[Central effect of xylazine and yohimbin on pain sensitivity of rat during estrous cycle in formalin test]

Sex hormone is supposed to modify pain sensitivity. The aim of the present study was to investigate, the role of 2 adrenergic receptors in nociception using formalin test. Formalin test was performed by subcutaneous injection of 50 ml formalin [%2.5] solution into hind paw. Animals were divided into 4 groups as control group [intact animal], sham group [received 2 micro l of artificial CSF by ICV route], agonist group [received 2 micro l of xylazine 5 and 10 mg/ rat by ICV route] and antagonist group [received 2 micro l of yohimbin 5 and 10 mg/ rat by ICV route]. Data were analyzed by two way ANOVA and post- hoc test of tukey's test. Data showed that xylazine significantly decreased [p<0.05] pain sensitivity during all stages of estrous cycle; analgesic effect of xylazine was high in estrus stage of estrous cycle and low in metestrous stage of estrous cycle. Yohimbin in all stages of estrous cycle significantly increased [p<0.05] pain sensitivity. Hyperalgesic effect of yohimbin was high during metestrous stage of estrous cycle and it was low in proestrous stage of estrous cycle. Results of present study indicated that interaction of alpha2 adrenergic system with endogenous sex steroid is important in the modulation of pain sensitivity

Role of peripheral alpha2 adrenergic receptors in tonic pain during different stages of estrous cycle in rats

Estrogen and progesterone are supposed to modify pain sensitivity. However, the actual role of each of these steroid hormones in this respect is not well known. Plasma concentrations of these hormones show variation during estrous cycle. The role of alpha2 receptors in tonic pain has been pointed out. The aim of the present study was to investigate the agonist and antagonist effect of alpha2 adrenergic receptors on tonic pain sensitivity during all stages of estrous cycle in female rats. Xylasine as alpha 2 agonist and yohimbin as alpha 2 antagonist were used via intraperitoneal route [IP]. Adult rats weighing 180-200 grams were used. Animals were maintained on 12h reverse light/dark cycle for 7 days prior to the experiment. Water and food was available ad libitum. Formalin test was performed by subcutaneous injection of 50 micro l formalin [2.5%] solution into the hind paw. Formalin test was performed in all stages of estrous cycle for 60 minutes. Animals were divided into four groups; 1- control group [intact animal], 2- Sham group [animals received 0.2 ml normal saline by IP route], 3- Agonist groups [animals received 0.2 ml xylasine 1, 3 mg/kg body weight by IP route] and 4- Antagonist group [animals received 0.2 ml yohimbine 1, 3 mg/kg body weight by IP route]. Data were statistically analyzed using 2 way ANOVA test followed by Tukey's test as posthoc test. P < 0.05 was considered significant. Results showed that xylasine significantly [p < 0.05] decreases pain sensitivity in all stages of estrous cycle. Analgesic effect of xylasine was maximum in estrus stage of estrous cycle and minimum in metestrus stage of estrous cycle. Yohimbine significantly [p < 0.05] increases pain sensitivity in all stages of estrous cycle. Hyperalgesic effect of yohimbine was maximum in metestrus stage of estrous cycle and minimum in estrus stage of estrous cycle. These results indicate that alpha2 adrenergic system and endogenous steroids have an important role in pain sensitivity

Surveying steroid participation on GABA- related activities

gamma-aminobutyricacid [GABA], a major neurotransmitter in the central nervous system, also acts as a paracrine or autocrine signaling molecule in endocrine tissues such as the pancreatic islets, adenohypophysis, and testis. It has been demonstrated that metabolites of progesterone and corticosterone naturally act via the GABA[A] - membrane receptor and they have sedative-hypnotic, anxiolytic, anticonvulsant, muscle-relaxant and anesthetic drugs properties. Also the brain as a steroidogenic organ contributes to produce these steroids. The aim of this study was to find out the steroids participation on the GABA- related activities. An injection canula was inserted into lateral ventricle of the sham and experimental adult female rats by stereotaxic surgery. One week late, at proesterus day, diazepam [GABA[A]-receptor agonist] with doses of 250 and 500microg/rat, bicuculine [GABA[A]-receptor antagonist] with doses of 1.5 and 3 ng/rat, baclofen [GABA[B] -receptor agonist] with doses of 4.27 and 8.54 microg/rat and CGP35348 [GABA[B] -receptor antagonist] with doses of 3 and 5 micro g/rat were intracerebroventriculary [ICV] injected to the experimental groups, while equal volume [2 micro l] of artificial CSF was injected to the sham operated group. Blood samples were collected thrice at 9 AM, 11 AM and 1PM. The serum progesterone level was determined using RIA method. Data were analyzed by one way ANOVA and Duncans test at p<0.05 for the significant level. The results showed that GABAergic system activity via both GABA[A] and GABA[B] receptors has significantly changed the serum progesterone level Comparing the results of this research with earlier studies, it is concluded that GABAergic system has a close relation with steroidogenesis and the steroids participate in GABA- related activities

Effect of xylazine and yohimbine on the phasic pain during the estrous cycle in the rat

The aim of the present study was to investigate the effect of alpha2-adrenergic agonist [xylazine] and antagonist [yohimbine] on phasic pain during estrous cycle in female rats. Adult female rats weighing 180-220 g were kept under controlled temperature [21-24[degree]C] and light/dark conditions [light on at 6:00 a.m. and light off at 6:00 p.m.]. Animals were divided into four groups: 1] control group which received 0.3 ml of normal saline by intraperitoneal [IP] route; 2] IP experimental group which received 0.3 ml xylazine 3, 4.5 and 6 mg/kg and yohimbine 1, 2 and 4 mg/kg by IP route; 3] sham group which received 2 micro l of artificial cerebrospinal fluid by intra cerebral ventricle [ICV] route and 4] ICV experimental which received 2 micro l xylazine 10 and 20 micro g/rat and yohimbine 5 and 10 micro g/rat by ICV route. Cannulae were implanted into the left lateral ventricle using stereotaxic method. Pain sensitivity was measured by tail flick test, which was performed before injection, 15 and 30 min after injection in all groups. Xylazine decreased pain sensitivity significantly [P<0.05] during the estrous cycle; while higher analgesia was observed in the proestrus phase for IP and ICV routes. Yohimbine increased pain sensitivity significantly [P<0.05] during the estrous cycle; while higher hyperalgesia was observed in the metestrus phase for IP and ICV route groups. There was interaction [P<0.05] between endogenous steroids and the alpha2-adrenergic system in the modulation of phasic pain sensitivity

[Role of central GABA[B] receptor in control of estraidol hormones secretion during proestrus phase in female rats]

The effect of ICV injection of baclofen [GABA[B] agonist and CGP35348 [GABA[B] antagonist] on serum concentration of estradiol and progesterone in proestrous phase. Experimental study. Twenty female Sperague Dawley rats weighning 200-250g were used. For ICV injection a director canula was inserted into the lateral ventricle by stereotaxic surgery. Each injection was performed 30 min before blood sampling. Blood samples were collected 9, 11 and 13h after initiation of proestrous. Estradiol and progesterone levels were determined using RIA method. Data were analyzed by One Way ANOVA, repeated meature ANOVA and post-hoc Tucky test. The level of significance was at P<0.05. Present data demonstrated that baclofen at doses of 4.27 and 8.54 ng/rat significantly increased and decreased serum concentration of estradiol, respectively [p<0.05]. baclofen at the same doses significantly increased serum concentration of progesterone in 11 a.m and 1 p.m [P<0.05]. CGP35348 in both doses had no significant effect on serum concentration of estradiol, while in 5 g/rat significantly increased the serum concentration of progesterone [P<0.05]. The results indicate that GABA[B] receptor may has an important role in the control of estradiol and progesterone secretion in the proestrous phase of female rats

[Effect of acute swimming stress on progesterone, testosterone, Na+ and K+ in male and female rats]

Objective: Comparison of serum progesterone and testosterone to acute swim stress

Design: This study examined the effect of acute swimming stress [for 10 min at 25C] on serum testosterone, progesterone, Na and + .K in male and female rats

Animals: Ten male and female rats were kept in 12:12 dark: light. Procedure: Experiments were carried out in 2 phases. First in the absent of stress blood samples were collected at 8 a.m. Second, after acute swim stress at 7:50 a.m., blood samples were taken at 8a.m. In female rats experiments were also carried out in the beginning of proestrous phase. Testosterone and progesterone were assayed by R1A method. Plasma Na+ and K+ were analyzed by Flame photometer.

Staistical analysis: Data were analyzed by Student T Test. The level of significance was considered to be P<0.05

Results: Serum testosterone and progesterone were significantly [P<0.05] increased in male rats, but serum Na+ and K+ had no significant [P>0.05] difference. In female rats, however serum testosterone was significantly [P<0.05] decreased, but serum progesterone, Na+ and K+ showed no significant [P>0.05] differences

Discussion: These results showed the existence of significant sex differences in response to acute swimming stress. Which most probably the differences in the serum concentration of Na+ and K+

Red nucleus and eyeblink conditioned response in rabbits

The role of red nucleus [RN] in the acquisition of rabbit eyeblink conditioned response has been a controversial issue. In the present study the effect of an RN lesion and changes in RN electrical activity during eyeblink conditioning have been investigated. Eighteen male albino rabbits, 1.5 to 2 kg in weight, were used. Animals were divided into four groups: The RN lesioned group which received a contralateral RN electrical lesion [2mA, 15 sec], the sham operated group, the electrophysiological group in which recording electrodes were implanted in the contralateral RN, and the intact [control] group. Rabbits received training for classical conditioning of the eyeblink response. A tone was the conditioned stimulus and an airpuff was the unconditioned stimulus. Our data shows that in the RN lesioned group eyeblink conditioned and unconditioned response amplitudes were significantly lower than the control and sham operated groups. Also the percentage of conditioned response incidence was decreased in the lesioned group and the latency of unconditioned response was significantly greater than the other two groups. In the electrophysiological group, RN rhythm was increased during learning. In conclusion it seems that the output of RN is capable of modulating the pathways mediating both conditioned and unconditioned responses