Pigmented Guinea Pigs Research Articles

Cisplatin ototoxicity in guinea pigs with special reference to toxic effects in the stria vascularis.

The toxic effects of cisplatin (cis-diamminedichloroplatinum [II]) on the organ of Corti are well established. Few and conflicting data on this drug's effects on the stria vascularis exist. The present study presents animal experiments on the toxic effects of cisplatin in the stria vascularis and in the organ of Corti. Cisplatin-induced toxicity in albino and pigmented guinea pigs was evaluated morphologically and functionally, using light and transmission electron microscopy as well as auditory brainstem-evoked potentials on the organ of Corti and the stria vascularis. The results showed variability in hearing thresholds, ranging from no change to hearing loss of 30 dB, and prominent damage in the organ of Corti and in the stria vascularis. The toxic effects to both the organ of Corti and the stria vascularis should be considered when cisplatin is used in chemotherapy.

Species differences in the distribution of infracuticular F-actin in outer hair cells of the cochlea

The distribution of filamentous actin (F-actin) in outer hair cells has been examined in several mammalian species using tetramethylrhodamine phalloidin, a specific marker for F-actin. The stereocilia and cuticular plates of the OHC in all species examined (pigmented guinea pig, hooded rat, chinchilla and squirrel monkey) contained F-actin; however, an infracuticular network of F-actin was present in OHC of the apical turns of the guinea pig cochlea but could not be identified in any other species examined.

Inhibition of renal ornithine decarboxylase by aminoglycoside antibiotics in vitro

The inhibition of renal ornithine decarboxylase (ODC) by aminoglycoside antibiotics was characterized in the postmitochondrial fraction of a kidney homogenate from adult pigmented guinea pigs. Enzymatic activity was defined as the rate of decarboxylation of [ 14C]ornithine sensitive to a specific ODC inhibitor, α-difluoromethylornithine (DFMO). The K m for ornithine was 61 ± 32 , μM. There were two forms of the enzyme with respect to their affinity for pyridoxal phosphate (PLP): (I) K m = 2.1 ± 1.8 μM; (II) K m = 36.2 ± 12.7 μM. Putrescine, a known ODC inhibitor, acted competitively on the renal enzyme with K i = 1.7 ± 1.4 mM. Aminoglycoside antibiotics inhibited ODC by an uncompetitive mechanism with inhibitor constants of comparable magnitude: neomycin, K i = 1.3 ± 0.1 mM; gentamicin, K i = 1.6 ± 0.1 mM; kanamycin, K i = 1.9 ± 0.2 mM; and netilmicin, K i = 1.7 ± 0.2 mM. Neomycin inhibited both forms of the enzyme (low and high affinity for PLP) uncompetitively with similar inhibitor constants (1.5 ± 0.3 and 1.8 ± 0.4 mM respectively), suggesting a single mechanism of action. Inhibition of ODC suggests that aminoglycoside-polyamine interactions may be an important component of the sequence of biochemical events associated with aminoglycoside toxicity.

Effects of aging on normal hearing loss and noise-induced threshold shift in albino and pigmented guinea pigs.

In a previous investigation into noise-induced hearing loss by comparing 2-month-old albino with pigmented guinea pigs, albinos displayed significantly greater shifts in cochlear microphonic (CM) threshold and less recovery than the pigmented animals 7 days after noise exposure. The present study compared the responses of 14-month-old albino and pigmented guinea pigs to the same noise parameters used previously. Thresholds for the first detectable elicitation of CM for three pure tones were recorded prior to, at 90 min and at 7 days after a 45-min exposure to 126 dB broadband noise. Before exposure to noise, thresholds for pigmented guinea pigs were 24 dB higher than those in the albinos. Following noise exposure, the pigmented animals showed less than half the amount of threshold shift displayed by the albinos. This change ws attributed to the higher pre-exposure thresholds in the pigmented guinea pigs. Converging lines of evidence suggest that cochlear pigmentation may have both protective and toxic influences on the inner ear.

Time sequence of degeneration pattern of the organ of Corti after acoustic overstimulation. A light microscopical and electrophysiological investigation in the guinea pig.

In order to obtain information about the sequence of events leading to degenerative changes in the cochlea after acoustic trauma, a systematic LM study was performed in the guinea pig organ of Corti. The results were correlated with measurements of CAP N1 thresholds from the same animals. Twenty pigmented guinea pigs were used in the study. Ten of these animals were exposed to a 3.85 kHz pure tone with an intensity varying between 108 and 120 dB SPL for 22.5 to 360 min and were sacrificed after 4 weeks. Eight animals were exposed to 120 dB SPL for 22.5 min and sacrificed at regular intervals after exposure, viz. 5 min, 4, 24 h and 5 days. Prior to sound exposure the animals in the 4-week group were implanted with a permanent round window electrode for measurements of CAP N1 thresholds. The study indicates that the degeneration and reparative processes are not entirely completed after 4 weeks. The development of holes in the reticular lamina may result in further degeneration of cells bilateral to the initial maximum damage. Darkly stained cells seem to be activated in the reparative process in the organ of Corti. Local appearance of dendritic macrophages in the organ of Corti indicate the existence of a local mechanism for disposal of degeneration products from the organ of Corti. The retrograde degeneration of radial nerve fibres seems to be closely associated with that of the pillar cells. A close correlation between structural hair cell damage and CAP N1 threshold shift was found in the region of the organ of Corti corresponding to the exposure frequency. The TS 5 min, 4 h and 24 h after exposure showed a close correlation with swellings in the afferent nerve endings below the IHC in the area of maximum damage and basalwards.

Time sequence of degeneration pattern of the organ of Corti after acoustic overstimulation. A transmission electron microscopy study.

Female pigmented guinea pigs were exposed to a 3.85 kHz pure tone of 120 dB SPL for 22.5 min. The exposed animals were sacrificed after varying post-exposure intervals (5 min, 4 and 24 h, 5 and 28 days). Transmission electron microscopical examination was performed after serial-sectioning in areas of maximum damage and both basal to and apical to this region. By serial-sectioning, the degradation pattern of the individual cell structures in the organ of Corti could be studied in relation to post-exposure time and proximity to the well-demarcated area of maximum damage in the organ of Corti. The results provide further information on the non-reversible changes leading to degeneration and loss of sensory and supportive structures in the organ of Corti.

Melanine Value in the Stria Vascularis of Pigmented Guinea-pigs Treated by Kanamycin

In a previous report, kanamycin (400 mg/kg/d) seemed to increase the number of melanine granulations in intermediate cells of the stria vascularis, especially in the second and third turns. To precise these data, melanine was studied in those turns by ultrastructural morphometry in a control group with 12 animals. We observed a large intra-individual and inter-individual variation before intoxication. Thus, the meaning of melanine modifications by kanamycin must be carefully evaluated.

Cochleotoxic effects of spermine and kanamycin.

Aminoglycosides are organic bases that contain multiple amino groups. The ototoxic potential of these amine groups was studied using spermine, which is a polyamine with four amine groups (two amino and two imino). Twenty-four pigmented guinea pigs were studied. One-tenth milliliter of different concentrations of kanamycin A sulfate or spermine were given intratympanically. The temporal bones were removed 4 days after the injections, and the cochleas were examined using the scanning electron microscope. The damage to the hair cells was recorded in cytocochleograms. The results show that spermine is cochleotoxic when given intratympanically. Dosage of 50 mumol for kanamycin A sulfate and 5 mumol for spermine caused total damage of the outer hair cells in all ears. Lower dosage of kanamycin A sulfate (20 mumol) and spermine (1 mumol) did not cause any histologically discernible changes.

Glycerol-induced changes in the cochlear responses of the guinea pig hydropic ear.

Pigmented guinea pigs were chronically implanted with bilateral round-window electrodes. Endolymphatic hydrops was induced by obstruction of the endolymphatic duct on one side. At 1-5 months post-surgery, glycerol was orally administered to each animal and the acute effect on cochlear and eighth nerve responses was investigated. Doses from half to four times the clinical dose of glycerol failed to improve the CAP audiogram in operated ears and were often found to raise the thresholds. Glycerol was found to diminish the amplitude of the summating potential as well as that of the compound action potential. Similar effects were observed for the higher doses in the control ears, although no effect was seen when doses used were equal to or less than the clinical dose. Our data suggest that the cochlear conditions in the guinea pig model of hydrops differ notably from those seen in patients with Ménière's disease.

Observation on the vestibular function after obliteration of the endolymphatic sac of guinea pig

The directional prepondance of vestibulo-ocular reflex (VOR-DP) by the pendular rotation were observed on the pigmented guinea pig after the surgical obliteration of unilateral endolymphatic sac.•Four out of five guinea pigs revealed DP to the non-operated side and one revealed to the operated side after operation. Then three guinea pig changed DP from the non-operated side to the operated side 2-6 weeks later.•The progressing stage of the experimental endolymphatic hydrops in guinea pig considered to be a model of the pre-vertigo stage of Meniere's disease.

Rapidly fluctuating thresholds at the onset of experimentally-induced hydrops in the guinea pig.

Pigmented guinea pigs were chronically implanted bilaterally with a platinum electrode on each round window. After recovery the endolymphatic sac was destroyed and the duct blocked on one side only; the other side was employed as a control. The round window response thresholds on both sides were recorded several times per week over a three month period. There were three main results. A sensitivity loss of up to 20 dB was observed for frequencies between 250 Hz and 6.4 kHz within two weeks post-op. At the end of three months the threshold elevation for these frequencies was as much as 50 dB. On the other hand the thresholds for frequencies between 8 and 16 kHz remained within 10 dB of their pre-operative value for at least two months. The thresholds fluctuated with a shift of as much as 25 dB within 24 h. The threshold elevation was associated with a decrease in the latency, at threshold, of the round window AP response which at frequencies between 250 Hz and 6.4 kHz was as short as that for 8 kHz. This observation suggested that it was the base, only, of the cochlea which responded. The present study has indicated that experimentally induced endolymphatic hydrops in the guinea pig mimics well the progressive and fluctuating hearing loss characteristic of Ménière's disease.

Cochlear hair cell damage from intermittent noise exposure in young and adult guinea pigs

A comparative study of age-dependent damage to cochlea from intermittent noise exposure was carried out on five-week-old and one-year-old pigmented guinea pigs. Hair cell loss in the organ of Corti was studied after five weeks' exposure to a pure tone stimulus (95 dB SPL at 2 kHz, one hour per day for five weeks). The noise-induced damage was sharply limited to the 7- and 11-mm marks from the apex. Damage was more marked in younger guinea pigs and was distinct from natural age-induced cell loss. When the 7- to 11-mm zone was further analyzed, outer hair cell damage appeared highly significant in both age groups but more severe in younger animals. Inner hair cell damage in this area was severe in both groups but statistically insignificant.

Differential analysis of experimental hypermelanosis induced by UVB, PUVA, and allergic contact dermatitis using a brownish guinea pig model.

In moderately colored guinea-pig skin, UVB, PUVA, and allergic contact dermatitis were shown to induce hyperpigmentation that resembled the pigmentary changes observed in mongoloid human skin. Using this model, we examined the effects of chemical agents, including tyrosinase inhibitors and sunscreen agents, on the color changes induced by UV irradiation. The daily exposure of brownish guinea-pig skin to UVB irradiation at a variety of energies for 3 successive days induced clearly visible black pigmentation on the irradiated rectangular areas of the flank within a few days of irradiation, the maximum being reached about 1 week after irradiation, i.e., similar to the changes that occur in pigmented human skin. Split epidermal sheets prepared from untreated pigmented guinea pigs exhibited 200-400 melanocytes/mm2; 1 week after UV irradiation, the applied areas show an increased number of strongly dopa-positive melanocytes with stout dendrites (800-1,000 cells/mm2). UVA irradiation following an intraperitoneal injection of 8-methoxypsoralen (8-MOP) also produced black pigmentation 1 week after irradiation, and this was paralleled by a marked increase in the number of dopa-positive melanocytes in dopa-reacted split epidermal sheets. Allergic contact dermatitis produced by the application of 1-phenylazo-2-naphthol induced hyperpigmentation after an interval of about 14 days in 10 of the 21 allergy-acquiring animals examined. This induced pigmentation was accompanied by an increase in the number of dopa-positive melanocytes as compared to the number seen in controls. In contrast, allergic contact dermatitis produced by the application of dinitrochlorobenzene failed to induce such a high ratio of postpigmentation, with only 3 of the 21 allergy-acquiring animals showing hyperpigmentation and 5 showing depigmentation; in the latter, there was a slight decrease in the number of dopa-positive melanocytes. To study the preventive effect of tyrosine inhibitors on UVB-induced pigmentation, daily topical applications of these compounds were performed after three daily UVB irradiations. Treatment with 10% hydroquinone for 10 days interrupted UVB-induced pigmentation and resulted in a marked reduction in the number of epidermal melanocytes as compared to the number found in UVB-irradiated, untreated control skin.

Detection of DNA-Psoralen Photoadducts in Mammalian Skin

An immunofluorescence (IF) method for the detection of 8-methoxypsoralen (8-MOP) photoadducts to DNA has been developed to assess nuclear damage in keratinocytes and melanocytes after psoralen plus UVA (PUVA) treatment, both under in vitro and in vivo conditions. Cryostat sections of the albino and pigmented guinea pig and human skin were used for in vitro studies to establish minimal and maximal drug concentration and UVA dosimetry for the detection of DNA-8-MOP photoadducts. Limits of detection were as low as 10 ng/cm2 8-MOP and 1 J/cm2 UVA for skin sections and sodium bromide-split epidermal sheets. Guinea pigs treated with topical PUVA revealed positive IF stain in epidermal cell nuclei at a threshold dose of 100 micrograms/cm2 8-MOP and 13 J/cm2 UVA. Pretreatments of cryostat cuts with ethanol and alkali before IF test enhanced the sensitivity of detection in vivo about 10-fold and enabled us to follow the repair of DNA damage after treating normal guinea pig skin with a dose of 50 micrograms/cm2 8-MOP plus 6 J/cm2 UVA. The most interesting findings were as follows: A sensitive method to detect PUVA-induced nuclear damage in epidermal and dermal cells was developed. PUVA treatment induced nuclear DNA damage to melanocytes as well as to adjacent keratinocytes, and melanocytes appeared to be 10 times less vulnerable to photo-damage than keratinocytes. There was a greater propensity for the proliferative cells to be damaged by PUVA. PUVA induced nuclear damage up to 700 micron depth in the dermis. The usefulness of the IF test in detecting DNA damage in microgram and ng amounts in vivo and in following the repair of damaged DNA induced by PUVA.

Differential susceptibility to noise-induced permanent threshold shift between albino and pigmented guinea pigs

Evidence that reduced levels of cochlear melanin are associated with increased auditory sensitivity, increased levels of auditory fatigue and an increased susceptibility to noise-induced hearing loss led us to investigate the effects of noise exposure on the cochlear microphonic (CM) in albino and pigmented English shorthair guinea pigs. CMs were recorded from the round window prior to and at 90 min and 7 days after exposure to 45 min of 126 dB noise. Thresholds for the first detectable elicitation of the CM for four pure tones were determined and the output voltage of each cochlea was measured in 10 dB steps through intensity levels which produced a maximum voltage amplitude in the CM and voltage rollover. This analysis demonstrated that: 1. (1) albino guinea pigs displayed significantly lower auditory thresholds than did pigmented animals before exposure to noise; 2. (2) thresholds were elevated to comparable levels in both groups 90 min after noise exposure; 3. (3) pigmented guinea pigs showed a reliable recovery in CM thresholds 7 days after exposure to noise while thresholds in the albinos remained elevated to the same degree at both 90 min and 7 days after noise; 4. (4) 90 min after noise exposure, the maximum voltage output of albino cochleas was significantly less than that recorded from the cochleas of the pigmented guinea pigs. These results demonstrate that albino guinea pigs are more susceptible to the ototoxic effects of high intensity noise than pigmented guinea pigs. Converging evidence indicates that some aspects of cochlear function involve melanin pigment and that its absence may produce auditory abnormalities. Reduced melanin pigmentation may also contribute to such phenomena as noise-induced threshold shifts and individual differences in noise-induced hearing loss.

Physiological characteristics of first order horizontal canal neurons in guinea pigs. 3. Relationship between spontaneous activity and response to angular acceleration

Physiological characteristics of first order horizontal canal neurons, especially the relationship between their spontaneous activity and response to angular acceleration were studied in 20 albino guinea pigs. The average resting ISI was 48.9ms and this was clearly lower than that in pigmented guinea pigs. The neurons differentiated into three groups according to their CV values. These called regular, intermediate, and irregular neurons. The average resting ISI of these three groups were 19.9, 32.9, and 124.8ms. respectively.The responses to sinusoidal rotation were similar to those found in pigmented guinea pigs and other spieces. That is the regular neurons tend to have lower gains re angular velocity (average-ing 0.16 spikes/sec/deg/sec) and a longer phase lag re acceleration (averageing 93.1 degrees), and the irregular neurons show higher sensitivity re angular acceleration (averageing 0.6 spikes/sec/ deg/sec) and shorter phase lag re acceleration (averageing 72.7 degrees) at a stimulus frequency of 0.3Hz.

Cyclosporine therapy of guinea-pig autoimmune uveoretinitis induced with autologous retina.

Pigmented guinea-pigs were immunized by a single bilateral footpad injection of their own retina from one enucleated eye, mixed with complete Freund's adjuvant. Ocular inflammation started on the third week, and was still detectable in the fourth month. Daily subcutaneous injections of Cyclosporine (CsA) (20 mg/kg) from the day of immunization totally prevented the ocular disease, clinically and histologically, confirming earlier experiments in S-antigen induced experimental autoimmune uveoretinitis in rats. When CsA injections (20 mg or 10 mg/kg) were started at the onset time of EAU, a rapid regression of the inflammation occurred. This curative therapy was given during two months. No relapse was observed after having stopped the treatment. On the fourth month, only mild lesions of photoreceptors were found histologically, compared to extensive retinal destruction in controls. Most control guinea-pigs developed antibodies to antigens contained in guinea-pig retinal extract as tested by ELISA. The serum antibody content was lower in treated than in control animals. The autologous model of EAU in pigmented guinea-pigs seems to be very appropriate for testing immunosuppressive drugs in conditions close to clinical practice.

Whole-body Autoradiography of [3H]Dihydrostreptomycin in Guinea Pigs and Rats: The Labelling of the Inner Ear in Relation to Other Tissues

[3H]Dihydrostreptomycin was given intramuscularly to young pigmented guinea pigs and rats. Whole-body autoradiography, combined with densitometric measurement of the blackening of the autoradiograms, and liquid scintillation counting were used to determine the levels of radioactivity in the inner ear in relation to blood and other tissues. It was found that there was an accumulation of radioactivity in the perilymph of both the cochlear and vestibular parts of the labyrinth. The labelling of the endolymph was weak. The levels of radioactivity in the membranous linings of the labyrinth including the areas covered with the neuroepithelial structures, were about the same as in the perilymph. The general distribution pictures were characterized by a localization of radioactivity in extracellular tissues, such as cartilages and connective tissues and by strong labelling of the kidney cortex. The preferential uptake in the perilymph indicates a route by which the inner ear hair cells can be exposed to high levels of aminoglycoside antibiotics.

Cochleotoxicity of amine groups.

It has previously been shown that polyamines are ototoxic. The relationship between the number of amine groups and ototoxicity was studied using spermine, spermidine and 1,3-diaminopropane, which are polyamines with differing numbers of amine groups. Fifty pigmented guinea pigs were studied by injecting 0.1 ml of different concentrations of spermine, spermidine or 1,3-diaminopropane intratympanically. The animals were sacrificed 4 days after the injection and the organ of Corti was studied by scanning electron microscopy. It was found that on an equimolar basis, spermine (with 4 amine groups) is more cochleotoxic than spermidine (with 3 amine groups), which is in turn more cochleotoxic than 1,3-diaminopropane (with 2 amine groups). The cochleotoxic potential of the amine groups may be a result of their cationic nature at physiological pH (7.4). This property might be part of the explanation of the ototoxicity of the aminoglycosides.

Morphological changes to the stereociliary bundles in the guinea pig cochlea after kanamycin treatment.

Pigmented guinea pigs were treated with 400 mg/kg of kanamycin for 8 days and sacrificed 13 days later. The upper surface structures of the organ of Corti were studied using high resolution scanning electron microscopy to reveal fine details of stereociliary fusion and damage to the reticular lamina. Outer hair cell stereocilia showed from partial to complete fusion and loss whilst the inner hair cells showed very little evidence of any damage. In particular, the possible effects of kanamycin on the cross-links between the stereocilia have been investigated. The cross-links are found to be present on all outer and inner hair cell bundles which show no fusion of stereocilia. Partially-fused stereocilia which have free tips still possess the upward-pointing links, and the remaining undamaged stereocilia in these bundles possess the normal cross-links. Where fusion occurs along the sides of the stereocilia, the side-to-side links are missing although whether their absence either results in, or else is caused by, the fusion is not known.