Physiological and behavioral traits in female guinea pigs: estrous cycle effects and repeatability.

SUMMARY Female guinea pigs were tested to determine whether they could serve as a model of zearalenone (zen) toxicosis during early pregnancy, as observed in domestic swine. Only 1 of 4 female guinea pigs that were given 21 mg of zen/kg of body weight orally during the first 8 days after mating was pregnant when examined 22 days after mating. Guinea pigs that were given 7 or 14 mg of zen/kg had normal fetal development. Serum concentrations of progesterone were < 12 ng/ml in all guinea pigs 8 and 15 days after mating. Serum concentrations of progesterone were > 100 ng/ml in pregnant guinea pigs on day 22, but remained < 12 ng/ml in nonpregnant guinea pigs. Three of 5 guinea pigs treated with 20 mg of zen/kg and only 1 of 4 guinea pigs given 30 mg of zen/kg on days 1 to 3 after mating were pregnant 22 days after mating. Female guinea pigs treated with 20 or 30 mg of zen/kg on days 4 to 5 or 6 to 8 after mating and female guinea pigs treated with 60 or 90 mg of zen/kg on days 4 and 5 after mating had normal pregnancies. Serum concentrations of progesterone were < 10 ng/ml in all guinea pigs on day 15 and remained low on day 22 only in nonpregnant guinea pigs. Pregnancy in domestic swine is disrupted by zen treatment on days 7 to 10 after mating, when embryos are migrating within the uterus, analagous to days 4 to 5 after mating in guinea pigs. Guinea pigs responded to the estrogenic effects of zen on early pregnancy in a manner similar to that seen in other rodents and dissimilar to that demonstrated by swine. Hence, despite its prolonged estrous cycle in comparison with other rodents, the guinea pig does not serve as a model for zen toxicosis in swine.

Effects of chronic morphine on biliary tract responses to cholecystokinin-octapeptide in female guinea pigs

Prolonged treatment with 8-hydroxy-2-(di- n-propylamino)tetralin (8-OHDPAT) differently affects the serotonergic modulation of cortical acetylcholine release in male and female guinea pigs

Lesions of the medial preoptic area (MPOA) result in the robust display of steroid-induced lordosis by otherwise unresponsive, immature guinea pigs. This study was designed to test the hypothesis that destruction of this region also hastens the onset of ovarian cyclicity, and to ascertain whether lesions of the septum produce effects on puberty similar to those observed following MPOA lesions. Juvenile (13-15 days old), ovariectomized or ovary-intact guinea pigs received bilateral electrolytic or sham lesions of the MPOA or septum. Bilateral lesions of the septum did not influence the display of lordosis or any aspect of estrous cyclicity. However, a higher percentage of guinea pigs with MPOA lesions than with sham lesions displayed progesterone-facilitated lordosis at 22, 29, and 39 days of age; by 49 days of age, the two groups responded in a similar, robust fashion. Females with MPOA lesions were significantly heavier and older than sham-lesioned or nonmanipulated females on the day of first vaginal opening. These data suggest that activity in the MPOA tonically inhibits the display of progesterone-facilitated lordosis through at least 39 days of age but does not suppress the onset of ovarian cyclicity in guinea pigs. Contrary to our hypothesis and in contrast to what has been observed in rats, signals originating in or passing through the MPOA may be required in order for estrous cyclicity to be initiated at the appropriate age. Furthermore, neither of these effects of MPOA lesions appears to be due to damaging efferent or afferent projections through the septum.

EFFECTS OF NATURAL ULTRAVIOLET RADIATION ON 25-HYDROXYVITAMIN D3 CONCENTRATIONS IN FEMALE GUINEA PIGS (CAVIA PORCELLUS)

Anxiety fluctuates across the human menstrual cycle, with symptoms worsening during phases of declining or low ovarian hormones. Similar findings have been observed across the rodent estrous cycle, however, the magnitude and robustness of these effects have not been meta-analytically quantified. We conducted a systematic review and meta-analysis of estrous cycle effects on anxiety-like behaviour (124 articles; k = 259 effect sizes). In both rats and mice, anxiety-like behaviour was higher during metestrus/diestrus (lower ovarian hormones) than proestrus (higher ovarian hormones) (g = 0.44 in rats, g = 0.43 in mice). There was large heterogeneity in the data, which was partially accounted for by strain, experimental task, and reproductive status. Nonetheless, the effect of estrous cycle on anxiety-like behaviour was highly robust, with the fail-safe N test revealing the effect would remain significant even if 21,388 additional studies yielded null results. These results suggest that estrous cycle should be accounted for in studies of anxiety in females. Doing so will facilitate knowledge about menstrual-cycle regulation of anxiety disorders in humans.

Several tissues contribute to the onset and advancement of knee osteoarthritis (OA). One tissue type that is worthy of closer evaluation, particularly in the context of sex, is the infrapatellar fat pad (IFP). We previously demonstrated that removal of the IFP had short-term beneficial effects for a cohort of male Dunkin-Hartley guinea pigs. The present project was designed to elucidate the influence of IFP removal in females of this OA-prone strain. It was hypothesized that resection of the IFP would reduce the development of OA in knees of a rodent model predisposed to the disease. Female guinea pigs (n=16) were acquired at an age of 2.5 months. Surgical removal of the IFP and associated synovium complex (IFP/SC) was executed at 3 months of age. One knee had the IFP/SC resected; a comparable sham surgery was performed on the contralateral knee. All animals were subjected to voluntary enclosure monitoring and dynamic weight-bearing, as well as compulsory treadmill-based gait analysis monthly; baseline data was collected prior to surgery. Guinea pigs were euthanized at 7 months. Knees from eight animals were evaluated via histology, mRNA expression, and immunohistochemistry (IHC); knees from the remaining eight animals were allocated to microcomputed tomography (microCT), biomechanical analyses (whole joint testing and indentation relaxation testing), and atomic absorption spectroscopy (AAS). Fibrous connective tissue (FCT) replaced the IFP/SC. Mobility/gait data indicated that unilateral IFP/SC removal did not affect bilateral hindlimb movement. MicroCT demonstrated that osteophytes were not a significant feature of OA in this sex; however, trabecular thickness (TbTh) in medial femorae decreased in knees containing the FCT. Histopathology scores were predominantly influenced by changes in the lateral tibia, which demonstrated that histologic signs of OA were increased in knees containing the native IFP/SC versus those with the FCT. Similarly, indentation testing demonstrated higher instantaneous and equilibrium moduli in the lateral tibial articular cartilage of control knees with native IFPs. AAS of multiple tissue types associated with the knee revealed that zinc was the major trace element influenced by removal of the IFP/SC. Our data suggest that the IFP/SC is a significant component driving knee OA in female guinea pigs and that resection of this tissue prior to disease has short-term benefits. Specifically, the formation of the FCT in place of the native tissue resulted in decreased cartilage-related OA changes, as demonstrated by reduced Osteoarthritis Research Society International (OARSI) histology scores, as well as changes in transcript, protein, and cartilage indentation analyses. Importantly, this model provides evidence that sex needs to be considered when investigating responses and associated mechanisms seen with this intervention.

α1- and α2-noradrenergic receptor binding in guinea pig brain: sex differences and effects of ovarian steroids

Proopiomelanocortin (POMC) mRNA expression: distribution and region-specific down-regulation by chronic morphine in female guinea pig hypothalamus

In vivo and in vitro effects of caffeine on hepatic mixed-function oxidases in rodents and chicks

The social environment affects behaviour and androgens, but not cortisol in pregnant female guinea pigs.

Facilitation of lordosis in guinea pigs by an α-noradrenergic agonist is independent of progestin receptor stimulation

Development of progesterone-facilitated lordosis in female guinea pigs: relationship to neural estrogen and progestin receptors

Methamphetamine use has increased over the past decade and the first use of methamphetamine is most often when women are of reproductive age. Methamphetamine accumulates in the liver; however, little is known about the effect of methamphetamine use on hepatic drug metabolism. Methamphetamine was administered on 3 occassions to female Dunkin Hartley guinea pigs of reproductive age, mimicking recreational drug use. Low doses of test drugs caffeine and midazolam were administered after the third dose of methamphetamine to assess the functional activity of cytochrome P450 1A2 and 3A, respectively. Real-time quantitative polymerase chain reaction was used to quantify the mRNA expression of factors involved in glucocorticoid signalling, inflammation, oxidative stress and drug transporters. This study showed that methamphetamine administration decreased hepatic CYP1A2 mRNA expression, but increased CYP1A2 enzyme activity. Methamphetamine had no effect on CYP3A enzyme activity. In addition, we found that methamphetamine may also result in changes in glucocorticoid bioavailability, as we found a decrease in 11β-hydroxysteroid dehydrogenase 1 mRNA expression, which converts inactive cortisone into active cortisol. This study has shown that methamphetamine administration has the potential to alter drug metabolism via the CYP1A2 metabolic pathway in female guinea pigs. This may have clinical implications for drug dosing in female methamphetamine users of reproductive age.

Ovaries were collected from normal cycling female guinea pigs on each day of the estrous cycle (n = 5 per day) for histological analysis of ovarian morphology. Three types of ovarian cysts were observed: serous cysts, follicular cysts and parovarian cysts. The most common were serous cysts (cystic rete ovarii), which were present throughout the estrous cycle with an overall incidence of 63.5% (54 out of 85 animals). Follicular cysts occurred in 22.4% of guinea pigs overall (19 out of 85). Only one parovarian cyst (1 out of 85) was observed in the present experiment. Follicular cysts always coincided with serous cysts and were less common during diestrus. The incidence of serous cysts did not vary significantly across the estrous cycle. In a second experiment, cycling female guinea pigs were arrested in a prolonged luteal phase by a progesterone implant in order to achieve ovarian synchrony. They were then treated with inhibin antiserum (0.5 or 1 ml per animal i.v.; n = 6 per group) or normal goat serum (controls; n = 6 per group). There was a dose dependent increase in the incidence of serous ovarian cysts following passive immunization against the inhibin alpha-subunit. These results suggest that serous cysts are a normal component of the cyclic guinea pig ovary and that alterations in the inhibin-follicle-stimulating hormone system appear to modulate the incidence of serous ovarian cysts in this species.