Intrauterine growth restriction (IUGR) and subsequent neonatal catch-up growth are implicated in the programming of increased appetite, adiposity and cardiometabolic diseases. Guinea pigs provide an alternate small animal model to rodents to investigate mechanisms underlying prenatal programming, being relatively precocial at birth, with smaller litter sizes and undergoing neonatal catch-up growth after IUGR. The current study, therefore, investigated postnatal consequences of spontaneous IUGR due to varying litter size in this species. Size at birth, neonatal, juvenile (post-weaning, 30–60 days) and adolescent (60–90 days) growth, juvenile and adolescent food intake, and body composition of young adults (120 days) were measured in 158 male and female guinea pigs from litter sizes of one to five pups. Compared with singleton pups, birth weight of pups from litters of five was reduced by 38%. Other birth size measures were reduced to lesser degrees with head dimensions being relatively conserved. Pups from larger litters had faster fractional neonatal growth and faster absolute and fractional juvenile growth rates (P<0.005 for all). Relationships of post-weaning growth, feed intakes and adult body composition with size at birth and neonatal growth rate were sex specific, with neonatal growth rates strongly and positively correlated with adiposity in males only. In conclusion, spontaneous IUGR due to large litter sizes in the guinea pig causes many of the programmed sequelae of IUGR reported in other species, including human. This may therefore be a useful model to investigate the mechanisms underpinning perinatal programming of hyperphagia, obesity and longer-term metabolic consequences.

Amacrine cells represent the most diverse class of retinal neuron, comprising dozens of distinct cell types. Each type exhibits a unique morphology and generates specific visual computations through its synapses with a subset of excitatory interneurons (bipolar cells), other amacrine cells, and output neurons (ganglion cells). Here, we review the intrinsic and network properties that underlie the function of the most common amacrine cell in the mammalian retina, the AII amacrine cell. The AII connects rod and cone photoreceptor pathways, forming an essential link in the circuit for rod-mediated (scotopic) vision. As such, the AII has become known as the rod–amacrine cell. We, however, now understand that AII function extends to cone-mediated (photopic) vision, and AII function in scotopic and photopic conditions utilizes the same underlying circuit: AIIs are electrically coupled to each other and to the terminals of some types of ON cone bipolar cells. The direction of signal flow, however, varies with illumination. Under photopic conditions, the AII network constitutes a crossover inhibition pathway that allows ON signals to inhibit OFF ganglion cells and contributes to motion sensitivity in certain ganglion cell types. We discuss how the AII’s combination of intrinsic and network properties accounts for its unique role in visual processing.

The relative timing of a number of events during the development of the visual system has recently been suggested to be consistent across a number of mammalian species (Dreher & Robinson, 1988). Some conflicting reports, however, had suggested that the precocial guinea pig might represent an exception to the generalized scheme. A quantitative study was thus carried out on the development of the optic nerve and retina of the guinea pig. Consistent with the prediction of a stable relative time course of mammalian visual development, axons and growth cones were found in the optic stalk from the 24th postconceptional day (40% of the period from conception to eye opening —the cecal period), the peak number of axons was observed on the 32nd postconceptional day (56% of the cecal period), and the phase of rapid axonal loss extended to the 39th and 42nd postconceptional days (68–74% of the cecal period). The number of axons in the adult optic nerve (117,000) represented about 37% of the peak number of axons. Additional observations indicated that during development of the optic nerve the mean axonal diameter increased approximately threefold from 0.31 μm to 1.06 μm. As in other mammals studied so far, myelination was first noted after the period of rapid axonal loss and continued until in the adult 97% of axons were found to be myelinated. In the retina, the presence of pyknotic profiles in the ganglion cell layers extends throughout the periods of loss of the optic nerve axons. Finally, the presence of pyknotic profiles in the amacrine sublayer suggest that in the guinea pig, as in other mammalian species, there is a loss of displaced amacrine cells as well as ganglion cells from the ganglion cell layer.

As in rabbit, gerbil, and rat, the guinea pig interstitial nucleus of the superior fasciculus, posterior bundle (INSFp) is a sparse assemblage of neurons scattered among the fibers forming the fasciculus bearing this name. Most of the INSFp neurons are small and are ovoid in shape. Interspersed among these, are a few larger, elongated neurons whose density becomes greater and whose shape becomes fusiform in correspondence to the zone of transition from the superior fasciculus to the ventral part of the medial terminal nucleus (MTN). Like the MTN, the INSFp is activated by retinal-slip signals evoked by whole-field visual patterns moving in the vertical direction, as shown by the increase of 14C-2-deoxyglucose (2DG) uptake into this nucleus. At the same level of luminous flux, neither pattern moving in the horizontal direction nor the same pattern held stationary can elicit increases in the INSFp 2DG assumption. The specificity of the observed increases in metabolic rates in INSFp following vertical whole-field motion suggests that this assemblage of neurons relays visual signals used in the control of vertical optokinetic nystagmus.

Endothelin 1 is a vasoconstrictive peptide with many biological functions. To investigate the distribution of endothelin 1 in guinea pig cochlear lateral wall and the significance of endothelin 1 in maintaining cochlear homeostasis, the immunohistochemistry avidin biotin complex method was applied by using rabbit anti-endothelin 1 polyclonal antibody as primary antibody. Endothelin-1-like activities were detected in the marginal cells, spiral prominence epithelial cells, outer sulcus cells, stria vascularis capillaries, basal cells and spiral ligament fibrocytes.

These results suggest that endothelin 1 may play an important role in maintaining cochlear homeostasis.

The ganglion cell layer of mammalian retina contains numerous amacrine cells. Many belong to one type, the cholinergic starburst cell, but the other types have not been systematically identified. Using a new method to target sparsely represented cell types, we filled about 200 amacrine neurons in the ganglion cell layer of the guinea pig visual streak and identified 11 types. Ten of these resemble types identified in other species with somas in the inner nuclear layer, but one type has not been previously reported. Most of the types and nearly all the injected cells (95%) arborized low in the synaptic layer where they would co-stratify with various classes of ON ganglion cell. The displaced somas (7% of all amacrine cells) thus represent a heterogeneous pool, which are relatively accessible for study of their interactions with ON ganglion cells.

In most species, females invest more in their offspring than males. In mammals, this also holds true after the birth of young since only mothers can lactate and fathers are thus more likely to desert and seek additional mating opportunities. These opportunities are largely dependent on resource distribution and the resulting distribution of females. The emerging social and mating systems of different species give rise to different benefits of investment in paternal care. Paternal care should have evolved in relation to the frequency of losing paternities to other males. Hence, in species living in one-male systems with little opportunity for female extra-pair copulations, paternal care should be more common than in those species living in multi-male groups. The guinea pigs (Caviinae) comprise closely related species exhibiting different social organizations and mating systems. The amount of paternal behaviour and offspring-directed aggression was investigated in three species kept under laboratory conditions: the polygynous Cavia aperea, the promiscuous Galea musteloides and a newly described monogamous species (Galea monasteriensis sp. nov.). All animals were kept in groups of one adult male and one adult female with their non-weaned offspring. Cavia aperea as well as G. monasteriensis males showed a high incidence of paternal behaviour, which consisted primarily of playing with offspring and grooming them. In contrast, G. musteloides males never engaged in paternal behaviour but directed more aggressive behaviour towards their offspring. Mating with multiple partners and multiple paternities are common in G. musteloides whereas in the former two species there is a much higher certainty of paternity. We conclude that paternal behaviour in guinea pigs probably co-evolved in alignment with the certainty of paternity that males of a species encounter under natural conditions.

The accepted biological potencies of vitamin E (United States Phamacopeia, 1985) for 1 mg all-rac-α-tocopheryl acetate (synthetic form) is 1·00 IU and that of 1 mg (RRR)-α-tocopheryl acetate (natural form) is 1·36 IU. In the present study, a stable isotopic (2H) technique was employed to evaluate the bioavailability of natural v. synthetic forms of vitamin E and to determine whether the potency of the forms is the stated relationship of 1·36:1·00 (RRR)-α-tocopheryl acetate:all-rac-α-tocopheryl acetate. Sixty female in-bred guinea pigs received either 40 or 80 mg vitamin E/kg diet with equal levels of (RRR)-α-tocopheryl acetate and all-rac-α-tocopheryl acetate throughout gestation and lactation. At late-term pregnancy (day 50 or 60) and during early lactation, dams and their corresponding fetuses or neonates were killed and various tissues collected for subsequent α-tocopherol analysis. Vitamin E analysis of fetal and neonatal tissues indicated a substantial transfer of 2H-labelled α-tocopherol across the placenta and through the mammary gland. Total α-tocopherol concentrations were significantly influenced by tissue type and dose level, but not by stage of gestation or lactation. The relative bioavailability (d3:d6) across fetal and neonatal tissues was on average 1·81:1·00, with a range from 1·62:1·00 to 2·01:1·00. Maternal tissues had a mean ratio of 1·77:1·00. A higher relative bioavailability (P≤0·05) was observed with natural compared with synthetic α-tocopherol as shown by a higher d3:d6 ratio in all tissues examined. Vitamin E was highest in colostrum on day 2 then declined through to day 5. Results from this present experiment further question the accepted biological potencies of natural:synthetic α-tocopheryl acetate of 1·36:1·00.

Certain ganglion cells in the mammalian retina are known to express a cGMP-gated cation channel. We found that a cGMP-gated current modulates spike responses of the ganglion cells in mammalian retinal slice preparation. In such cells under current clamp, bath application of the membrane-permeant cGMP analog (8-bromo-cGMP, 8-p-chlorophenylthio-cGMP) or a nitric oxide donor (sodium nitroprusside, S-nitroso-N-acetyl-penicillamine) depolarized the membrane potential by 5–15 mV, and reduced the amount of current needed to evoke action potentials. Similar effects were observed when the membrane potential was simply depolarized by steady current. The responses to cGMP are unaffected by inhibitors of cGMP-dependent protein kinase and Ca2+/calmodulin-dependent protein kinase. The response to cGMP persisted in Ca2+-free bath solution with Ca2+ buffers in the pipette. Under voltage clamp, cGMP analogs did not affect the response kinetics of voltage-gated currents. We conclude that cGMP modulates ganglion cell spiking simply by depolarizing the membrane potential via the inward current through the cGMP-gated channel. Modulation of this channel via the long-range NO-synthase amacrine cell may contribute to control of contrast gain by peripheral mechanisms.

The effects of feeding beef suet (mostly saturated and monoenoic fatty acids), sunflower oil (rich in n-6 fatty acids) and fish oil (rich in n-3 fatty acids) on the response of mesenteric, omental, popliteal and perirenal adipocytes to experimentally-induced local inflammation were studied in adult guinea pigs. After 6 weeks on the experimental diets, the animals were fed standard chow, and lipopolysaccharide was injected unilaterally daily for 4 d to induce swelling of one popliteal lymph node. Basal lipolysis in the perinodal adipocytes of all depots studied was higher in the sunflower oil-fed animals than in the controls fed on standard chow, and lower in those fed on suet or fish oil. Dietary lipids altered rates of lipolysis during incubation with 10-5 M noradrenaline in all samples studied from the locally-activated popliteal depot, but only in adipocytes within 5 mm of a large lymph node in the other depots. The fish-oil diet attenuated the spread of increased lipolysis within the locally-activated popliteal adipose tissue, and from this depot to other node-containing depots. These experiments show that n-6 polyunsaturated fatty acids promote and n-3 fatty acids suppress the spread of immune activation to adipocytes within and between depots, and alter the sensitivity of perinodal adipocytes to noradrenaline. Dietary effects are reduced or absent in adipocytes in sites remote from lymph nodes, and thus such samples do not adequately represent processes in perinodal adipose tissue. These results are consistent with the hypothesis that perinodal adipocytes interact with adjacent lymphoid cells during immune responses.

Retinal neurons are generated in overlapping growth spurts with ganglion cell and cone populations peaking sooner than rod and bipolar cell numbers. As such the functional development of the inner and outer retinal components and elements within these strata (rods vs. cones) may differ. We considered the postnatal development of the postreceptoral components of the ERG (P2, oscillatory potentials) in the guinea pig. ERGs were also evaluated across albino and pigmented strains in order to consider the role that pigmentation has for functional development. Electroretinograms were collected on postnatal days PD1 to PD60 (n = 4–7 per time point). The postreceptoral P2 amplitude and implicit time was extracted (digital subtraction of modelled P3 and filtering, 0.5–49 Hz). Intensity–response relationships were described using Naka–Rushton functions whose parameters were compared using a nonparametric bootstrap. Oscillatory potentials (OPs) were extracted following signal conditioning and filtering to remove the a- and b-waves and were described using a Gabor function. OP response parameters were compared using repeated measures ANOVA. Postreceptoral P2 amplitudes mature soon after birth (PD10–PD12). Oscillatory potentials show a similar postnatal amplitude development (PD10–PD12) but a later maturation in timing (PD20) compared with the postreceptoral waveform. All components (P3, P2, and OPs) declined at the same relative rate with age after PD12. Albino animals gave larger, faster, and more sensitive waveforms at all ages but showed the same age-related trends as did pigmented animals. Early development of inner retinal synapses in guinea pigs may underlie the rapid postnatal maturation of their postreceptoral response. These appear to be constrained by the development of receptoral responses. All components declined at the same rate suggesting either a change in the photoreceptoral response or changes to ocular impedance with age.

Previous studies have suggested that both acrosome-intact and acrosome-reacted guinea pig sperm are capable of binding to the zona pellucida of cumulus-free oocytes, but the acrosomal status of guinea pig sperm during penetration of the cumulus has not been reported. We made video recordings of the interaction between capacitated guinea pig sperm and cumulus-invested guinea pig oocytes. The videotapes were analysed to identify sperm with hyperactivated motility and to classify the acrosomal status of sperm during penetration of the cumulus and after binding to the zona pellucida. The resolution of the video recordings was not sufficient to recognise sperm with swollen acrosomes. However, sperm that had completed the acrosome reaction were easily identified. Acrosome-reacted sperm were found adherent to the outer boundary of the cumulus, but were never observed to penetrate the cumulus. The percentage of acrosome-intact, hyperactivated sperm was higher in the cumulus oophorus than in culture medium, suggesting that changes in motility were elicited in response to contact with the cumulus. Fully acrosome-reacted sperm were found adherent to the zona pellucida, and solubilised guinea pig zona pellucida was capable of inducing acrosome reactions in capacitated guinea pig sperm. Acrosome-intact sperm were also observed on the zona, but they were not tightly bound and did not have hyperactivated motility, suggesting that these sperm were not functionally capacitated. Our observations demonstrate that guinea pig sperm penetrate the cumulus matrix in an acrosome-intact state. Although we did not observe sperm undergoing the acrosome reaction, our observations and experimental data suggest that the acrosome reaction of guinea pig sperm is completed on or near the surface of the zona pellucida.

The cell population and distribution of NADPH-diaphorase positive and NOS immunoreactive intramural ganglion cells were examined on stretched whole-mount preparations of the guinea pig urinary bladder which was divided into 3 regions: base, body and dome. The results showed that the highest frequency both of NADPH-d and NOS positive neurons was observed in the bladder base. Cell counts in the whole bladder showed that the number of NADPH-d positive neurons was much more than that of NOS immunoreactive neurons. Using neuron specific enolase (NSE) positive neurons as a reference (100%), NADPH-d positive neurons accounted for 84% while NOS immunoreactive neurons only made up 45% of the total neuronal population. These results, along with previous studies on the function of nitric oxide, suggest that nitric oxide may be involved in the relaxation activity in the bladder base during micturition. The significant difference in the number of NADPH-d positive and NOS immunoreactive neurons suggests that the localisation of one enzyme does not necessarily reflect the presence of the other.

Residual cholesteatoma was experimentally produced in guinea pigs by transplanting a free skin graft into the middle ear bulla. In group A, the graft was placed on the mucosa after scratching the surface with a pick, while in group B, it was placed on the bone surface following removal of the mucosa and drilling with a diamond burr. The group A procedure was conducted on the left ear and the group B procedure on the right ear in 12 guinea pigs. The animals were sacrificed at two, four and eight weeks after transplantation. In all 12 ears of group A, the graft kept its original flat shape, resembling an open type residue. In eight of 12 ears of group B, the graft grew forming a squamous pearl, while in the remaining four ears it retained a flat shape. The difference in configuration is thought to be due to the amount of granulation around the graft.