Relationship of the ipsilateral rotation in night period and striatal dopamine content reduction in unilateral nigrostriatal 6-OHDA lesioned rats

Emerging preclinical interest concerning the role of circadian function in Parkinson's disease

The importance of circadian function in the aetiology, progression and treatment of Parkinson's disease is a topic of increasing interest to the scientific and clinical community. While clinical studies on this theme are relatively new and limited in number there are many preclinical studies which explore possible circadian involvement in Parkinson's disease and speculate as to the mechanism by which clinical benefit can be derived by manipulating the circadian system. The present review explores the sequelae of circadian related studies from a historical perspective and reveals mechanisms that may be involved in the aetiology and progression of the disease. A systematic review of these studies also sets the stage for understanding the basic neuroscientific approaches which have been applied and provides new direction from which circadian function can be explored.

Acute intranigral homocysteine administration produces stereotypic behavioral changes and striatal dopamine depletion in Sprague–Dawley rats

Homocysteine has been considered a major risk factor for cardiovascular diseases, and patients with hyperhomocystinemia exhibit neurological and psychological abnormalities. Elevated level of this molecule in the blood of Parkinson's disease patients receiving long-term l-DOPA therapy prompted us to investigate whether homocysteine is neurotoxic to the nigrostriatal dopaminergic system in Sprague-Dawley rats. Animals infused unilaterally with different doses of homocysteine (0.25-1 micromol in 1 microl) intranigrally exhibited significant and dose-dependent decrease in dopamine levels in the ipsilateral striatum as assayed employing an HPLC coupled with electrochemical detector, 19 days post-infusion. While 3,4-dihydroxyphenylacetic acid level in the striatum showed a dose-dependent decrease, homovanillic acid was found to be inhibited only for the highest dose. Amphetamine administration in these animals on the 14th day caused stereotypic turning behavior ipsilateral to the side of infusion. Apomorphine challenge on the 16th day elicited stereotypic contralateral circling behavior. Neurotransmitter levels in the serotonergic perikarya or terminals were unaltered 19 days following intraraphe infusion of homocysteine, which suggested the specificity of its action to dopaminergic neurons. These results indicate nigrostriatal lesions similar to that observed following intranigral infusion of the dopaminergic neurotoxin, 6-hydroxydopamine and suggest its closeness to the parkinsonian animal model. Furthermore, these findings provide evidence for the neurotoxic nature of homocysteine to dopaminergic neurons and suggest that elevated level of this molecule in parkinsonian patients may be conducive to accelerate the progression of the disease.

Behavioral differences in a rotenone-induced hemiparkinsonian rat model developed following intranigral or median forebrain bundle infusion

A mitochondrial complex-I inhibitor, rotenone was unilaterally infused into the substantia nigra pars compacta (SNpc) or median forebrain bundle (MFB) to create hemiparkinsonian animal models and investigated spontaneous and drug-induced stereotypic rotations, as well as certain postural behaviors in Sprague-Dawley rats. Animals infused intranigrally, but not intra-MFB, with rotenone exhibited spontaneous contralateral rotations immediately after recovery from anesthesia. Head position bias and elevated body swing test showed insignificant contralateral bias in animals with nigral damage but a significant ipsilateral bias in MFB-lesioned rats. General motor activity of the animals was reduced in both the groups as indicated by reduced performance on a Plus-Maze. Intranigrally, rotenone-infused animals exhibited progressive ipsilateral rotations when challenged with d-amphetamine on the 7th, 14th, 21st, and 28th days or with apomorphine on 9th, 16th, 23rd, and 30th days. However, animals that received rotenone in MFB exhibited ipsilateral or contralateral rotations when challenged respectively with d-amphetamine or apomorphine only in the 5th week (28th and 30th days). Stereotaxic administration of rotenone into SNpc or MFB caused a significant loss of dopamine in the ipsilateral striatum (>80% in SNpc; >95% in MFB), when assayed employing an HPLC equipped with electrochemical detector on the 32nd day. Neuronal loss in SNpc was confirmed in coronal sections stained with cresyl violet and revealed extension of lesion towards SN pars reticulata, in SNpc-infused animals. Our results demonstrate that rotenone-induced neurodegeneration is a slow, yet progressive process similar to that in idiopathic Parkinson's disease and unlike that observed in other classical neurotoxin-mediated lesions which are abrupt and developed in few hours to days. Thus, intranigral or intra-MFB infusion of rotenone could be used for producing hemiparkinsonian animal models in rats. These findings further suggest that, while both d-amphetamine and apomorphine-induced stereotypic rotations could be used as a valuable behavioral assay procedure to test novel drugs against Parkinson's disease, yet apomorpine-induced contralateral bias in turning is a reliable indicator of specific destruction in nigrostriatal pathway and development of postsynaptic dopamine receptor supersensitivity.

Pharmacokinetic and pharmacodynamic analyses, based on dopamine D2-receptor occupancy of bromocriptine, of bromocriptine-induced contralateral rotations in unilaterally 6-OHDA-lesioned rats

Bromocriptine is a selective agonist for dopamine D2-receptors and is used in the treatment of Parkinson's disease. In this study, we performed pharmacokinetic and pharmacodynamic (PK/PD) analyses of the antiparkinsonian effect of bromocriptine and evaluated drug-induced contralateral rotations in rats in which unilateral striatal lesions had been generated by microinjection of 6-hydroxydopamine (6-OHDA) into the medial forebrain bundle. The plasma concentration (Cp) and D2 receptor occupancy (Phi(D2)) were quantitated by HPLC and with an in vivo back-titration method using [(3)H]-raclopride, respectively. Bromocriptine induced contralateral rotations (E(rot)) in a dose-dependent manner following intraperitoneal administration in an animal model of Parkinson's disease. The Cp of bromocriptine peaked at 15-30 min after the administration and decreased time-dependently, whereas the Phi(D2) of bromocriptine increased gradually for 180 min after administration. The relationship between Cp and E(rot) exhibited an anticlockwise hysteresis, whereas the relationship between Phi(D2) and E(rot) showed a linear correlation. These results suggest that in vivo Phi(D2) is a good pharmacological indicator of the effect of a D2 agonist.

Behavioural sensitization in 6-hydroxydopamine-lesioned rats is related to compositional changes of the AP-1 transcription factor: evidence for induction of FosB- and JunD-related proteins

Rats with unilateral dopamine denervation exhibit turning behaviour in response to the selective D1 agonist SKF 38393 only after a previous exposure to dopamine agonists. We demonstrate here that this 'priming' phenomenon is related to both an increased expression of the pre-existing AP-1 complex and the occurrence of novel AP-1 complexes which are formed by FosB- and JunD-related proteins. While the former protein is expressed as a consequence of the dopamine denervation, the latter is related to the first exposure to a dopamine agonist. Pre-treatment with MK-801, an antagonist for glutamatergic receptors, prevents both the priming development and the AP-1 compositional changes. Rotational behaviour induced by SKF 38393 closely correlates with the presence of the priming AP-1 complexes, regardless of the capability of the D1 agonist to induce the immediate-early gene cFos.

Effect of MK 801 on priming of D1-dependent contralateral turning and its relationship to c-fos expression in the rat caudate-putamen

In rats with a unilateral 6-hydroxydopamine lesion of the ascending dopamine neurons, we investigated the relationship between the expression of Fos-like immunoreactivity in the caudate-putamen and contralateral turning behavior in response to dopamine agonists during the induction and expression of sensitization (priming) to D1-dependent turning behavior. Priming was induced by apomorphine (0.1 mg/kg s.c.) or by SKF 38393 (10 mg/kg s.c.) 14 days after 6-hydroxydopamine lesions and was expressed by challenge with SKF 38393 (3 mg/kg s.c.). In the induction phase of priming, administration of MK 801 (0.1 mg/kg s.c.) potentiated contralateral turning but differentially influenced stimulation of Fos expression in the caudate-putamen by apomorphine and by SKF 38393. Thus, MK 801 reduced in the expression phase of priming the stimulation of Fos expression by apomorphine in the dorsolateral caudate-putamen, but did not affect that by SKF 38393. MK 801, while preventing priming of SKF 38393-induced turning by apomorphine, failed to affect priming by SKF 38393. MK 801, given with apomorphine in the induction phase, reduced the stimulation of Fos expression in the dorsolateral caudate-putamen by SKF 38393. No such inhibitory effect of MK 801 on SKF 38393-stimulated Fos expression was observed in rats primed with SKF 38393. These results are consistent with the possibility that MK 801 disrupts sensitization of D1 transduction by reducing the activation of c-fos by the DA agonist during the induction phase of priming.