Hypothalamic releasing factors and Parkinson disease

Antiparkinsonian activity of L-propyl-L-leucyl-glycinamide or melanocyte-inhibiting factor in MPTP-treated common marmosets

The neuropeptide melanocyte-inhibiting factor (MIF) or L-propyl-L-leucyl-glycinamide (PLG) has been reported in some studies to improve the motor signs of Parkinson's disease (PD) and in rodent models of PD. In this study of oral and intravenous MIF in N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned marmosets, a wide range of doses of MIF administered alone (0.25, 1, 2, 5, 10, 20 mg/kg orally) did not increase locomotor activity, relieve motor disability, or induce dyskinesias. When MIF (1.0 and 5.0 mg/kg orally or 10 and 20 mg/kg intravenously) was administered concomitantly with levodopa/benserazide, no significant differences in motor function or dyskinesias were observed compared with levodopa/benserazide alone. The results of this first study of MIF in the marmoset MPTP model provide no encouragement for the reinvestigation of MIF in the clinical management of the motor signs of PD.

TRH: behavioral and endocrine effects in man

1. The tripeptide TRH exerts a spectrum of biological activities in both animals and man. Some of these activities have been extensively studied, particularly in psychiatric patients. 2. Behaviorally, TRH appears to increase the sense of well-being, motivation, relaxation, and coping capacity in both normal subjects and patients with psychiatric and neurologic disease. These effects are not disease-specific; attempts to use TRH as a treatment tool have thus been disappointing. 3. Endocrinologically, administration of TRH stimulates the response of TSH; this response has been reported to be blunted in approximately 30% of patients with major depression. However, TSH blunting is not specific for depression, it has also been observed in a variety of other psychiatric conditions. 4. The relevance of these effects for psychiatry in general, and for psychoneuroendocrinology especially, is discussed in this review.

Cyclo (Leu-Gly) + haloperidol: effects on dopamine receptors and conditioned avoidance responding

Behavioral effects of cyclo (Leu-Gly) (cLG), administered either acutely or chronically, were assessed in combination with haloperidol in the rat. cLG administered chronically, produced a significant reduction in the increase in apomorphine-induced stereotypy produced by chronic haloperidol infusion. On the other hand, the same dose of cLG which reduced this induction of dopamine receptor supersensitivity due to chronic haloperidol treatment, failed to produce a change in the potency of haloperidol in blocking conditioned avoidance responding in the rat. Furthermore, degeneration-induced supersensitivity of dopamine neurons, produced by unilateral destruction of the nigrostriatal pathway, was not reduced by acute or chronic treatment with cLG as measured by apomorphine-induced rotation. These data suggest that cLG may decrease motor system side effects thought to be caused by chronic antipsychotic administration without affecting the therapeutic efficacy of the antipsychotic agent.

Active and inactive L-prolyl-L-leucyl glycinamide synthetic analogs in rat models of levodopa-treated Parkinson's disease

The tripeptide, L-prolyl-L-leucyl-glycinamide (PLG) has been shown to facilitate dopaminergic mechanisms in the brain. In the present study, we evaluated the interaction of PLG and its synthetic analogs with levodopa in two animal models of Parkinson's disease. In one experiment using rats with chronic unilateral lesions of the nigrostriatal dopamine pathway, PLG and Z-PLG potentiated the contraversive rotation elicited by levodopa with carbidopa (L/C). In a second experiment using reserpinized rats, PLG, Z-PLG and cyclo-LG potentiated L/C reversal of hypokinesia. Further studies of the PLG analogs, Z-PLG and cyclo-LG as adjunctive drugs with levodopa in the treatment of parkinsonism are warranted.

Behavioral effects of melanocyte stimulating hormone release-inhibiting factor-1 (MIF-1)

Consideration of the isolation, structure, localization, and behavioral effects of melanocyte stimulating hormone release inhibiting factor (MIF-1) is followed by a review of its opiate antagonistic and clinical effects. Evidence pertaining to various hypotheses offered in explanation of these behavioral effects is examined and evaluated. It is concluded that MIF-1 affects behavior in many instances with possible antagonistic effects as well as clinical possibilities.

Pituitary responses to a neuroactive tripeptide (TRH) in Friedreich's ataxia families

Oral glucose tolerance, thyroid function tests, as well as thyrotropin, prolactin and growth hormone release after administration of thyrotropin releasing hormone, were evaluated in patients with Friedreich's ataxia and unaffected family members. Impaired glucose tolerance was found in the majority of family members, affected or not. Thyroid hormone levels and PRL and TSH responses to TRH, were similar in all and normal. However, GH responses to TRH were abnormal in half of the patients, but in none of the unaffected family members. Paradoxical responses to neuropeptides may characterize some Friedreich's ataxia patients, and may predict the possibility of therapeutic maneuvers with such peptides in these patients.

Estradiol, TRH and striatal dopaminergic mechanisms

1. Estrogens have been shown to decrease the effect of apomorphine in a variety of animal behavioral models reflecting the sensitivity of striatal and mesolimbic dopamine receptors. 2. These include circling, and locomotor activity, in rats and suppression of midbrain tremor as well as lingual dyskinesia in monkeys. 3. Estradiol also increases the haloperidol-induced catalepsy in rats. Moreover estradiol increases 3H spiroperidol specific binding in the rat striatum and potentiates the increase caused by haloperidol or denervation with 6-hydroxydopamine. 4. These findings point to an action of estradiol similar to a week neuroleptic. 5. Thyrotropin-releasing hormone when injected into the head of the caudate nucleus in cats induces a head turning response which may be ipsilateral or contralateral depending upon the injection site. The response is similar to the effect of dopamine injected into the same site. 6. The effect of dopamine but not that of TRH is blocked by prior administration of haloperidol indicating that although TRH has a dopamine-like action in the caudate nucleus, it is not mediated via the dopamine terminals or the dopamine receptors.

The effects of prolyl-leucyl-glycine amide on drug-induced rotation in lesioned rats

1. The effects of L-prolyl-L-leucyl-glycine amide (PLG) on drug-induced rotational behavior were studied in rats with unilateral 6-hydroxydopamine (6-OHDA) lesions of the substantia nigra. 2. Although PLG alone was found to be ineffective at inducing rotation in these animals, pretreatment with PLG at various doses was found to enhance both amphetamine and apomorphine-induced rotation. 3. This response proved to be biphasic with loss of activity in the higher dose ranges. 4. The pattern of effects observed suggests that PLG may act postsynaptically at a non-striatal site.

Endocrine and behavioral changes in depression after thyrotropin-releasing hormone (TRH). Alteration by pretreatment with thyroid hormones

The effects of pretreatment with a single dose of thyroid hormones (TH) on the subsequent endocrine and behavioral response to TRH was evaluated in unipolar depressed women. TH pretreatment altered neither serum levels of thyroid hormones nor the TRH-induced TSH response. It antagonized, however, the behavioral response to TRH. This was apparent in 2 self-assessment scales but not in an objective rating scale. Taken together the data suggest that (a) there is an impaired pituitary response to TH feedback in depressed patients; (b) TH pretreatment may affect self-assessment of behavioral effects of TRH in depression.

Vasopressin therapy in Parkinson's disease

A double-blind crossover pilot study was carried out in six patients with Parkinson's disease in order to test the possible therapeutic effect of L-vasopressin after treatment for 1 month with 30 I.U. intranasally daily. The investigation was completed in five cases. No effects was noticed after LVP treatment.

MSH and MIF-I in animal models of tardive dyskinesia

alpha-Melanocyte stimulating hormone (MSH) and MSH release inhibiting factor (MIF-I) were tested for their effects on animals with prior exposure to haloperidol. Such animals are known to have an augmented sterotypic response to dopamine agonists and have been used as an animal model of tardive dyskinesia. Both MSH and MIF-I increased the stereotypy that followed the administration of the lowest dose of apomorphine (0.125 mg/kg), suggesting that MSH and MIF-I might weakly increase dopaminergic transmission.

Striatal dopamine turnover and MIF-I

Because of conflicting reports of the actions of the antiparkinsonian agent L-prolyl-L-leucyl-glycine amide (PLG, MIF-I) on the turnover of striatal dopamine (DA), this process was reinvestigated. In the present series of studies, it was found that neither our MIF-I (200 ng ICV) nor the MIF-I used by Versteeg et al. [25] was effective in altering the rate of decline of endogenous DA in the caudate nucleus of rats pretreated with alpha-methyl-p-tyrosine (300 mg/kg IP). In addition, our MIF-I (1 mg/kg IP) did not change endogenous dihydroxyphenylacetic acid (DOPAC) or homovanillic acid (HVA) in rat striatum. These studies indicate that MIF-I does not alter the turnover rate of DA in nigrostriatal neurons. It is possible that MIF-I or some substance released by MIF-I acts at a postsynaptic receptor site.

Failure of MIF-I to affect behavioral responses in patients with Parkinson's diseases under L-dopa therapy

In eight subjects with Parkinson's disease under an optimal daily dose of L-dopa, acute administration of MIF-I (200 mg i.v.) did not ameliorate either the total disability score or the intellectual test PM 38 when evaluated in comparison with the effect induced by acute administration of a placebo. Also concomitant evaluation of the effect of MIF-I on the secretion of anterior pituitary hormones which are under dopaminergic control i.e., growth hormone and prolactin, did not reveal any potentiation of the L-dopa-induced stimulus.

Potentiation of apomorphine action in rats by l-prolyl-l-leucyl-glycine amide

Although the antiparkinsonian activity of 1-prolyl-l-leucyl-glycine amide (PLG=MIF-I) has been previously observed in several clinical trials, little is known of the mechanism of action of this tripeptide on the brain. Our study demonstrated potentiation of the action of apomorphine by PLG on the rotational behavior of mature rats which received unilateral 6-OHDA (16 microgram) lesions of the striatum as neonates. No change in tyrosine hydroxylase or dopa decarboxylase activities in rat striatal homogenates was found after addition of PLG (10(-8-10(-3) M). The results suggest that PLG modifies the dopamine receptor, making it more responsive to stimulation by the agonistic agent apomorphine and perhaps by the natural neurotransmitter dopamine.

Endocrine aspects of bromocriptine therapy in Parkinsonism

Plasma growth hormone (GH) concentrations in Parkinsonian patients following 3 months optimum therapy with bromocriptine showed no significant change from pretreatment values, whilst plasma prolactin concentrations were uniformly suppressed. Pretreatment GH and prolactin levels were unrelated to clinical disability, and no correlation between hormonal changes and therapeutic response was found. These results suggest the presence of different dopaminergic receptor mechanisms for GH and prolactin release as well as between the extrapyramidal and neuroendocrine systems.

Comparison of thyrotropin-releasing hormone with melanocyte-stimulating-hormone-release-inhibiting factor as pentobarbital antagonists in monkeys

Thyrotropin-releasing hormone (TRH), 0.1 mg/kg, i.m., significantly counteracted pentobarbital narcosis in six monkeys, but melanocyte-stimulating-hormone-release-inhibiting factor (MIF), 0.1 mg/kg i.m., did not. Earlier dose-response studies in unanesthetized monkeys had shown that this dose of MIF stimulated motor activity; this dose of TRH had shown no stimulant effect, but a higher dose depressed activity. Thus, an MIF dose that stimulates unanesthetized monkeys does not reverse pentobarbital narcosis; a TRH dose that by itself is neither stimulant nor depressant does partially reverse pentobarbital narcosis.

Effect of a large dose of thyrotrophin releasing factor on pituitary and thyroid function in patients with Parkinsonism

Thyrotrophin releasing factor (TRF) was given intravenously in doses of 0-5 mg and 20 mg to six patients with Parkinsonism treated with L-dopa. Plasma thyrotrophin (TSH), prolactin, lutenizing hormone (LH), follicle stimulating hormone (FSH), thyroxine (T4) and triiodothyronine (T3) were measured before and after TRF infusion. The observation that FSH and LH did not change in response to either dose of TRF confirmed specificity of the effects TRF for certain anterior pituitary functions. The plasma TSH and prolactin levels achieved after 20 mg TRF were considerably greater and were maintained longer than those after 0-5 mg TRF. However, despite a seven fold increase in the overall TSH response, the T4 and T3 responses to 20 mg TRF were not significantly greater than those to 0-5 mg TRF. The explanation for this discrepancy between immunoreactive TSH levels and apparent biologic effect is unclear.

Progress in understanding and treating Parkinson's disease

This review evaluates the long-term results of Levodopa therapy in Parkinson's disease upon quality of life, prolongation of survival and excess mortality. It also focuses on recent and new therapeutic approaches: Levodopa in combindation with a Dopa-decarboxylase inhibitor or MAO-B inhibitor, dopamine agonists and an active tripeptide: L-prolyl-L-leucylglycine amide (MIF-I). It ends by looking at new avenues of etiological research in Parkinson's disease which may indicate specific accelerated ageing of catecholaminergic (pigmented) neuronal systems.

A comparison between a melanocyte-stimulating hormone inhibitory factor (MIF-I) and substances known to activate central dopamine receptors

The tripeptide, prolyl-leucyl glycine amide, a melanocyte-stimulating hormone inhibitory factor (MIF-I), which has been reported to be effective in improving symptoms of Parkinson's disease, has been compared with drugs known to activate dopamine receptors in rat and mouse brain. Unlike apomorphine, amphetamine and amantadine it was incapable of producing sterotyped behaviour in the rat and unlike 1-dopa it was also ineffective in rats pretreated with the monoamineoxidase inhibitor mebanazine. Neither did it potentiate apomorphine nor amphetamine in this test. MIF-I did not antagonise chlorpromazine-induced loss of locomotor activity in mice, an effect which was antagonised by apomorphine, amphetamine and amantadine. Chlorpromazine hypothermia in the mouse was antagonised by 1-dopa but not by MIF-I; similar findings were obtained in reserpine-pretreated mice. These results suggest that the reported beneficial effect of MIF-I in Parkinson's disease is unlikely to be due to an interaction with dopamine systems in the brain.

Neurologically active peptides

This paper reviews recent evidence that a number of small peptides found in the brain are active in the central nervous system and behaviorally. Attention is focused on MSH/ACTH 4-10, alpha- and beta-MSH, and the prohormone beta-LPH, as they produce a syndrome of yawning and stretching. Studies with substance P and mainly with MIF-I are also reviewed. It is shown that substance P is an excitatory transmitter or modulator in the dorsal spinal cord with that MIF-I has antiparkinson properties. It is concluded that many polypeptides have direct actions on the central nervous system independent of their neuroendocrine properties.

MIF, TRH, and simian social and motor behavior

MSH-release-inhibiting factor (MIF) and thyrotropin-releasing hormone (TRH) both have been reported to modify mood and activity in man. These two hypothalamic peptides were given intramuscularly across a 1000-fold dose range to 5 juvenile male M. nemestrina monkeys living in a social group. Motor activity was recorded automatically, and an observer counted various social behaviors. MIF increased motor activity for up to 11 hr. It decreased quiet foraging behavior, but did not change behaviors of social interaction. TRH did not stimulate motor behavior; high doses strongly suppressed it and produced apparent somatic distress. TRH increased behaviors of quiet rest and association and decreased environment exploration and low-intensity dominance behaviors. The lowest dose of TRH increased social play. Two monkeys showed repetitive, stereotyped behaviors even in baseline observations, and certain doses of TRH and MIF may have increased the frequency of these behaviors.

Effects of L-prolyl-L-leucyl-glycine amide (MIF-I) on dopaminergic neurons

In an attempt to determine the mechanism of action of L-proly-L-leucyl-glycine amide (MIF-I) in the treatment of Parkinson's disease, various parameters of dopaminergic neuronal function were studied in rats. It was found that the active uptake of 3H-dopamine (3H-DA) by synaptosome-rich homogenates of the striatum of rats treated with MIF-I (1 mg/kg IP X 3, 24 hr intervals) was unaltered 1 hr after final treatment with MIF-I. Also, neither tyrosine hydroxylase nor dopa decarboxylase activity was altered in the striatum and substantia nigra of rats treated with MIF-I (20 mg/kg IP X 3, 24 hr intervals). Thus, vital functional processes associated with dopaminergic neurons apparently are not altered by MIF-I under the conditions studied. These findings illustrate the importance of concurrent DOPA administration in observing an effect of MIF-I on dopaminergic neuronal function.

Alpha-MSH and MIF-I effects on catecholamine levels and synthesis in various rat brain areas

Attempts were made to find a biochemical correlate with previously observed behavioral alterations after administration of alpha-melanocyte-stimulating hormone (MSH) and MSH release-inhibiting factor (MIF-I). Brains of intact and hypophysectomized (hypox) rats were analyzed for endogenous catecholamine levels and the disappearance rate of endogenous norepinephrine (NE) after treatment with the tyrosine hydroxylase inhibitor alpha-methyl-para-tyrosine (AMPT). The studies undertaken show the following: (1) After the injection of MSH (100 mug/kg IP daily x 3) and AMPT, samples in different groups of intact and hypox rats were taken at 0, 1, 2, 4 and 6 hrs in 7 different brain areas. In the mid-brain area for the intact group of rats, the rate of disappearance of NE was faster and for the hypox rats it was slower than the rate for control rats not treated with the peptides. NE levels in the same area at time 0 were 11 percent lower than controls in hypox rats and unchanged in unoperated animals. (2) After the injection of MIF-I (20 mg/kg IP daily x 3) in similar experiments as with MSH, a reduced rate (p less than 0.05) of NE disappearance for the first 4 hr and an increased rate (p less than 0.05) of NE disappearance for the last 2 hr of the experiments occurred for both the intact and hypox rats in the mid-brain area where endogenous NE levels were lowered by 11 and 12 percent at 0 min. In no other brain areas were alterations in NE breakdown found in both the intact and hypox rat groups. Behavioral changes have been found previously under similar experimental conditions in both intact and hypox rats. (3) Rates of dopamine disappearance in experiments similar to those described for NE disappearance indicated that in the striatal brain area no change was found in the intact rats after either MSH or MIF-I, whereas a decrease in DA disappearance was found for hypox rats during the six hour experimental period only after MSH. The results indicate that a correlation between behavioral changes, rates of disappearance and endogenous levels of NE in the mid-brain area may occur after MIF-I at the times examined but that a similar correlation for MSH did not appear likely.

Radioautographic localization of radioactivity in rat brain after intraventricular or intracarotid injection of 3H-L-prolyl-L-leucyl glycinamide

Tritiated L-prolyl-L-leucyl-glycinamide was injected into the carotid artery or lateral ventricle of rats and the radioactivity localized by radioautography. After intracarotid administration, the radioactivity labeled the meninges, ependymal cells bordering the ventricles, and cells of the choroid plexus, as well as the median eminence and subfornical organ and thus may have reached the cerebrospinal fluid. After intraventricular injection, globus pallidus, indusium griseum, hippocampus, corpus callosum, and meninges. The results after intracarotid injection suggest that L-prolyl-L-leucyl-glycinamide may cross the blood brain barrier and the results after intraventricular injection suggest sites of localization which might be correlated with the previously reported effects of the tripeptide on the brain.