Immunoreactive thyrotrophin releasing factor in gastropod circumoesophageal ganglia

TRH-like antidepressant peptide, pyroglutamyltyroslyprolineamide, occurs in rat brain

We have previously reported the occurrence of pGlu-Glu-Pro-NH(2)(Glu-TRH, EEP), Val-TRH, Tyr-TRH, Leu-TRH, Phe-TRH, and Trp-TRH in rat brain using a combination of HPLC and radioimmunoassays with antibodies that cross-react with the general structure pGlu-X-Pro-NH(2) where 'X' maybe any amino acid residue (Peptides 2004; 25 : 647). This new family of TRH-like peptides, along with TRH (pGlu-His-Pro-NH(2)), has neuroprotective, anticonvulsant, antidepressant, euphoric, anti-amnesic, and analeptic effects. We now report that a combination of affinity chromatography using a rabbit antibody specific for Tyr-TRH and Phe-TRH, along with HPLC and tandem mass spectrometry operating in the multiple reaction monitoring (MRM) mode, provide conclusive evidence for the presence of Tyr-TRH in rat brain. Furthermore, synthetic Tyr-TRH is active in the Porsolt Swim Test suggesting that it is a fourth member of this family of in vivo neuroregulatory agents that have psychopharmacotherapeutic properties.

Development of an enzyme immunoassay for arginine-vasopressin (AVP)-like insect diuretic hormone

1. The AVP-like insect diuretic hormone is a biologically active antiparallel dimer present, along with its non-active monomeric form (Cys-Leu-Ile-Thr-Asn-Cys-Pro-Arg-GlyNH2), in the African locust. 2. It exhibits diuretic activity by increasing fluid excretion at the level of the Malpighian tubules. 3. To date, both monomer and dimer have been assayed using a radioimmunoassay originally prepared for mammalian AVP. 4. We have developed here an original enzyme immunoassay based on the use of antibodies to insect AVP-like raised in rabbits against synthetic monomers and dimers, using acetylcholinesterase conjugate as an enzymatic tracer. 5. This enzyme immunoassay enables measurement of the dimer to be made with adequate sensitivity (0.3 nmol/l, i.e. 21 pg/well) and reproducibility while sensitivity of the monomer is somewhat lower (14 nmol/l, i.e. 480 pg/well). 6. The assay was validated by assaying native dimer and monomer throughout the different steps of purification (from a crude extract to reversed-phase liquid chromatographic fractions). 7. A good correlation was observed between radioimmunoassays and enzyme immunoassays. 8. The enzyme immunoassay was also used to measure the level of AVP-like peptides in several insect tissues not explored to date.

Effects of sustained release formulation of thyrotropin-releasing hormone on learning impairments caused by scopolamine and AF64A in rodents

The effects of a sustained-release formulation of thyrotropin-releasing hormone (TRH-SR) on learning impairments induced by scopolamine and a cholinergic neurotoxin, ethylcholine aziridinium ion (AF64A), were examined in rodents. Subcutaneous injection of TRH-SR (2.8 mg/kg as free TRH) produced a sustained increase in immunoreactive plasma TRH levels up to about 2 weeks after dosing in rats. TRH-SR (0.56 and 2.8 mg/kg) given subcutaneously 7 days before the acquisition trial markedly ameliorated scopolamine-induced amnesia in mice, as evaluated with a passive avoidance task. Repeated administration of TRH for 7 days at doses of 0.2-5 mg/kg s.c. elicited a dose-dependent recovery from amnesia induced by scopolamine, whereas only the group treated with 5 mg/kg/day showed a significant improvement. The rats with bilateral intracerebroventricular injection of AF64A (3.75 nmol/brain) showed a significant impairment in the water maze task 2 weeks after surgery. TRH-SR (0.56 and 2.8 mg/kg) also exhibited a dose-dependent ameliorating action on the deficit. These findings indicate that TRH-SR ameliorates learning impairments produced by scopolamine and AF64A, and suggest that continuous infusion of TRH may have a potent learning and memory improving action at low doses.

TRH-induced blood flow and mean arterial pressure changes in the rabbit are not dependent on the anaesthetic used

1. The effects of thyrotropin releasing hormone (TRH) on regional cerebral blood flow were studied in rabbits anaesthetized with pentobarbitone or ketamine. The blood flow was determined with the labelled microsphere method before and after the i.v. administration of either 50 micrograms kg-1 or 2 mg kg-1 TRH. 2. In order to measure the cerebral O2 consumption the arteriovenous difference in oxygen saturation in the brain (CAVOD) was measured before and after the administration of 2 mg kg-1 TRH. 3. In animals under pentobarbitone anaesthesia 50 micrograms kg-1 TRH elicited an increase in mean arterial blood pressure (MAP) of about 1 kPa and 2 mg kg-1 TRH elevated the MAP by about 2 kPa. With ketamine as the anaesthetic the corresponding values were 0.5 kPa and 7 kPa, respectively. TRH induced significant vasoconstriction in several peripheral tissues. 4. The total cerebral blood flow (CBFtot) increased from 54 +/- 4 to 78 +/- 5 g min-1 100 g-1 after the administration of 50 micrograms kg-1 TRH in pentobarbitone-anaesthetized animals. An even greater effect was elicited by 2 mg kg-1 TRH, from 48 +/- 6 to 113 +/- 19 g min-1 100 g-1. In ketamine-anaesthetized rabbits, 50 micrograms kg-1 TRH tended to enhance the CBFtot and 2 mg kg-1 increased it from 71 +/- 6 to 141 +/- 19 g min-1 100 g-1. 5. In animals anaesthetized with pentobarbitone, the CAVOD decreased from 47.3 +/- 1.7% to 35.1 +/- 2.2% at 3 min after TRH delivery, and then gradually increased to the control level. In animals under ketamine anaesthesia the CAVOD decreased from 63.3 + 2.0% to 45.2 + 7.4% after the administration of 2 mg kg'- TRH. 6. It is concluded that TRH elicits cerebral vasodilatation in excess of that required by the change in cerebral metabolism which may have taken place. The pattern of responses was similar to that produced in rabbits under urethane anaesthesia.

Effects of hypothalamic releasing hormones and biogenic amines on identified neurones in the circumoesophageal ganglia of the water snail (Planorbis corneus)

1. The effect of locally applied releasing hormones, thyrotropin-releasing hormone (TRH) and luteinizing-hormone-releasing hormone (LHRH) and the putative neurotransmitters, acetylcholine (ACh) and dopamine (DA), on the neuronal excitability of identified invertebrate giant dopaminergic neurone (GDN) and serotoninergic neurone (5-HT) (Planorbis corneus) were investigated by intracellular recording in vitro. 2. The membrane potential of GDN was of the order of -60 to -70 mV. The microiontophoretically applied substances produced membrane depolarization as well as spike activation. Their order of efficacy was as follows: TRH greater than ACh greater than DA greater than LHRH. 3. The effects of the tested TRH, ACh, LHRH and DA on serotoninergic neurones were less pronounced. 4. During ACh depolarization the membrane resistance of GDN was found to be strongly reduced, whereas TRH produced only a small reduction in membrane resistance. 5. Dihydro-beta-erythroidin (DHE) added to the bath solution reversibly blocked ACh depolarization without influencing TRH depolarization. Concentrations of atropine sulfate required to block the ACh depolarization were higher by at least 100 order of magnitude. 6. These effects are discussed in relation to the immunoreactive TRH detected earlier in the central nervous system of invertebrates and vertebrates. The results are consistent with the postulate that TRH acts as a neuromodulator and/or neurotransmitter on invertebrate and vertebrate neurones.

Somatostatin and calcitonin stimulate neurite regeneration of molluscan neurons in vitro

Isolated neurons from the gastropod Physella heterostropha fail to regenerate their neurites if cultured in defined medium in the absence of growth factors. A significant number of cultured neurons extend neurites if they are cultured in brain-conditioned or hemocyte-conditioned medium. Synthetic somatostatin and salmon calcitonin also stimulate neurite regeneration in a dose-dependent manner. Thyrotropin-releasing hormone, arginine vasotocin, and eledoisin fail to promote neurite outgrowth. It is concluded that, like other molluscan neurons, isolated neurons from Physella require the presence of factors that are released by brain tissue or are present in the hemolymph, and that somatostatin and calcitonin can, in part, substitute for the endogenous neurite-regenerating activities.

Effect of thyrotropin-releasing hormone and its metabolites on the secretion of sulfated polysaccharides by foot integument of a pond snail

The effect of thyrotropin-releasing hormone (TRH), TRH metabolites, and a TRH analog on the secretion of 35S-labeled sulfated polysaccharides from in vitro incubated foot integument of the pond snail Lymnaea stagnalis palustris was assessed. Whereas TRH significantly inhibited the secretion of 35S-labeled polysaccharides, its metabolite deamido TRH significantly stimulated polysaccharide secretion. Histidyl-proline-diketopiperazine did not alter the secretion of 35S-labeled sulfated polysaccharides. Foot integument exhibited considerable TRH-peptidase activity in vitro. The principal proline-containing TRH metabolites were deamido-TRH and proline. The deamido-TRH content of the foot, mantle, and hemolymph was determined by radioimmunoassay. All tissues contained deamido-TRH. These findings suggest that the secretory activity of skin mucus glands of L. stagnalis palustris is the result of the stimulatory action of deamido-TRH and the inhibitory action of TRH. 3Methyl-2histidyl-TRH, TRH, vasotocin, and bombesin did not alter the polysaccharide secretion by in vitro incubated foot integument, indicating that the changes in mucus secretion after TRH and deamido-TRH administration are specific and that the gastropod "TRH receptors" may differ from the mammalian brain and anterior pituitary gland TRH receptors.

Effect of thyrotropin-releasing hormone (TRH) on the synthesis and secretion of polysaccharides by the integument of gastropods

The hypothesis that thyrotropin-releasing hormone (TRH) affects salt and water transport in gastropod skin by means of altering the secretion of epithelial surface mucus was tested. The synthesis and secretion of 35S-labeled sulfated polysaccharides was measured as an index for the synthesis and secretion of mucus. It was found that physiological concentrations of TRH significantly inhibited the secretion of 35S-labeled sulfated polysaccharides by short-term in vitro incubated gastropod foot integument. TRH did not alter the rate of synthesis of 35S-labeled sulfated polysaccharides in short-term in vitro incubated gastropod foot skin. The synthesis and release, but not the tissue/medium ratio of 35S-labeled sulfated polysaccharides was significantly lower in animals with an elevated endogenous TRH content than in control animals. The results from these studies suggest that acute exposure of gastropod skin to TRH results in a decrease in the secretion of preformed epithelial surface mucus and that chronic exposure also results in a reduction of the synthesis of surface mucus. It thus appears that TRH indirectly modulates gastropod skin ion transport by altering the thickness of the surface mucus coat which results in a change in the ion concentration at the cell surface and a change in the activity of the ion transporting mechanisms.

Effect of thyrotropin releasing hormone on the accumulation of cAMP by parietal ganglia of a gastropod

1. We had previously shown that thyrotropin releasing hormone (TRH) can stimulate the in vitro accumulation of cAMP by the parietal ganglia of the pond snail Lymnaea emarginata (Grimm-Jørgensen, 1980). 2. The mechanism by which TRH affects cAMP metabolism in parietal ganglia was further studied. 3. The TRH-induced accumulation of cAMP is preceded by a lag period and is of long duration. 4. TRH does not stimulate basal or guanylylimidodiphosphate-stimulated adenylate cyclase activity and is unable to cause an increase in cAMP accumulation when the incubation is carried out in the presence of a phosphodiesterase inhibitor. 5. This finding is compatible with the hypothesis that TRH may cause an increase in cAMP accumulation by means of decreasing phosphodiesterase activity. 6. When the ganglia were incubated with 3H-TRH and the localization of the labeled TRH examined by autoradiographic techniques, reduced silver grains were present only over glial and connective tissue elements. 7. The observed effect of TRH on the cAMP metabolism in parietal ganglia may be due to its action on non-neuronal cells.

TRH and its novel analog (DN-1417): antipentobarbital action and involvement of cholinergic mechanisms

Possible neuroanatomical loci and the mode of action of thyrotropin-releasing hormone (TRH) or its analog, gamma-butyrolactone-gamma-carbonyl-histidyl-prolinamide citrate (DN-1417), in reducing the pentobarbital-induced sleeping time were investigated by using an intracerebral microinjection technique in rats. Intravenous, intraperitoneal or intracerebroventricular (ICV) injection of TRH or DN-1417 produced a dose-related reduction of the sleeping time induced by pentobarbital. TRH or DN-1417 given into the posterior hypothalamic regions including the dorsal premammillary nucleus, lateral hypothalamic area and posterior nucleus of hypothalamus had a significant pentobarbital sleep shortening action in low doses. Injection of these peptides into the dorsomedial nucleus of thalamus, mesencephalic reticular formation, medial septal nucleus or hippocampus was also effective, in comparatively low doses. However, higher doses were required to elicit the effect when the injections were made into the nucleus accumbens, lateral preoptic area or caudate nucleus. In this respect, the parietal cortex was insensitive to TRH or DN-1417. The pentobarbital sleep shortening action of TRH or DN-1417 injected peripherally or into the hypothalamic regions was markedly antagonized by ICV or intrahypothalamic pretreatment with atropine methyl bromide. On the contrary, ICV injection of atropine methyl bromide had a weak or no antagonizing action on the effect of TRH injected ICV or into the reticular formation, medial septal nucleus or hippocampus. These results suggest that possible neuroanatomical sites mediating the pentobarbital sleep shortening action of TRH or DN-1417 may be posterior hypothalamic regions, dorsomedial nucleus of thalamus, reticular formation, medial septal nucleus or hippocampus. A cholinergic mechanism may also be involved in the effect of TRH on the hypothalamus.

Immunocytochemical identification of neural elements in the central nervous systems of a snail, some insects, a fish, and a mammal with an antiserum to the molluscan cardio-excitatory tetrapeptide FMRF-amide

With an antiserum to the molluscan cardio-excitatory tetrapeptide FMRF-amide neurons and/or nerve fibers were immunocytochemically identified in the central nervous systems of a snail (Lymnaea stagnalis), some insects (Leptinotarsa decemlineata, Periplaneta americana, Locusta migratoria, Pieris brassicae), a fish (Poecilia latipinna) and a mammal (mouse). The fact that immunoreactive material was observed in neurohaemal organs (corpora cardiaca of the insects) as well as in axon terminals ending on other neurons, seems to indicate that this peptide can function as a neurohormone and/or as a neurotransmitter. The results sustain the hypothesis that biologically active peptides have a wide distribution in the animal kingdom.

Effect of thyrotropin-releasing hormone on 22Na uptake by the pond snail Helisoma carabaceum

The effect of thyrotropin-releasing hormone, added to the external environment, on in vivo Na+ uptake by Helisoma carabaceum was assessed. It was found that 10(-5) M TRH significantly decreased unidirectional sodium flux. The Na+ concentration in the tissues and hemolymph was not affected by the hormone. Histidyl-proline-diketopiperazine, a TRH-metabolite, had no effect on Na+ uptake in vivo.

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.

Thyrotropin releasing hormone (TRH): restoration of oxotremorine tremor in mice. Comparison with quipazine, a serotoninergic and dopaminergic stimulant

Both TRH and quipazine (2.5-25 mg/kg) were found to restore and to intensify the oxotremorine-induced tremor in mice when injected i.p. 60 min after oxotremorine 0.5 mg/kg s.c. This phenomenon does not seem to be due to an increase in body temperature or muscle tone. Also other dopaminergic drugs, e.g. amphetamine, methylphenidate, nomifensine and apomorphine had a significant but lesser effect than TRH or quipazine. Haloperidol and methysergide both antagonized the effect of quipazine but not that of TRH. Neither propranolol, phenoxybenzamine, alpha-methyl-p-tyrosine, nor p-chlorophenylalanine inhibited the activity of TRH or quipazine. The restoration of oxotremorine-induced tremor could be prevented by atropine but not by methylatropine. It is concluded that quipazine exerts its effect by direct stimulation of serotoninergic and dopaminergic receptors, whereas TRH receptors may represent separate entities and TRH may function as a neurotransmitter or neuromodulator.