Changes in N-acetyl-beta-D-glucosaminidase activities in relation to other milk components throughout normal lactation in the guinea pig

Changes in milk production, NAGase activities, Na, Cl, K, lactose, total N, and fat were followed throughout normal lactation in 26 healthy guinea pigs. Appropriate microassays were used and all determinations were performed on the same small skim milk sample (microhematocrit tube). A very sensitive and rapid spectrofluorimetric determination of NAGase in 10-microliters skim milk samples was evaluated. Four days after parturition, daily milk production reached a maximum of about 20 ml. Thereafter milk yield decreased progressively to about 7 ml on d 15. During the entire course of lactation, a progressive increase in NAGase, total N, fat, Na, and Cl was observed. However, K and lactose decreased. Highly significant positive correlations between NAGase and Na, Cl, fat, and total N were evident, whereas correlations were negative between NAGase and K, lactose, and milk production. These changes can be explained on basis of alterations that occur at the level of the blood-milk barrier. The short lactation period of the guinea pig, the easy handling and milking practices, together with the available sensitive micromethods can lead to the establishment of a convenient guinea pig mastitis model.

Lower boundaries of two-tone suppression regions in the guinea pig

Lower boundaries of two-tone suppression regions were determined in single fibres of the guinea pig with a tracking algorithm as described by Schmiedt (1982). For a suppressee at CF having a level of 20 dB above the threshold of the tip, suppression at the high-frequency (hf) side of the FTC could almost always be found. With the method used, the percentage of fibres in which suppression could be found at the low-frequency (lf) side of the FTC decreased with decreasing CF. Moreover, the occurrence of lf-suppression decreased for lower suppressee levels for fibres with CF approximately 2-5 kHz. For each fibre the minimum level difference between lf-suppression boundary and tip threshold was larger than 20 dB, for the whole group of fibres the difference was 34 dB on average. The hf-suppression regions sometimes reached below the tip for fibres with CFs in the 4 kHz region. The frequency at the lowest level of the hf-suppression boundary, best suppression frequency or BSF, is related to the CF as: BSF = 0.55 + 1.13 CF. When the suppressee level increased, the lower boundary at the hf side shifted upwards with a rate greater than 1 dB/dB. On the whole the two-tone suppression data in the guinea pig agree with those found in other rodents.

Effect of zearalenone on early pregnancy in guinea pigs

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 less than 12 ng/ml in all guinea pigs 8 and 15 days after mating. Serum concentrations of progesterone were greater than 100 ng/ml in pregnant guinea pigs on day 22, but remained less than 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 less than 10 ng/ml in all guinea pigs on day 15 and remained low on day 22 only in nonpregnant guinea pigs.(ABSTRACT TRUNCATED AT 250 WORDS)

A comparison of the effects of denervation on the mechanical properties of rat and guinea-pig skeletal muscle

1. A fast (extensor digitorum longus) and slow (soleus) twitch muscle were denervated in rats and guinea-pigs and isometric and isotonic contractions were followed for periods of up to 6 months after. 2. The decay of tetanic tension with time could be described as exponential. The rate of decay of tension was greatest in rat soleus and least in guinea-pig soleus by a factor of more than three. The fast muscles atrophied at intermediate rates. 3. The contraction and relaxation times of soleus and extensor digitorum longus of rat, initially prolonged by denervation, became shorter after 3 weeks. There was no such reversal in either guinea-pig muscle, indeed extensor digitorum longus twitch became even more prolonged. Guinea-pig muscles often showed signs of repetitive response to a single stimulus, resulting in distortion of relaxation of the twitch. 4. There was a slowing of isotonic shortening velocity in the late stage of denervation of guinea-pig extensor digitorum longus, accompanied by a fall in the rate of development of isometric tetanic tension. There was a just-significant (P less than 0.1) increase in the shortening velocity of rat soleus. None of the other muscles showed any change in either rate characteristic. 5. In guinea-pig extensor digitorum longus the type I fibres atrophied less than type II fibres; in all other muscles the atrophy was more uniform, possibly faster in type II. Guinea-pig soleus remained pure type I contrasting with an increase in the numbers of type II fibres in rat soleus. There was a possible increase in the number of type I fibres in guinea-pig fast muscle and no change in the rat.

Use of cage space by guineapigs

Cage space requirements for laboratory animals have been established by Government Regulation and Recommendations. In order to test the adequacy of these space allocations, the use of cage floor area by breeding groups of guineapigs was studied. A computer-coupled video tracking system capable of imaging in low light intensity as well as total darkness was used to determine the average per cent occupancy by guineapigs in all portions of a cage over 12-h light and dark cycles. Simultaneous time synchronized slow motion video recordings permitted an analysis of activity to be coordinated with cage use data. Results of the study revealed that breeding groups of guineapigs utilize the periphery of the cage almost to the total exclusion of the centre of the cage. Approximately 75-85% of all occupancy in both the day and evening hours occurred in 47% of the cage floor area located along the periphery. Analysis of video recordings revealed that the animals remained active throughout the day and night with no prolonged period of quiescence that could be associated with sleep. Results of this study suggest that while guidelines for housing guineapigs based on area allocation per animal can be formulated and are easy to administer, they cannot be supported by the behavioural characteristics of these animals or careful quantitation of their pattern of cage space utilization.

Spontaneous contractile activity of guinea-pig gall-bladder in vitro

Some parameters of rhythmic mechanical and electrical events of guinea-pig gall-bladder were investigated. Pressure-volume (P-V) responses, extracellular electrical activity and gall-bladder morphology were recorded. Rhythmic gall-bladder activity consisted of waves of pressure at intraluminal volumes between 0.5 and 1.8 ml. The pressure waveforms developed in a single contraction were usually oscillatory, containing two or more peaks which were more or less separated. The maximum amplitude value of phasic pressure waves was 1.8 +/- 0.6 cmH2O. Bursts of spike potentials appeared at three equidistant electrodes along the longitudinal diameter of the bladder with variable delays indicating absence of propagation of the fast electrical activity. By analysing the morphological changes of gall-bladder silhouette during the P-V curve it was evident that the maximum amplitude and duration of contractile events occurred when the whole muscular wall was stretched. Tetrodotoxin added to the bath solution did not abolish rhythmic activity--indicating its myogenic nature--and shifted the P-V curve to the left of the control, confirming the inhibitory role of the intrinsic nervous plexus of guinea-pig gall-bladder.

Location of pulmonary stretch receptors in the guinea-pig

The site of pulmonary slowly adapting stretch receptors (SRs) was investigated in anaesthetized, thoracotomized and artificially ventilated guinea-pigs. The location of SRs within the lungs and airways was determined by analyzing the changes of SR single fibres discharge patterns in response to (a) occlusion of the airways, (b) local probing, and (c) microinjection of the non-diffusible local anaesthetic cinchocaine into the presumed receptor site. The great majority (92%) of the 79 SRs examined was localized in small airways or in lung parenchyma ('peripheral SRs'), whereas only 8% were located in large airways, i.e., in the trachea, main bronchi and lobar bronchi ('central SRs'). The discharge responses to lung inflation and to ammonia inhalation slightly differed between these two SR groups. With the pronounced prevalence of peripheral SRs, the guinea-pig seems to take a unique position among the species examined hitherto.

The fate of intravenously injected tissue ferritin in pregnant guinea-pigs

The organ distribution of intravenously injected hepatic ferritin either labelled with 59Fe or with 59Fe and 125I, was studied in pregnant guinea-pigs. At 5 h 71.2% of injected 59Fe was present in the placenta and fetus. Transfer of 59Fe to the fetus was slow, with 11.2% present at 5 h and 38.6% at 21 h. Analysis of a placental cellular lysate for 59Fe and 125I revealed that the injected iron was present as intact ferritin at 2 h but by 21 h the ferritin had been catabolized, the 125I excreted and the 59Fe incorporated into endogenous ferritin. Most of the fetal 59Fe counts were detected in the liver, with 35.3% of the transferred 59Fe in ferritin, 30.4% in haemoglobin and 10.6% in a low molecular weight pool. The uptake of labelled ferritin by the placenta was inhibited by a 300-fold molar excess of unlabelled ferritin but not by albumin, asialofetuin or by the injection of carbon particles. A nonsignificant reduction in uptake was noted after injection of mannosylated bovine serum albumin. The mannosidase inhibitor swainsonine had no effect. Iron transfer to the fetus was not affected by various microtubular inhibitors. Presaturation of endogenous transferrin with oral carbonyl iron prevented iron release from the feto-placental unit back into the maternal circulation. In consequence, marrow 59Fe uptake by the maternal marrow was reduced. The ferrous chelator 2,2'-bipyridine significantly reduced 59Fe transfer to the fetus and this occurred irrespective of whether the chelator was given prior to or after 59Fe ferritin administration. The ferric chelator desferrioxamine had no such effect. Electron microscopy of placental tissues revealed endocytosis of ferritin molecules. These results indicate that the guinea-pig placenta takes up homologous tissue ferritin and transfers the iron slowly to the fetus after reductive mobilization. The process is compatible with a receptor-mediated pathway.

Functional subdivisions in the auditory cortex of the guinea pig

The auditory fields in the cortex of the guinea pig were investigated with microelectrode mapping techniques. Pure tones of varying frequencies and amplitudes were used as acoustic stimuli. Mainly, multiunit activity was recorded. A large tonotopic area is found in the anterior half of the auditory cortex. This area is named the anterior field (field A). Frequency tuning curves of multiunits in field A are generally narrow. Responses to tone stimuli are strong, and latencies are short. Low best frequencies are represented rostrally, high best frequencies caudally. The tonotopy is continuous and quite regular. Field A is narrow dorsally and becomes gradually broader ventrally. Correspondingly, the isofrequency lines slightly diverge from dorsal to ventral. Caudal to the first field, there is a second, smaller tonotopic area. It lies in the dorsal half of the posterior auditory cortex and is therefore named the dorsocaudal field (field DC). The frequency specificity of the cell clusters in this area is as strong as in field A, but the tonotopy is discontinuous: In the dorsal half of field DC, high best frequencies (16-32 kHz) are represented rostrally; the low frequencies (0.5-2.8 kHz) are represented immediately caudal to the high frequencies, while the intermediate frequencies are missing. Ventrally in field DC, the frequency representation is more complete. Except for this discontinuous map, we did not notice any differences between fields A and DC. A third tonotopic field was found rostral to field A. This field extends over a surface of less than 1 mm2 and was named the small field (field S). It contains a complete representation of the frequency range; high best frequencies are located rostrally, low frequencies caudally. The response latencies are slightly longer in field S than in fields A or DC, and the tuning curves are broader. A broad strip of nontonotopic cortex (auditory belt) surrounds fields A and DC caudally. We subdivided this area into the dorsocaudal and the ventrocaudal belt region. In both areas, tuning curves are often broad, and response latencies are longer than in the tonotopic cortex. In the dorsocaudal belt, most multiunits react with a phasic on-response to pure tones; in the ventrocaudal belt, tonic responses occur more frequently. Another nontonotopic region is located in the anterior auditory cortex, rostral to the tonotopic fields, and was therefore named the rostral belt. Tuning curves in this area are broad, latencies are short, and response thresholds are often high. In the discussion, the guinea pig is compared with other mammalian species.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of chloropheniramine maleate on liver and kidney functions as well as blood count of guinea pigs

The present study aimed at exploring the effect of antihistamine chloropheniramine maleate (H1-blocker) on liver and kidney functions as well as on blood count. 60 mature guinea pigs were used. Histamine or chloropheniramine maleate was given, either alone or together, intramuscularly for 7 successive days. At the end of the experimental period, blood samples were collected for determination of blood counts and of the levels of urea, creatinine, GOT, GPT, and alkaline phosphatase in the sera of different groups. The results showed significant groupwise variations in blood count, liver function as well as kidney function.

Blood pressure and other physiological responses in awake and anesthetized guinea pigs

The effect of combinations of injectable anesthetics on mean arterial blood pressure, blood gases, heart rate and respiration of the guinea pig (NIH Outbred strain) was investigated. After a 30 minute period in which baseline resting cardiorespiratory measurements were obtained, five groups of six pigmented animals having indwelling carotid cannulas were anesthetized with (a) ketamine hydrochloride (30 mg/kg, im)/xylazine (5 mg/kg, im); (b) sodium pentobarbital (15 mg/kg, ip)/fentanyl-droperidol (0.4 mg/kg, im); (c) diazepam (5mg/kg, ip)/fentanyl citrate (0.32 mg/kg, im); (d) diazepam (5 mg/kg, ip)/alphaxalone-alphadolone acetate (45 mg/kg, im); or (e) 1% alpha-chloralose-40% urethane (0.8 ml/100g, ip). Animals were not respirated artificially and no supplemental doses of anesthetic were given. Resting blood pressure in awake animals was measured over time for as long as cannulas remained patent (109 measurements). Mean resting blood pressure, for this strain of guinea pigs, was determined to be 53.1 +/- 4.2 mmHg. There was no indication that mean arterial blood pressure changed with age in animals varying in weight from 215 g to 550 g. Under diazepam/fentanyl, blood pressure rose significantly above resting level to a mean of 71.1 +/- 6.1 mmHg. With the other four combinations, blood pressure stabilized near, but below pre-anesthesia levels (ketamine/xylazine 47.1 +/- 6.8 mmHg; pentobarbital/fentanyl-droperidol, 46.9 +/- 3.2 mmHg; diazepam/alphaxalone-alphadolone, 47.8 +/- 4.8 mmHg; chloralose-urethane, 51.0 +/- 1.2 mmHg). Under diazepam/alphaxalone-alphadolone and chloralose-urethane, respiration was depressed and blood gas levels deviated from normal to the extent that artificial ventilation would be necessary to maintain an adequate physiological state.

Inter-species variations in myocardial responsiveness to cardiac glycosides: possible relations to the thyroid status

Mammalian species differ in their myocardial responsiveness to cardiac glycosides; whereas glycosides induce a marked positive inotropic effect in species such as dog, rabbit and guinea-pig, the rat myocardium is virtually insensitive. We investigated the physiological basis for this phenomenon by testing the hypothesis that the inter-species variations in the response of the myocardium to cardiac glycosides results, at least in part, from species-related differences in the "thyroid status". In the present study we focused on the toxic effects of the glycosides, and studied ouabain-induced delayed afterdepolarizations (DAD): (1) in guinea-pigs, rats and mice, which encompass a wide range of thyroid statuses, as indicated by their O2 consumption and thyroid hormone levels; (2) in guinea-pigs and rats in which the thyroid status was decreased by propylthiouracil treatment or increased by thyroxine administration (in the former species only). DAD were readily induced in guinea-pigs after 40 to 60 min superfusion with 10(-6) M ouabain and 5.4 mM Ca2+. In rats, DAD were induced only when the Ca2+ concentration was raised to 8.1 mM, but were absent in mice even after 2 h of superfusion with ouabain and 8.1 mM Ca2+. In guinea-pigs and rats (at cycle length = 500 ms), DAD amplitude was (means +/- S.E.): 2.8 +/- 0.7 mV and 1.1 +/- 0.4 mV, respectively. The slope of the DAD ascending limb (dV/dt) in guinea-pigs was 47.6 +/- 8.6 mV/s and in rats was 8.1 +/- 3.4 mV/s. In both species DAD characteristics were altered by the thyroid status. In eu-, hyper- and hypothyroid guinea-pigs, DAD amplitude and dV/dt (cycle length = 500 ms) were as follows: 2.8 +/- 0.7 mV and 47.6 +/- 8.6 mV/s; 1.2 +/- 0.4* mV and 12.6 +/- 3.9* mV/s; 7.5 +/- 0.6* mV and 204.0 +/- 18.4* mV/s, respectively (*, P less than 0.005, compared to euthyroid guinea-pigs). The occurrence of triggered beats was also dependent on the thyroid status. They occur more frequently in hypothyroidism and less frequently in hyperthyroidism. Hypothyroidism in rats augmented ouabain toxicity as reflected by an increase in DAD amplitude and dV/dt by 109% and 105%, respectively (P less than 0.05, as compared to euthyroid rats). In conclusion, we suggest that species-related differences in the thyroid status may contribute to the inter-species (as well as for the intra-species) variations in the myocardial responsiveness to cardiac glycosides.

Comparative studies on the adhesiveness of granulocytes of guinea pig and man

The high affinity of granulocytes of guinea pig and man to glass surfaces is modified by serum. Native serum contains both an adherence-promoting activity, which is related to complement, and components which reduce the adhesiveness of granulocytes. These components are stable at 56 degrees C for 30 min and are tightly bound to the glass surface. beta-Lipoproteins are candidates for this adherence reducing ability of serum. Adherence promotion by native serum is mediated by coating the glass surface with C3b/C3bi. Human granulocytes from the peripheral blood adhered pig serum with C3b/C3bi to almost the same extent as in the presence of native serum, but on guinea pig granulocytes elicited in the peritoneal cavity, a cell surface metalloproteinase degraded the C3b/C3bi, thus reducing the adhesiveness of these cells. This proteinase was inhibited by MgEDTA, DTT, and 1,10-phenanthroline, whereby the high adhesiveness of granulocytes was restored to C3b/C3bi-coated glass.

Ultradian and circadian CO2 emission variations in nocturnal and diurnal animals exposed to a light stimulus

1. Carbon dioxide emission (VCO2) has been continuously recorded in three laboratory animal species (Sprague-Dawley rats, Japanese quail, Hartley guinea-pigs) which differ by their nocturnal and diurnal activities. A 100 lux stimulus has been delivered at various time intervals. 2. A regular alternation of 12, 3 or 1.5 hr light (L) and darkness (D) gives VCO2 circadian and ultradian rhythms of 24, 6 or 3 hr periods, respectively, in quail and rats. 3. Such circadian and ultradian LD rhythms are not induced in all guinea-pigs. 4. The amplitudes of the VCO2 responses are greatest at D----L when the animals have a maximum diurnal activity and at L----D when their maximum activity is nocturnal. 5. Interactions between circadian and ultradian rhythms are seen in all LD experiments, as well as in continuous light (LL) or continuous dark (DD). 6. No more well-marked or even inverted VCO2 responses to the light stimuli may occur after several days of exposure to these LD alternations.

Evidence for a lower oesophageal sphincter in the guinea-pig

1. In vitro balloon pull-through experiments have been used to identify the guinea-pig lower oesophageal sphincter (LOS). 2. Histologically, the LOS forms a 1-2 mm ring of smooth muscle at the distal termination of the oesophagus, immediately adjacent to the gastric sling muscle. 3. Tetrodotoxin (10(-6) M) sensitive, guanethidine (10(-6) M) insensitive "on" relaxation of circular LOS muscle strips was evoked by electrical field stimulation (ES). 4. ES evoked atropine (10(-6) M) sensitive "on" contractions of gastric sling and fundus smooth muscle strips. 5. Following cessation of ES a partially atropine-sensitive "off" contraction was observed in all the smooth muscle strips. 6. The predominant response of the LOS to ES was relaxation.

Maximal expiratory flow in the guinea pig

Using the whole body plethysmograph, the maximal expiratory flow-volume (MEFV) curve was performed in anesthetized-paralyzed guinea pigs with intact chest (n = 7) and in anesthetized, chest-open animals following exsanguination (n = 13). The pressure-volume (PV) curve was also measured. Before and after the MEFV and PV maneuvers, lung volume was determined with a neon dilution method. Peak maximal expiratory flow (Vmax) of 178 +/- 7 ml/sec occurring at 83% TLC. After the peak flow, Vmax decreased gradually with reducing lung volume. The Vmax-static recoil pressure curve was relatively linear up to PL = 5 cmH2O. Density-dependence of Vmax (helium-Vmax was significantly higher than air-Vmax) was found at or above 60% TLC but not at lung volume below 60% TLC. For the chest-open postmortem guinea pig, Vmax and TLC decreased while trapped gas volume increased gradually with time after exsanguination, indicating that bronchoconstriction gradually became more severe. The magnitude of this postmortem airway spasm was related to age and anesthetic used.

Midline and temporal lobe MLRs in the guinea pig originate from different generator systems: a conceptual framework for new and existing data

In the guinea pig and gerbil, individual components within the MLR time frame differ in optimal recording location. Specifically, MLR components obtained from the midline differ from those obtained over the temporal lobe. In the present paper midline and temporal lobe components were shown to differ not only in scalp topography but also in response to the following experimental manipulations: intracortical injection of neural inactivating agents (lidocaine and kainic acid), temporal lobe ablation, electrolytic lesions, systemic anesthesia, stimulation rate and course of development. Since midline and temporal lobe components respond differently to experimental manipulations, it can be concluded that the midline and temporal lobe responses are mediated by different generator sources. The particular orientation of the generators responsible for the MLR in the guinea pig and gerbil facilitates the identification of individual components. Results from simultaneous recordings of these components during experimental manipulations support the hypothesis of multiple MLR generators in laboratory animals and provide insight into the generators and developmental aspects of the MLR in humans.

Body surface areas and K values in strain 13 guinea pigs with different body weights and ages

Body surface areas (BSA) were determined for strain 13 guinea pigs with body weights ranging from 191 to 1011 g. For this determination, the entire skin of each animal was removed immediately after death and flattened on a wax film with a homogeneous paper. The skin outlines on the paper were cut and weighed for determining BSA. The K value was calculated for each guinea pig as the ratio of BSA (cm2)/body weight (g)2/3. Significantly different K values of 11.31 +/- 0.11, 9.66 +/- 0.09, 9.22 +/- 0.05, and 9.17 +/- 0.05 were determined for average body weights of 218 +/- 24, 527 +/- 33, 706 +/- 60, and 943 +/- 30 g, respectively. By plotting these K values on semilog paper and determining the best fit curve of the slope, it was possible to extrapolate exponentially the K values for different body weights. The relationship between age and body weight was also established for guinea pigs, and a series of K values were determined from birth to 35 weeks of life. We conclude that a different K value should be used for calculating BSA for various ages and body weights of strain 13 guinea pigs.

Hypothermic effects on action potential and force production of hedgehog and guinea pig papillary muscles

Action potentials and isometric force were recorded in papillary muscles from guinea pigs and summer hedgehogs at different temperatures between 37 and 0 degrees C. The action potential of the hedgehog was of a lower amplitude (mean 83 +/- 6 mV) than that of the guinea pig (mean 110 +/- 5 mV). The action potential duration at 50% repolarization was 22 +/- 2 msec in the hedgehog as compared to 105 +/- 11 msec in the guinea pig. Moreover, there was no distinct plateau phase of the hedgehog action potential. Lowering temperature prolonged the action potential duration in the two preparations by about the same percentage. However, the guinea pig preparation became progressively less excitable below 20 degrees C. Lowered temperature produced a positive inotropic effect in the guinea pig, whereas this effect was very slight in the hedgehog heart. Postextrasystolic potentiation was seen in the guinea pig but not in the hedgehog preparation. It is suggested that this difference between the preparations may be due to a greater relative amount of activator calcium in the hedgehog heart. The difference in cold tolerance between the preparations may reflect a difference in chemical composition of the sarcolemma.

Potassium ion conductance of the cochlear partition: differences between the chinchilla and guinea pig

The time courses of the endocochlear potential (EP) and the K+ concentrations in the inner ear fluid under permanent anoxia were observed in the chinchilla and guinea pig using K+-selective microelectrodes. The EP following 30 min of anoxia in the chinchilla (-10.9 +/- 2.2 mV) showed a significantly less negative value than that of the guinea pig (-25.7 +/- 2.6 mV). The K+ concentration in endolymph induced by anoxia decreased less in the chinchilla than in the guinea pig. The average K+ conductance of the cochlear partition 10-30 min after anoxia in the guinea pig (0.1703 +/- 0.0792 S) was approximately 7.9 times that of the chinchilla (0.0216 +/- 0.0042 S), which is thought to be responsible for the difference of the anoxic EP between the two species.

Electrophysiological analysis of the dorsal hippocampal commissure projections to the entorhinal area

Synaptic effects evoked in the entorhinal area by dorsal hippocampal commissure (dorsal psalterium) projections were analysed in anesthetized adult guinea-pigs by means of a field potential analysis. Stimuli applied to the caudal part of the dorsal psalterium evoked a complex response in the dorsal third of the entorhinal area. The early part of the entorhinal response consisted of a slow wave interrupted by a spike potential. The electrophysiological characteristics and the laminar distribution of the slow wave and of the spike potential, together with the presence of time-locked unit activity, suggested that dorsal psalterium projections evoke monosynaptic excitatory postsynaptic potentials leading to cellular discharge in radially oriented neurons of layers II and III. The commissural fibers responsible for these effects originate in the contralateral presubiculum. The early part of the entorhinal response was followed by three waves in close temporal sequence. These waves were polysynaptically generated and associated with excitatory and inhibitory synaptic effects. Inhibition was demonstrated for the monosynaptically generated spike potential. Whether these effects were mediated by intracortical circuits and/or extrinsic projections cannot be stated from the present results. Causal relations were observed between the entorhinal monosynaptic response and that evoked by dorsal psalterium stimulation in the ipsilateral dentate gyrus, previously shown to be relayed by perforant path fibers. The results indicate that presubicular commissural projections to the entorhinal area monosynaptically activate neurons of the perforant pathway, whose discharge brings about activation of the ipsilateral dentate gyrus.

Spontaneous cartilage degeneration in guinea pigs

Spontaneous degeneration of the knee joint cartilage in male Hartley guinea pigs was studied by light microscopy in animals aged 3-18 months. Unilateral focal degeneration, characterized by chondrocyte death and proteoglycan loss with surface fibrillation, was observed on the medial tibial plateau in 2 of 5 guinea pigs that were 3 months old. The incidence and severity of the lesions increased with age, and by 12-18 months of age, all animals had moderate-to-severe degeneration of the medial tibial plateau, femoral condyle, and meniscus. Lesions were not present on the lateral aspect of the knee joint in any of the animals.

Circadian oscillation of the multiple unit activity in the guinea pig suprachiasmatic nucleus

In the guinea pig with chronically implanted electrodes, neuronal multiple unit activity (MUA) was recorded inside and outside the suprachiasmatic nucleus (SCN). Long-term recording of the SCN indicated distinct daily rhythms with a daytime peak in MUA during a 24-h light-dark (LD 12:12) cycle. On the other hand, MUA recorded from adjacent hypothalamic regions outside the SCN showed a phase reversal with a nighttime peak, similarly to the rat. The amplitude of the rhythms recorded outside the SCN was much smaller (one-half to one-quarter) than that inside the SCN. These rhythms persisted during constant darkness indicating characteristics of endogenous circadian rhythmicity. When the external light-dark cycle was delayed abruptly for 12 h, MUA rhythms showed a gradual phase shift taking 7-10 days for complete reentrainment. Overt behavior including sleep-wakefulness did not show significant and consistent daily or circadian rhythms in spite of the distinct oscillation in neuronal activity inside the SCN.

Effect of metopirone-ditartrate on thermogenesis in the guinea-pig

1. Cortisol is the major corticosteroid in the guinea-pig plasma; cortisone is detected in minor concentrations. 2. An increase in the plasma cortisol level is observed during acute cold exposure. 3. After application of metopirone-ditartrate the standard metabolic rate is depressed significantly at thermoneutrality. 4. In metopirone-treated guinea-pigs the cold-induced increase in heat production is depressed by 47% concomitant with a marked drop in body temperature. 5. It is concluded that the formation of cortisol is essential for regulatory heat production induced by acute cold exposure in the guinea-pig.

A sexually dimorphic vasopressin innervation of auditory pathways in the guinea pig brain

Vasopressin-like immunoreactivity was detected in the auditory brainstem of female guinea pigs. Stained cell bodies and fibres were found in the inferior colliculus and in the ventral trapezoid body, and immunoreactive fibres in the dorsal cochlear nucleus. No vasopressin immunoreactivity was detected in the auditory brainstem of male guinea pigs. Using oxytocin antisera we found neither immunoreactive perikarya nor fibres in the auditory pathways of guinea pigs of both sexes.