Effects of locus coeruleus lesions on parkinsonian signs, striatal dopamine and substantia nigra cell loss after 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine in monkeys: a possible role for the locus coeruleus in the progression of Parkinson's disease

Attenuation of haloperidol-induced catalepsy by noradrenaline and L-threo-DOPS

In addition to impaired dopaminergic neurotransmission a dysfunctional noradrenergic system has been demonstrated in Parkinson's disease. L-threo-3,4-dihydroxyphenylserine (DOPS), a synthetic precursor of noradrenaline (NA), appears to be effective in the treatment of some akinetic symptoms in parkinsonian patients. In the present study the possible effect of DOPS was studied in rats, in which catalepsy was induced with haloperidol as a model for parkinsonian akinesia. Intravenous infusion of NA (1.5 and 15 micrograms/kg) or DOPS (2 and 4 mg/kg) in male Wistar rats (240-290 g) significantly decreased catalepsy. The effect of DOPS was abolished by pretreatment with the peripheral decarboxylase inhibitor benserazide (2 mg/kg). Pretreatment with Ro 40-7592, a catechol-O-methyltransferase inhibitor, potentiated and prolonged the anticataleptic effect of DOPS. The findings suggest a peripheral site of NA mediated anticataleptic action. Therapy with DOPS may be successful only without a peripheral decarboxylase inhibitor. Moreover, the therapeutic effect of DOPS may be potentiated by COMT inhibition.

Noradrenergic modulation of midbrain dopamine cell firing elicited by stimulation of the locus coeruleus in the rat

Electrical stimulation techniques were employed in the chloral hydrate anaesthetized male rat to evaluate if the pontine noradrenergic nucleus locus coeruleus can influence the activity of midbrain dopamine neurons in the ventral tegmental area and zona compacta, substantia nigra. Single-pulse locus coeruleus stimulation evoked an excitation, followed by an inhibition, of the electrical activity of single midbrain dopamine neurons. Neither of these responses were observed in animals pretreated with reserpine, implicating noradrenaline as a mediator. The alpha 1-adrenoceptor antagonist prazosin decreased the excitation, while other adrenoceptor antagonists were without general effect. Burst-type stimulation produced only a more long-lasting inhibition. The influence from the locus coeruleus on midbrain dopamine neurons could be important in behavioural situations involving novelty and reward, and might also be of importance for the actions of psychotropic drugs.

Disease-specific patterns of locus coeruleus cell loss

Computer visualization techniques were used to map and to quantitatively reconstruct the entire locus coeruleus, including the nucleus subcoeruleus, to compare the topographic patterns of cell loss in postmortem brains from patients with Parkinson's disease, Alzheimer's disease, and Down syndrome. There was comparable cell loss in all three diseases (approximately 60%) compared with aged normal subjects, and there was a significant loss of nucleus subcoeruleus cells specifically in patients with Parkinson's disease (63%). There was a significant positive correlation between the magnitude of locus coeruleus cell loss and the duration of Alzheimer's disease, but no such correlation was found for Parkinson's disease. In patients with Parkinson's disease, there was comparable cell loss throughout the rostral-caudal extent of the nucleus; however, in patients with Alzheimer's disease and Down syndrome, the greatest cell loss always occurred within the rostral portion of the nucleus, with a relative sparing of caudal cells. These data are consistent with the hypothesis that cell loss in Parkinson's disease is the result of a pathological process that attacks the catecholaminergic cells of the locus coeruleus and the subcoeruleus in general; in Alzheimer's disease and Down syndrome, however, the pathological process only affects the rostral, cortical-projecting locus coeruleus cells and spares the caudal, noncortical-projecting cells.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) reduces norepinephrine concentrations in the olfactory bulbs of male mice

Male retired breeder C57/Bl and CD-1 mice were treated with either MPTP or its vehicle. At 7-10 days post-treatment, catecholamine concentrations within the olfactory bulbs (OB) and hypothalamus were determined. Norepinephrine concentrations within the OB were significantly decreased in MPTP-treated mice. These effects were more pronounced in the CD-1 (50% reduction) compared to the C57/Bl (20% reduction) strain. No effects of MPTP were observed on norepinephrine concentrations within the hypothalamus. Dopamine concentrations in the OB and hypothalamus did not differ between MPTP- and vehicle-treated mice in either strain. Overall, catecholamine concentrations within the OB, but not the hypothalamus, were significantly greater in C57/Bl compared to CD-1 mice. The reduction in OB norepinephrine concentration in the MPTP-treated animals may be related to the olfactory deficits which accompany Parkinson's disease.

Accelerated communication α2-adrenoceptor antagonists block the stimulant effects of cocaine in mice

In the present study we have investigated the effects of the alpha 2-adrenoceptor antagonist idazoxan and its 2-ethoxy derivative RX811059 on the locomotor activity induced by cocaine in mice. The stimulant effects of cocaine (15 mg/kg i.p.) were significantly antagonised by idazoxan (3 mg/kg i.p.) and RX811059 (1 mg/kg i.p.) and also initially suppressed by idazoxan (1 mg/kg i.p.) and RX811059 (0.3 mg/kg i.p.). The alpha 2-adrenoceptor antagonists had no effect on locomotion when given alone. These results suggest that noradrenergic mechanisms may play a role in the stimulant effects of cocaine and that alpha 2-adrenoceptor antagonists like idazoxan may be of some benefit in the clinical management of cocaine abuse.

Suppression of nigrostriatal and mesolimbic dopamine release following noradrenaline depletion by DSP-4: A microdialysis study

Pretreatment of rats with the noradrenergic neurotoxin DSP-4 selectively reduced regional levels of noradrenaline in the brain by more than 75%, and decreased the concentration of endogenous DA in microdialysates of the caudate nucleus and nucleus accumbens by 52% and 28%, respectively. Results support the hypothesis that central noradrenergic mechanisms facilitate nigrostriatal and mesolimbic dopamine transmission in vivo.

Effects of an alpha 2 antagonist in a 20-year-old Java monkey with MPTP-induced parkinsonian signs

The study attempted to verify whether activation of locus coeruleus neurons by alpha 2 antagonists might improve parkinsonian signs. Treatment with the racemic alpha 2 antagonist R 47 243 of a monkey with MPTP-induced parkinsonian signs normalized blink rate, reduced resting tremor, and improved several other parkinsonian signs. In a second experiment, the (-)-isomer R 62 651 produced a gradual change in tremor which was the inverse of the mannner in which tremor had become installed as the result of progression earlier upon the MPTP challenge. It is proposed that further research be conducted to determine whether alpha 2 antagonists may beneficially influence the progression of Parkinson's disease.