Effects of the 5-HT1A antagonist (+)-WAY-100135 on murine social and agonistic behavior

Interactions of a standardized flavonoid fraction from Tilia americana with Serotoninergic drugs in elevated plus maze

ETHNOPHARMACOLOGICAL RELEVANCE

Tilia americana var. mexicana (Schltdl) Hardin (Tiliaceae) aerial parts (bracts and flowers) are used in the traditional Mexican medicine to treat nervous disorders, as sedative and to treat insomnia. A fraction of this species called FC1 (organic fraction from this plant) was proposed, described as anxiolytic and characterized by the presence of flavonoids. In the present work, this fraction was standardized, and its interaction with different serotonergic drugs was tested. We used the elevated plus maze model as anxiety test and the open field test so as to observe a possible effect on mice׳s motor behavior.

MATERIAL AND METHODOLOGY

HPLC technique was used to quantify the flavonoids contained in a fraction called F1C. Different doses of F1C were administered to ICR mice (12.5, 25, 37.5 and 50mg/kg, oral pathway) then they were exposed to elevated plus maze or open field test. After, each dose of F1C fraction was co-administered with different drugs, in order to evaluate the animal׳s behavior: DOI agonist (2.0mg/kg) and KET antagonist (0.03mg/kg) of 5-HT2A receptors; 8-OH-DPAT (0.1mg/kg) selective agonist and WAY100635 (0.5mg/kg) antagonist of 5HT1 receptors.

RESULTS

The HPLC quantitative analysis revealed the F1C composition (mg/g of extract): tiliroside (28.56), glucoside of quercetin (16.25), quercitrin (7.96), rutin (3.93), Kaempferol (2.83). The Emax for F1C curve was 80.6% for time to open arms with an ED50 of 15.09 mg/kg. The combination of F1C with DOI gives a significant increase of the F1C anxiolytic effect (Emax=111% and ED50=13.51 mg/kg), while KET blocks it completely (Emax=12.25% and ED50=2.4 mg/kg). The administration of F1C with 8-OH-DPAT does not generate significant changes on the time to open arms, although it does induce a decrement in F1C potency (Emax=83.3% and ED50=33.3mg/kg). When F1C and WAY-100365 are combined, the anxiolytic activity of the fraction decreases (Emax=33.3% and ED50=102.10mg/kg).

CONCLUSIONS

The medicinal use attributed to Tilia americana for their effect on central nervous system, could be in part in the flavonoid fraction (F1C) with anxiolytic activity which is dose dependent, and has the ability to interact with the serotonergic system. It is necessary to advance in the study of the mechanism of action, using other techniques such in vitro analysis.

Serotonin, social status and sex change in the bluebanded goby Lythrypnus dalli

In a variety of vertebrates, highly aggressive individuals tend to have high social status and low serotonergic function. In the sex changing fish Lythrypnus dalli, serotonin (5-HT) may be involved as a mediator between the social environment and the reproductive system because social status is a critical cue in regulating sex change. Subordination inhibits sex change in L. dalli, and it is associated with higher serotonergic activity in other species. We tested the hypothesis that high serotonergic activity has an inhibitory effect on sex change. In a social situation permissive to sex change, we administered to the dominant female implants containing the serotonin precursor 5-hydroxytryptophan (5-HTP). In a social situation not conducive to sex change, we administered either the serotonin synthesis inhibitor p-chlorophenylalanine (PCPA) or the 5-HT(1A) receptor antagonist p-MPPI. After three weeks we used HPLC to measure brain levels of 5-HT and its metabolite 5-hydroxyindoleacetic acid (5-HIAA). We also performed PCPA, p-MPPI and fluoxetine injections in size-matched pairs of females to assess its effect on dominance status. Males and newly sex changed fish showed a trend for higher levels of 5-HIAA and 5-HT/5-HIAA ratio than females. The different implants treatments did not affect the probability of sex change. Interestingly, this species does not seem to fit the pattern seen in other vertebrates where dominant individuals have lower serotonergic activity than subordinates.

Female gastrin-releasing peptide receptor (GRP-R)-deficient mice exhibit altered social preference for male conspecifics: implications for GRP/GRP-R modulation of GABAergic function

We studied female GRP-R-deficient mice with respect to olfactory function and social behavior toward male conspecifics. Results of a food exploration test (hidden cookie method) revealed that the olfactory ability of these mutant mice is identical to that of wild-type mice. However, when preference toward either a socially dominant or subordinate male mouse was assessed in a social preference test, wild-type mice showed a greater preference for socially dominant males than did GRP-R-deficient mice. In contrast, in a social investigation test to an anesthetized male mouse, GRP-R-deficient mice exhibited greater investigatory behavior toward the target male than did wild-type mice. When female C57BL/6J mice were given diazepam (0, 1, 2 or 4 mg/kg, i.p.), their investigatory behavior to the anesthetized male target was increased in a dose-dependent manner. Conversely, i.p. administration of bicuculline (1 mg/kg) significantly decreased the social investigatory behavior of female GRP-R-deficient mice, but not of wild-type mice. These results indicate that female GRP-R-deficient mice exhibit altered responsiveness to male conspecifics relative to their wild-type counterparts, and suggest that this outcome may be attributable, at least in part, to altered GABAergic function in these mutant mice.

Male mice lacking the gastrin-releasing peptide receptor (GRP-R) display elevated preference for conspecific odors and increased social investigatory behaviors

Previously, we generated gastrin-releasing peptide receptor null mutant mice (GRP-R-deficient mice), and found that these animals displayed increased non-aggressive social responses in an ordinary social interaction test using a resident-intruder method. In the present study, we examined in more detail the social behaviors of GRP-R-deficient male mice. In social interaction tests, GRP-R-deficient mice showed more social responses, such as sniffing and nosing, relative to wild-type mice, and similar results were obtained whether GRP-R-deficient mice served as intruders or residents. In the same way, they showed more contact behaviors toward an anesthetized conspecific, and less locomotor activity than wild-type mice in a social investigation test toward an anesthetized male mouse. Since olfactory systems play important roles in the social behavior of rodents, olfactory preference tests were conducted in order to evaluate the olfactory properties of GRP-R-deficient mice. The results suggest that no differences exist between wild-type mice and GRP-R-deficient mice in the preference between a novel sawdust odor and their own odor, or that of other male mice. However, GRP-R-deficient mice preferred the odor of other male mice to their own, in contrast to wild-type mice. Furthermore, the preferences of GRP-R-deficient and wild-type mice were not disrupted by intraperitoneal infusion of diazepam (1.5 mg/kg). These results indicate that neither the motion, nor the behavior of conspecifics, nor reduced anxiety lead to the increased non-aggressive social responses and/or social investigatory behaviors in GRP-R-deficient mice. Rather, these latter behaviors may be a consequence of altered cognition of conspecific odors in the mutant mice.

Lack of effect of the 5-HT(1A) receptor antagonist WAY-100635 on murine agonistic behaviour

The present study examined the influences of the selective 5-HT1A receptor antagonist, WAY-100635, on the social and agonistic behavior exhibited by male resident mice during encounters with unfamiliar intruder conspecifics. Acute administration of WAY-100635 (0.01-1.0 mg/kg sc) dose dependently enhanced the duration of resident maintenance behavior, reaching statistical significance at 1.0 mg/kg. The duration of resident attend/approach behavior was reduced at 0.01 mg/kg. Drug-free intruder animals showed a reduction in the frequency and duration of attend/approach behavior when the resident mice were treated with 0.01 mg/kg WAY-100635. No other significant effects on behavior were detected for WAY-100635. A previous investigation reported that WAY-100635 induced anxiolytic-like effects in the mouse light/dark box test. In the present study, however, the level of defensive behavior of the saline-treated resident mice was too low for any further anxiolytic-like attenuation of this behavior to be observed. Therefore, no conclusions regarding the potential anxiolytic activity of WAY-100635 may be drawn from the data presented here. Current results are consistent with data for the lack of effect of WAY-100635 on rat agonistic behavior but contrast with findings for the effects of the 5-HT1A receptor antagonists (+)-WAY-100135 and SDZ 216-525 on mouse agonistic behavior.

Testosterone and its metabolites modulate 5HT1A and 5HT1B agonist effects on intermale aggression

Our understanding of the neurochemical and neuroendocrine systems' regulating the display of offensive intermale aggression has progressed substantially over the past twenty years. Pharmacological studies have shown that serotonin, via its action at 5HT1A and/or 5HT1B receptor sites, modulates the display of intermale aggressive behavior and that its effects serve to decrease behavioral expression. Neuroendocrine investigations, in turn, have demonstrated that male-typical aggression is testosterone-dependent and studies of genetic effects, metabolic function and steroid receptor binding have shown that facilitation of behavioral displays can occur via independent androgen-sensitive or estrogen-sensitive pathways. Remarkably, there have been virtually no studies that examined the interrelationship between these facilitative and inhibitory systems. As an initial step toward characterizing the interaction between the systems, studies were conducted that assessed hormonal modulation of serotonin function at 5HT1A and 5HT1B receptor sites. They demonstrated: (1) that the androgenic and estrogenic metabolites of testosterone differentially modulate the ability of systemically administered 8-OH-DPAT (a 5HT1A agonist) and CGS12066B (a 5HT1B agonist) to decrease offensive aggression; and (2) when microinjected into the lateral septum (LS) or medial preoptic area (MPO), the aggression-attenuating effects of 1A and 1B agonists differ regionally and vary with the steroidal milieu. In general, the results suggest that estrogens establish a restrictive environment for attenuation of T-dependent aggression by 8-OH-DPAT and CGS 12066B, while androgens either do not inhibit, or perhaps even facilitate, the ability of 5HT1A and 5HT1B agonists to reduce aggression. Potential mechanisms involved in the production of these steroidal effects are discussed and emerging issues that may impact on efforts to develop an integrative neurobiological model of offensive, intermale aggression are considered.

Androgens and estrogens modulate 5-HT1A and 5-HT1B agonist effects on aggression

Intermale offensive aggressive behavior is facilitated by gonadal steroids and inhibited by serotonin (5-HT), presumably through its effects at 5-HT1A and 5-HT1B receptor sites. To examine the interaction between these neuroendocrine and neurochemical regulatory systems, CF-1 male mice were gonadectomized and implanted with silastic capsules containing either diethylstilbestrol (DES, a synthetic estrogen), the nonaromatizable androgens methyltrienolone (R1881) or dihydrotestosterone (DHT), or testosterone (T). Two weeks later, they were given 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT, a 5-HT1A agonist; 0.1 or 1.0 mg/kg), CGS12066B (a 5-HT1B agonist; 4.0 or 8.0 mg/kg), 0.1 or 1.0 mg/kg 8-OH-DPAT + 4.0 mg/kg CGS12066B, or vehicle, and tested for aggression. In the presence of DES, the higher 8-OH-DPAT dose given in combination with CGS attenuated aggression in comparison to vehicle controls. When given nonaromatizable androgen (R1881 or DHT), all drug treatments except 0.1 mg/kg 8-OH-DPAT significantly reduced offensive attack behavior. In the presence of T, which provides estrogenic and androgenic stimulation, aggression scores were significantly reduced when males were given the high dose of 8-OH-DPAT or CGS12066B, as well as in the 1.0 mg/kg 8-OH-DPAT + CGS12066B condition. Assessments of changes in motor behavior showed significant impairment when 8.0 mg/kg CGS12066B was administered across all hormonal conditions, indicating that reductions in offensive aggression in these treatment groups were nonspecific. The results demonstrate differential effects of the steroidal environment on the ability of 5-HT1A and 5-HT1B agonists to modulate aggression, with estrogens producing a more restrictive environment than androgens for serotonergic inhibition of male-typical aggressive behavior.

Combined effects of Gepirone and (+)WAY 100135 on territorial aggression in mice

The purpose of this investigation was to elucidate the involvement of the serotonergic 5-HT1A system in the control of aggression. The paradigm was the response of a resident mouse to an intruder into its territory. Three experiments were performed to assess the action of various doses of Gepirone (a partial agonist) and (+)WAY 100135 (a putative antagonist), separately and in combination, on aggression and on rectal body temperature. The most consistent action of Gepirone was an increase in the latency to attack. After initiation of fighting, rates of attack, chase, and tail rattling were reduced in a dose-dependent manner by i.p. administration of 2.5, 5, and 10 mg/kg of Gepirone. There was no evidence of sedation or motor impairment, but autogrooming was decreased. When doses of 2.5, 5, and 10 mg/kg of (+)WAY 100135 (WAY) were given, no effects whatsoever on aggressive or other behaviors were observed. In a third experiment, a two-factor design was followed in which injection of WAY (0, 2.5, and 5 mg/kg) was followed 15 min later by injection of Gepirone (0, 2.5, 5, and 10 mg/kg). WAY decreased attack latency, increased attack rate, and attenuated the marked dose-dependent aggression reducing properties of Gepirone. The test procedure resulted in "stress hyperthermia," which was reduced by Gepirone and increased by WAY. In both behavioral and temperature measures, the larger dose of WAY proved to be less effective than the smaller one. The results support the involvement of the 5-HT1A system in the modulation of some forms of aggression.

Recent developments in anxiety, stress, and depression

Recent research in the development, analysis, and pharmacology of animal tests of state anxiety is discussed, including the use of responses to predator odours, the role of learning in modifying the anxiety measured in the plus-maze, and the roles of cholinergic, NMDA, and dopaminergic systems. Developmental and genetic factors are considered with particular reference to the development of tests of trait anxiety. The roles of 5-HT1A receptors in anxiety, depression, impulsivitity, and agonistic behaviours are discussed. Recent studies on the impacts of stress on neurotransmitter, endocrine, and immune systems and the interactions between these systems are discussed, with particular emphasis on their contributions to the development of pathologic states relevant to anxiety and depression.