A therapeutic role for melatonin antagonism in experimental models of Parkinson's disease.

To determine the effects of endogenous and exogenous melatonin on experimental models of Parkinson's disease (PD), Sprague-Dawley rats were exposed to intracerebroventricular implants of slow release melatonin, pinealectomy (PX), or constant light (LL) and then injected with central 6-hydroxydopamine (6-OHDA) or i.p. 1-methyl-4-phenyl,1-1,2,3,6-tetrahydropyridine (MPTP). The resulting impairment of motor function and related behavioural impairment were exacerbated by melatonin implantation, while PX and exposure to LL significantly reduced the severity of experimental PD. These results are consistent with previous work highlighting the importance of aberrant amine production in neurological disease and demonstrate that treatments that reduce endogenous melatonin bioavailability can ameliorate experimental PD. Furthermore, these findings illustrate that melatonin is not the universal remedy that it is currently claimed to be, and may pose considerable problems in neurological diseases characterised by dopamine degeneration.

Orphan neurones and amine excess: the functional neuropathology of Parkinsonism and neuropsychiatric disease.

The aetiology and treatment of Parkinsonism is currently conceptualised within a dopamine (DA) deficiency-repletion framework. Loss of striatal DA is thought to cause motor impairment of which tremor, bradykinaesia and rigidity are prominent features. Repletion of deficient DA should at least minimise parkinsonian signs and symptoms. In Section 2, based on extensive pre-clinical and clinical findings, the instability of this approach to Parkinsonism is scrutinised as the existing negative findings challenging the DA deficiency hypothesis are reviewed and reinterpreted. In Section 3 it is suggested that Parkinsonism is due to a DA excess far from the striatum in the area of the posterior lateral hypothalamus (PLH) and the substantia nigra (SN). This unique area, around the diencephalon/mesencephalon border (DCMCB), is packed with many ascending and descending fibres which undergo functional transformation during degeneration, collectively labelled 'orphan neurones'. These malformed cells remain functional resulting in pathological release of transmitter and perpetual neurotoxicity. Orphan neurone formation is commonly observed in the PLH of animals and in man exhibiting Parkinsonism. The mechanism by which orphan neurones impair motor function is analogous to that seen in the diseased human heart. From this perspective, to conceptualise orphan neurones at the DCMCB as 'Time bombs in the brain' is neither fanciful nor unrealistic [E.M. Stricker, M.J. Zigmond, Comments on effects of nigro-striatal dopamine lesions, Appetite 5 (1984) 266-267] as the DA excess phenomenon demands a different therapeutic approach for the management of Parkinsonism. In Section 4 the focus is on this novel concept of treatment strategies by concentrating on non-invasive, pharmacological and surgical modification of functional orphan neurones as they affect adjacent systems. The Orphan neurone/DA excess hypothesis permits a more comprehensive and defendable interpretation of the interrelationship between Parkinsonism and schizophrenia and other related disorders.

Amphetamine-induced rotational behavior in rats: relationship to hypothalamic and striatal degeneration.

When lesions are placed unilaterally in the nigrostriatal system of experimental animals, rotational behavior occurs in response to peripheral administration of dopamine (DA) agonists. In spite of considerable evidence to the contrary, it is assumed that in order for this rotation to occur, an almost complete depletion of striatal DA must be achieved. To test this hypothesis further, 20 male Sprague-Dawley rats were injected unilaterally with 2 microL of 8 micrograms/microL of 6-hydroxydopamine (6-OHDA) via acute injection needles or chronically indwelling cannulae. Acute injection of 6-OHDA resulted in a rotation rate of 7.2 to 18.9 revolutions per minute in response to peripheral amphetamine injection (5 mg/Kg) while injection of 6-OHDA through chronically indwelling cannulae produced rotation ranging from 1.4 to 9.9 rotations per minute. Under the conditions of either method of injection, the animals displaying the most severe rotation still showed partial denervation of striatal DA as revealed by catecholamine fluorescence histochemistry. Conversely, numerous animals demonstrating very low rates of amphetamine-induced rotation often displayed a complete loss of striatal, accumbens, and olfactory tubercle catecholamine fluorescence. Moreover, large quantities of lateral hypothalamic amine accumulation were observed in rotating rats indicating that this neurochemical change may be of functional significance for rotational responses. The present results, when taken into consideration with previous work, indicate that the routine selection of rotating animals for pharmacological testing for potential antiParkinsonian medication or intracerebral grafting purely on the basis of their rotational behavior does not necessarily imply that complete striatal denervation has occurred. Moreover, these findings demonstrate that amine accumulation in the lateral hypothalamus of rotating animals with DA depleting lesions is an important phenomenon implicated in the expression of rotational behavior in animals and possibly in the pathophysiology of Parkinson's disease.

Amine accumulation: a possible precursor of Lewy body formation in Parkinson's disease.

It is now well recognized that the hypothalamus is an important site of neuropathology in Parkinson's disease (PD). Lewy bodies, a marker of nerve cell degeneration and a pathological hallmark of PD, have been observed frequently in the hypothalamus of PD patients by Lewy (1923) and other investigators and confirmed by more recent systematic studies by Langston & Forno (1978). Both Lewy and Langston & Forno found a predilection of Lewy body formation in specific hypothalamic nuclei with the tuberomammillary, lateral, and posterior areas containing by far the highest average counts per nucleus. Selective vulnerability of the tuberomammillary, lateral, and posterior hypothalamic cell groups to degeneration has been observed also in aging, postencephalitic Parkinsonism, Alzheimer's disease, and schizophrenia. The susceptibility of these particular nuclei to degenerative changes including Lewy body formation is not presently understood nor are the mechanisms by which Lewy bodies are formed in PD and other CNS disorders. Accumulation of amines, a pathological process which follows degeneration of catecholamine-containing neurons in experimental animals, also occurs most frequently in the lateral and posterior hypothalamic areas. In the present communication we propose that in PD, amine accumulation may be a precursor to Lewy body formation and that the susceptibility of certain hypothalamic areas to Lewy body formation may be related to their propensity to accumulate amines. Furthermore, the frequent co-existence of Lewy bodies and Alzheimer's neurofibrillary tangles in the lateral and posterior hypothalamic nuclei suggest that they may share a common pathogenetic etiology. If confirmed, this hypothesis may provide an experimental model by which the formation of Lewy bodies and neurofibrillary tangles may be investigated.

Sensitivity of dopamine receptors in the lateral hypothalamus is altered in 6-hydroxydopamine treated rats.

Amine accumulation is observed in the lateral hypothalamus (LH) after nigrostriatal neurons degenerate. It has been proposed that this accumulation is a source of amines which are released into the hypothalamus thereby affecting the function of adjacent aminergic receptors. To approximate this condition of continuous exposure of LH receptors to endogenous amines, dopamine (DA) was injected into the LH of rats once daily for 5 consecutive days. A control group received 4 daily injections of tartaric acid vehicle and then DA on day 5. Rats pretreated with DA showed severe impairment of open field performance and motor reflex control on day 5 when they were compared to control animals which received vehicle pretreatment. In a second study, the DA receptor antagonist haloperidol was injected into the area of amine accumulation in the LH to determine whether this might block amine release from areas of accumulation thereby to attenuate lesion-induced rotation. Haloperidol administered once daily for 4 out of 7 days, once daily for 7 days or via a continuous infusion for 7 days, all reduced d,l-amphetamine-induced turning to control levels. These results suggest that prolonged exposure of hypothalamic DA receptors alters their sensitivity to subsequent doses of DA and that amine released from areas of accumulation may be blocked by haloperidol to enhance behavioral recovery from DA depleting lesions. Moreover, these findings indicate that the hypothalamus participates in the behavioral effects induced by DA depleting lesions and highlight the importance of hypothalamic pathology in Parkinson's disease.

Amelioration of experimental parkinsonism by intrahypothalamic administration of haloperidol.

Accumulation of amines in the degenerating axons of ascending catecholamine-containing neurons in the hypothalamus has been proposed as a site of function neurotransmitter release and may thereby participate in the development of motor impairment seen after central dopamine-depleting lesions. To test this hypothesis further the dopamine receptor antagonist haloperidol (1 microL of a 14 nmol solution) was injected directly into the lateral hypothalamus (LH) in 6 different injection regimes to determine whether amphetamine-induced turning could be attenuated with this treatment. The injection of haloperidol at 1 and 24 h (group 1), 24 h (group 2) or 6+ 7 d (group 3) after 6-hydroxydopamine (6-OHDA) did not modify amphetamine-induced turning. However, the injection of haloperidol at 1 h, 24 h, 7 d, and 8 d (group 4), days 1-7 (group 5), or gradual infusion (14 nmol/microliters/h) for 7 days (group 6) all reduced the 6-OHDA-induced turning to a level similar to that of controls. These results add further support to the contention that amines are released from the axons of degenerating neurones in the hypothalamus and that this phenomenon participates in the elicitation of behavioral impairment attributed solely to the loss of functional neurotransmitters from terminal fields. Furthermore, the data emphasize the importance of hypothalamic pathology in the development of Parkinsonism and suggest that intrahypothalamic administration of dopamine blocking agents might be useful in the treatment of Parkinsonism.

Changes in food intake and stomach contents of tumor-bearing rats after treatment with dopamine antagonists.

The appetite-stimulating (orexigenic) potential of the peripheral dopamine (DA) receptor antagonist domperidone was compared with that of the central DA antagonist pimozide in anorexic, tumor-bearing rats. DA antagonists were administered via the intraperitoneal route on Days 7-15 after the subcutaneous implantation of the Walker 256 carcinosarcoma. The doses of domperidone injected were 0.05 and 0.1 mg/kg once daily and 0.1 mg/kg twice daily. The dose of pimozide given was 0.1 mg/kg daily. While all doses of DA antagonists caused an initial drop in body weight and food intake, the body weight of pimozide-injected animals was not reduced significantly (in the early stages of drug treatment) as it was with the various doses of domperidone. There was significantly more food in the stomachs of domperidone- and pimozide-treated animals compared with those of the vehicle-treated, tumor-bearing animals at the time of sacrifice. These results indicate that short- and long-term satiety factors, in addition to gastric motility, should be considered when assessing the orexigenic potential of various drugs.

Observations on dopamine receptor antagonists and gastric ulceration associated with experimental anorexia cachexia.

Gastric ulceration is frequently reported to occur in tumour-bearing animals and man, even when such tumours are not associated with organs of digestion. That central and peripheral dopamine (DA) containing neurones may be relevant to this phenomenon, is supported by the fact that the DA receptor antagonists domperidone (0.1 and 0.05 mg/kg) and pimozide (0.1 mg/kg) were observed to prevent gastric ulceration commonly reported in rats bearing the Walker 256 carcinosarcoma. Daily administration of these drugs prevented the formation of ulcers similar to those observed in vehicle-treated animals. These results demonstrate that DA neurone function is important in the formation of gastric ulcers in tumour-bearing animals and suggest that such compounds may be useful in cancer management.

i.r. Beta-endorphin, corticosterone, cholesterol and triglyceride concentrations in rat plasma after stress, cingulotomy or both.

Plasma i.r. beta-endorphin, corticosterone, cholesterol and triglyceride concentrations were determined in male Sprague-Dawley rats after exposure to running or swimming stressors or after surgical ablation of the cingulum bundle. While cingulotomy alone altered only the plasma triglyceride concentrations, the combination of cingulotomy plus running stress significantly increased plasma i.r. beta-endorphin and triglyceride concentrations above those seen in animals receiving only a running stress. Triglyceride concentrations in cingulotomy plus swimming stress were significantly elevated above those in animals receiving a severe stress only. While the exposure to running and swimming increased plasma beta-endorphin significantly above control levels, plasma corticosterone was not affected by these stressors. Changes in plasma cholesterol and triglycerides were also differentially affected by cingulotomy or stress exposure. These results indicate that various stress hormones are affected differentially by exposure to various experimental procedures which are employed as stressors.

Facilitation of cancer-associated anorexia by cholecystokinin.

Cholecystokinin octapeptide (CCK-8, 5 micrograms/kg) was injected i.p. into male Sprague-Dawley rats bearing the Walker 256-carcinosarcoma, or into non-tumour bearing controls, on a 20-h food deprivation schedule. Food and water intake and body weight maintenance were monitored for 15 days after tumour implantation and compared to that of tumour-bearing animals not injected with CCK-8. Food intake was significantly reduced for the duration of the two 4-day periods of CCK-8 injection, indicating that behavioural tolerance to this peptide did not occur. The severity of anorexia and body weight loss in tumour-bearing animals was significantly greater than that observed in non-tumour bearing controls, for the first 13 days of observation. These results indicate that endogenous peptides, such as CCK, may function in tumour-bearing animals to enhance the anorexia and wasting which typifies the anorexia cachexia syndrome.

Amine accumulation, catecholamine depletion and motor impairment in Macaca fasicularis and the C-57 black mouse after MPTP administration.

1. Macaca fasicularis monkeys and C-57 black mice were injected with N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine in different injection regimes. 2. The performance of monkeys on a rapid alternating movement task was measured before, during and after drug injection. 3. The open field performance of C-57 black mice was assessed 0.5hr, 24hr and 7 days after the completion of the injection regime. 4. Only the monkey receiving the 2mg/kg dose over 8 days displayed progressive akinesia and muscular rigidity. 5. Only a very slight impairment of motor function was seen in the C-57 black mice 0.5hr after injection. 6. Fluorescent histochemical analysis revealed that while striatal depletion was severe in monkeys and mice, accumulation of amines was seen only in the brain tissue of the severely impaired monkey. 7. Degeneration-associated increases in amines are important in the aetiology of Parkinsonian-like motor impairment produced by selective neurotoxins across different species.

Cingulotomy in the rat fails to block opiate withdrawal effects but elevates stress-induced plasma beta-endorphin.

1. Male, albino, Sprague Dawley rats underwent surgical cingulotomy or sham operation and were then implanted with subcutaneous morphine pellets or exposed to forced running. 2. The conditions of cingulotomy or forced running alone did not cause a significant increase in plasma i.r. Beta endorphin concentrations. 3. The combined treatment of cingulotomy plus forced running caused a significant elevation of plasma beta-endorphin concentrations. 4. The cingulum is involved in the elicitation of stress hormone responses in the rat.

The function of lateral hypothalamic catecholamine and endorphin systems in the control of motor performance.

Morphine (1 or 10 micrograms in 1 microliter) or beta-endorphin (1 microgram in 1 microliter) were injected bilaterally into the posterior lateral hypothalamus of Sprague-Dawley rats to determine what effect they may have on motor performance. Severe reductions in open field performance and motor reflex control were observed after the injection of 1 microgram of beta-endorphin or morphine into this area. The injection of 10 micrograms of morphine into the same area was less effective in causing motor impairment. The central (32.7 micrograms in 1 microliter) and peripheral (2 mg/kg) injection of naloxone did not prevent the motor impairment observed after the injection of beta-endorphin or morphine. Pretreatment with 6-hydroxydopamine into the lateral hypothalamus in a multistage regime did not prevent the motor impairment observed after beta-endorphin or morphine injection. These results indicate that lateral hypothalamic participation in the control of motor function may not involve the ascending nigrostriatal and mesocortical dopamine systems and that endogenous opiate systems may function independently to influence motor performance.

MPTP, impairment of motor performance and amine accumulation in Macaca fascicularis.

The selective neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) was injected (IV) into monkeys (Macaca fascicularis) in two different injection regimes. With the small dose regime, one monkey was injected with 0.25 mg/kg, every other day, over a 16 day period. In the large dose regime, another monkey was injected with 0.5 mg/kg every other day, over an 8 day period. While the time required for drug delivery was varied between animals, the total dose delivered was 2 mg/kg in both animals. Before, during and for 14 days after the course of drug administration both animals were assessed on several motor function tests. The animal receiving the small dose regime showed normal motor performance on all tests for the duration of the study, however, the monkey receiving the large dose regime displayed progressive akinesia, muscular rigidity, and aphagia. In fact, impairment was so severe that this animal had to be force fed and maintained with daily oral L-dopa. Fluorescent histochemical assessment of forebrain in both monkeys revealed that striatal tissue was totally devoid of fluorescence in both cases. Large, swollen axons in the internal capsule, hypothalamus and midbrain were visible only in the severely impaired animal. These results suggest that, as with other neurotoxins, degeneration associated increases in amines may be important in the aetiology of Parkinson-like motor impairment produced by selective neurotoxins.

Cholecystokinin, behavioral tolerance and tumor-induced anorexia.

Cholecystokinin octapeptide (CCK-8, 5 micrograms/kg, IP) was injected daily, for two 4-day periods, into rats bearing the Walker 256 carcinosarcoma (TB) and non-tumor bearing (NTB) control animals. All animals were on a 20 hr food and water deprivation schedule and monitored for food and water intake and bodyweight for 4 hr daily. Food intake was significantly reduced by the daily administration of CCK. Behavioral tolerance to CCK was not observed in either the NTB or TB rats. These results indicate that the parameters describing the phenomenon of behavioral tolerance to CCK are yet to be clearly defined and that peptides other than CCK may underlie the mechanism primarily responsible for producing anorexia associated with cancer.

Histochemical, biochemical and behavioural consequences of MPTP treatment in C-57 black mice.

The histochemical, biochemical and behavioural consequences of MPTP administration in C-57 black mice was assessed 0.5 h, 24 h and 7 days after the last injection of this drug administered daily for 10 days during a 12 day period (30 mg/kg/injection or vehicle). A slight but significant impairment of open field performance was observed at 0.5 h after the last injection of MPTP while a facilitation of locomotory behaviour was observed only in the 24 h post-injection group. Striatal dopamine levels were reduced to 14, 18 and 27% of control levels in the 0.5 h, 24 h and 7 day post-MPTP treated groups, respectively. Histochemical assessment was in agreement with the biochemical assay results in that all MPTP treated animals showed severe depletion of striatal terminal fields. Other terminal fields were occasionally affected by MPTP treatment and only rarely was any change in the fluorescence or morphology of nigral cell bodies seen. Accumulation of amines in the degenerating amine-containing axons which traverse the lateral hypothalamus was not seen in any of the MPTP treated animals. These results indicate that, in the C-57 black mouse, MPTP causes a depletion of striatal dopamine without causing nigral cell loss or axon swelling as is observed with other experimental treatments such as 6-hydroxydopamine. Consistent with this is the behavioural data, indicating that severe deficits in motor function which are associated with nigrostriatal cell loss were not seen.(ABSTRACT TRUNCATED AT 250 WORDS)

Motor function in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-treated mouse.

Motor function was assessed by use of a swim test in C57 Black mice treated with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Thirty minutes after the last MPTP injection significant motor impairment was observed while striatal dopamine was reduced to 13.9% of control levels. At 24 h and 7 days post MPTP injection dopamine levels were still reduced to 17.3% and 26.4% of control values but swimming abilities of the mice were unimpaired. Histofluorescence of catecholaminergic neurons confirmed the presence of catecholamine depletion but showed little evidence of neuronal destruction. The use of MPTP as a non-invasive means of nigrostriatal dopamine depletion in rodents and higher animals allows a re-evaluation of the role of the dopaminergic system in the modulation of movement.

Further studies on the neurochemical specificity of 6-hydroxydopamine as compared to radiofrequency lesions.

Despite the large volume of literature during the past 15 years addressing the problem concerning the neurochemical specificity of 6-hydroxydopamine (6-OHDA), there is still disagreement over this issue. While some claim that the catecholamine-specific effects of this drug can be maximized by controlling the dose injected, others claim that all doses of 6-OHDA produce non-specific damage (NSD), thereby contraindicating its use in experimental paradigms. In the present study, we examined the degree of neurochemical specificity of 6-OHDA by comparing the volume of proximal accumulation to that of NSD, produced by 6-OHDA (2 microliter of 8 micrograms/microliter) or radiofrequency (RF) lesions (60 degrees C for 50 s and 45 degrees C for 30 s), placed in the medial forebrain bundle. The volume of NSD and accumulation produced by 6-OHDA was significantly less than that produced by large RF lesions which had a similar effect on the gross behaviour of albino rats. Smaller RF lesions produced similar volumes of NSD but less amine accumulation than did 6-OHDA, and did so without affecting normal behaviour. The ratio of NSD to accumulation in 6-OHDA treated rats was 3/1, while large and small RF lesions produced a NSD/accumulation ratio of 15/1. The present study introduces a novel method of determining the degree of neurochemical specificity which can be achieved with 6-OHDA and reveals that it is several magnitudes more neurochemically specific than RF lesions.

Amine accumulation in Parkinson's disease and other disorders.

Amine accumulation in the axons of degenerating, amine-containing neurones is a natural component of neurone death in many species, including man. While it is becoming increasingly clear that this phenomenon may have functional significance in animal models of Parkinson's Disease, its potential importance in the clinical syndrome has been pretermitted. There are several reasons for this. Failure to sample tissue which contains accumulated amines, the masking of accumulation by adjacent depleted tissues and the degradation of accumulated amines in post-mortem tissues from Parkinsonian brains could account for the low incidence of detection of accumulation in this disorder. Increased levels of amines have been detected in the brains of patients with other conditions including cerebral infarction, Alzheimer's Disease and Huntington's Chorea. These increases have been attributed previously to enhanced aminergic activity, rather than a stage in the degenerative process, as our hypothesis suggests. In addition to the potential importance of amine accumulation in the pathophysiology of various clinical syndromes, a more thorough investigation of this phenomenon in animal models would seem essential since they are used routinely to both describe the basic principles of dopamine function and to evaluate therapeutic possibilities in Parkinson's Disease.