MPTP or vehicle at one day. Six days after treatment, animals were sacrificed and the substantia nigra analyzed for TH levels. n = 3-5 per group; unpaired t-test; Mean + SEM. *p<0.05.
6-OHDA Lesion Model
Unilateral local application of 6-hydroxydopamine (6-OHDA), a neurotoxic substance that preferentially affects catecholaminergic neurons, is a well-established model for analyzing effects of loss of dopaminergic neurons in the substantia nigra pars compacta and their major target area, the dorsal striatum.
The advantage of unilateral lesions is two fold, I. the contralateral hemisphere serves as an internal control that facilitates comparison of lesion effects between individuals and experimental groups during histological analysis, and II. lesion efficacy in individual animals can be estimated prior to sacrifice using certain behavioral tests.
Figure 1. Coronal sections of 6-OHDA-injected mice. Tyrosine hydroxylase (TH) immunofluorescent labeling (upper picture). GFAP and TH immunofluorescent labeling to visualize astrocytosis (lower picture). Cpu: Caudate-Putamen; VTA: ventral tegmental area; SNpc: substantia nigra pars compacta. Arrows indicate injection canal.
Figure 2: Analysis of mice in the corridor test revealed that 6-OHDA injected mice preferred the right corridor side over the left while sham injected mice had no preference. n = 16-30; Mean + SEM. Two way ANOVA with Bonferroni’s post hoc test. ***p<0.001.
Haloperidol Induced Catalepsy
Catalepsy is a neuronal condition that can be observed in Parkinson’s disease, epilepsy, catatonia but also as adverse reaction to prescribed medications e.g. against schizophrenia. It is characterized by seizures with a loss of sensation and consciousness accompanied by rigidity of the body. By treating rats with the dopamine D2 receptor antagonist haloperidol, catalepsy can be acutely induced for several hours, mimicking the typical symptoms like loss of consciousness and rigidity.
Sprague Dawley rats were subcutaneously injected with 1 mg/kg Haloperidol. After 30 minutes, catalepsy was measured and additionally, animals showing a full catalepsy were treated orally with the positive compound or vehicle. Animals were retested for catalepsy at several time points after drug administration.
Catalepsy was evaluated by gently placing the front limbs of each rat over an 8 cm high horizontal bar; catalepsy was measured as time animals spent motionless. A cut-off time of 120 seconds was used.
Figure 1: Haloperidol-induced Catalepsy after treatment with a positive compound: Time animals spent rigid after s.c. treatment with 1 mg/kg haloperidol, followed by oral treatment with a positive compound. Animals were repeatedly tested for catalepsy. n = 10. Mean ± SEM. Two-way ANOVA with Bonferroni’s repeated measure post hoc test. ***p<0.001. T.I.: Test item / positive compound.