The contrasting actions of TRH and cycloheximide in altering the effects of centrally acting drugs: evidence for the non-involvement of dopamine sensitive adenylate cyclase

Central dopaminergic actions of YM-14673, a new TRH analogue, in rodents

The effects of a new TRH analogue, YM-14673 (N alpha-[[(S)-4-oxo-2-azetidinyl]carbonyl]-L-histidyl-L-prolinamide dihydrate) on spontaneous movement, sniffing, climbing, licking, biting and circling behaviors were compared with those of TRH and methamphetamine, in rodents. YM-14673 in a dose of 1 mg/kg (i.p.) enhanced spontaneous motor activity in rats, and induced sniffing and climbing behaviors in mice. The licking and biting behaviors were not induced by administration of YM-14673 even in a high dose (30-100 mg/kg i.p.) to mice. In addition, ipsilateral circling did not follow the i.p. administration of YM-14673 in rats receiving cis-flupenthixol unilaterally into the striatum. YM-14673 was about 20-30 times more potent than TRH to induce sniffing and climbing behaviors and to increase spontaneous movement. The sniffing and climbing behaviors induced by administration of YM-14673 and TRH were antagonized by treatment with haloperidol and alpha-methyl-para-tyrosine (alpha-MT). Methamphetamine (0.5-10 mg/kg i.p.), unlike YM-14673, showed significant pharmacological effects in all behavioral experiments, so that the pharmacological profile of YM-14673 was different from that of methamphetamine. These results suggest that both YM-14673 and TRH induced behavioral changes, presumably due to facilitatory effects on the central dopaminergic system.

Effect of TRH analog (DN-1417) on tyrosine hydroxylase activity in mesocortical, mesolimbic and nigrostriatal dopaminergic neurons of rat brain

Tyrosine hydroxylase (TH) was assayed in eight regions of rat brain following repeated treatment with a TRH analog, DN-1417 (gamma-butyrolactone-gamma-carbonyl-histidyl-prolinamide). Repeated DN-1417 treatment (20 mg/kg/day, IP) for 7 days increased TH activity in the ventral tegmental area and decreased in the prefrontal cortex polar, medial and lateral fields and olfactory tubercles. No significant change in TH activity was found in the nucleus accumbens, striatum and substantia nigra. Kinetic analysis showed that the increased TH activity in the ventral tegmental area was due to an increase in Vmax, but not a change in the apparent Km of TH for a cofactor, 6-methyl-tetrahydropteridine. When TH was assayed at a suboptimal pH and in the presence of a subsaturating cofactor, the striatal TH was activated significantly after DN-1417. In the prefrontal cortex medial field, nucleus accumbens and olfactory tubercles, TH activity assayed under the suboptimal condition was not modified by DN-1417 treatment. These results suggest an intimate involvement of central dopaminergic systems in the actions of DN-1417.

A possible mechanism of action of thyrotropin-releasing hormone (TRH) and its analog DN-1417 on the release of dopamine from the nucleus accumbens and striatum in rats

Slices of the nucleus accumbens, the terminus of the mesolimbic dopaminergic system and the striatum, the terminus of the nigrostriatal dopaminergic system obtained from rats, were used for analyzing the dopamine releasing effects of TRH and its analog DN-1417 (gamma-butyrolactone-gamma-carbonyl-L-histidyl-L-prolinamide citrate). (1) Dopamine release: The addition of DN-1417 (5 X 10(-5) M) or TRH (5 X 10(-4) M) stimulated the release of prelabelled [3H]-dopamine (DA) from the superfused nucleus accumbens slices, and 100 or 20 times higher concentrations of each compound stimulated DA release from the striatal slices. The omission of Ca2+ from the superfusion medium or the addition of ouabain (5 X 10(-3) M), a (Na+ + K+) stimulated adenosine triphosphate (ATP) phosphohydrolase [(Na+ + K+)-ATPase] inhibitor, almost completely abolished the DN-1417- or TRH-induced DA releasing effect. (2) 45Ca2+ uptake: The addition of DN-1417 (10(-4) M) or TRH (10(-4) M) stimulated 45Ca2+ uptake into the nucleus accumbens slices in a time-dependent manner from 1 to 5 min at 30 degrees C. On the other hand, both drugs (10(-4) M) had no effect on 45Ca2+ uptake into the striatal slices. A Ca2+ ionophore, A-23187 (10(-6) M), stimulated 45Ca2+ uptake into slices of the nucleus accumbens and striatum. Ouabain abolished the DN-1417-, TRH- and A-23187-induced effects. (3) Cyclic AMP formation: The addition of DN-1417 (10(-4) M) or TRH (10(-4) and 10(-3) M) accelerated cyclic AMP formation in the nucleus accumbens, but not in the striatal slices. A Ca2+ antagonist, methoxyverapamil (D-600, 10(-6) M) almost completely abolished the DN-1417- and TRH-effects. (4) (Na+ + K+)-ATPase activity: The addition of DN-1417 (10(-5) and 10(-4) M) or TRH (10(-4) M) activated (Na+ + K+)-ATPase in the P1 fraction (cell debris, nuclei) of the nucleus accumbens, but had little effect on the same activity in the striatum. (5) [3H]-TRH binding: The addition of 10(-6) to 10(-4) M of DN-1417 and TRH inhibited concentration-dependently [3H]-TRH binding in the nucleus accumbens and striatal slices. Ouabain (5 X 10(-3) M) almost completely abolished [3H]-TRH binding in both types of slices.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of DN-1417, a thyrotropin releasing hormone analog, on dopaminergic neurons in rat brain

Acute and chronic effects of gamma-butyrolactone-gamma-carbonyl-histidyl-prolinamide (DN-1417) were investigated on motor activity, dopamine (DA) metabolites and DA receptors in various brain regions of rats. The motor activity, as measured with Automex recorder, was enhanced after a single injection with DN-1417 (20 mg/kg, IP), and the motor stimulating action persisted during 21 daily injections. Acute DN-1417 elevated both homovanillic acid (HVA) and 3,4-dihydroxyphenylacetic acid (DOPAC) levels in 7 brain regions, prefrontal cortex polar, medial and lateral fields, nucleus accumbens, olfactory tubercles, amygdala and striatum. After chronic treatment for 7 days, the acute effect of DN-1417 on DA metabolites disappeared in all regions except for the striatum in which DN-1417 still increased HVA and DOPAC. The response of striatal DA metabolites was also observed after chronic treatment for 21 days. Chronic DN-1417 produced no significant change in 3H-spiperone binding in the prefrontal cortex, nucleus accumbens, olfactory tubercles and striatum, while striatal 3H-DA binding displaced by 30 nM spiperone was enhanced after chronic treatment. These results indicate that DN-1417 interacts with mesocortical, mesolimbic and nigrostriatal DA systems in the different modes of action. The lack of tolerance to motor hyperactivity, however, raises the question as to whether DN-1417-induced hyperactivity may be mediated by the activation of mesolimbic DA neurons. The involvement of nigrostriatal neurons in DN-1417-induced motor hyperactivity is suggested.

Thyrotropin-releasing hormone and its analog MK-771 increase the cerebroventricular perfusate content of dihydroxyphenylacetic acid

The effects of thyrotropin-releasing hormone (TRH) and its synthetic analog, pyro-2-aminoadipyl-histidyl-thiazolidine-4-carboxamide (MK-771), were determined on the efflux of dihydroxyphenylacetic acid (DOPAC) collected from push-pull cannulae chronically implanted into the lateral cerebral ventricles of rats. Intracerebroventricular and intraperitoneal injections of both peptides increased the efflux of DOPAC. These results suggest that TRH and MK-771 increase the activity of dopaminergic neurons that terminate in periventricular regions.

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.

Regulatory peptides as a source of new drugs--the clinical prospects for analogues of TRH which are resistant to metabolic degradation

The biological properties of several analogues of TRH (Pyr-His-Pro X NH2) are reviewed. Analogues discussed include those with modifications to the Pyr moiety (e.g. DN-1417, CG 3509 and CG 3703), the Pro moiety (e.g. RX 77368) and MK-771 which has both terminal residues modified. The analogues have enhanced biological half-lives compared to TRH because of their resistance to enzymatic degradation. Neuropharmacological evaluation indicates the analogues to be active in antidepressant screening tests, to reverse the effects of diverse CNS depressants and to promote arousal when given alone. The analogues all exhibit enhanced potency compared to TRH in such tests. In contrast they appear equipotent to TRH in endocrine tests. An explanation is offered for this paradox in terms of metabolic stability and bioavailability to the requisite sites of action. The prospects for clinical utilization of the neuropharmacological properties common to TRH and its analogues are considered.

Jumping behavior induced by thyrotropin releasing hormone in combination with apomorphine in mice

Neuronal mechanisms involved in the jumping produced by thyrotropin releasing hormone (TRH) plus apomorphine were studied in mice. TRH (5--20 mg/kg IP) administered after apomorphine (0.25--2.0 mg/kg IP) elicited jumping behavior, the frequency of jumping being proportional to the dose of TRH but inversely related to the dose of apomorphine. Jumping behavior was also induced by TRH (20 mg/kg IP) administered after atropine (5 mg/kg IP) or clonidine (0.5 mg/kg IP). The jumping elicited by TRH (20 mg/kg IP) in combination with apomorphine (0.25 mg/kg IP) was decreased by pretreatment with haloperidol (1 mg/kg IP), physostigmine (0.2 mg/kg IP) or phentolamine (10 mg/kg IP), unaffected by propranolol (10 mg/kg IP), and markedly increased by atropine (5 mg/kg IP) or clonidine (0.5 mg/kg IP). The results suggest that TRH in combination with apomorphine, atropine or clonidine elicits jumping in which dopaminergic, cholinergic and noradrenergic functions are concomitantly involved.

The effects of drugs on the processes regulating the functional activity of brain monoamines

1. By study of the synthesis and turnover of brain monoamines and with the use of behavioral models which indicate the functional activity of brain 5HT and dopamine, it is possible to unravel the mechanisms by which some drugs produce behavioral effects. 2. Using these techniques the acute and chronic effects of certain neuroleptics, propranolol and other beta-adrenergic blocking agents, repeated electroconvulsive shock, and lithium upon the functional activity of brain 5HT and dopamine are examined. 3. The clinical relevance of these studies is discussed.

Mesolimbic involvement in the locomotor stimulant action of thyrotropin-releasing hormone (TRH) in rats

Thyrotropin-releasing hormone (TRH) injected i.p. in doses of 5 mg/kg and higher had a strong locomotor stimulant action with development of frequent rearing, mild sniffing, grooming, preening and other excitatory behaviours. The locomotor stimulation was also produced by bilateral injection of TRH and dopamine (DA) into the nucleus accumbens but not by bilateral injection of these substances into the caudate nucleus. Unilateral intracaudate injection of TRH provoked no behavioural changes in contrast to a distinct circling response to similarly injected DA. Either i.p. or bilateral intra-accumbens injection of haloperidol or pimozide on low doses effectively blocked the locomotor stimulant action of TRH. These results indicate that the DA system in the nucleus accumbens may be of importance in mediation of the locomotor stimulant action of TRH. Differential affinity of TRH to the two DA systems, the mesolimbic and nigrostriatal DA systems is also suggested.