Thyrotropin Releasing Hormone Analog TA-0910 Suppresses Alcohol Intake in Alcohol Drinking African Green Monkeys

Modulation of high alcohol drinking in the inbred Fawn-Hooded (FH/Wjd) rat strain: implications for treatment

The Fawn-Hooded rat (FH/Wjd) is an inbred alcohol-preferring rat strain, unlike most of the other strains that were selectively bred for high alcohol intake and preference. It was chosen for study some 16 years ago because of a reported mutation that disrupted platelet serotonin function. Although the FH/Wjd rat has high alcohol intake (>5 g/kg/day) and preference (>65%), interbreeding with an alcohol-non-preferring inbred strain suggested that these measures are unrelated to the serotonin abnormality. Similarly, the exaggerated immobility of the FH/Wjd rats in the forced swim test did not correlate with the high alcohol intake. Many compounds have been tested in the FH/Wjd rats after both acute and chronic treatment and a substantial number of them have proved effective. However, as the case with opiate antagonists, tolerance to the effects of the drug can develop. An up-regulation of opioid receptors accompanied the chronic treatment and this mechanism may account for the development of tolerance. Tolerance to opiate antagonists has also been demonstrated in two of the selectively bred alcohol-preferring rat lines, but it is unknown whether this process may contribute to the relapses seen in individuals being treated with naltrexone. Other drugs that reliably decrease alcohol intake in the FH/Wjd rats include the 5-hydroxytryptamine-2A receptor antagonist, amperozide, the mGlu5 receptor antagonist 3-[(2-methyl-1,3-thiazol-4-yl)ethynyl]pyridine (MTEP) and herbal derivatives such as ibogaine, St. John's wort and kudzu extract. Thus, studies in the FH/Wjd rat have led to the discovery of a wide variety of targets for the development of novel agents to treat alcoholism. The fact that several of these drugs were shown to reduce alcohol intake in some of the selectively bred alcohol-preferring rat lines and/or alcohol-preferring vervet monkeys increases our confidence that they are good candidates for further development.

Central nervous system effects of thyrotropin-releasing hormone and its analogues: opportunities and perspectives for drug discovery and development

Besides its well-known endocrine role in the thyroid system, thyrotropin-releasing hormone (L-pyroglutamyl-L-histidyl-L-prolinamide) has been long recognized as a modulatory neuropeptide. After a brief overview of the extrahypothalamic and receptor distribution, and of the neurophysiological, neuropharmacological and neurochemical effects of this tripeptide, this review discusses efforts devoted to enhance therapeutically beneficial central nervous system effects via structural modifications of the endogenous peptide. An enormous array of maladies affecting the brain and the spinal cord has been a potential target for therapeutic interventions involving agents derived from thyrotropin-releasing hormone as a molecular lead. Successful development of several centrally active analogues and recent accounts of efforts aimed at improving metabolic stability, selectivity and bioavailability are highlighted.

Distribution of thyrotropin-releasing hormone immunoreactivity in the brain of the dogfish Scyliorhinus canicula

To improve knowledge of the peptidergic systems of elasmobranch brains, the distribution of thyrotropin-releasing hormone-immunoreactive (TRHir) neurons and fibers was studied in the brain of the small-spotted dogfish (Scyliorhinus canicula L.). In the olfactory bulbs, small granule neurons richly innervated the olfactory glomeruli. In the telencephalic hemispheres, small TRHir neurons were observed in the superficial dorsal pallium, whereas TRHir fibers were widely distributed in pallial and subpallial regions. In the preoptic region, TRHir neurons formed a caudal ventrolateral group in the preoptic nucleus. In the hypothalamus, the most conspicuous TRHir populations were associated with the lateral hypothalamic recess, but small TRHir populations were found in the posterior tubercle and ventral wall of the posterior recess. The preoptic region and hypothalamus exhibited rich innervation by TRHir fibers. TRHir fibers were observed coursing to the neurohypophysis and the neuroepithelium of the saccus vasculosus, but not to the neurohemal region of the median eminence. Some stellate-like TRHir cells were observed in a few cell cords of the neurointermediate lobe of the hypophysis. The thalamus, pretectum, and midbrain lacked TRHir neurons. Further TRHir neuronal populations were observed in the central gray and superior raphe nucleus of the isthmus, and a few TRHir cells were located in the nucleus of the trigeminal descending tract at the level of the rostral spinal cord. In the brainstem, the central gray, interpeduncular nucleus, secondary visceral region of the isthmus, rhombencephalic raphe, inferior olive, vagal lobe, and Cajal's commissural nucleus were all richly TRHir-innervated. Comparison of the distribution of TRHir neurons observed in the dogfish brain with that observed in teleosts and tetrapods reveals strong resemblance but also interesting differences, indicating the presence of both a conserved basic vertebrate pattern and a number of derived characters.

Distribution of thyrotropin-releasing hormone (TRH) immunoreactivity in the brain of the zebrafish (Danio rerio)

The distribution of thyrotropin-releasing hormone (TRH) in the brain of the adult zebrafish was studied with immunohistochemical techniques. In the telencephalon, abundant TRH-immunoreactive (TRHir) neurons were observed in the central, ventral, and supra- and postcommissural regions of the ventral telencephalic area. In the diencephalon, TRHir neurons were observed in the anterior parvocellular preoptic nucleus, the suprachiasmatic nucleus, the lateral hypothalamic nucleus, the rostral parts of the anterior tuberal nucleus and torus lateralis, and the posterior tuberal nucleus. Some TRHir neurons were also observed in the central posterior thalamic nucleus and in the habenula. The mesencephalon contained TRHir cells in the rostrodorsal tegmentum, the Edinger-Westphal nucleus, the torus semicircularis, and the nucleus of the lateral lemniscus. Further TRHir neurons were observed in the interpeduncular nucleus. In the rhombencephalon, TRHir cells were observed in the nucleus isthmi and the locus coeruleus, rostrally, and in the vagal lobe and vagal motor nucleus, caudally. In the forebrain, TRHir fibers were abundant in several regions, including the medial and caudodorsal parts of the dorsal telencephalic area, the ventral and commissural parts of the ventral telencephalic area, the preoptic area, the posterior tubercle, the anterior tuberal nucleus, and the posterior hypothalamic lobe. The dorsal thalamus exhibited moderate TRHir innervation. In the mesencephalon, the optic tectum received a rich TRHir innervation between the periventricular gray zone and the stratum griseum centrale. A conspicuous TRHir longitudinal tract traversed the tegmentum and extended to the rhombencephalon. The medial and lateral mesencephalic reticular areas and the interpeduncular nucleus were richly innervated by TRHir fibers. In the rhombencephalon, the secondary gustatory nucleus received abundant TRHir fibers. TRHir fibers moderately innervated the ventrolateral and ventromedial reticular area and richly innervated the vagal lobe and Cajal's commissural nucleus. Some TRHir fibers coursed in the lateral funiculus of the spinal cord. Some TRHir amacrine cells were observed in the retina. The wide distribution of TRHir neurons and fibers observed in the zebrafish brain suggests that TRH plays different roles. These results in the adult zebrafish reveal a number of differences with respect to the TRHir systems reported in other adult teleosts but were similar to those found during late developmental stages of trout (Díaz et al., 2001).

Thyrotropin releasing hormone decreases alcohol intake and preference in rats

Thyrotropin releasing hormone (TRH) has been reported to reduce stress- and deprivation-induced eating, hypothetically by induction of satiation. Early work demonstrated thyroid extracts reduced alcohol intake, and recent research shows a TRH analog specifically inhibits alcohol preference. We determined whether parenteral administration of TRH reduces alcohol consumption and choice in a manner consistent with a satiation effect. Water-restricted ad lib fed female and male rats (n = 12) were given access to 5% w/v ethanol 0 or 30 minutes after intraperitoneal (i.p.) injection of TRH. TRH (20-40 mg/kg) inhibited alcohol intake only if injected immediately before alcohol access. Inhibition of alcohol intake was reliably accompanied by increased production of fecal boli but not by reliably decreased food intake. Rats given a choice of 2% w/v ethanol and water decreased alcohol preference after TRH (20 mg/kg) but did not reduce total fluid intake. Results are partially consistent with the hypothesis of TRH as one of several functional elements in the integrative neuropeptide control of alcohol consumption via short-term satiation.