Establishing New Isosexual Pairs in Adult Male Guinea Pigs (Cavia porcellus) to Facilitate Social Housing

Guinea pigs (Cavia porcellus) are a commonly used species in biomedical research. As social creatures, compatible guinea pigs should be housed together unless scientific objectives or veterinary care require otherwise. Extensive literature suggests that adult male guinea pigs are highly aggressive in the presence of females, but data are lacking regarding the compatibility of cohoused adult males in the absence of females. Most studies that use adult males do not report housing densities. We used serial wound scoring and observations of behavior to determine whether unfamiliar adult male guinea pigs will develop stable, prosocial isosexual pairs. Wound scoring was performed before and 24 h after pairing. Serial behavioral observations assessed affiliative and agonistic behaviors at 0.5, 2, 24, and 48 h after pairing. Wound scoring and behavioral observations continued weekly for 1 mo and monthly thereafter. Wound scores were significantly higher at 24 h after pairing as compared with baseline and all other time points. Wounding was rare after week 2, indicating reduced aggression. Furthermore, affiliative behaviors significantly increased over time while agonistic behaviors were rare. Together, these data suggest that unfamiliar adult male guinea pigs establish stable prosocial pairs after an acclimation period. As was done in the present study, providing ample space, separate shelters for each animal, and the absence of female guinea pigs will likely facilitate successful pairing. We recommend consideration of a social housing program for adult male guinea pigs to provide companionship and enrich their housing environment.

Growth performance and reproductive function impairment of glyphosate-based herbicide in male guinea pig (Cavia porcellus)

Glyphosate formulations, widely applied non-selective systemic herbicides, are progressively becoming the most controversial pesticides on the market due the adverse effects they pose to humans and environment. The information on these potential hazardous effects to the handlers of the pesticide remains obscure. This study investigated effects of glyphosate-based herbicide on growth performance, seminal parameters and hemato-biochemical profiles in male guinea pig. Forty sexually mature male guinea pigs weighing between 393.3 and 418.4 g were divided into four groups of 10 animals each and orally administered 0, 186, 280 and 560 mg/kg body weight of WILLOSATE daily for 60 days. Daily feed intake and body weight gain were recorded. At the end of experimental period all animals were humanely sacrificed, and blood samples and vital organs were collected for appropriate analysis. Results showed a significant decrease (p < 0.05) in body weight gain (-102.2%), final body weight (-9.8%) and feed intake (-13.1%) of animals following sub-chronic exposure of WILLOSATE. The weights of the liver and kidney increased significantly (p < 0.05) by 25.4% and 28.8%, respectively, while testicular weights decreased (p < 0.05) by 24% with increasing doses of WILLOSATE. A decrease in sperm motility (-67.9%), viability (-52.7%) and concentration per vas deferens (-40.7%), and an increase in sperm major (28.1%) and minor (45.3%) morphological aberrations were recorded in WILLOSATE - exposed guinea pigs when compared to controls. There was a dose-dependent increase (p < 0.05) in MCV and WBC and a decrease in Hb content and RBC, as well as serum content in total protein (-11.8%). The serum content of cholesterol (37.8%), urea (87.1%), creatinine (22.4%), ALAT (74.2%) and ASAT (88.7%) were significantly higher in treated groups compared to controls. These results point toward the toxic effects of WILLOSATE on vital organs and reproductive function of the body at high doses and long-term exposure.

Effect of Photoperiod with Sunlight at Thermal Stress and Sperm Parameters in Guinea Pigs

&lt;b&gt;Background and Objective:&lt;/b&gt; Photoperiod can regulate reproductive physiological processes in mammals, in which improvements in testosterone concentration, testicular volume and seminal quality have been reported. The aim was to evaluate the influence of photoperiod treatments on guinea pigs' spermatic parameters. &lt;b&gt;Materials and Methods:&lt;/b&gt; Thirty guinea pigs, between males and females, were distributed in two rooms with the photoperiodic treatment of 10 hrs light and 14 hrs dark (PT&lt;sub&gt;1&lt;/sub&gt; with artificial photoperiod and PT&lt;sub&gt;2&lt;/sub&gt; photoperiod with sunlight by opening windows from 08:00-18:00) and one without any direct light stimulus (PT&lt;sub&gt;0&lt;/sub&gt;) for 78 days. The temperature and humidity were recorded and the TH index was calculated for each room. The sperms were recovered in Tris base medium from the epididymis of 16 males to determine sperm concentration, motility, kinetic parameters, vitality, HOST, acrosomal integrity and DNA fragmentation. &lt;b&gt;Results:&lt;/b&gt; Sperm values in PT&lt;sub&gt;1&lt;/sub&gt; and PT&lt;sub&gt;0&lt;/sub&gt; were similar but PT&lt;sub&gt;2&lt;/sub&gt; obtained values lower in sperm concentration, non-progressive motility, total motility, VCL, ALH, vitality, HOST+, acrosomal integrity, sperm with non-fragmented DNA and no pregnancies were reported (0/5). A 100% pregnancy was observed in PT&lt;sub&gt;0&lt;/sub&gt; (4/4) and 50% in PT&lt;sub&gt;1&lt;/sub&gt; (2/4). However, precocity was evidenced in PT&lt;sub&gt;1&lt;/sub&gt; compared to PT&lt;sub&gt;0&lt;/sub&gt;. PT&lt;sub&gt;2&lt;/sub&gt; recorded higher peaks in temperature (33.8°C, THI 81, considered as thermal stress) compared to PT&lt;sub&gt;0&lt;/sub&gt; (32.65°C, THI 81.8) and PT&lt;sub&gt;1&lt;/sub&gt; (32.75°C, THI 81.6). &lt;b&gt;Conclusion:&lt;/b&gt; An artificial photoperiod can improve sperm characteristics and reproductive precociousness of guinea pigs, unlike the photoperiod with sunlight, which generated low spermiogram values and absence of pregnancy due to thermal stress.

Use of the guinea pig in studies on the development and prevention of acquired sensorineural hearing loss, with an emphasis on noise

Guinea pigs have been used in diverse studies to better understand acquired hearing loss induced by noise and ototoxic drugs. The guinea pig has its best hearing at slightly higher frequencies relative to humans, but its hearing is more similar to humans than the rat or mouse. Like other rodents, it is more vulnerable to noise injury than the human or nonhuman primate models. There is a wealth of information on auditory function and vulnerability of the inner ear to diverse insults in the guinea pig. With respect to the assessment of potential otoprotective agents, guinea pigs are also docile animals that are relatively easy to dose via systemic injections or gavage. Of interest, the cochlea and the round window are easily accessible, notably for direct cochlear therapy, as in the chinchilla, making the guinea pig a most relevant and suitable model for hearing. This article reviews the use of the guinea pig in basic auditory research, provides detailed discussion of its use in studies on noise injury and other injuries leading to acquired sensorineural hearing loss, and lists some therapeutics assessed in these laboratory animal models to prevent acquired sensorineural hearing loss.

The way wear goes: phytolith-based wear on the dentine-enamel system in guinea pigs (Cavia porcellus)

The effect of phytoliths on tooth wear and function has been contested in studies of animal-plant interactions. For herbivores whose occlusal chewing surface consists of enamel ridges and dentine tissue, the phytoliths might particularly erode the softer dentine, exposing the enamel ridges to different occlusal forces and thus contributing to enamel wear. To test this hypothesis, we fed guinea pigs (Cavia porcellus; n = 36 in six groups) for three weeks exclusively on dry or fresh forage of low (lucerne), moderate (fresh timothy grass) or very high (bamboo leaves) silica content representing corresponding levels of phytoliths. We quantified the effect of these treatments with measurements from micro-computed tomography scans. Tooth height indicated extreme wear due to the bamboo diet that apparently brought maxillary incisors and molars close to the minimum required for functionality. There were negative relationships between a cheek tooth's height and the depth of its dentine basin, corroborating the hypothesis that dentine erosion plays an important role in herbivore tooth wear. In spite of lower body mass, bamboo-fed animals paradoxically had longer cheek tooth rows and larger occlusal surfaces. Because ever-growing teeth can only change in shape from the base upwards, this is a strong indication that failure to compensate for wear by dental height-growth additionally triggered general expansive growth of the tooth bases. The results suggest that enamel wear may intensify after enamel has been exposed due to a faster wear of the surrounding dentine tissue (and not the other way around), and illustrate a surprising plasticity in the reactivity of this rodent's system that adjusts tooth growth to wear.

Cortisol during adolescence organises personality traits and behavioural syndromes

Despite the growing evidence for the importance of developmental experiences shaping consistent individual differences in behaviour and physiology, the role of endocrine factors underlying the development and maintenance of such differences across multiple traits, remains poorly understood. Here, we investigated how an experimental manipulation of circulating glucocorticoids during early adolescence affects behavioural and physiological variation and covariation later in life in the precocial cavy (Cavia aperea). Plasma cortisol concentrations were experimentally elevated by administering cortisol via food for 3 weeks. Struggle docility, escape latency, boldness, exploration and social behaviour were then tested three times after individuals attained sexual maturity. In addition, blood samples were taken repeatedly to monitor circulating cortisol concentrations. Exogenous cortisol affected mean trait expression of plasma cortisol levels, struggle docility and escape latency. Repeatability of cortisol and escape latency was increased and repeatability of struggle docility tended to be higher (approaching significance) in treated individuals. Increased repeatability was mainly caused by an increase of among-individual variance. Correlations among docility, escape latency and cortisol were stronger in treated animals compared to control animals. These results suggest that exposure to elevated levels of cortisol during adolescence can alter animal personality traits as well as behavioural syndromes. Social and risk-taking traits showed no correlation with cortisol levels and were unaffected by the experimental manipulation, indicating behavioural modularity. Taken together, our data highlight that cortisol can have organising effects during adolescence on the development of personality traits and behavioural syndromes, adding to the increasing evidence that not only early life but also adolescence is an important sensitive period for behavioural development.

Pharmacokinetics and Adverse Effects of 3 Sustained-release Buprenorphine Dosages in Healthy Guinea Pigs (Cavia porcellus)

In guinea pigs, studies addressing the efficacy, safety, and pharmacokinetic profiles of different sustained-release buprenorphine (SRB) formulations are still in their infancy. Here we assessed the pharmacokinetic profiles of 3 SRB dosages (SR-LAB, ZooPharm; SRBLow, 0.15 mg/kg; SRBMedium, 0.3 mg/kg; and SRBHigh, 0.6 mg/kg) for 72 h after a single subcutaneous administration to 8 (4 male and 4 female) healthy guinea pigs. Body weight, fecal output, and cortisol levels were also monitored and the results compared with those of the sham group. Within the first h after administration, the maximal plasma concentration (Cmax) of the drug was 64.3 ± 9.2 ng/mL (males) and 71.3 ± 3.7 ng/mL (females) in the SRBHigh group; 11.5 ± 3.2 ng/mL (males) and 6.9 ± 0.9 ng/mL (females) in the SRBMedium group; and 2.3 ± 0.8 ng/mL (males) and 2.0 ± 0.5 ng/mL (females) in the SRBLow group. After 72 h, therapeutic levels of the drug (>1 ng/mL) were observed only in guinea pigs treated with SRBHigh (both sexes) and males treated with SRBMediu cm. Fecal output (quantity and distribution) and body weight were significantly lower in the SRB groups as compared with the sham group, and with the SRBHigh group showing larger reductions. Baseline levels of serum cortisol in healthy females (1440 ± 106 ng/mL) were significantly greater than in males (550 ± 66 ng/mL). But, independent of the sex, SRB administration significantly reduced those levels. In conclusion, the data indicate that all 3 SRB dosages can be safely used in guinea pigs. However, therapeutic levels of the drug were observed for at least 48 h only guinea pigs treated with SRBHigh and SRBMedium. Further investigation is needed to determine if these dosages can alleviate pain in guinea pigs.

Echocardiographic variables in healthy guineapigs anaesthetized with ketamine–xylazine

Echocardiographic parameters were recorded, measured and statistically analysed on a population of 12 male Hartley albino guineapigs under ketamine–xylazine anaesthesia. Additionally, the effect of body weight on these parameters and the correlation between the parameters were assessed. The mean values of left ventricular internal diameter in end diastole (LVIDD), left ventricular internal diameter in end systole (LVIDS), interventricular septum thickness in diastole (IVSD), interventricular septum thickness in systole (IVSS), left ventricular posterior wall thickness in diastole (LVPWD), left ventricular posterior wall thickness in systole (LVPWS), left atrial diameter (LA), aortic diameter (AO), left ventricular fractional shortening (FS) and left ventricular ejection fraction (EF) were measured or calculated as 6.85 ± 0.36, 4.35 ± 0.17, 1.75 ± 0.31, 2.26 ± 0.35, 2.28 ± 0.40, 2.80 ± 0.58, 4.95 ± 0.34, 4.65 ± 0.25 mm, 35.62 ± 2.62 and 70.87 ± 3.01%, respectively. A significant ( P <0.01) positive correlation to body weight was found with LVIDD, LVPWD, IVSD, aortic root diameter and LA. Significant correlation was also found between a number of echocardiographic parameters.

Temperature Preference in IAF Hairless and Hartley Guinea Pigs (Cavia porcellus)

The Hairless strain of guinea pigs (Cavia porcellus) is the result of a spontaneous recessive mutation first identified at the Institute Armand Frappier (IAF) in 1978. Despite the longstanding availability of this strain, little is known about its thermoregulatory behavior. The aim of this study was to determine temperature preference in Hartley and Hairless guinea pigs by observing each strain in a ring-shaped apparatus containing a nonlinear temperature gradient. Temperatures were maintained by separately controlled heating mats lining the apparatus. Set point temperatures ranged from 24 to 38 °C. Guinea pigs (Hartley female, Hairless female, and Hairless male guinea pigs; n = 8 each group) were placed either singly or in pairs at 1 of the 8 randomized starting points within the apparatus. Subjects were observed for 30 min and coded for location within the temperature gradient by both frequency and duration. When placed singly in the apparatus, all 3 groups spent more time in the 30 °C zones. However, when placed as pairs with a cagemate, Hartley female guinea pigs spent more time in the cooler range of temperatures from 24 to 30 °C, whereas Hairless guinea pigs preferred a range of 30 to 38 °C. These results confirm a temperature preference of 30 ± 2 °C for both Hartley and Hairless guinea pigs when singly housed. However, data from the paired housing condition suggest that context plays an important role in thermoregulatory behavior.

Effects of Changing to Individually Ventilated Caging on Guinea Pigs (Cavia porcellus)

The goal of this study was to evaluate the effect of changing to IVC housing on guinea pigs by recording several physiologic parameters in guinea pigs housed sequentially in open-top cages (OTC) and IVC. To register heart rate and locomotor activity, 10 male Dunkin-Hartley guinea pigs implanted with telemetric transmitters were moved from OTC to new, freshly prepared OTC or IVC and subsequently monitored by telemetry during the 4 d after the first cage change. Body weight and food consumption were measured twice during the study. Comparison of data from OTC- and IVC-housed guinea pigs showed no relevant differences in heart rate (mean ± 1 SD; 213 ± 10 bpm and 207 ± 9 bpm, respectively) at any time point. In contrast, locomotor activity varied: whereas activity during the first 4 h after the change of cage type was greater in IVC-housed animals, that during the following 24 h was greater in OTC but was similar between groups thereafter. Animals housed in OTC consumed more food than did those in IVC and, under both conditions, consumption was statistically related to body weight changes. Together, these results show that a change to IVC housing induced only transient increases in locomotor activity in guinea pigs without a marked increase in heart rate but with a decrease in food consumption. Because decreased food consumption was the only stress-associated sign during the 4-d observation, longer studies are needed to ascertain the importance of this finding.

Progesterone receptor expression declines in the guinea pig uterus during functional progesterone withdrawal and in response to prostaglandins

Progesterone withdrawal is essential for parturition, but the mechanism of this pivotal hormonal change is unclear in women and other mammals that give birth without a pre-labor drop in maternal progesterone levels. One possibility suggested by uterine tissue analyses and cell culture models is that progesterone receptor levels change at term decreasing the progesterone responsiveness of the myometrium, which causes progesterone withdrawal at the functional level and results in estrogen dominance enhancing uterine contractility. In this investigation we have explored whether receptor mediated functional progesterone withdrawal occurs during late pregnancy and labor in vivo. We have also determined whether prostaglandins that induce labor cause functional progesterone withdrawal by altering myometrial progesterone receptor expression. Pregnant guinea pigs were used, since this animal loses progesterone responsiveness at term and gives birth in the presence of high maternal progesterone level similarly to primates. We found that progesterone receptor mRNA and protein A and B expression decreased in the guinea pig uterus during the last third of gestation and in labor. Prostaglandin administration reduced while prostaglandin synthesis inhibitor treatment increased progesterone receptor A protein abundance. Estrogen receptor-1 protein levels remained unchanged during late gestation, in labor and after prostaglandin or prostaglandin synthesis inhibitor administration. Steroid receptor levels were higher in the non-pregnant than in the pregnant uterine horns. We conclude that the decreasing expression of both progesterone receptors A and B is a physiological mechanism of functional progesterone withdrawal in the guinea pig during late pregnancy and in labor. Further, prostaglandins administered exogenously or produced endogenously stimulate labor in part by suppressing uterine progesterone receptor A expression, which may cause functional progesterone withdrawal, promote estrogen dominance and foster myometrial contractions.

Enriched open field facilitates exercise and social interaction in 2 strains of guinea pigs (Cavia porcellus)

Current housing guidelines for laboratory rodents include recommendations for enrichment. Working with guinea pigs, we have developed an open-field enrichment paradigm that provides several aspects of this species' natural environment. These naturalistic aspects include access to increased space for exploration, access to western timothy (Phleum pratense L.) hay, and grouping as a herd to facilitate social interaction. To determine the immediate effect on behavior from access to the enriched environment, female guinea pigs from 2 strains, IAF Hairless and NIH Hartley, were observed in both standard home cages and an open-field enriched environment. Subjects were housed with cagemates in pairs for the home-cage observation and were grouped as a herd when in the open-field arena. Behaviors were videorecorded for 1 h and then scored. Salivary cortisol levels were measured both prior to and immediately after behavioral observations. Analyses revealed higher levels of activity and social interaction in the open-field arena compared with the home cage, with no significant change in salivary cortisol levels. These results suggest that exposure to the open-field environment provide increased opportunities for exercise and social enrichment. Although additional studies are needed to determine long-term effects on experimental outcomes, the open-field configuration holds promise as a laboratory enrichment paradigm for guinea pigs.

Influence of sodium selenite on growth, nutrient utilization and selenium uptake in Cavia porcellus

A 70 day experiment on forty guinea pigs (Cavia porcellus) was conducted to find the influence of different level of sodium selenite (inorganic selenium supplementation) on growth, nutrient utilization and selenium uptake. The sodium selenite was supplemented into a basal diet at 0, 0.1, 0.2 and 0.3 ppm, respectively and the basal diet comprised of 25% ground cowpea (Vigna unguiculata) hay, 30% ground maize (Zea mays) grain, 22% ground gram (Cicer arietinum) grain, 9.5% deoiled rice (Oryza sativa) bran, 6% soybean (Glycine max) meal, 6% fish meal, 1.5% mineral mixture (without Se), ascorbic acid (200 mg kg) and 0.1 ppm Se to meet their nutrient requirements. Daily feed intake and weekly body weights were recorded. Intake and digestibility of dry matter, organic matter, ether extract, crude fiber and nitrogen-free extract as well as uptake of calcium and phosphorus, total body weight and average daily gain were similar (p>0.05) among the four groups. However, there was a trend of increase in Se absorption of the guinea pigs with the increasing levels of Se, in the groups given 0.2 and 0.3 ppm of Se. It can be concluded that requirement of Se in guinea pigs is 0.1 ppm, as supplementation of > or =0.1 ppm sodium selenite in the diet (having 0.1 ppm Se) did not enhanced their growth rate and nutrient utilization.

Effects of prenatal stress on hypothalamic-pituitary-adrenal (HPA) axis function over two generations of guinea pigs (Cavia aperea f. porcellus)

Prenatal stress can alter hypothalamic-pituitary-adrenal axis function with potential consequences for later life. The aim of our study was to examine in guinea pigs (Cavia aperea f. porcellus) the effects of stress experienced during F0 pregnancy on glucocorticoid levels in plasma and feces, as well as challenge performance, in F1 offspring (n=44) and fecal glucocorticoid levels in F2 offspring (n=67). F1 animals were either born to F0 dams that had been stressed with strobe light during early to mid pregnancy, resulting in a short term increase but long-term down-regulation of maternal glucocorticoid levels, or to undisturbed F0 dams. The same stressor was used as a challenge for F1 offspring at age 26 days and around 100 days. Basal plasma cortisol concentrations during early F1 development, as well as overall glucocorticoid levels at challenge tests, were lower in F1 animals that were prenatally stressed than in control animals. Fecal cortisol metabolites were initially at lower levels in prenatally stressed F1 animals, relative to control animals, but shifted to higher levels around day 68, with an additional sex difference. Effects were also seen in the F2 generation, as male but not female offspring of prenatally stressed F1 animals had significantly higher levels of cortisol metabolites in feces after weaning. We conclude that stress exposure of F0 dams resulted in lower basal glucocorticoid levels in F1 offspring during the pre-pubertal phase and during stress exposure, but higher glucocorticoid levels in post-adolescent F1 animals. Also in males of F2 generation effects of stress exposure of F0 dams were detected.

Effects of changes in vertical occlusal dimension on heart rate fluctuations in guinea pigs

BACKGROUND

We have previously reported that the decrease of the vertical occlusal dimension (VOD) led to heart failure and abnormalities in creatine phosphokinase (CPK) in guinea pigs. In the present study, we investigated the autonomic activity and the origin of the abnormality in CPK under different occlusal conditions.

MATERIALS AND METHODS

Guinea pigs were separated into the following five groups: untreated control, reduced VOD, slit, restored VOD and increased VOD groups and compared for their electrocardiogram and heart rate fluctuations for two weeks using Fluclet, computer software.

RESULTS

The control group revealed no changes in heart rate fluctuations or posture. The reduced VOD group exhibited a two-phase wave of heart rate fluctuations, with the first peak 0-2 days after teeth grinding, and the second peak starting from 4 days after teeth grinding until sudden death (usually 12th day), accompanied by head drop. The slit and the restored VOD groups exhibited only the first peak. The increased VOD group, with approximately 3 mm-thick acrylic pellets bonded to the posterior teeth, showed no heart rate fluctuations. Body weight loss was most prominent in the reduced VOD group, and became much milder in the order of increased VOD, restored and slit groups. The reduced VOD group exhibited transient elevation of skeletal muscle type of CPK isozyme activity within two days after treatment.

CONCLUSION

The present study suggests that the first peak of heart rate fluctuations is caused by pulpal stimulation, and the second peak by excessive contraction (excessive excitation of the motor output system and the autonomic nervous system) of the masticatory muscles. On the other hand, increased VOD did not influence either the motor or the autonomic nervous system.

High doses of ketamine-xylazine anesthesia reduce cardiac ischemia-reperfusion injury in guinea pigs

Choosing an appropriate anesthetic protocol that will have minimal effect on experimental design can be difficult. Guinea pigs have highly variable responses to a variety of injectable anesthetics, including ketamine-xylazine (KX). Because of this variability, supplemental doses often are required to obtain an adequate plane of anesthesia. Our group studies the isolated guinea pig heart, and we must anesthetize guinea pigs prior to harvesting this organ. In this study, we sought to determine whether a higher dose of KX protected isolated guinea pig hearts against myocardial ischemia-reperfusion injury. Male Hartley guinea pigs (Crl:HA; 275 to 300 g; n = 14) were anesthetized with either of 2 doses of KX (K: 85 mg/kg, X: 15 mg/kg; or K: 200 mg/kg, X: 60 mg/kg). After thoracotomy, hearts underwent 20 min of ischemia followed by 2 h of reperfusion. The high dose of KX significantly reduced myocardial infarct size as compared with the low dose (36% ± 3% and 51% ± 6%, respectively). Furthermore, the high dose of KX improved hemodynamic function over that associated with the low dose as measured by increases in both left ventricular developed pressure (49 ± 4 and 30 ± 8 mm Hg, respectively) and maximal rate of left ventricular relaxation (-876 ± 70 and -576 ± 120 mm Hg/s, respectively). However, the high dose of KX did not alter the maximal rate of left ventricular contraction or coronary flow. These results suggest that supplementation of KX to ensure an adequate anesthetic plane may introduce unwanted variability in ischemia-reperfusion studies.

Structure of the altitude adapted hemoglobin of guinea pig in the R2-state

BACKGROUND

Guinea pigs are considered to be genetically adapted to a high altitude environment based on the consistent finding of a high oxygen affinity of their blood.

METHODOLOGY/PRINCIPAL FINDINGS

The crystal structure of guinea pig hemoglobin at 1.8 A resolution suggests that the increased oxygen affinity of guinea pig hemoglobin can be explained by two factors, namely a decreased stability of the T-state and an increased stability of the R2-state. The destabilization of the T-state can be related to the substitution of a highly conserved proline (P44) to histidine (H44) in the alpha-subunit, which causes a steric hindrance with H97 of the beta-subunit in the switch region. The stabilization of the R2-state is caused by two additional salt bridges at the beta1/beta2 interface.

CONCLUSIONS/SIGNIFICANCE

Both factors together are supposed to serve to shift the equilibrium between the conformational states towards the high affinity relaxed states resulting in an increased oxygen affinity.

Some behavioural changes associated with the guinea-pig oestrous cycle

This paper describes some behaviour patterns of the guinea-pig, Cavia porcellus, which vary systematically with the oestrous cycle. Oestrus is characterised by an increase in locomotion, and scent-marking, as well as by greater interest in conspecifics. All of these are behaviours known to increase at oestrus in other rodent species. The significance of these changes for the social organisation of this species is discussed.

Effects of nutritional quality during early development on body weight and reproductive maturation of guinea pigs (Cavia aperea f. porcellus)

In many species, somatic and reproductive maturation are sensitive to seasonally-fluctuating environmental conditions such as food quality. The protein content of the diet during early development has been considered to be particularly important, a low-protein diet during gestation and lactation typically delaying growth and reproductive onset. To investigate the effects of maternal and early postnatal diet quality on body weight and puberty of male and female domestic guinea pigs, we fed F0-mothers either a low-protein (14%, LQ-group) or a high-protein diet (23%, HQ-group) during gestation and lactation. Their male and female offspring received the same respective diets until six weeks of age; afterward they were switched to an intermediate control diet. Body weight of F1-subjects was significantly affected by the dietary treatment. Reproductive parameters were only affected in F1-females but not in F1-males. We conclude that in guinea pigs, growth is sensitive to the quality of the maternal and early postnatal diet, and that reproductive maturation is more sensitive in females.

Regional changes in the spatio-temporal pattern of progesterone receptor (PR) expression in the guinea-pig genital tract as parturition approaches

Normal parturition in guinea-pig involves changes in responsiveness of the genital tract to estrogen and progesterone. To better characterize endocrine control of guinea-pig parturition, protein and mRNA expression of estrogen receptor-alpha (ERalpha) and progesterone receptor (PR) were quantitatively evaluated in lower (LUS) and upper (UUS) uterine segments, cervix (C) and pubic symphyseal ligament (PSL) at three stages of pregnancy (established based on interpubic distance, 0mm: non-relaxed group, 4-6mm: 5 days before parturition, 11-14 mm: 1-2 days prepartum) and immediately after parturition. Towards parturition, no changes in PR mRNA levels were recorded in the UUS, whereas the LUS displayed a gradual increase. PR transcripts exhibited decreased levels during parturition in C and PSL. Levels of PR mRNA were increased in the LUS compared with that of the UUS only at parturition. Regarding protein expression during parturition, PR levels decreased in the UUS whereas in the LUS increased. In C and PSL, PR protein expression decreased 1-2 days prepartum and remained low during parturition. None of the regions studied showed changes in mRNA or protein expression of ERalpha. Therefore, functional regionalization of the guinea-pig genital tract is associated with changes in the spatio-temporal pattern of PR expression as parturition approaches.

[Relationships between the hippocampus and medial septal region and their alterations during epileptogenesis]

EEGs of the hippocampus and the medial septal region (MSR) in the control conditions and during repeated stimulation of the perforant path were simultaneously recorded in awake guinea pigs. Changes in correlation of activity of these structures during seizures provoked by the stimulation (model of acute epilepsy) and in the process of epileptogenesis induced by the kindling (model of chronic epilepsy) were analyzed. A high correlation of the baseline activities of the hippocampus and MSR observed in the control sharply decreased during acute and chronic seizures. Kindling led to emergence of the MSR capability of hippocampus-independent generation of the field seizure discharges. In the process of kindling the progressive disintegration of activities of the hippocampus and the MSR was revealed being indicative of disorders in functioning of the septohippocampal network during epileptogenesis.

Caviomorph placentation as a model for trophoblast invasion

The guinea pig and its relatives are promising candidates as animal models for studying trophoblast invasion. The origin, migration routes and kinetics of invasive trophoblast cells were examined in two caviomorph species. Histology and immunohistochemistry were done on placentas from 38 guinea pigs of days 20-47 and 13 degus of days 25-51 of gestation. BrdU was used as an in vivo marker for proliferation and for tracing of migration routes in the placenta; it was injected 24h to 15 days before collecting the material. In both species extravillous-like trophoblast cells are derived from proliferating stem cell aggregations in the subplacenta, which are comparable to the cell columns in humans. Migration routes and kinetics under in vivo conditions revealed a mean invasive depth of 300-350 microm/day and a mean life span of the extravillous-like trophoblast of 30 days. The patterns of trophoblast invasion in caviomorphs are analogous to the situation in humans, suggesting that these rodents are appropriate animal models for the study of the dynamics of trophoblast invasion.

Comparison of opioid receptor binding in horse, guinea pig, and rat cerebral cortex and cerebellum

OBJECTIVE

To compare the density and binding characteristics of opioid receptor subtypes in horse, rat, and guinea pig cerebral cortex and cerebellum.

STUDY DESIGN

Prospective receptor binding study.

ANIMALS

Whole brains were obtained from four neurologically normal adult horses during necropsy. Rat and guinea pig brains were obtained commercially.

METHODS

The cerebellum and cerebral cortex were dissected from each brain, and tissue homogenates prepared. A radioligand binding technique with the highly selective ligands [(3)H]-DAMGO, [(3)H]-U69593, and [(3)H]-DPDPE was used to identify the mu- (mu), kappa- (kappa) and delta- (delta) opioid receptors, respectively. Competitive binding assays were performed with these ligands and varying concentrations of one of multiple unlabeled ligands.

RESULTS

While there were marked species differences in relative densities of opioid receptors, all radioligands interacted with their binding sites with high, nanomolar affinity in both the cerebral cortex and cerebellum. In the horse cerebral cortex, the percentages of total opioid binding sites for the mu-, kappa- and delta-receptors were 71%, 14% and 15%, respectively. In the rat and guinea pig cerebral cortex, the corresponding values were 56% mu-, 4% kappa- and 40% delta-receptors, and 25% mu-, 37% kappa- and 38% delta-receptors, respectively. In horse and guinea pig cerebellum, the binding was 37% mu-, 59% kappa- and 4% delta-receptors, and 15% mu-, 76% kappa- and 10% delta-receptors, respectively. For competitive analysis, all competitors of the mu-, kappa- and delta-receptors completely displaced [(3)H]-DAMGO, [(3)H]-U69593, and [(3)H]-DPDPE and had inhibitory constants in the nanomolar range.

CONCLUSION AND CLINICAL RELEVANCE

Horses used in this study had a greater density of mu-receptors in the cerebral cortex compared with rats and guinea pigs but without further characterization of the functional role of these receptors it is impossible to determine the clinical significance of these data.

Schirmer tear test, phenol red thread tear test, eye blink frequency and corneal sensitivity in the guinea pig

OBJECTIVE

To establish reference values for Schirmer tear tests (STT) I and II, phenol red thread (PRT) tear test and eye blink frequency, and to determine corneal sensitivity for normal guinea pigs.

ANIMALS STUDIED

One hundred and eight eyes of 54 adult Duncan-Hartley guinea pigs.

PROCEDURE

Schirmer tear test (STT) I and then STT II were performed in 36 guinea pigs. PRT and STT I were compared in 18 adult Duncan-Hartley guinea pigs. Corneal sensitivity was determined in 23 guinea pigs by evaluating the corneal touch threshold (CTT) of five different regions using a Cochet-Bonnet esthesiometer. Eye blink frequency was measured in 10 guinea pigs over a period of 20 min and in 17 guinea pigs over a period of 10 min.

RESULTS

Mean STT I was 0.36 mm +/- 1.09 mm (wetting/min) and mean STT II was 0.43 mm +/- 1.29 mm (wetting/min). There was no significant difference between mean STT I and mean STT II (P = 0.79). The mean PRT-value was 16 +/- 4.7 mm (wetting/15 s), and the mean STT I-value in the same guinea pigs was 0.6 +/- 1.83 mm (wetting/min). Corneal sensitivity was significantly higher in the center than in the four limbal regions. The mean CTT for central, ventral, nasal, temporal and dorsal regions was 2, 1.7, 1.7, 1.7 and 1.6 cm or 3.7, 5.2, 5.6, 5.7 and 6.4 g/mm(2), respectively. Eye blink frequency was between two to five (mean 3.4 +/- 1.04) blinks per eye over 20 min in guinea pigs in their home environment, while in handheld and restrained guinea pigs eye blink frequency showed a variation between 0 and 17 blinks per eye (mean 3.24 +/- 3.64 blinks per eye) over 10 min.

CONCLUSIONS

As there were no significant differences between STT I and STT II results, reflex tear secretion in the guinea pig may not exist. The most likely explanation is a lower corneal sensitivity in the guinea pig than in other species, such as cats, dogs and horses. Because of the small amount of tears, PRT is the preferred test for tear measurement in the guinea pig.

Emmetropization and schematic eye models in developing pigmented guinea pigs

A model of the axial change in ocular parameters of the guinea pig eye from 2 to 825 days of age was developed and a corresponding paraxial schematic eye model applicable from 2 to 100 days of age was constructed. Axial distances increased logarithmically over time except for the lens in which growth was more complex. Over the first 30 days, ocular elongation was approximately linear: ocular length increased by 37 microm/day, the majority due lens expansion. The choroid and sclera thickened with age, while the retina thinned in proportion to the increased ocular size, and the model suggests that there is no small eye artefact for white light retinoscopy. Refractive error just after birth was +4.8D but halved within the first week. Emmetropization occurred within the first month of life similar to that in other species when aligned at the point of sexual maturity and scaled by the time taken to reach adulthood. The power of the eye was 227D at 2 days of age and reduced by 19.7D by 100 days due to a 22% decrease in the power of the cornea. The posterior nodal distance (PND) was 4.7 mm at 30 days of age, with a maximum rate of change of 13 microm/day during the first week. The ratio of PND to axial length declined until at least 100 days of age, well after emmetropia was reached. This suggests that the maintenance of emmetropia is not sustained through proportional axial growth, but involves some active mechanism beyond simple scaling. The model predicts that 1D of myopia requires an elongation of between 23 and 32 microm, depending upon age, suggesting that a resolution of at least 50 microm is required in methods used to determine the significance of ocular length changes in guinea pig models of refractive development. Retinal magnification averaged 80 microm/degree, and the maximum potential brightness of the retinal image was high, which together with a ratio of lens power to corneal power of 1.7-2.0 suggests that the guinea pig eye is adapted for nocturnal conditions.

Exploring efferent-mediated DPOAE adaptation in three different guinea pig strains

The aims of this study were to explore the correlation between DPOAE adaptation magnitude in three different guinea pig strains to examine if the genetic component affects the DPOAE adaptation magnitude. It was also to investigate the correlation between strains with certain characteristics i.e. reduced susceptibility to noise, and early onset of age-dependent hearing loss and the DPOAE adaptation magnitude. The animals were anaesthetized and the 2f1-f2 DPOAE (f1=8k Hz, and f2/f1=1.2) adaptation was established with a minimum of 144 combinations of f1; f2 where f1 was held fixed and f2 was varied in 1 dB or 0.4 dB steps. The DPOAE adaptation magnitude was defined as the difference between maximum positive level and the maximum negative level. ABRs were conducted at different age-groups (at 4, 6.3, and 12.5k Hz) to evaluate the progress of hearing thresholds by age. There was a significant difference between strains regarding the hearing loss at one year of age. There was no significant difference in DPOAE adaptation magnitude between strains included in this study and from this we conclude that the DPOAE adaptation magnitude is not a predictor for the susceptibility to noise trauma, or early onset of age-dependent hearing loss, using the methods described in this paper.

New Field With Tonotopic Organization in Guinea Pig Auditory Cortex

In guinea pig auditory cortex, two core areas, a primary area (AI) and a dorsocaudal field (DC), and two belt regions ventral to AI and DC (VRB and VCB) with an intermediate zone (T) in between, together with a small field (S) rostral to AI, have been reported in single-electrode studies although field S and zone T have not been observed in imaging studies. Using a high-resolution in vivo optical-imaging system with the voltage-sensitive dye RH-795, we report here the successful imaging of a rostral small field and zone T and a ventral-to-dorsal frequency gradient in zone T. Further, we found that VRB can be subdivided into two areas, a ventrorostral field (VR) with properties similar to those reported for VRB, and a ventrocaudal field (VC) with novel properties. With increasing stimulus tone frequency, activation in VR shifted caudally while activation in VC shifted rostrally. Thus we have newly identified field VC that has mirror-symmetric tonotopy to that of VR.

Are the carotid bodies of the guinea-pig functional?

We have previously observed that the guinea-pig appears to have a relatively poor ventilatory (V (E)) response to hypoxia, compared to other mammals. Therefore, in this study, we questioned the ability of the carotid bodies (primary peripheral chemoreceptors) in the guinea-pig to detect hypoxia. The ventilatory responses to poikilocapnic hypoxia (8% O(2)), poikilooxic hypercapnia (8% CO(2)), hyperoxia (100% O(2)) and cyanide (NaCN - 200 mug/kg, i.v.) were assessed before and after carotid body denervation (CBD) in anaesthetized guinea-pigs. Although CBD attenuated the V (E) responses to hypercapnia and cyanide, it had no effect on normoxic breathing or the V (E) responses to hypoxia or hyperoxia. In a separate group of guinea-pigs, nerve activity was recorded from single or few-fibre preparations of the carotid sinus nerve (CSN). Basal chemoreceptor activity could not be detected from any of the nerve preparations. NaCN and hypercapnia consistently provoked an increase in neural activity. In contrast, hypoxia never clearly increased activity in any of the single or few-fibre preparations isolated from the CSN. In conclusion, although the carotid bodies of the guinea-pig, like those of other mammals, are able to detect hypercapnia and histotoxic hypoxia and elicit a reflex increase in V (E), they are essentially hypoxia-insensitive. The latter may explain, at least in part, the relatively poor V (E) response to hypoxia shown by the guinea-pig.

Auditory function and cochlear morphology in the German waltzing guinea pig

The German waltzing guinea pig is a new strain of animals with a recessively inherited inner ear defect resulting in deafness and severe vestibular dysfunction. Measurements of auditory brainstem responses (ABRs) demonstrated that the homozygotes (gw/gw) are deaf while the heterozygotes (gw/+) have normal hearing. In the gw/gw cochlea, a collapse of Reissner's membrane leads to the absence of scala media. Melanin pigment accumulation was clearly observed in the gw/gw stria vascularis, and both the height and width of stria vascularis were significantly reduced. Ultrastructural observations further detailed the disorganization of stria vascularis in the gw/gw animals: marginal cells lacked basolateral infoldings; intermediate cells (melanocytes) were scarce and degenerated; and basal cells were difficult to identify. The level of degeneration of the organ of Corti varied between individual gw/gw animals. The density of spiral ganglion neurons was significantly decreased in old (1-2 years of age) gw/gw animals. In contrast, no pathological changes were observed in the cochleae of gw/+ animals. Our data suggest that the degeneration originates in the stria vascularis (most likely in the melanocytes), and that this is the primary cause for inner ear defects in the German waltzing guinea pig. Here, we describe the auditory function and cochlear morphology in this spontaneously mutated guinea pig strain.

Is duration tuning a transient process in the inferior colliculus of guinea pigs?

Duration selectivity appears to be a fundamental neural encoding mechanism found throughout the animal kingdom. Previous studies reported that band-pass duration-tuned neurons typically show offset responses and occupy a small portion of auditory neurons in non-echolocation mammals relative to echolocation bats. Therefore, duration tuning is generally weaker in non-echolocation mammals. In the present study, duration tuning was analyzed for 207 neurons recorded in the inferior colliculus (IC) of guinea pigs. Duration tuning was found to be stronger in the onset component of the responses from sustained, on-off and pause neurons than had been reported previously, when a short analysis window was applied. The need for an appropriate time window for duration tuning analysis was also supported by the fact that the on and off responses from an on-off neuron may show different duration tuning features. Therefore, duration tuning appears to be a transient neural coding process in the IC of guinea pigs. Duration tuning for these types of neurons may have been blurred by the use of a relatively unselective, long window.

Na+-K+-2Cl− cotransporters and Cl− channels regulate citric acid cough in guinea pigs

Loop diuretics have been shown to inhibit cough and other airway defensive reflexes via poorly defined mechanisms. We test the hypothesis that the furosemide-sensitive Na+-K+-2Cl− cotransporter (NKCC1) is expressed by sensory nerve fibers innervating the airways where it plays an important role in regulating sensory neural activity. NKCC1 immunoreactivity was present on the cell membranes of most nodose and jugular ganglia neurons projecting to the trachea, and it was present on the peripheral terminals of putative mechanosensory nerve fibers in the airways. In urethane-anesthetized, spontaneously breathing guinea pigs, bolus application of citric acid (1 mM to 2 M) to an isolated and perfused segment of the tracheal mucosa evoked coughing and respiratory slowing. Removal of Cl− from the tracheal perfusate evoked spontaneous coughing and significantly potentiated cough and respiratory slowing reflexes evoked by citric acid. The NKCC1 inhibitor furosemide (10–100 μM) significantly reduced both the number of coughs evoked by citric acid and the degree of acid-evoked respiratory slowing ( P < 0.05). Localized tracheal pretreatment with the Cl− channel inhibitors DIDS or niflumic acid (100 μM) also significantly reduced cough, whereas the GABAA receptor agonist muscimol potentiated acid-evoked responses. These data suggest that vagal sensory neurons may accumulate Cl− due to the expression of the furosemide-sensitive Cl− transporter, NKCC1. Efflux of intracellular Cl−, in part through calcium-activated Cl− channels, may play an important role in regulating airway afferent neuron activity.

Social stimuli cause changes of plasma oxytocin and behavior in guinea pigs

The neuropeptide oxytocin (OXT) is a key factor in the initiation and regulation of sociosexual behavior. The present study analyzes the effects of cohabitation and social challenge on plasma OXT concentration rates in guinea pig pairs in relation to male sociosexual behavior. The cohabitation phase lasted 3 days. On day 4, the pair was socially challenged by introducing an unfamiliar male. Displayed male sexual behavior varied significantly during cohabitation, with peaks on day 1. Sociopositive behavior, i.e., side-by-side contact, was increased on days 3 and 4. Cohabitation per se led to elevated plasma OXT concentrations only in males. In contrast, both sexes reacted with increased plasma OXT concentrations to the social challenge (day 4). At that time, male OXT was significantly correlated with sexual behavior and female OXT with sociosexual behavior received from the partner. Additionally, pairs were synchronized in their OXT release during days 3 and 4. We conclude that cohabitation causes sexually dimorphic plasma OXT concentration patterns in guinea pigs. Secondly, the conformity of OXT release in both sexes may represent an endocrine marker for long-term cohabitation, which is reflected behaviorally by increased spatial proximity.

Protease-activated receptor-2 activation exaggerates TRPV1-mediated cough in guinea pigs

A lowered threshold to the cough response frequently accompanies chronic airway inflammatory conditions. However, the mechanism(s) that from chronic inflammation results in a lowered cough threshold is poorly understood. Irritant agents, including capsaicin, resiniferatoxin, and citric acid, elicit cough in humans and in experimental animals through the activation of the transient receptor potential vanilloid 1 (TRPV1). Protease-activated receptor-2 (PAR2) activation plays a role in inflammation and sensitizes TRPV1 in cultured sensory neurons by a PKC-dependent pathway. Here, we have investigated whether PAR2 activation exaggerates TRPV1-dependent cough in guinea pigs and whether protein kinases are involved in the PAR2-induced cough modulation. Aerosolized PAR2 agonists (PAR2-activating peptide and trypsin) did not produce any cough per se. However, they potentiated citric acid- and resiniferatoxin-induced cough, an effect that was completely prevented by the TRPV1 receptor antagonist capsazepine. In contrast, cough induced by hypertonic saline, a stimulus that provokes cough in a TRPV1-independent manner, was not modified by aerosolized PAR2 agonists. The PKC inhibitor GF-109203X, the PKA inhibitor H-89, and the cyclooxygenase inhibitor indomethacin did not affect cough induced by TRPV1 agonists, but abated the exaggeration of this response produced by PAR2 agonists. In conclusion, PAR2 stimulation exaggerates TRPV1-dependent cough by activation of diverse mechanism(s), including PKC, PKA, and prostanoid release. PAR2 activation, by sensitizing TRPV1 in primary sensory neurons, may play a role in the exaggerated cough observed in certain airways inflammatory diseases such as asthma and chronic obstructive pulmonary disease.

Representation of the purr call in the guinea pig primary auditory cortex

Guinea pigs produce the low-frequency purr or rumble call as an alerting signal. A digitised example of the call was presented to anaesthetised guinea pigs via a closed sound system while recording from the primary auditory cortex. The exemplar used in this study had 9 regular phrases each spaced with their centres about 80 ms apart. Low-frequency (1.1 kHz) units responded best to the call but within this population there were four separate groups: (1) cells that responded vigorously to many or all of the 9 phrases; (2) cells that gave an onset response; (3) cells that only responded to a click embedded in the call; (4) cells that did not respond. Particular response types were often grouped together. Thus when orthogonal electrode tracks were used most units gave a similar response. There was no correlation between the type of response and the cortical depth. A similar range of response types was also found in the thalamus and there was no evidence of a distinct response in the cortex that was due to intracortical processing. Cells in the cortex were able to represent the temporal structure of the purr with the same fidelity as cells in the thalamus.

Spatial aspects of intracellular pH regulation in heart muscle

Intracellular pH (pH(i)) is an important modulator of cardiac function. Because it is readily influenced by metabolic processes, pH(i) is controlled physiologically. Classical models of intracellular pH regulation comprise acid/base transport proteins expressed in the sarcolemma, acting in concert with intracellular buffers. These two processes are coupled via a diffusive movement of protons. Because intracellular H(+) buffering is high, H(i)(+)-diffusion occurs through a passive shuttling on intrinsic mobile buffers such as acetylated carnosine, anserine and homocarnosine: low molecular weight imidazole compounds. This mechanism is assisted by carbonic buffer, a system regulated biochemically by the enzyme carbonic anhydrase. H(i)(+)-mobility via the buffer shuttles is low, and this can result in significant pH(i) non-uniformity under conditions of high proton flux across the sarcolemma or within the cell. Spatial regulation of pH(i) is complemented by passive H(+) permeation between cells through gap junctions. This permeation is also mediated via protonated buffers. The control of pH(i) is therefore dependent on carrier molecules that spatially shuttle protons within and between cells. In this review, we consider the physiological regulation of H(i)(+)-mobility and permeation, and its relevance to pH(i)-control in normal and pathophysiological states such as myocardial ischaemia, a clinical condition associated with severe intracellular acidosis.

Does the Unusual Life History of the Precocial Cavy (Cavia magna) Translate into an Exceptional Field Metabolic Rate?

An association between metabolic rate and life history has been predicted but not demonstrated yet. To test this prediction, we measured the field metabolic rate (FMR) of a rodent, Cavia magna, which has an unusual combination of life-history traits. Cavies live aboveground, feed on energy-poor diets, and take relatively long to produce a few highly precocial young. This "slow-living" life history might predict a relatively low metabolic rate. We recorded FMR of 29 individuals of C. magna in Uruguay using doubly labeled water. This represents the first FMR record for a hystricomorph rodent. Besides body mass, season best explained variation in recorded FMR, with higher daily energy expenditures during winter. Surprisingly, the reproductive state of females did not affect FMR. Comparison with allometric prediction did not support the hypothesis that the slow-living life history of precocial grazing cavies translates into relatively low FMR. However, the clear effect of season on FMR as well as the fact that cavies appear able to compensate for the energy cost of reproduction might be associated with the nonburrowing precocial life history of this species.

Isolation induced changes in Guinea Pig Cavia porcellus pup distress whistles

Guinea Pig Cavia porcellus pups emit high-pitched distress whistles when separated from their mother. In order to assess the influence of the duration of a brief isolation period on whistle acoustic structure, we recorded the distress whistles of six 8-day old pups separated for 15 min from their group in a novel environment and compared the mean values of the first and last 30 whistle notes. Acoustic analysis revealed, throughout the session, a significant decrease in whistle duration, an increase in mean frequency and a tendency for a decrease in number of harmonics in the first part of the note. Results demonstrate that, throughout a brief isolation period, the vocal response of Guinea Pig pups to isolation undergoes structural changes possibly related to time-dependent changes in motivational state.

Optimum primary tone level setting for measuring high amplitude DPOAEs in guinea pigs

A special stimulus paradigm needs to be applied when distortion product otoacoustic emission (DPOAE) input/output functions are used to investigate the loss of sensitivity and loss of compression of outer hair cell cochlear amplifiers during noise exposure, drug treatment, etc. This stimulus paradigm should be able to reflect cochlear non-linear compressive sound processing known from direct basilar membrane measurements. Such a paradigm has already been established for humans that accounts for the different compression of the primary tones at the DPOAE generation site at f2 with L1 = 0.4 L2 + 39 dB SPL ('scissor paradigm'). The purpose of the present study was to develop an equivalent parameter setting for guinea pigs. Ninety-six different L1 - L2 combinations were presented to 24 ears in 18 pigmented guinea pigs at seven f2 frequencies between 2 and 16 kHz. L2 ranged from 20 to 60 dB SPL, L1 from 20 to 65 dB SPL. An extreme value analysis was performed to achieve the maximum DPOAE level for L1 in relation to L2. Linear regression analysis yielded a scissor paradigm specific to guinea pigs (L1 = 0.46 L2 + 41 dB SPL) which is similar to that of humans.

The Daily Pattern of Heart Rate, Body Temperature, Locomotor Activity, and Autonomic Nervous Activity in Congenitally Bronchial-Hypersensitive (BHS) and Bronchial-Hyposensitive (BHR) Guinea Pigs

We studied the characteristics of the rhythmicity of heart rate (HR), body temperature (BT), locomotor activity (LA) and autonomic nervous activity in bronchial-hypersensitive (BHS) and bronchial-hyposensitive (BHR) guinea pigs. For this purpose, HR, BT, LA, and electrocardiogram (ECG) were recorded from conscious and unrestrained guinea pigs using a telemetry system. Autonomic nervous activity was analyzed by power spectral analysis of heart rate variability. Nocturnal patterns, in which the values in the dark phase (20:00-06:00) were higher than those in the light phase (06:00-20:00), were observed in HR, BT and LA in both strains of guinea pigs. The autonomic nervous activity in BHS guinea pigs showed a daily pattern, although BHR guinea pigs did not show such a rhythmicity. The high frequency (HF) power in BHS guinea pigs was higher than that in BHR guinea pigs throughout the day. Moreover, the low frequency/high frequency (LF/HF) ratio in BHS guinea pigs was lower than that in BHR guinea pigs throughout the day. These results suggest that parasympathetic nervous activity may be predominant in BHS guinea pigs.

Dyslipidogenic microangiopathy in guinea pigs at early stages of atherogenesis

We studied the effect of dyslipidemia on lipid metabolism, state of microcirculatory system, and morphological alterations in the aorta and liver of guinea pigs at the early stages of experimental atherogenesis. The important role of microcirculatory disorders in the development of regional pathology and atherosclerosis is confirmed. The proposed alimentary model can be used in the development of novel methods for prevention and treatment of atherosclerosis.

Effects of chronic hypoxia on maternal vasodilation and vascular reactivity in guinea pig and ovine pregnancy

During pregnancy, exposure to chronic hypoxia is thought to be associated with an increased risk of preeclampsia and fetal intrauterine growth restriction (IUGR). While some studies suggest that this process may be mediated through effects of chronic hypoxia on uterine artery vasodilation and growth, these observations are likely to be species specific and may represent genetic variability in maternal adaptation to hypoxia. This review is a comparative analysis of the effects of chronic hypoxia on vascular reactivity in pregnant and nonpregnant guinea pig and sheep. Data suggest that exposure to chronic hypoxia is associated with enhanced uterine artery blood flow in the sheep, whereas, in the guinea pig, blood flow is decreased.

Distribution of the vanilloid receptor (VR1) in the gastrointestinal tract

The gastrointestinal (GI) tract responds to a variety of stimuli through local and centrally mediated pathways. Changes in the intestinal microenvironment are sensed by vagal, spinal, and intrinsic primary afferent fibers. Sensory nerve endings located close to the lumen of the GI tract respond to pH, chemical composition of lumenal contents, or distortion of the mucosa. Afferents within the muscle layers are thought to be tension sensitive, whereas those located within the myenteric plexus are also thought to respond to changes in chemical composition and humoral substances. Subpopulations of these afferent fibers are activated by capsaicin. However, the exact location of these nerves is currently not known. The vanilloid receptor (VR1) is a nonselective cation channel that is activated by capsaicin, acid, and temperature. Antibodies to VR1 make it possible to determine the location of these afferents, their morphology, and their relationships with enteric nerves and other cell types in the GI tract. VR1-like immunoreactivity was observed on nerves within myenteric ganglia and interganglionic fiber tracts throughout the GI tract. VR1 nerves were also observed within the muscle layers and had an irregular profile, with varicose-like swellings along their lengths. Blood vessels within the GI wall had VR1-immunoreactive nerve fibers associated with them. VR1-like nerves and other immunopositive cells were also observed within the mucosa. In summary, VR1-like immunoreactivity was found in several locations within the GI tract and may provide sensory integration of chemical, physical, or inflammatory stimuli. VR1-like fibers appear to be predominantly spinal in origin, but a few vagal VR1-like fibers exist in the stomach.

The effects of superior ovarian nerve sectioning on ovulation in the guinea pig

The effects on spontaneous ovulation associated with the unilateral or bilateral sectioning of the superior ovarian nerves (SON) were analyzed in guinea pigs at different time intervals of the estrous cycle. Day 1 of the estrous cycle was defined as the day when the animal presents complete loss of the vaginal membrane (open vagina). Subsequent phases of the cycle were determined by counting the days after Day 1. All animals were autopsied on the fifth day of the estrous cycle after surgery. Sectioning the right, left, or both SONs on day 5 (early luteal phase) resulted in a significant increase in the number of fresh corpora lutea. Ovulation increased significantly when the left SON (L-SON) was sectioned during late follicular phase (day 1) and medium luteal phase (day 8). When surgery was performed on days 1 or 8, neither sectioning the right SON (R-SON) nor sectioning the SON bilaterally had an apparent effect on ovulation rates. Similarly, ovulation rates were not affected when unilateral (right or left) or bilateral sectioning of the SON was performed during late luteal phase two (day 12). Unilateral or bilateral sectioning of the SON performed during the early luteal phase (day 5) was associated with a significant decrease in uterine weight. A comparable effect was observed when the L-SON was sectioned during late follicular phase (day 1), or medium luteal phase (day 8). No effects on uterine weight were observed when unilateral or bilateral sectioning of the SON was performed during late luteal phase. Our results suggest that in the guinea pig the SON modulates ovulation, and that the degree of modulation varies along the estrous cycle. The strongest influence of the SONs on ovulation occurs during early luteal phase, and decrease thereafter, being absent by late luteal phase. In addition, sectioning the left or the right SON caused different responses by the ovaries of adult guinea pigs. This paper discusses the mechanisms by which ovulation increased when the SON was surgically cut.

Contribution of tachykinin receptor subtypes to micturition reflex in guinea pigs

The aim of the present study was to determine the role of tachykinin in the micturition reflex in guinea pigs. We investigated the effects of tachykinin NK(1) receptor antagonists, GR205171 ([2-methoxy-5-(5-trifluoromethyl-tetrazol-1-yl)-benzyl]-(2S-phenyl-piperidin-3S-yl)-amine), CP99994 ((+), (2R, 3R)-3-(2-methoxybenzyl-amino)-2-phenylpiperidine) and FK888 (N(2)-[(4R)-4-hydroxy-1-(1-methyl-1H-indol-3-yl) carbonyl-L-prolyl]-N-methyl-N-phenylmethyl-3-(2-naphthyl)-L-alaninamide), the tachykinin NK(2) receptor antagonist, SR48968 ((+)-N-methyl-[4-(4-acetylamino-4-phenyl piperidino)-2-(3, 4-dichloro-phenyl)butyl] benzamide), and the tachykinin NK(3) receptor antagonist, SB223412 ((S)-(-)-N-(alpha-ethylbenzyl)-3-hydroxy-2-phenylquinoline-4-carboxamide) on rhythmic bladder contraction. GR205171 and CP99994 but not SR48968 or SB223412 reduced bladder contraction frequency. FK888 inhibited the frequency very slightly at the highest dose tested. The distribution of tachykinin NK(1) receptor antagonists to the central nervous system after intravenous administration was examined using an ex vivo binding assay. GR205171 was distributed to the brain and spinal cord, but the tachykinin NK(1) receptor antagonist, FK888, was not. These results suggest that tachykinin NK(1) receptors, which are located in the central nervous system, play an important role in micturition in guinea pigs.

Generation of DPOAEs in the guinea pig

In humans, distortion product otoacoustic emissions (DPOAEs) at frequencies lower than the f(2) stimulus frequency are a composite of two separate sources, these two sources involving two distinctly different mechanisms for their production: non-linear distortion and linear coherent reflection [Talmadge et al., J. Acoust. Soc. Am. 104 (1998) 1517-1543; Talmadge et al., J. Acoust. Soc. Am. 105 (1999) 275-292; Shera and Guinan, J. Acoust. Soc. Am. 105 (1999) 332-348; Kalluri and Shera, J. Acoust. Soc. Am. 109 (2001) 662-637]. In rodents, DPOAEs are larger, consistent with broader filters; however the evidence for two separate mechanisms of DPOAE production as seen in humans is limited. In this study, we report DPOAE amplitude and phase fine structure from the guinea pig with f(2)/f(1) held constant at 1.2 and f(2) swept over a range of frequencies. Inverse Fast Fourier Transform analysis and time-domain windowing were used to separate the two components. Both the 2f(1)-f(2) DPOAE and the 2f(2)-f(1) DPOAE were examined. It was found that, commensurate with human data, the guinea pig DPOAE is a composite of two components arising from different mechanisms. It would appear that the 2f(1)-f(2) emission measured in the ear canal is usually dominated by non-linear distortion, at least for a stimulus frequency ratio of 1.2. The 2f(2)-f(1) DPOAE exhibits amplitude fine structure that, for the animals examined, is predominantly due to the variation in amplitude of the place-fixed component. Cochlear delay times appear consistent with a linear coherent reflection mechanism from the distortion product place for both the 2f(1)-f(2) and 2f(2)-f(1) place-fixed components.

An in vivo guinea pig preparation for studying the autonomic regulation of airway smooth muscle tone

The autonomic nervous system plays a primary role in regulating airway smooth muscle tone. Here, we describe the development of an in vivo guinea pig model that permits systematic studies of the autonomic control of airway smooth muscle. The model is based on preparations previously described and utilizes measurements of isometric tension in a perfused segment of extrathoracic guinea pig trachea in situ. It has the advantage that the autonomic innervation to the tracheal segment under study can be physiologically or pharmacologically isolated and studied independently from other mechanisms regulating airway smooth muscle tone. Initial experiments were conducted to optimize model conditions. Subsequent experiments were designed to highlight the usefulness of this preparation for studying parasympathetic regulation of airway caliber. The results of the study demonstrate the utility of this model for future studies into the neural regulation of bronchomotor tone and the mechanisms of airway obstruction and hyperreactivity associated with disease.

Is a wild mammal kept and reared in captivity still a wild animal?

This study compared domestic guinea pigs (Cavia aperea f. porcellus; DGP) and two different populations of the wild cavy (Cavia aperea), its ancestor, to examine whether rearing of wild mammals in captivity affects their behavior and physiological stress responses. One population of wild cavies consisted of wild-trapped animals and their first laboratory-reared offspring (WGP-1). The animals of the other population were reared in captivity for about 30 generations (WGP-30). The spontaneous behavior of each of six groups of WGP-1 and WGP-30 and nine groups of DGP, each consisting of one adult male and two adult females, was analyzed quantitatively. Blood samples of the males were taken to determine cortisol, epinephrine, and norepinephrine concentrations. In addition, the exploratory behavior of 60-day-old male WGP-1, WGP-30, and DGP was investigated in an exploration apparatus. The domesticated animals displayed significantly less aggression, but significantly more sociopositive and male courtship behavior than their wild ancestors. In addition, DGP were much less attentive to their physical environment. Surprisingly, no behavioral difference was found between WGP-1 and WGP-30. Basal cortisol concentrations did not differ between wild and domestic guinea pigs. Catecholamine concentrations, however, as well as the challenge values of cortisol, were distinctly reduced in the DGP. WGP-1 and WGP-30 did not differ with respect to their endocrine stress responses. In the exploration apparatus both forms of wild cavies were much more explorative than the domestic animals. These data suggest that the long-term breeding and rearing of wild guinea pigs in captivity do not result in significant changes in behavior and hormonal stress responses. It appears to take much longer periods of time and artificial selection by humans to bring about characters of domestication in wild animals.

Effects of sympathetic denervation on follicular distribution, oestradiol and progesterone serum levels in prepubertal hemi-ovariectomized female guinea pig

Hemi-gonadectomy performed in prepubertal female guinea pigs is followed by a compensatory ovarian hypertrophy (COH) and compensatory ovulation (CO). Sympathetic denervation diminished the COH (left ovary: 28 +/- 1.6% versus 46 +/- 4% (control), P < 0.05; and right ovary: 21.3 +/- 3.2% versus 34.2 +/- 3.7% (control), P < 0.01) and does not modify the CO. The mean follicular diameter increased only in the right ovary of hemi-gonadectomized animals. This increase is greater in the hemi-gonadectomized-denervated groups. The mean follicular diameter measured in the right and left ovaries showed an opposite response in hemi-ovariectomized and hemi-ovariectomized-denervated animals: the diameter increased in the right ovary without modifications in the left. Present results add further support to the participation of ovarian innervation on the mechanisms, which regulate follicular development.

Hemoglobin affinity in Andean rodents

Blood hemoglobin oxygen affinity (P50) was measured in three Andean species and in the laboratory rat (control), all raised near sea level. Chinchilla lanigera (Molina, 1792) has an altitudinal habitat range from low Andean slopes up to 3000 m., while Chinchilla brevicaudata (Waterhouse, 1848) has an altitudinal range from 3000 to 5000 m. The laboratory type guinea pig, wild type guinea pig (Cavia porcellus), (Waterhouse, 1748), and laboratory rat (Rattus norvegicus) were also raised at sea level. The Andean species had high hemoglobin oxygen affinities (low P50) compared with the rat. Chinchilla brevicaudata had a higher affinity than Chinchilla lanigera. The wild type guinea pig had a higher affinity than the laboratory type. As has been shown in other species, this is another example of an inverse correlation between the altitude level and the P50 values. This is the first hemoglobin oxygen affinity study in Chinchilla brevicaudata.

Reproductive medicine of rabbits and rodents

The small animal practitioner is likely to be called upon to help nontraditional pets such as rabbits, rodents, and ferrets. The more information veterinarians have regarding normal anatomy, physiology, reproduction, medicine, anesthesia, and surgery of these unusual pets, the more likely they will be able to help their owners. This article presents an overview of routine and emergency reproductive concerns that the small animal practitioner may face when presented with nontraditional mammalian patients.