Action of two hypothalamic factors (TRH, MIF) and of angiotensin II on the behavioral effects of L-DOPA and 5-hydroxytryptophan in mice

Concepts for biologically active peptides

Here we review a unique aspect of CNS research on biologically active peptides that started against a background of prevalent dogmas but ended by exerting considerable influence on the field. During the course of refuting some doctrines, we introduced several concepts that were unconventional and paradigm-shifting at the time. We showed that (1) hypothalamic peptides can act 'up' on the brain as well as 'down' on the pituitary, (2) peripheral peptides can affect the brain, (3) peptides can cross the blood-brain barrier, (4) the actions of peptides can persist longer than their half-lives in blood, (5) perinatal administration of peptides can exert actions persisting into adulthood, (6) a single peptide can have more than one action, (7) dose-response relationships of peptides need not be linear, (8) the brain produces antiopiate as well as opiate peptides, (9) there is a selective high affinity endogenous peptide ligand for the mu-opiate receptor, (10) a peptide's name does not restrict its effects, and (11) astrocytes assume an active role in response to metabolic disturbance and hyperleptinemia. The evolving questions in our laboratories reflect the diligent effort of the neuropeptide community to identify the roles of peptides in the CNS. The next decade is expected to see greater progress in the following areas: (a) interactions of peptides with other molecules in the CNS; (b) peptide involvement in cell-cell interactions; and (c) peptides in neuropsychiatric, autoimmune, and neurodegenerative diseases. The development of peptidomics and gene silencing approaches will expedite the formation of many new concepts in a new era.

Mass spectrometric quantification of MIF-1 in mouse brain by multiple reaction monitoring

MIF-1 (Pro-Leu-Gly-NH(2)) has potent therapeutic effects in depression and Parkinson's disease, but its CNS sites of production are not yet clear. In this study, the concentration of MIF-1 in different brain regions was measured by the multiple reaction monitoring technique on a 4000 QTRAP mass spectrometer. The limit of quantification was 300 fg of MIF-1, and limit of detection was 60 fg. The low molecular weight fractions of tissue homogenates from different regions of mouse brain were analyzed. The concentration of MIF-1 ranged from 22+/-3 fg/microg protein in cerebral cortex to 930+/-60 fg/microg protein in the hypothalamus. Moderate concentrations were also detected in all other regions tested, including the striatum, thalamus, and hippocampus. By incubation of stable isotope-labeled oxytocin with tissue preparations, it was also confirmed that oxytocin at least partially contributed to the production of MIF-1 in the hypothalamus by action of peptidases. Regional differences were also found. The results are the first to show the ultrasensitive quantification of MIF-1 in different brain regions, and support the neuromodulatory actions of MIF-1 in the striatum.

From MIF-1 to endomorphin: the Tyr-MIF-1 family of peptides

The Tyr-MIF-1 family of small peptides has served a prototypic role in the introduction of several novel concepts into the peptide field of research. MIF-1 (Pro-Leu-Gly-NH(2)) was the first hypothalamic peptide shown to act "up" on the brain, not just "down" on the pituitary. In several situations, including clinical depression, MIF-1 exhibits an inverted U-shaped dose-response relationship in which increasing doses can result in decreasing effects. This tripeptide also can antagonize opiate actions, and the first report of such activity also correctly predicted the discovery of other endogenous antiopiate peptides. The tetrapeptide Tyr-MIF-1 (Tyr-Pro-Leu-Gly-NH(2)) not only shows antiopiate activity, but also considerable selectivity for the mu-opiate binding site. Tyr-W-MIF-1 (Tyr-Pro-Trp-Gly-NH(2)) is an even more selective ligand for the mu receptor, leading to the discovery of two more Tyr-Pro tetrapeptides that have the highest specificity and affinity for this site. These are the endomorphins: endomorphin-1 is Tyr-Pro-Trp-Phe-NH(2) and endomorphin-2 is Tyr-Pro-Phe-Phe-NH(2). Tyr-MIF-1 proved, contrary to the then prevailing dogma, that peptides can be saturably transported across the blood-brain barrier by a quantifiable transport system. Unexpectedly, the Tyr-MIF-1 transporter is shared with Met-enkephalin. In the era in which it was doubtful whether a peripheral peptide could exert CNS effects, the Tyr-MIF-1 family of peptides also explicitly showed that they can exert more than one central action that persists longer than their half-lives in blood. These peptides clearly illustrate that the name of a peptide restricts neither its actions nor its conceptual implications.

Modulatory effects of PLG and its peptidomimetics on haloperidol-induced catalepsy in rats

A behavioral model of dopaminergic function in the rat was used to examine the anticataleptic effects of L-prolyl-L-leucyl-glycinamide (PLG) and peptidomimetic analogs of PLG. Administration of 1 mg/kg PLG intraperitoneally significantly attenuated haloperidol (1 mg/kg)-induced catalepsy (as measured by the standard horizontal bar test), whereas doses of 0.1 and 10 mg/kg PLG did not. Eight synthetic PLG peptidomimetics (Calpha, alpha-dialkylated glycyl residues with lactam bridge constraint [1-4] and without [5-8]) were tested in the same manner (at a dose of 1 microg/kg) and categorized according to their activity, i.e. very active (5), moderately active (2, 3, 4, and 6), and inactive (1, 7, and 8). The catalepsy-reversal action of the diethylglycine-substituted peptidomimetic 5 was examined further and found to exhibit a U-shaped dose-response effect with an optimal dose of 1 microg/kg. The similarity between the effects of PLG and the synthetic peptidomimetics suggests a common mechanism of action. Finally, the synthetic peptidomimetics examined here, particularly peptidomimetic 5, were more effective than PLG in attenuating haloperidol-induced catalepsy.

Drug effects on active immobility responses: what they tell us about neurotransmitter systems and motor functions

The literature reviewed indicates that active immobility can be promoted by systemic injections of various neurotransmitter systems, as follows: (1) Dopaminergic blockade of both D1 and D2 receptor subtypes. (2) Cholinergic agonism of both muscarinic and nicotinic receptors. (3) Noradrenergic agonism of both alpha-1 and alpha-2 receptors (but these agonists may interfere with haloperidol- and reserpine-induced catalepsy). (4) GABA agonism. (5) Histamine agonism, particularly at the H1 receptor. (6) Opiate agonism, including action of many endogenous opiate peptides, particularly those affecting mu and delta receptors. (7) Agonism by certain other peptides (neurotensin, cholecystokinin). Among the major interactions of neurotransmitter systems that regulate immobility, are the following: (1) Cholinergic-dopaminergic (cholinolytics disrupt catalepsy of dopaminergic blockade and dopaminergic agonists tend to disrupt cholinomimetic catalepsy). (2) Opiate-induced catalepsy is antagonized by the dopamine agonist, apomorphine, but is enhanced by amphetamine. It is also antagonized by certain alpha-2 adrenergic agonists, while it does not seem to be antagonized by anticholinergics. (3) Numerous other interactions have been reported, involving opiates and MSH, serotonin and dopamine mimetics, serotonin and ketamine, GABA and neuroleptics, neurotensin and anticholinergics and histamine. The significance of the multiple neurotransmitter systems is unknown. One possible explanation is that the various neurotransmitter systems participate in mediating the sensory inputs that are involved in triggering immobility and regulate the higher-order limbic and basal ganglia processing reactions that engage a final motor output pathway from the brainstem. The brain is assumed to contain two sets of systems, each with its own, or possibly overlapping, set of neurotransmitter systems, that promote either active immobility or locomotion. The systems reciprocally inhibit each other. Another view, not mutually exclusive, is that output from the locomotor-promoting system provides a negative feedback, via the active immobility pathways, to act as a "brake" on movement, while at the same time maintaining the muscular tonus that is characteristic of active immobility.

Influence of protease inhibitors on the antidepressant activity of oxytocin

Both in the behavioral despair test and in the learned helplessness test, the antidepressant-like activity of oxytocin (0.500 mg/Kg i.p.) was prevented by the administration of a protease inhibitor (EACA, 400 mg/Kg i.p.; pepstatin, 0.1 mg/Kg i.p.). On the other hand, the linear tripeptide tail of oxytocin, MIF-1, was inactive in the behavioral despair test, and less active than oxytocin in the learned helplessness test. We conclude that the antidepressant activity of oxytocin is due to its cleavage to some smaller fragment(s) different from MIF-1.

Biphasic effects of MIF-1 and Tyr-MIF-1 on apomorphine-induced stereotypy in rats

The effects of several doses of MIF-1 and Tyr-MIF-1 (0.2, 0.5, 1.0 and 5.0 mg/kg, SC) on the stereotypic behavior induced by various doses (0.08, 0.2, 0.5, 1.0 and 2.0 mg/kg, SC) of apomorphine (APO) were tested in rats. MIF-1 increased the stereotypic behavior induced by 0.5 and 1.0 mg/kg of APO, but decreased the stereotypic behavior induced by 2.0 mg/kg of APO. Tyr-MIF-1 showed a biphasic effect similar to that exerted by MIF-1. The results suggest that the type of response to MIF-1 and Tyr-MIF-1 after APO is influenced by the activity of central dopaminergic neurons.

Tyr-MIF-1 and MIF-1 are active in the water wheel test for antidepressant drugs

MIF-1 [Pro-Leu-Gly-NH2] and Tyr-MIF-1 [Tyr-Pro-Leu-Gly-NH2] were tested in a system in which antidepressant drugs are known to result in increased wheel turning as mice attempt to escape from a small tank of water. One hr after injection, both peptides were found to cause a significant increase of the number of rotations of the wheel at doses as low as 0.01 mg/kg IP, the dose-response pattern for MIF-1 resembling an inverted-U. DSIP and morphine, by contrast, decreased the number of rotations. Under the conditions tested, neither MIF-1 nor Tyr-MIF-1 reversed the effect of morphine. The results demonstrate that MIF-1 and Tyr-MIF-1 are active in another test for antidepressants.

Behavioral effects of thyrotropin releasing hormone in frontal decorticated rats

A low dose intracerebroventricular injection of thyrotropin releasing hormone (TRH, 100 ng) changed many behavioral responses in the rat. TRH increased locomotion, scratching, body shaking, piloerection, and rearing, but decreased sniffing, and resting. Ablation of frontal neocortex further enhanced the TRH effects on locomotion and resting. A dose effect of TRH (0, 5, 10, 50, 100 ng) to increase general activity was established and the effect was further enhanced by decortication. In our test situations decortication had no effect by itself. Since the TRH effects became much more pronounced without the frontal neocortex it appears that the cortex exerts a powerful inhibitory effect to moderate the TRH effects. The TRH effect does not depend upon the frontal cortex, actually a cortical function is to dampen the TRH effects on various behavioral responses.

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.

Peptide inhibition of morphine-induced dopaminergic supersensitivity

Injection of the peptide cyclo(Leu-Gly) into rats prior to chronic exposure to morphine, inhibits: 1) the development of analgesic tolerance; 2) some signs of physical dependence; and, 3) morphine-induced increases in behavioral responses to dopamine agonists. Although there was no change in the total number of high affinity striatal dopamine receptors, chronic morphine treatment did increase the affinity of the ligand at the receptor. The peptide blocked not only the affinity change, but the increased behavioral response to apomorphine as well. These behavioral changes correlate significantly with the neurochemical changes in dopamine receptors following chronic morphine treatment. Therefore, some of the pharmacological efforts of morphine may be mediated by changes in CNS dopamine receptors and that the peptides may act by inhibiting these neurochemical changes.

MIF-1: effects on norepinephrine, dopamine and serotonin metabolism in certain discrete brain regions

A single injection of melanocyte-stimulating hormone inhibitory factor (MIF-1) in a dose of 3 mg/kg IP produced no significant effect on dopamine turnover. However, a dose of 5 mg/kg increased striatal tyrosine hydroxylase activity by 25% and homovanillic acid level by 27% when compared to control values. No change in either parameter was detected in olfactory tubercles. Dopamine levels also were elevated in striatum, pons-medulla and cerebral cortex in rats receiving 5 mg/kg dose of MIF-1. In olfactory tubercles, dopamine levels were however, reduced to 71% of control values taken as 100%. The concentration of norepinephrine tended to increase in several brain areas examined but, the change was statistically significant only in olfactory tubercles and cerebral cortex. The level of norepinephrine metabolite, 3-methoxy-4-hydroxyphenylethylene glycol, was lowered to 63% in whole brain of animals given MIF-1 at the dose of 5 mg/kg. These data suggest that MIF-1 enhances the turnover of dopamine and norepinephrine in the brain. However, MIF-1 treatment seemed to produce no consistent change in brain serotonin turnover. In striatum and cortex, this neuropeptide increased serotonin but elevated the level of its metabolite, 5-hydroxyindoleacetic acid indicating that the release of this brain amine was decreased in these two brain regions. The levels of 5-hydroxyindoleacetic acid were enhanced in hypothalamus and pons-medulla regardless of the dose of MIF-1 administered.

Effect of L-prolyl-L-leucyl-glycinamide (PLG) on neuroleptic-induced catalepsy and dopamine/neuroleptic receptor bindings

The mechanism of action subserving the potential anti-Parkinsonian properties of L-prolyl-L-leucyl-glycinamide (PLG) was investigated in behavioural and neurochemical models of dopaminergic function in the rat. Acute administration of PLG (20 and 40 mg kg-1 SC) failed to alter appreciably the intensity of the cataleptic response elicited by haloperidol (3 mg kg-1 IP). By contrast, chronic PLG treatment (20, 40 and 80 mg kg-1 SC twice daily for five days) significantly attenuated haloperidol-induced catalepsy. The effect of PLG on in vitro dopamine/neuroleptic receptor binding in rat striatum as differentially labelled by apomorphine and spiroperidol was also examined. PLG selectively enhanced the affinity of the specific binding of agonist [3H] apomorphine to dopamine receptors in the striatum, but had no effect on [3H] spiroperidol binding. The behavioural and biochemical results obtained in the present study raise the possibility that PLG may facilitate nigro-striatal dopaminergic neurotransmission through interacting with a unique PLG receptor functionally coupled to the dopamine receptor-adenylate cyclase complex.

Effect of L-prolyl-L-leucyl-glycinamide (MIF-I) on some neutrotransmitter-receptor interactions

Some neurotransmitter-receptor interactions have been studied in an attempt to determine how L-prolyl-L-leucyl-glycinamide (MIF-I) exerts its antiparkinson effect. MIF-I affected neither the contractile responses of isolated mouse vas deferens and guinea pig ileum to noradrenaline, acetylcholine, substance P and histamine, nor the inhibitory effects of dopamine and GABA on the rat vas deferens and guinea pig ileum. MIF-I, as well as L-leucine and Pro-Leu, antagonized the contractile response of the ileum to 5-hydroxytryptamine (5-HT). Behavioural tests were used to examine the action of MIF-I on CNS transmitter-receptor interactions. MIF-I did not modify the circling produced by either dopamine agonists in nigro-striatal lesioned rats of 5-HT agonists in rats with a lesion of the medial raphe nucleus. MIF-I affected neither 5-hydroxytryptophan-induced head twitches in mice, which is a measure of 5-HT receptor stimulation, nor striatally-evoked head turning in the rat, which is a model for brain GABA function. It is concluded that MIF-I, at the doses used, does not directly modify the function of any of the CNS transmitter examined. Other possibilities to explain its antiparkinson action are discussed.

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.

MIF-I and postsynaptic receptor sites for dopamine

In an attempt to determine the mechanism by which the tripeptide l-prolyl-l-leucyl-glycine amide (PLG, MIF-I) exerts its antiparkinsonian effect, the action of this substance on various postsynaptic components of striatal dopaminergic nerves was studied. It was shown that injection of rats with MIF-I (1 mg/kg, IPX5, 24 hr intervals) did not alter tyrosine hydroxylase, dopa decarboxylase, choline acetyltransferase and glutamic acid decarboxylase activities in the striatum under the conditions tested. The activities of adenylate cyclase, dopamine-stimulated adenylate cyclase, and guanylate cyclase were not altered in vitro by various concentrations of MIF-I (0.1 to 1000 micrometer), although VIP and neurotensin had some effect. Also the rate of uptake of 3H-dopamine by rat striatal synaptosomes was unchanged, as was the binding of 3H-dopamine and 3H-spiperone to beef caudate membranes. This series of studies indicates that MIF-I does not act directly on the striatal dopamine postsynaptic receptor under the conditions tested, although it is possible that MIF-I could act indirectly at this or another site in vivo by releasing or activating some other factor.

Effect of brain peptides on hypokinesia produced by anterolateral hypothalamic 6-OHDA lesions in rats

Intraventricular injections of substance P, TRH and somatostatin were administered to rats rendered hypokinetic by bilateral microinjections of 6-hydroxydopamine into the anterolateral hypothalamus, Only substance P in a dose of 0.30 micrigrams/rat significantly increased motor activity as determined by photocell counts in a 5 min test session immediately after administration of the peptide. Behavioral observations indicated that grooming and not locomotion was mainly responsible for the greater activity scores. None of the three peptides at the doses examined potentiated or reduced the increased activity induced by 1 mg/kg apomorphine. Stereotyped behavior was also not affected by previous injections of substance P and somatostatin but was enhanced in animals which had received 5 micrograms/rat TRH 30 min prior to apomorphine.

Thyrotropin-releasing hormone and amphetamine: a comparison of pharmacological profiles in animals

1. The pharmacological effects of TRH are compared to those produced by d-amphetamine in an attempt to elucidate the mechanisms underlying the activity of this endogenous peptide. 2. Although numerous amphetamine-like actions have been attributed to TRH, several differences have been noted between these compounds and are discussed. 3. At present, it is impossible to propose a single mechanism of action to explain the behavioral effects of TRH.

Antagonism of morphine-induced catalepsy by L-prolyl-L-leucyl-glycinamide

In view of the recently demonstrated extra-endocrine central actions of hypothalamic releasing hormones, we have investigated the effects of prolyl-leucyl-glycinamide (PLG) and thyrotropin releasing hormone (TRH) on morphine-induced catalepsy. Although acute administration of PLG (10 mg kg-1 s.c.) slightly attenuated the cataleptic response, chronic PLG treatment (10 mg kg-1 s.c. for 10 days) virtually abolished morphine-induced catalepsy. TRH, administered subcutaneously, exhibited little or no anti-cataleptic activity. These results are discussed in relation to the possible central site of narcotic-induced catalepsy and the therapeutic potential of PLG in Parkinson's disease.

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.

Lack of effect of chronically administered thyrotropin-releasing hormone (TRH) on regional rat brain tyrosine hydroxylase activity

Chronic treatment of adult male rats with TRH (1 or 10 mg/kg IP) for 5 or 9 days failed to alter the activity of tyrosine hydroxylase (TH), the enzyme regulating the rate-limiting step in catecholamine biosynthesis. In contrast, as previously described, chronic reserpine administration (0.5 mg/kg IP: 9 days) resulted in a significant rise in TH activity in midbrain, hypothalamus, pons-medulla and forebrain. These results suggest that the enhanced brain norepinephrine turnover reported to occur after treatment with TRH is not due to synthesis of new TH enzyme protein.

A comparison between the hypothermia induced by intra-ventricular injections of thyrotropin releasing hormone, noradrenaline or calcium ions in unanaesthetized cats

1 The hypothermia produced by intraventricular injections of thyrotropin releasing hormone (TRH) in unanaesthetized cats has been investigated. 2 TRH is more potent than either noradrenaline or calcium ions. It is estimated that the equi-potent molar ratio for TRH: noradrenaline:calcium is 1:900:27,000. 3 TRH injections is also produce profuse salivation, tachypnoea, cutaneous vasodilatation and frequently defaecation and vomiting. It is considered that the increased respiration is a major cause of the hypothermia. 4 Prior administration of phentolamine antagonized noradrenaline-induced hypothermia but did not affect hypothermia produced by TRH or calcium ions. Pretreatment with alpha-methyltyrosine did not affect the hypothermia induced by TRH, calcium ions or noradrenaline. 5 The calcium antagonists verapamil and xylocaine did not antagonize hypothermia induced by an injection of calcium ions. 6 The constituent amino acids of TRH did not produce hypothermia either individually or collectively. Thyroxine sodium produced a rise in temperature that was slow in onset, consistent with its known metabolic effects. TSH produced a small hypothermia unrelated to dose.

Evidence concerning the involvement of 5-hydroxytryptamine in the locomotor activity produced by amphetamine or tranylcypromine plus L-DOPA

1 Pretreatment of rats with p-chlorophenylalanine (PCPA; 2 X 200 mg/kg) decreased the concentration of 5-hydroxytryptamine (5-HT) in the brain. It also decreased the locomotor activity produced by tranylcypromine plus L-DOPA administration 24 h after the second dose of PCPA. 2 Pretreatment with p-chloroamphetamine, which produced a similar decrease in brain 5-HT concentrations did not decrease the locomotor response to tranylcypromine and L-DOPA. 3 PCPA pretreatment decreased the rise in the concentration of DOPA and dopamine in the brain following tranylcypromine and L-DOPA, suggesting its effect on the dopamine-induced locomotor activity was the result of this drug diminishing dopamine formation in the brain, probably by inhibiting L-DOPA uptake. 4 The locomotor activity produced by tranylcypromine and L-DOPA was not decreased by pretreatment 6 h earlier with disulfiram (400 mg/kg). This argues against the locomotor activity being due to noradrenergic stimulation. 5 PCPA pretreatment did not alter amphetamine-induced stereotypy or the circling behaviour in unilateral nigro-striatal lesioned rats.

Regulation of behavioral events by thyrotropin releasing factor and cyclic AMP

Like dibutyryl cyclic AMP, thyrotropin releasing factor (TRF) has potent antianesthetic properties, but only dibutyryl cyclic AMP shortens narcosis dose-relatedly. In contrast, only TRF reverses amobarbital-induced hypothermia (dose-relatedly). In naive rats, dibutyryl cyclic AMP (25-200 mug) induces convulsions while TRF (5-100 mug) produces intermittent hyperactivity and sedation but never convulsions. To determine whether behavioral events may be regulated in the central nervous system through an interaction of the two naturally occurring compounds, TRF (5-100 mug) and dibutyryl cyclic AMP (25-200 mug) were injected simultaneously into the lateral ventricle of the brain of naive rats or rats anesthetized with amobarbital (80 mg/kg). TRF (12.5-50 mug) and dibutyryl cyclic AMP (100-200 MUG) DID NOT SHORTEN NARCOSIS FURTHER THAN DIBUTYRYL CYCLIC AMP alone. Amobarbital protected against the lethal effects of the two compounds injected simultaneously. Long-lasting locomotor disorders and mortality rate increased with increasing doses of TRF (12.5-25 mug) and dibutyryl cyclic AMP (100-200 MUG) GIVEN TO NAIVE RATS. Results did not support the postulate that cyclic AMP is the second messenger of TRF.

Possible association of increased rat behavioral effects and increased striatal dopamine and norepinephrine levels during the DOPA-potentiation test

Previous reports have indicated that alpha-MSH release inhibiting hormone (MIF-1) increased the behavior occurring as a result of the dihydroxyphenylalanine (DOPA) potentiation test [3,7]. This study was undertaken to see whether dopamine (DA) or norepinephrine (NE) levels likewise increased in the test animals. The DOPA potentiation test was performed as follows: 2-4 hr before behavior measurement, 40 mg/kg of the monoamine oxidase inhibitor pargyline HCl was given orally. Two hr later this was followed by the intraperitoneal (IP) injection of MIF-1 at doses of 0.1, 0.3 or 1.0 mg/kg. Behavioral measurement was begun after the IP injection of 200 mg/kg of dl-DOPA 1-2 hr after the MIF-1. The parameters included social interaction, aggressiveness, fighting, ataxia, jumping, defecation, urination and salivation. The animals were beheaded while the behavior was still increased and the striatal area removed, placed in aluminum foil, and kept at -50 degrees C until assayed. In general, especially among the younger animals, a significant correlation (p=0.05 to p=0.01) was found between the increased behavioral responses to MIF-I and the rise in DA. Because of a few exceptions to this correlation the possibility is suggested that MIF-I might also affect behavior by acting directly on the postsynaptic membrane thus bypassing any change in NE or DA which is known to increase cycli AMP in the striatum.

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.

Investigations on alpha-MSH and MIF-1 effects on cyclic AMP levels in rat brain

It has been suggested that the peptides alpha-metanocyte stimulating hormone (alpha-MSH) and MSH-release inhibitory factor (MIF-1) may alter adenosine-3', 5'-cyclic monophosphate (cAMP) metabolism [13,26]. Normal and hypophysectomized (hypoxed) rats were administered saline (controls IP daily X 3), alpha-MSH (80 mug/kg IP daily X 3) or MIF-1 (1 or 10 mg/kg IP daily X 3) and sacrificed 30 min after the third injection in a focused microwave oven (1.5 KW; 2-3 sec). Various brain areas were then assayed for cAMP levels after each treatment. The occipital cortex area was the only area to show consistent changes in both normal and hypoxed rats after alpha-MSH treatment. These findings were replicated for the occipital cortex in a second group of normal and hypoxed rats which were similarly treated. The results suggest a correlation between the rise in cAMP found and reported changes in visual acuity and attention in rats and human after treatment with alpha-MSH [8,14, 23].

Thyrotropin releasing hormone (TRH): DOPA potentiation and biogenic amine studies

The present study in mice demonstrated the TRH when administered over 5 days remained active in the Everett Dopamine Potentiation Test. No evidence of tolerance was observed. In fact, an accumulative effect of TRH appeared to take place. Ablation of the adrenals, ovaries, testes, pineal, spleen, parathyroid, one kidney, or thymus did disrupt this behavioral potentiation of dopamine by TRH. TRH was found to potentiate the effects of imipramine. T3, T4, and TSH were found to be active in the DOPA potentiating test. No overt toxicity was observed between TRH and pargyline or between TRH and DOPA. Toxicity was seen only when all three agents were used together. TRH was found active in young and old mice. TRH was also found active in potentiating the central effects of serotonin. Biogenic amine brain levels in mice were not altered by TRH when administered for five days. Alpha-methyl-p-tyrosine reduced the activity of TRH in the dopamine potentiation test, suggesting dopaminergic mechanisms are involved by a direct receptor interaction.