Gregory L. Willis

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)

Ventricular, paraventricular and circumventricular structures involved in peptide-induced satiety

Cholecystokinin, bombesin or gastrin (2 microliter of 50 ng/microliter) was injected stereotaxically into the paraventricular nucleus of the hypothalamus, the arcuate/ventromedial area, the subfornical organ, the area postrema and the cerebral aqueduct of Sprague-Dawley rats and the effects of these injections on food and water intake were studied. While the injection of cholecystokinin reduced food intake when it was injected into both hypothalamic loci, food and water intake were most severely affected by the injection of this peptide into the cerebral aqueduct. Bombesin reduced food intake after its injection into all areas except the subfornical organ and reliable reductions in water intake were seen after injection of this peptide into all areas except the paraventricular nucleus. Minor reductions in food intake were seen following gastrin injection into the paraventricular nucleus while increased water consumption was observed after this peptide was injected into the paraventricular nucleus and cerebral aqueduct. In a second study 6-hydroxydopamine injections (2 microliter of 8 micrograms/microliter were made into the five areas studied 10 days before animals were injected with 100 micrograms/kg of cholecystokinin (i.p.). All 6-hydroxydopamine-injected animals reduced their food and water intake in response to the cholecystokinin challenge as did intact controls. These results indicate that while the changes in food and water intake produced by the central injection of cholecystokinin, bombesin or gastrin may involve central catecholamine systems, those occurring after its systemic administration do not. Therefore, if the release of gastrointestinal peptides during natural feeding is part of a homeostatic mechanism regulating hunger and satiety, this mechanism may operate without directly involving central catecholamine systems.

Recovery of experimental Parkinson's disease with the melatonin analogues ML-23 and S-20928 in a chronic, bilateral 6-OHDA model: a new mechanism involving antagonism of the melatonin receptor

Over the past 10 years, there has been a resurgence of interest in examining the role of melatonin in health and disease. While the brunt of research in this area has portrayed melatonin in a favorable light, there is a growing body of evidence suggesting that melatonin may possess adverse effects contributing to the development of various neuropsychiatric disease states. In preclinical models of Parkinsons disease (PD), melatonin has been shown to enhance the severity of this condition while its antagonism, using constant light or pinealectomy, facilitates recovery. To test this hypothesis further, the present study employed the melatonin analogues ML-23 and S-20928 in a post-6-OHDA injection regime to determine whether they may have a favorable effect on the symptoms of this more chronic model of PD. When ML-23 was injected I.P. in a dose of 3 mg/kg twice daily for 3.5 days after 6-OHDA, significant improvement in motor function and regulatory deficits was observed. Similarly, the injection of S-20928 in a 1 mg/kg dose (I.P.), in the same regimen, facilitated modest improvement in motor function and regulatory deficits while the larger dose enhanced the severity of behavioural deficits and produced severe side effects causing deterioration in condition during the course of drug administration. ML-23 administration totally abolished the 6-OHDA-induced mortality, which accompanies dopamine (DA) degeneration, while S-20928 had no effect on this parameter. These results suggest that some melatonin analogues can aid in recovery from DA depleting lesions after DA degeneration has commenced and the recovery is not attributable to the antioxidative properties of this hormone. While the exact mechanism by which ML-23 and S-20928 are exerting their therapeutic effect is unclear, it is possible that antagonism of melatonin receptors may play some role and this should be considered when assessing the potential of melatonin analogues for treatment of human neuropsychiatric disorders.

Amine accumulation in behavioural pathology

When nigro-striatal and meso-cortical neurons degenerate there is a loss of dopamine in the terminal fields and an accumulation of amines in the axons of these systems as they traverse the hypothalamus through the medial forebrain bundle. Traditional lines of thought have attributed the occurrence of motor and consummatory deficits which occur after dopamine neuron degeneration to the loss of functional dopamine neurotransmitter in the terminal fields. However, we have hypothesized that hypothalamic amine accumulation represents an area of brain tissue where processes such as neurotransmitter release, ephaptic transmission or local axon swelling may be affecting adjacent neurons and may thereby participate in the production of behavioural deficits. There is a considerable amount of evidence from studies on both peripheral and central catecholamine-containing neurons indicating that when their axons degenerate a release of functional neurotransmitter can occur. Information from neuropharmacological studies indicates that several drugs which facilitate behavioural recovery from dopamine-depleting lesions may do so by affecting amine release or receptor sensitivity near areas of accumulation rather than depleted terminal fields. We conclude that amine accumulation is a component of dopamine neuron degeneration which should be considered when assessing the role of the central catecholamine systems in the control of various behavioural and physiological processes.

Deficits in locomotor behaviour and motor performance after central 6-hydroxydopamine or peripheralL-DOPA

Intracerebral injections of 6-hydroxydopamine (6-OHDA) which produce deficits in locomotor behaviour and motor performance cause localized accumulation of monoamines as well as depletion of central catecholamines (CA). To determine whether the localized increases in monoamines could be contributing to the behavioural deficits seen after intracerebral 6-OHDA injection, the behavioural and biochemical effects of peripherally administered L-DOPA were compared to those which occurred after central injections of 6-OHDA. Forty-five minutes after the injection of 40 mg/kg of L-DOPA, in animals pretreated with 50 mg/kg of R04-4602, the ability to step down, to retract a limb and to ambulate were significantly impaired. Locomotor behaviour and body temperature of L-DOPA-injected animals were similar to those displayed by animals receiving intracerebral injections of 6-OHDA. Fluorescent histochemical and biochemical assessment of diencephalic and telencephalic CA revealed that depletion of CA was not related to the severity of the motor deficits which occurred, but that increased diencephalic CA were present in impaired animals injected with either 6-OHDA or L-DOPA. These findings support the contention that increased CA in degenerating hypothalamic neurones may contribute to behavioural deficits seen after the injection of 6-OHDA.

The behavioural effects of intrahypothalamic multistage versus single injections of 6-hydroxydopamine

16 micrograms of 6-hydroxydopamine were injected bilaterally into the lateral hypothalamus of male Sprague-Dawley rats in either a single injection or in a series of multistage injections over a period of 75 days. While the single injection produced behavioural deficits typical of those seen following catecholamine depletion of the forebrain, the behaviour of animals injected incrementally with the same dose was indistinguishable from that of controls. Fluorescent histochemical assessment revealed that the animals in the multistage injection group, the behaviourally unimpaired, suffered more severe depletion of forebrain catecholamines than those in the single-stage injection group. Accumulation of amines proximal to the site of drug injection was extensive only in those animals displaying behavioural deficits, that is, the group with the lesser amount of forebrain catecholamine depletion. It is suggested that the severity of deficits in consummatory and motor behaviour occurring after hypothalamic trauma is determined by a lesions effectiveness in producing amine accumulation rather than catecholamine depletion.

The role of some central catecholamine systems in cholecystokinin-induced satiety

Cholecystokinin (CCK), bombesin and gastrin were stereotaxically injected into catecholamine (CA) innervated areas of the lateral hypothalamus (LH), the nucleus caudatus putamen (NP) and the olfactory tubercle (OT) in male Sprague Dawley rats. Bilateral injections of 100 ng of CCK in 2 microliters of vehicle into the LH produced a slight but significant decrease in food intake during the first hour of a 4 hour eating test. The other peptides when injected into any of the brain areas did not significantly alter food intake. Water intake was affected by the injection of all three hormones although differentially in all 3 sites. The observed changes in drinking were not related to the prandial characteristics of drinking typically seen in rodents. Denervation of the CA innervation of the OT, LH or NP with 6-hydroxydopamine did not change the satiety response to peripherally administered CCK displayed by intact animals. These results suggest that the satiety which occurs after the central and peripheral administration of CCK may be mediated by different mechanisms and that central CA systems may not be necessary for CCK-induced satiety to occur during natural feeding.

A role for amine accumulation in the syndrome of ingestive deficits following lateral hypothalamic lesions.

Lesions of the lateral hypothalamus produce ascending catecholamine neuron degeneration which results in terminal depletion and proximal accumulation above the lesions. The occurrence of deficits in ingestive behaviour has been attributed traditionally to the loss of functional dopamine neurotransmitter in the terminal fields. However, release of functional amines may occur in the lateral hypothalamus at areas of accumulation, to produce at least some of the behavioural symptoms characterizing the lateral hypothalamic syndrome. Recovery from behavioural deficits as a result of various pharmacological treatments, after dopamine-depleting lesions, may be mediated by changes in amine release or modified sensitivity of receptors affected by released amines. We conclude that amine accumulation should be considered when interpreting experiments implicating central catecholamine systems in the control of consumatory behaviour and the regulation of body weight.

Intraocular microinjections repair experimental Parkinson's disease.

Circadian involvement in Parkinsons disease (PD) and more specifically in nigro-striatal dopamine (NSD) function is of increasing interest to the neurosciences. Given that bright light therapy is of therapeutic value in PD, possible mechanisms underlying retinal involvement in this phenomenon was explored further by administering anti-Parkinsonian chemotherapies into the vitreus humour directly adjacent to the retina. 2 microl of a 100 mM solution of L-Dopa significantly improved motor function in the later stages of degeneration and during the day while the injection of 2 microl of a 10 mM solution of the melatonin receptor antagonist ML-23 improved motor function in the early stages of PD and during the dark phase of the light/dark cycle. The results suggest that the function of nigral cells is regulated by a more global system embracing circadian physiology that extends from the retina to the pineal. Furthermore, the induction of PD is characterised by an imbalance between melatonin and dopamine (DA) whereby this ratio is elevated at least 6 to 1 in favour of melatonin. The commonly observed treatment failures and side effects of DA replacement therapy probably result from increasing endogenous DA without taking parallel melatonin dysfunction into account. The proposed integrated function of the NSD and circadian systems may permit therapeutic targeting at a level which is safer, more effective and without the side effects of systemically administered regimens of DA replacement.

Short-term effects of intrahypothalamic colchicine.

Colchicine was injected in the vicinity of the medial forebrain bundle to cause an accumulation of catecholamines in the lateral hypothalamus proximal to the injection site. Such injections caused severe deficits in consummatory behavior and motor performance within a few hours after injection, which were accompanied by the accumulation of catecholamines in the hypothalamus. Behavioural deficits occurring within 24 h after colchicine injection cannot be attributed to reduced synaptic transmission in the striatum or to dopamine depletion because these events do not commence until 24-48 h after colchicine administration. This study demonstrates the importance of considering all neurochemical changes which accompany catecholamine depletion when assessing the role of the catecholamine-containing system in the regulation of behaviour.