Experimental in vivo fenestration of guinea pig cochlea using 2.79 Μm laser radiation

Erbium-YSGG laser systems are promising tools in ear, nose and throat (ENT) surgery. The high absorption in biological tissues, resulting in precise tissue ablation with minimal thermal tissue damage, and the possibility to guide the radiation through optical fibres make the 2.79 Μm wavelength a favourite for microsurgery. In order to simulate the fenestration of the human stapes foot plate required for prosthesis implantation when treating otosclerosis, five guinea pig cochleae were irradiated in vivo until perforation was achieved. The laser-induced temperature rise and pressure transients evoke activity in the inner hair cells that was investigated by micro-iontophoresis. Perforation of the cochlea bone (hole diameter of 350 Μm) can be performed with a few laser pulses and high precision with a thermal damage zone of<100 Μm. The bone ablation rate is 10 ± 2 Μm pulse^-1 at a radiant exposure of 12 J cm^-2. The functionality of the afferent inner hair cells in the guinea pig cochlea was verified before and after laser treatment using glutamate receptor agonists AMPA and NMDA. For the above selected laser parameters, the induced 15-min enhanced activity was blockable with the specific reversible AMPA and NMDA antagonists CNQX and AP-7. Micro-iontophoresis confirms the reversibility of cochlea functionality after its perforation with Er-YSGG laser pulses. A limit of radiant exposure around 12 J cm^-2 is found for safe fenestration. It is demonstrated that the Er-YSGG laser is a precise and safe instrument whilst still using adequate laser parameters. On the other hand, this study demonstrates the potential of uncontrollable and unintended induced damage, resulting from vapour channel formation in the perilymph, if a high laser radiant exposure is applied.     

Stapedectomy in the guinea pig.

Stapedectomy has traditionally been studied in the feline model. Ethical considerations and costs have made this model less feasible for ongoing research. The purpose of this study was to examine the guinea pig as a model for research on stapedectomy. Technical difficulties included limited exposure and small dimensions of the ossicles. The surgical technique with and without the use of a CO(2) laser and the relevant anatomy of the guinea pig middle ear are described.     

Diabetes mellitus in the guinea pig.

Spontaneous diabetes mellitus has been documented in a colony of guinea pigs. The contagious nature of the disease has been verified, but the nature of the infectious agent is not known. Animals from the original colony or animals exposed to the colony with normal glucose tolerance tests (GTT) became diabetic, as evidenced by elevated one- and four-hour GTT values, and in most cases have significant glycosuria. The severity of pathologic changes in the pancreatic islets parallel, in general, the severity of the clinical symptoms (glycosuria and abnormal GTT). Those animals with severe glycosuria and elevated FBS as well as one- and four-hour GTT values had the most pronounced degranulation and most prominent cytoplasmic inclusions in islet B cells. The severity of scarring in the islets can be correlated with the duration of the overt diabetic state. The other clinical parameters of note were elevated serum triglycerides, normal serum but elevated aortic cholesterol, and absence of ketonemia or ketonuria. The reproductive capacity of diabetic females was compromised. While the clinical manifestations are mild or variable, the presence of significant islet pathology is reminiscent of human juvenile diabetes mellitus. These findings lend support to the concept that infectious and/or immune mechanisms could be operative in the etiology and pathogenesis of human diabetes mellitus.     

Complement-independent nephrotoxic nephritis in the guinea pig.

Immunologic mechanisms of proteinuria were investigated in guinea pigs (GP) injected with sheep antiserum (NTS) to GP glomerular basement membrane (GBM). Linear deposition of sheep gamma 1 and gamma 2 IgG led to a prompt but transient (36 hr) increase in albumin excretion from control values of 0.026 +/- 0.013 mg/hr to maximal values of 26+/-12.1 mg/rh at six hours without detectable histologic or electron microscopic changes except for decreased staining for glomerular polyanion and epithelial cell foot process fusion. GBM permeability to anionic ferritin was not increased during proteinuria. Anti-GBM antibody deposits did not fix GP C3 or C4 in vivo or in vitro. NTS-induced proteinuria was the same in guinea pigs that were normal, greater than 95% depleted of C3 through C9, genetically deficient in C4, and depleted of circulating polymorphonuclear leukocytes (PMN). Prior administration of antihistamines, steroids, azathioprine, colchicine, indomethacin, heparin, aprotinin (Trasylol), and niridazole also failed to reduced proteinuria. Initial proteinuria subsided by 36 hr, did not recur despite linear deposition of GP gemma 1 and gemma 2 after day seven, and antibody to GMB-bound sheep globlin. In the GP nephrotoxic nephritis model, anti-GBM antibody deposits apparently mediate increased permeability to albumin by a currently undefined mechanism which is independent of complement, PMN, and other know mediators of inflammation.     

Bone wax prevents nystagmus after labyrinthine fenestration in guinea pigs.

OBJECTIVE: We examined the effect of 3 methods of closure of labyrinthine fenestrations. STUDY DESIGN AND SETTING: A guinea pig animal model was developed to examine the effect of 3 methods of closure of labyrinthine fenestrations. These methods included bone wax alone, fascia and fibrin glue, and fascia alone. Nystagmus, a reproducible sign of labyrinthine injury, was chosen as an end point for comparing materials commonly used in human ear surgery. RESULTS: Animals repaired with bone wax showed no postoperative nystagmus, whereas animals repaired with other materials or that underwent canal fenestration without repair showed 3 to 5 days of postoperative nystagmus. CONCLUSIONS: Although it is premature to extrapolate our results to human surgery, postoperative nystagmus can be eliminated in guinea pigs by sealing labyrinthine fenestrations with bone wax. SIGNIFICANCE: Given the intimate relationship between the vestibular and cochlear systems, it is possible that prevention of vestibular irritation might be associated with preservation of cochlear function.     

Subanesthetic halothane is hepatotoxic in the guinea pig.

Subanesthetic concentrations of halothane were examined for their hepatotoxic potential in the guinea pig. Outbred male, Hartley guinea pigs (600-700 g) were exposed to either 1.0%, 0.25%, or 0.10% (vol/vol) halothane, 40% O2, for 4 h. Plasma isocitrate dehydrogenase (ICDH) activity was compared to plasma alanine aminotransferase (ALT) for sensitivity as an indicator of hepatic injury. As previously seen, exposure to the anesthetic concentration of 1.0% halothane produced limited to confluent centrilobular necrosis in 50% (4/8) of the guinea pigs. The subanesthetic concentrations of 0.25% and 0.1% halothane were also hepatotoxic. After exposure to 0.25%, confluent centrilobular necrosis developed in 2 of 8 animals, whereas 0.10% halothane produced limited centrilobular necrosis in 3 of 8. Plasma ICDH activity was a more sensitive indicator of halothane-induced hepatic injury than ALT. Mean plasma ALT activity increased significantly after 1.0% halothane exposure only. However, ICDH activity was significantly increased after exposure to all three concentrations of halothane. Comparison of peak plasma enzyme activities demonstrated significantly larger increases in ICDH than in ALT when centrilobular necrosis was present. Use of subanesthetic concentrations of halothane should help overcome the many transient effect that high concentrations of halothane have on whole liver and hepatocyte functions. By being able to isolate and titrate the bioactivation of halothane, the mechanisms through which halothane biotransformation produces acute hepatotoxicity should be more easily elucidated.     

Hyperbaric compression in the guinea pig with perilymph fistula.

OBJECTIVE: The study goal was to evaluate the effects of hyperbaric therapy on the auditory and vestibular function of guinea pigs compromised by perilymph fistula (PLF). METHODS: Twenty-four pigmented guinea pigs underwent induction of bilateral eustachian tube dysfunction before the creation of a unilateral PLF. Half of the animals were randomly assigned to receive immediate hyperbaric compression treatment of 4 "dives" each. Hearing was tested electrocochleographically, and signs of vestibulopathy were recorded before and after compression. RESULTS: After accounting for the effects of PLF, compression was not associated with significant hearing loss (P = 0.5411). Vestibulopathy was seen only in ears with PLF, and its incidence was similar for compression and noncompression groups. CONCLUSION: Hyperbaric compression does not compromise auditory or vestibular function in guinea pig ears with experimental PLF. SIGNIFICANCE: Our observations support the relative safety of recompression in patients with PLF.     

Effect of ibuprofen upon hearing in the guinea pig.

The authors investigated the effect of varying doses of ibuprofen upon the hearing of guinea pigs monitored with brain stem-evoked response procedures. In daily dosages comparable on a weight basis to therapeutic levels in humans, ibuprofen was found not to have significant effects on response threshold or latency characteristics.     

Gonadotrophin-like substance in the testis. Immunocytochemical localization in the guinea pig

A gonadotrophin-like material (GLM) was observed by immunocytochemical methods in prepuberal guinea pig testes, not only on Sertoli and interstitial cells, but also on spermatogonia and spermatocytes. The intracellular cytoplasmic localization of GLM is discussed in relation to the receptor internalization theory. Variations between young and adult animals allowed us to approach the physiological significance of testicular GLM.     

Changes in testis of guinea pig after vasectomy.

Thirty adult guinea pigs were bilaterally vasectomized and subsequently sacrificed at one, three, and six months after operation. Cell counts were performed on five seminiferous tubules from each animal to identify and quantitate changes in spermatogenesis. Forty-three per cent of the animals had alterations in spermatogenesis that were characterized by generalized hypospermatogenesis and presence of multinucleated spermatids. There was a high incidence (93 per cent) of sperm-agglutinating antibodies in the vasectomized group. Sperm antibodies were not detected in the normal and sham-operated animals. Mean testicular weights and seminiferous tubule diameters were significantly reduced in the hypospermatogenic animals. The intersitial tissue of the vasectomized and sham-operated animals was morphologically indistinguishable from that of unoperated animals.     

Xenoantibodies in the rat against guinea pig tissues

Abstract. The role of naturally occurring antibodies in discordant xenograft rejection is poorly defined. This is partly attributable to a lack of information regarding their tissue specificity and titers. Sera from different rat strains were studied for naturally occurring antibodies against guinea pig tissues using immunofluorescence and immunoperoxydase staining techniques. All sera contained IgG and IgM antibodies in low titers against erythrocytes. lymphoid cells, and a variety of tissue structures. Intentional immunizations of adult rats with guinea pig cells resulted in the production of xenoantibody specificities that were not detectable in nonimmunized animals. Immunizations of Munich-Wistar rats with guinea pig skin grafts occasionally resulted in the formation of antibodies that reacted with allogeneic and syngeneic cells of the liver, lung, and lymphoid organs. We conclude that rats have low titers of naturally occurring xenoantibodies against various tissue structures of the guinea pig, but their importance in xenograft rejection remains to be established.     

Reaction to silicone implants in the guinea pig

Many papers have been published on the lack of reaction around silicone implants both in the experimental animal and the human. A study with human silicone implants with silicone gel interior shows loss of the silicone fluid from intact silicone sac. A solid silicone disc subjected to 5 pounds weight for one week loses silicone to the underlying paper. In the guinea pig, some capsules surrounding solid silicone implants, silicone sacs with saline, and silicone sac with silicone gel show vacuole or amorphous materials (silicone) with a thickening of the capsule and associated inflammatory reaction. These vacuoles or amorphous material resembles the silicone found in capsules around intact human silicone jell prosthesis. The presence of silicone with associated thickening of the capsule and inflammatory reaction may be one cause of firmness in the human after breast augmentation by silicone implants.     

Kit positive cells in the guinea pig bladder

PURPOSE: We describe the presence of interstitial cells of Cajal (ICC) throughout the wall of the guinea pig bladder. MATERIALS AND METHODS: Bladders obtained from male guinea pigs were prepared for immunohistochemical investigations using various primary antibodies, including the specific ICC marker c-kit (Gibco BRL, Grand Island, New York). Enzymatically dispersed cells with a branched morphology were identified as ICC using anti-c-kit. They were loaded with fluo-4acetoxymethyl (Molecular Probes, Eugene, Oregon) and studied using confocal laser scanning microscopy. RESULTS: Anti-c-kit labeling demonstrated that ICC were oriented in parallel with the smooth muscle bundles that run diagonally throughout the bladder. Double labeling with anti-smooth muscle myosin (Sigma Chemical Co., St. Louis, Missouri) revealed that ICC were located on the boundary of smooth muscle bundles. When anti-c-kit was used in combination with the general neuronal antibody protein gene product 9.5 (Ultraclone Ltd., Isle of Wight, United Kingdom) or anti-neuronal nitric oxide synthase, it was noted that there was a close association between nerves and ICC. Enzymatic dissociation of cells from tissue pieces yielded a heterogeneous population of cells containing typical spindle-shaped smooth muscle cells and branched cells resembling ICC from other preparations. The latter could be identified immunohistochemically as ICC using anti-c-kit, whereas the majority of spindle-shaped cells were not Kit positive. Branched cells responded to the application of carbachol by firing Ca2+ waves and they were often spontaneously active. CONCLUSIONS: ICC are located on the boundary of smooth muscle bundles in the guinea pig bladder. They fire Ca2+ waves in response to cholinergic stimulation and can be spontaneously active, suggesting that they could act as pacemakers or intermediaries in the transmission of nerve signals to smooth muscle cells.     

Droperidol prevents serotonin-induced bronchospasm in the guinea pig

The effects of droperidol on bronchoconstriction induced by serotonin (5-HT) were studied in mechanically ventilated, paralyzed guinea pigs that had been anesthetized with pentobarbital. Droperidol did not modify the resting bronchial tone but prevented the bronchoconstrictor effects of 5-HT in a dose-related manner. Pretreatment with propranolol, hexamethonium, or prazosin did not alter the protective effects of droperidol on 5-HT-induced bronchoconstriction. The bronchoconstrictor responses to histamine or acetylcholine were not affected by droperidol. These results suggest that the protective effects of droperidol on 5-HT-induced bronchoconstriction are mediated through 5-HT receptor blockade on bronchial smooth muscle.     

Xenoantibodies in the rat against guinea pig tissues

The role of naturally occurring antibodies in discordant xenograft rejection is poorly defined. This is partly attributable to a lack of information regarding their tissue specificity and titers. Sera from different rat strains were studied for naturally occurring antibodies against guinea pig tissues using immunofluorescence and immunoperoxydase staining techniques. All sera contained IgG and IgM antibodies in low titers against erythrocytes, lymphoid cells, and a variety of tissue structures. Intentional immunizations of adult rats with guinea pig cells resulted in the production of xenoantibody specificities that were not detectable in nonimmunized animals. Immunizations of Munich-Wistar rats with guinea pig skin grafts occasionally resulted in the formation of antibodies that reacted with allogeneic and syngeneic cells of the liver, lung, and lymphoid organs. We conclude that rats have low titers of naturally occurring xenoantibodies against various tissue structures of the guinea pig, but their importance in xenograft rejection remains to be established.     

Electrical stimulation of the guinea pig cochlea

As a result of practical considerations, histopathologic findings of the temporal bone in humans with cochlear prosthesis implants have been limited. This project attempts to better define safe parameters of electrical stimulation of the inner ear and compare the safe limits of intracochlear vs. extracochlear stimulation sites. Guinea pigs were implanted with single electrodes either on the promontory or in the scala tympani and were stimulated relative to a remote indifferent for 12 hours distributed over a 4-week period. Electrical auditory brainstem evoked responses (EABRs) were tested before and after each of four 3-hour stimulation sessions. Six weeks after implantation, the animals were killed, and their cochleas were examined under the scanning electron microscope. Intracochlear electrodes exhibited thresholds for damage well below one half of that found for most extracochlear stimulation sites. The function-relating damage threshold (in amperes) to frequency of intracochlear stimulation is represented by two straight lines, with an intercept of 1 kHz. The low-frequency limb exhibited a slope of 3 to 4 dB/octave, whereas the high-frequency limb exhibited a slope of 9 to 10 dB/octave. Extracochlear results were too variable to permit speculation. Changes in EABRs were only variably related to histopathologic findings.     

Characterisation of the beta adrenergic response cascade in fetal guinea pig lung.

BACKGROUND--Suitable models for the study of lung development are needed. The suitability of the guinea pig for studying the role of the beta adrenergic response cascade in fetal lung development has been evaluated. METHODS--Radioligand binding assays with iodine-125 labelled iodopindolol were performed to identify and characterise the beta adrenergic receptors. To demonstrate that these receptors were functional, isoprenaline and forskolin stimulated generation of cyclic AMP (cAMP) in the lung tissue was quantitated by radioimmunoassay. RESULTS--The concentration of beta receptors increased with gestational age from 23 fmol/mg at 35 days to 140 fmol/mg at 64 days. Competition binding studies were consistent with a predominance of beta 2 receptors. The ability of isoprenaline to stimulate cAMP generation was greater during the saccular phase than during the canalicular phase of lung development. Incorporation of tritium labelled choline into phosphatidylcholine increased significantly between the canalicular and saccular phases. CONCLUSIONS--The beta adrenergic response cascade in fetal guinea pig lung exhibits similar characteristics to those previously described in fetal human lung and is therefore a good model in which to study the effects of beta agonists on fetal lung development.