Receptor-genes cross-talk: effect of chronic 5-HT1A agonist 8-hydroxy-2-(di-n-propylamino) tetralin treatment on the expression of key genes in brain serotonin system and on behavior

Dysfunction in brain serotonin (5-HT) system has been implicated in the psychopathology of anxiety, depression, drug addiction, and schizophrenia. The 5-HT_1A receptors play a central role in the control of 5-HTergic neurotransmission. There are some scarce data showing cross-regulation between 5-HT receptors. Here, we investigated whether interaction exists between 5-HT_1A receptor and genes encoding key members in brain 5-HT system. Chronic treatment with selective agonist of 5-HT_1A receptor 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) (1.0 mg/kg i.p., 14 days) produced considerable decrease in hypothermic response to acute administration of 8-OH-DPAT in CBA/Lac mice indicating desensitization of 5-HT_1A receptors. The decrease in 5-HT_1A gene expression as well as decrease in the expression of gene encoding key enzyme in 5-HT synthesis, tryptophan hydroxylase-2 (TPH-2) in the midbrain, and the expression of the gene encoding 5-HT_2A receptor in the frontal cortex was shown. There were no significant changes in 5-HT transporter mRNA level in the midbrain. Despite considerable decrease in the expression of the genes encoding tryptophan hydroxylase-2, 5-HT_1A and 5-HT_2A receptors, chronic 8-OH-DPAT treatment failed to produce significant changes in 5-HT_1A-linked behavior (intermale aggression, open-field behavior, light-dark box, and pinch-induced catalepsy), suggesting compensatory and adaptive effect of genes suppression. The obtained data on the effect of 8-OH-DPAT-induced desensitization of 5-HT_1A receptors on 5-HT_1A, 5-HT_2A and TPH-2 gene expression demonstrated the role of 5-HT_1A receptor as indirect regulator of gene expression. The results provide the first evidence of receptor-key genes interaction in brain 5-HT system and may have profound implications in understanding the functioning of the brain neurotransmitter systems.     

The Effects of Hypothyroidism on 5-HT1A and 5-HT2A Receptors and the Serotonin Transporter Protein in the Rat Brain

The effects of hypothyroidism on 5-HT_1A and 5-HT_2A receptors and the serotonin transporter protein were studied in thyroidectomized male Wistar rats in two experimental groups: 1) animals kept on an iodine-free diet (hypothyroid rats) and 2) animals kept on thyroxine (15 g/kg) for 21 days (giving normal thyroid hormone levels, euthyroid animals). Sham-operated rats served as controls. Binding of [³H]8-OH-DPAT with 5-HT_1A receptors and [³H]citalopram with the transporter protein in the hippocampus and midbrain showed no changes in hypothyroid rats as compared with controls. Conversely, there were significant decreases in [³H]ketanserin binding to 5-HT_2A receptors in the frontal cortex in hypothyroid rats as compared with controls; this decrease was reversed by thyroxine treatment. Thus, losses of cortical 5-HT_2A receptors appears to be the main consequence of hypothyroidism at the level of the serotonin system of the brain.     

Role of the interaction between different types of serotonin and α2-adrenergic receptors in the regulation of audiogenic seizures in DBA/2 micereceptors in the regulation of audiogenic seizures in DBA/2 mice

It is shown that the serotonin receptors 5-HT_1c, 5-HT₃, and 5-HT₄ and α₂-adrenergic receptors are involved in the regulation of audiogenic seizures in DBA/2 mice, and that the effects of these serotonin receptors on the duration and magnitude of convulsive activity are the opoosite of those produced by α₂-adrenergic receptors. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 119, N ^o 4, pp. 381–383, April, 1995     

Significance of initial emotional state for neuroimmunomodulation in conditions of activation and blockade of 5-HT1A receptors

Experiments performed on male CBA mice immunized with sheep erythrocytes at a dose of 5·10⁸ cells showed that the selective agonist of serotonin 5-HT_1A receptors 8-OH-DPAT (1 mg/kg) suppresses the immune response in aggressive animals. In mice demonstrating the submissive type of behavior, formed during 10 days of experience of defeats, activation of 5-HT_1A receptors with 8-OH-DPAT had no effect on the immune response. However, treatment with the selective 5-HT_1A receptor blocker WAY-100635 stimulated the immune response, but only in submissive mice. These data lead to the conclusion that activation and blockade of 5-HT_1A receptors have different effects on the immune response in CBA mice depending on the initial emotional state of the animals, due to different activities of neurotransmitter systems, particularly the serotoninergic, in aggressive and submissive mice. __________ Translated from Zhurnal Vysshei Nervnoi Deyatel’nosti imeni I. P. Pavlova, Vol. 55, No. 4, pp. 567–572, July–August, 2005.     

Identification of neonatal rat hippocampal radial glia cells in vitro

Activation of central 5-HT₃ receptors by the selective agonist m-CPBG (1-(3-chlorophenyl)biguanide hydrochloride, 40 nM i.c.v.) produced stronger hypothermic effect in mice than activation of 5-HT_1A receptors by their agonist 8-OH-DPAT (8-hydroxy-2-(di-n-propilamino)tetralin) injected by the same route at an equimolar dose. The hypothermic effect of m-CPBG was realized by influence on both the heat production and the heat loss: oxygen consumption and CO₂ expiration were decreased; heat dissipation determined by the tail skin temperature was increased. The heat loss effect of 5-HT₃ receptors was significantly shorter than the decrease in metabolism indicating the prevalent role of heat production decrease in 5-HT₃ receptor-induced deep and long-lasing hypothermia. In addition, the decrease in the respiratory exchange ratio (RER) was shown suggesting that the activation of the 5-HT₃ receptors switched metabolism to prevalent use of lipids as the main energetic substrate. 5-HT_1A receptor agonist 8-OH-DPAT (40 nM i.c.v.) produced less depressing effect on general metabolism: a decrease in oxygen consumption and CO₂ excretion began later and was not so deep as after m-CPBG administration. Heat-loss effect of 5-HT_1A receptors activation was not observed. In contrast to m-CPBG effect, RER after 5-HT_1A receptors activation raised immediately after injection and then gradually decreased to the values observed in m-CPBG-treated mice. Obtained results show that activation of central 5-HT₃ receptors are more effective in hypothermia induction due to marked decrease in thermogenesis and increase in heat loss.     

Effect of serotonin 5-HT1A receptor agonists on sexual motivation of male mice

The effect of selective agonists of serotonin 5-HT_1A receptors on sexual arousal (its behavioral and hormonal components) in male CBA mice caused by estral females was studied. Injections of 8-OH-DPAT, flesinoxane, and ipsapirone significantly decreased the main behavioral parameter of sexual motivation (duration of the male's stay near the wall separating it from the receptive female). The activating effect of the female on the pituitary gonadal system of the male was completely blocked: the blood testosterone level did not increase. Therefore, the behavioral and hormonal components of sexual activation of males are regulated by the serotonin mechanisms alone, in which the cerebral 5-HT_1A receptors are involved. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 127, No. 2, pp. 224–226, February, 1999     

Effect of imipramine on the behavior and cerebral 5-HT1A serotonin receptors in mice genetically predisposed to catalepsy

Acute injection of imipramine to NPK mice hereditary predisposed to pinching catalepsy reduced immobility in the forced swimming test, but had no effect on catalepsy. Chronic treatment with imipramine reduced the severity of catalepsy and functional activity of 5-HT_1A serotonin receptors, but did not modify their expression in the hippocampus. NPK mice can be a convenient model for studies of the effects of antidepressant. __________ Translated from Byulleten’ Eksperimental’noi Biologii i Meditsiny, Vol. 141, No. 1, pp. 53–55, January, 2006     

Effect of chronic activation of 5-HT3 receptors on 5-HT3, 5-HT1A and 5-HT2A receptors functional activity and expression of key genes of the brain serotonin system

Among serotonin (5-HT) receptors, the 5-HT₃ receptor is the only ligand-gated ion-channel. Little is known about the interaction between the 5-HT₃ receptor and other 5-HT receptors and influence of 5-HT₃ chronic activation on other 5-HT receptors and the expression of key genes of 5-HT system. Chronic activation of 5-HT₃ receptor with intracerebroventricularly administrated selective agonist 1-(3-chlorophenyl)biguanide hydrochloride (m-CPBG) (14 days, 40 nmol, i.c.v.) produced significant desensitization of 5-HT₃ and 5-HT_1A receptors. The hypothermic responses produced by acute administration of selective agonist of 5-HT₃ receptor (m-CPBG, 40 nmol, i.c.v.) or selective agonist of 5-HT_1A receptor (8-hydroxy-2-(di-n-propylamino)tetralin) (8-OH-DPAT, 1 mg/kg, i.p.) was significantly lower in m-CPBG treated mice compared with the mice of control groups. Chronic m-CPBG administration failed to induce any significant change in the 5-HT_2A receptor functional activity and in the expression of the gene encoding 5-HT_2A receptor. Chronic activation of 5-HT₃ receptor produced no considerable effect on the expression on 5-HT₃, 5-HT_1A, and 5-HT transporter (5-HTT) and tryptophan hydroxylase-2 (TPH-2) genes – the key genes of brain 5-HT system, in the midbrain, frontal cortex and hippocampus. In conclusion, chronic activation of ionotropic 5-HT₃ receptor produced significant desensitization of 5-HT₃ and postsynaptic 5-HT_1A receptors but caused no considerable changes in the expression of key genes of the brain 5-HT system.     

Chronic Actions of Thyroxine on Behavior and Serotonin Receptors in Mouse Strains with Contrasting Predispositions to Catalepsy

The studies reported here addressed the effects of chronic administration of thyroxine (2 mg/liter for 60 days) on catalepsy and the functional activity and expression of the 5-HT_1A and 5-HT_2A receptor genes in the brains of adult male mice of the cataleptic ASC strain and the catalepsy-resistant AKR strain. Thyroxine induced cataleptics in AKR mice but had anticataleptic activity in ASC animals. Chronic thyroxine administration increased the functional activity and expression of 5-HT_2A receptors in the frontal cortex in AKR mice but not in ASC mice. In ASC mice, the hormone significantly weakened the hypothermic effect of the 5-HT_1A receptor agonist 8-OH-DPAT, though it did not alter the expression of these receptors. These results suggest that 5-HT_2A receptors are involved in the cataleptogenic while 5-HT_1A receptors are involved in the anticataleptic effects of the hormone in mice.     

Effect of Selective Agonist of Serotonin 5-HT<Subscript>1A</Subscript> Receptors on Defensive Behavior in Mice with Different Predisposition to Catalepsy

We studied the effect of activation of serotonin 5-HT_1A receptors with selective agonist 8-OHDPAT (0.1, 0.5, and 1.0 mg/kg) on intraspecies aggression and freezing reaction (catalepsy) in male mice of catalepsy-resistant AKR/J and two catalepsy-prone strains CBA/Lac and congenic AKR.CBA-D13Mit76. The latter strain differs from AKR strain only by terminal chromosome 13 fragment transferred from CBA strain and containing a locus determining predisposition to catalepsy and a gene encoding 5-HT_1A receptor. 8-OH-DPAT in a low dose (0.1 mg/kg) affecting primarily presynaptic receptors suppressed aggressive behavior in CBA mice, but had no effect on the time of cataleptic freezing. At the same time, this dose of the drug produced no significant effect on aggression in AKR and AKR.CBA-D13Mit76 mice, but significantly attenuated freezing in AKR.CBA-D13Mit76 mice. High doses of 8-OHDPAT (0.5 and 1 mg/kg) which affected mainly postsynaptic receptors inhibited catalepsy in CBA and AKR.CBA-D13Mit76 mice and in a dose of 1 mg/kg it suppressed aggression in all tested mouse strains. We concluded that the genome of the recipient strain (AKR) modulated the involvement of 5-HT_1A receptors into the regulation of aggression and catalepsy in mice.     

Involvement of brain serotonin 5-HT<Subscript>1A</Subscript> receptors in genetic predisposition to aggressive behavior

Experiments were performed on Norwegian rats selected over more than 59 generations for high and low levels of high-affective defensive aggressivity and on highly aggressive (offensive) Tg8 mice with irreversible monoamine oxidase A knockout. There were significant differences in the functional state and expression of 5-HT_1A receptors between highly aggressive and non-aggressive animals. Functional activity assessed in terms of hypothermia evoked by a 5-HT_1A agonist was significantly greater in non-aggressive rats and mice than in aggressive animals. The high level of functional activity in non-aggressive rats coincided with a greater level of expression of 5-HT_1A receptors in the midbrain. The level of 5-HT^1A receptor mRNA in aggressive mice was unchanged in the midbrain and hypothalamus and was increased in the frontal cortex and amygdaloid complex. These results led to the conclusion that 5-HT_1A receptors play a significant role in the mechanisms of genetic predisposition to aggressive behavior. __________ Translated from Zhurnal Vysshei Nervnoi Deyatel’nosti imeni I. P. Pavlova, Vol. 56, No. 4, pp. 537–542, July–August, 2006.     

5-HT1A receptor activation counteracts c-Fos immunoreactivity induced in serotonin neurons of the raphe nuclei after immobilization stress in the male rat

The serotoninergic system and the 5-HT_1A receptors have been involved in the brain response to acute stress. The aim of our study was evaluate the role of the 5-HT_1A receptors in serotoninergic cells of rostral and caudal raphe nuclei under acute immobilization in rats. Double immunocytochemical staining of 5-hydroxy-tryptamine and c-Fos protein and stereology techniques were used to study the specific cell activation in the raphe nuclei neurons in five groups (control group, immobilization group (immobilization lasting 1 h), DPAT group (8-OH-DPAT 0.3 mg/kg, s.c.), DPAT + IMMO group (8-OH-DPAT 0.3 mg/kg, s.c., 30′ prior acute immobilization) and WAY + DPAT + IMMO group (WAY-100635 0.3 mg/kg, s.c. and 8-OH-DPAT 0.3 mg/kg, s.c., 45′ and 30′, respectively, before immobilization). Our results showed an increase in the number of c-Fos immunoreactive nuclei in serotoninergic cells in both dorsal and median raphe nuclei in the immobilized group. The 8-OH-DPAT pretreatment counteracted the excitatory effects of the acute immobilization in these brain regions. In addition, WAY-100635 administration reduced the effect of 8-OH-DPAT injection, suggesting a selective 5-HT_1A receptor role. Raphe pallidus and raphe obscurus did not show any differences among experimental groups. We suggest that somatodendritic 5-HT_1A receptors in rostral raphe nuclei may play a crucial role in both mediating the consequences of uncontrollable stress and the possible beneficial effects of treatment with 5-HT_1A receptor agonists.     

Role of various types of serotonin receptors in regulation of drinking behavior and salt appetite in vasopressin-deficient brattleboro rats

Serotonin 5-HT_1A receptor agonist 8-OH DPAT suppressed drinking behavior in Brattleboro and Wistar rats. 5-HT_1B agonist CGS-12066A and 5-HT_2A antagonist ketanserin did not affect drinking behavior in Brattleboro rats; 5-HT₃ antagonist ondansetron suppressed water consumption and 5-HT_1A agonist stimulated salt appetite in Brattleboro, but not in Wistar rats. Presumably, vasopressin regulates thirst and salt appetite by modulating sensitivity/density of various types of 5-HT receptors.     

Age-related alterations in brain α1-adrenoceptors of hypertensive rats: Their possible role in the development of arterial hypertensionof hypertensive rats: Their possible role in the development of arterial hypertension

The binding of labeled agonist (³H-prazosin) to α₁-receptors in the frontal cortex, hypothalamus, and medulla oblongata of hypertensive (NISAG) and normotensive (Wistar) rats of different age is studied to elucidate the role of these receptors in the development of hereditary stress-induced arterial hypertension. It is found that the density of α₁-adrenoceptors in the hypothalamus of 30-day-old and adult NISAG rats is decreased, while in the medulla oblongata the number of these receptors, starting from the first week of life, is greater than in Wistar rats of the same age. From a comparison of these findings with the development of hypertension in NISAG rats it is concluded that α₁-adrenoceptors of the medulla oblongata are involved in this process. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 120, N ^o 7, pp. 78–80, July, 1995 Presented by V. P. Kaznacheev, Member of the Russian Academy of Medical Sciences     

Central 5-HT3 receptor-induced hypothermia in mice: Interstrain differences and comparison with hypothermia mediated via 5-HT1A receptor

The selective agonist of serotonin 5-HT₃ receptor 1-(3-chlorophenyl)biguanide hydrochloride (m-CPBG) administered intracerebroventricularly (40, 80 or 160 nmol) produced long-lasting dose-dependent hypothermic response in AKR/2J mice. m-CPBG (160 nmol i.c.v.) induced profound hypothermia (delta t = −4 °C) that lasted up to 7 h. m-CPBG (40 nmol i.c.v.)-induced hypothermia was attenuated by 5-HT₃ receptor antagonist ondansetron pretreatment. At the same time, intraperitoneal administration of m-CPBG in a wide range of doses (0.5, 1.0, 5.0 or 10.0 mg/kg) did not affect the body temperature. These findings indicate: (1) the implication of central, rather than peripheral 5-HT₃ receptor in the thermoregulation; (2) the inability of m-CPBG to cross blood–brain barrier in mice. The comparison of brain 5-HT₃-induced hypothermic reaction in six inbred mouse strains (DBA/2J, CBA/Lac, C57BL/6, BALB/c, ICR, AKR/J) was performed and two highly sensitive to m-CPBG strains (CBA/Lac and C57BL/6) were found. In the same six mouse strains the functional activity of 5-HT_1A receptor was studied. The comparison of hypothermic reactions produced by 5-HT_1A receptor agonist 8-OH-DPAT (1.0 mg/kg i.p.) and m-CPBG revealed significant correlation between 5-HT₃ and 5-HT_1A-induced hypothermia in five out of six investigated mouse strains. 5-HT_1A receptor antagonist p-MPPI pretreatment (1 mg/kg i.p.) diminished hypothermia produced by centrally administered m-CPBG (40 nmol i.c.v.). The data suggest the cross-talk between 5-HT_1A and 5-HT₃ receptors in the mechanism of 5-HT-related hypothermia.     

UHF-dielectrometry of the urine in prognosis of aggregation stability

The hypothermic effects of 5-HT_1A serotonin receptor agonist 8-OH-DPAT after intranasal, intraperitoneal, and subcutaneous administration were compared. In a dose of 1 mg/kg 8-OH-DPAT induced similar thermal reactions after administration by all three routes. In a dose of 0.5 mg/kg 8-OH-DPAT caused no appreciable changes in body temperature after intraperitoneal injection and decreased it after subcutaneous and intranasal administration. No genotypic differences in the effects of 5-HT_1A receptor agonist administered by different routes were detected in four inbred mouse strains. Translated from Byulleten’ Eksperimental’noi Biologii i Meditsiny, Vol. 146, No. 10, pp. 413-415, October, 2008     

Autoradiographic mapping of serotonin 5-HT1A, 5-HT1D, 5-HT2A and 5-HT3 receptors in the aged human spinal cord

Quantitative autoradiography with selective radioligands was used to establish the respective distribution of serotonin 5-HT_1A, 5-HT_1D, 5-HT_2A and 5-HT₃ receptors at the cervical, thoracic and lumbar levels of the spinal cord from subjects who died at 81–94 years. A high density of 5-HT_1A receptors, labeled by [³H]8-hydroxy-2-(di-n-propylamino)tetralin ([³H]8-OH-DPAT), was found in the superficial layers of the dorsal horn, with a significant enrichment ( 20%) in the lumbar vs. the thoracic and cervical segments. In contrast, only very low specific labeling by [³H]8-OH-DPAT (i.e. less than 10% of that measured in the dorsal horn), was detected in the ventral horn. 5-HT_1D sites labeled by [¹²⁵I]serotonin-O-carboxymethyl-glycyl-iodo-tyrosinamide ([¹²⁵I]GTI) were also mainly located within the superficial layers of the dorsal horn, but no difference in their relative density was noted at the three levels of the spinal cord examined. 5-HT_2A sites labeled by [³H]ketanserin were found in the dorsal horn of the cervical segments but no specific binding of this radioligand could be detected at any other level of the spinal cord of such aged subjects. Finally, a high density of [³H]S-zacopride-labeled 5-HT₃ receptors was noted especially in the most superficial layer (lamina I) of the dorsal horn at all segments examined. These data provide anatomical support for a role of spinal serotonin especially in nociception processing.     

Effects of Chronic Fluoxetine Treatment on Catalepsy and the Immune Response in Mice with a Genetic Predisposition to Freezing Reactions: The Roles of Types 1A and 2A Serotonin Receptors and the tph2 and SERT Genes

ASC (Antidepressant-Sensitive Catalepsy) mice, bred for a high predisposition to catalepsy, are characterized by depression-like behavior and decreased immune responses. Chronic administration of fluoxetine, which is a selective serotonin reuptake inhibitor antidepressant widely used in clinical practice, to mice of this strain weakened catalepsy and normalized the number of rosette-forming cells in the spleen. In mice of the parental cataleptic strain CBA/Lac, fluoxetine had no effect on the level of catalepsy or the immune response. Analysis of the effects of fluoxetine on the functional activity of 5-HT_1A and 5-HT_2A receptors, and the expression of 5-HT_1A receptor genes in the frontal cortex and midbrain and 5-HT_2A receptors in the frontal cortex, as well as the tryptophan hydroxylase-2 and the serotonin transporter genes in the midbrain showed that the antidepressant had no effect on these parameters in ASC mice, but decreased the functional activity of 5-HT_2A receptors in CBA/Lac mice. The possibility that the actions of fluoxetine on catalepsy and the immune response in mice with depression-like states are mediated via other serotoninergic mechanisms is discussed.     

On the role of brain serotonin in expression of genetic predisposition to catalepsy in animal models

The activity of the rate-limiting enzyme of serotonin biosynthesis, tryptophan hydroxylase, in the striatum but not in the hippocampus and midbrain of rats bred for predisposition to catalepsy was higher than in nonselected rats. Mice of the highly susceptible to catalepsy CBA strain also differed from other noncataleptic mouse strains by the highest tryptophan hydroxylase activity in the striatum. Inhibition of tryptophan hydroxylase with p-chlorophenylalanine and p-chloromethamphetamine drastically decreased immobility time in hereditary predisposed to catalepsy animals. A decrease in the ³H-ketanserin specific binding in the striatum of cataleptic rats and CBA mice was found. It was suggested that this decrease in 5-HT2A serotonin receptor density represented a down regulation of the receptors due to an activation of serotonergic transmission in striatum. It is suggested that hereditary catalepsy may be resulted from genetic changes in the regulation of serotonin metabolism in striatum. © 1995 Wiley-Liss, Inc.     

Cloning of serotonin 5-HT1 receptor subtypes from the chimpanzee, gorilla and Rhesus monkey and their agonist-induced guanosine 5′γS triphosphate binding

5-HT₁ receptor subtypes (_1B, _1D and _1F) have been implicated in migraine pathophysiology and their ligands have been examined for pharmacological actions in various experimental animal models. Considerable divergences exist, however, in their primary sequences between experimental animals and human, and additional models closer to human, such as non-human primates seem to be useful for migraine research. Earlier, we cloned the 5-HT_1D, and here 5-HT_1B and 5-HT_1F receptors from the chimpanzee, gorilla and Rhesus monkey, via polymerase chain reactions with their genomic DNAs and primers designed from the corresponding human receptors. Direct sequencing of PCR products showed that the 5-HT_1B receptors from the chimpanzee, gorilla and monkey differ from the human receptor by 0, 1 and 7 residues, respectively while 5-HT_1F receptors differ by 0, 3 and 10 residues, respectively. These divergent residues are mostly conservatively substituted and also largely confined to the N-terminal region and the 3rd intracellular loop, away from transmembrane segments and intracellular loops near membrane which are critical for ligand binding and G protein coupling. The chimpanzee 5-HT_1D, 5-HT_1B and monkey 5-HT_1F receptors, as heterologously expressed in human embryonic kidney 293 cells, showed robust agonist-induced guanosine 5′gamma ³⁵S triphosphate (GTPγ³⁵S) binding through activation of G proteins containing Gγ_i subunits. Moreover, pronounced inhibition of basal GTPγ³⁵S binding by methiothepin (an antagonist), representing constitutively active receptors, was observed with only 5-HT_1D. Overall, ligand binding and GTPγ³⁵S binding profiles for these primate receptors are comparable to those for the human receptors and validate non-human primates as useful models for human migraine research.