Oral Cavity Of Rats Research Articles

Nicotine-Derived N-Nitrosamines (TSNA) and their Relevance in Tobacco Carcinogenesis

Biochemical studies and bioassays support the concept that the increased risk for cancer of the oral cavity in snuff dippers and cancer of the lung, upper aerodigestive tract, and pancreas in smokers is most likely associated with the exposure to tobacco-specific N-nitrosamines. The doses of TSNA required to induce tumors in the oral cavity in rats and tumors in the lungs of rats and hamsters are comparable to the total doses of TSNA to which a long-term snuff dipper, respectively a cigarette smoker, are exposed over 4 decades. The carcinogenic NNN and NNK are metabolized to highly reactive electrophiles which react with nucleophilic centers of DNA and with proteins. The DNA-adducts are known to cause miscoding which can activate K-ras proto-oncogenes. K-ras oncogenes have been detected in adenocarcinomas of the lung of smokers. TSNA also form globin adducts in the blood of laboratory animals as well as of snuff dippers and smokers. Such adducts are currently being evaluated for their significance as biochemical markers of exposure to TSNA. These biomarkers may also serve as indicators for the possible endogenous formation of TSNA in tobacco chewers and smokers. Additional research needs in TSNA carcinogenesis include the development of modified methods for the reduction of TSNA in tobacco and smoke, inhibition of TSNA carcinogenesis by nutrients and micro-nutrients and the testing of chemopreventive agents.

Effect of a bacteriocin-producing strain of Streptococcus sobrinus on infection and establishment of Streptococcus mutans on tooth surfaces in rats.

The effect of bacteriocin produced by Streptococcus sobrinus MT6223 on infection and establishment of Streptococcus mutans MT6222 was studied in specific pathogen-free rats. These strains were isolated from a carious lesion of a single subject. S. mutans MT6222 was found to be susceptible to the growth inhibitory action of S. sobrinus MT6223. When simultaneously inoculated into the oral cavity of rats, even a small inoculum (10(5) CFU) of S. sobrinus MT6223 completely inhibited colonization of S. mutans MT6222 on the tooth surface. Also, S. sobrinus MT6223 eliminated S. mutans MT6222 when MT6223 (10(8) CFU) was inoculated 2 days after the inoculation of 10(8) CFU cells of MT6222. Similar results were obtained in dental plaque samples from the tooth surface and the fissures of the upper molars at the end of the experiment. However, when S. sobrinus MT6223 (10(8) CFU) was inoculated 2 weeks after the inoculation of S. mutans MT6222 (10(8) CFU), MT6223 coexisted with MT6222. However, the plaque samples showed that MT6223 inhibited the establishment of MT6222 on smooth surfaces, but not in fissures. In addition, MT6223 protected against subsequent infection with MT6222. However, a nonbacteriocinogenic mutant of S. sobrinus MT6223 did not inhibit the infection and establishment of S. mutans MT6222.

A dense plexus of CGRP-immunoreactive nerve fibers in portions of the major salivary excretory ducts close to their opening into the oral cavity of rats.

A dense plexus of CGRP-immunoreactive nerve fibers was found subjacent to and within the epithelium of the excretory ducts of the parotid, submandibular and sublingual glands in the rat, in close proximity to the opening into the oral cavity. The immunoreactive nerve fibers disappeared after a neonatal administration of capsaicin. In immuno-electron microscopy, the immunoreactive nerve fibers were characterized by abundant small clear vesicles mixed with some large granular vesicles, but not by any particular abundance of small mitochondria. Intraepithelial immunoreactive fibers were directly apposed to adjacent epithelial cells without any membrane specializations. They did not exceed the subapical junctional complex of the epithelial cells.

Tobacco-specific nitrosamines, an important group of carcinogens in tobacco and tobacco smoke.

Tobacco-specific nitrosamines are a group of carcinogens that are present in tobacco and tobacco smoke. They are formed from nicotine and related tobacco alkaloids. Two of the nicotine-derived nitrosamines, NNK and NNN, are strong carcinogens in laboratory animals. They can induce tumors both locally and systemically. The induction of oral cavity tumors by a mixture of NNK and NNN, and the organospecificity of NNK for the lung are particularly noteworthy. The amounts of NNK and NNN in tobacco and tobacco smoke are high enough that their total estimated doses to long-term snuff-dippers or smokers are similar in magnitude to the total doses required to produce cancer in laboratory animals. These exposures thus represent an unacceptable risk to tobacco consumers, and possibly to non-smokers exposed for years to environmental tobacco smoke. The permission of such high levels of carcinogens in consumer products used by millions of people represents a major legislative failure. Indeed, the levels of tobacco-specific nitrosamines in tobacco are thousands of times higher than the amounts of other nitrosamines in consumer products that are regulated by government authorities. Although the role of tobacco-specific nitrosamines as causative factors in tobacco-related human cancers cannot be assessed with certainty because of the complexity of tobacco and tobacco smoke, several lines of evidence strongly indicate that they have a major role, especially in the causation of oral cancer in snuff-dippers. Epidemiologic studies have demonstrated that snuff-dipping causes oral cancer. NNK and NNN are quantitatively the most prevalent known carcinogens in snuff, and they induce oral tumors when applied to the rat oral cavity. A role for NNK in the induction of lung cancer by tobacco smoke is likely because of its organospecificity for the lung. Tobacco-specific nitrosamines may also be involved in the etiology of tobacco-related cancers of the esophagus, nasal cavity, and pancreas. Because they are derived from nicotine, and therefore should be associated only with tobacco, tobacco smoke and other nicotine-containing products, tobacco-specific nitrosamines as well as their metabolites and macromolecular adducts should be ideal markers for assessing human exposure to, and metabolic activation of, tobacco smoke carcinogens. Ongoing research has demonstrated the formation of globin and DNA adducts of NNK and NNN in experimental animals. Sensitive methods for the detection and quantitation of these adducts in humans would provide an approach to assessing individual risk for tobacco-related cancers.(ABSTRACT TRUNCATED AT 400 WORDS)

Receptive field properties of the parabrachio-thalamic taste and mechanoreceptive neurons in rats.

Receptive fields (RFs) of 36 taste (the 22 parabrachio-thalamic relay (P-T) and 14 non-P-T) and 23 mechanoreceptive neurons (7 P-T and 16 non-P-T) were located in the oral cavity of rats. All of the taste and most of the mechanoreceptive units examined had an RF on the ipsilateral side of the tongue or palate, but some mechanoreceptive P-T and non-P-T units had RFs bilaterally. When the RFs of taste neurons were examined with the most effective of the four basic taste (the best stimulus) and non-best stimuli, no difference was noticed in the location of RFs between the P-T and non-P-T neurons. Though most of the P-T neurons (7/11) and all of the non-P-T neurons (6/6) had an RF for non-best stimuli at a region similar to that for the best stimulus, some P-T neurons (4/11) had an RFs for non-best stimulus outside the RF for the best stimulus and/or on the region separate from the RF for the best stimulus. The P-T neurons, responding vigorously to non-optimal stimuli as well as to the best stimulus, had an RF outside the RF for the best stimulus. RFs for mechanical stimulation were also examined in some taste and mechanoreceptive neurons. The mechanoreceptive P-T units rarely had an RF exclusively on the palate. Some mechanoreceptive units had an RF on the region where no taste RF has been found, e.g. the intermolar eminence and the folium of the hard palate.

Response Properties of Thalamocortical Relay Neurons Responsive to Natural Stimulation of the Oral Cavity in Rats

Response Properties of Thalamocortical Relay Neurons Responsive to Natural Stimulation of the Oral Cavity in Rats

Effect of mutacin administration on Streptococcus mutans-induced dental caries in rats.

A bacteriocin from serotype c Streptococcus mutans strain C3603 was examined for its inhibitory effect on experimental dental caries in rats infected with S. mutans MT8148R (serotype c). Significant reduction in the incidence of dental caries was found only when bacteriocin was incorporated both in the drinking water and in the diet at a high concentration. However, caries reduction was not as great as expected and the addition of bacteriocin to drinking water alone had no effect on the recovery of S. mutans, plaque deposition or caries incidence. The bacteriocin activity must have been reduced in the oral cavity of rats, and the reasons were examined. Bacteriocin-resistant mutants were not detected and the bacteriocin was not inactivated by saliva. Whereas the bacteriocin did not kill the S. mutans cells grown in a sucrose-containing medium, it completely killed the cells grown in a sucrose-free medium.

Receptive fields of solitario-parabrachial relay neurons responsive to natural stimulation of the oral cavity in rats.

The receptive field (RF) of 67 taste and 85 mechanoreceptive neurons in the solitary tract nucleus (NTS) were located in the oral cavity in albino rats. All of the taste and most (62.4%) of the mechanoreceptive neurons examined had an RF on the ipsilateral side of the tongue and/or the palate. Regardless of whether they were solitario-parabrachial relay (SP) neurons or non-SP neurons, RFs of taste neurons were found on the anterior as well as the posterior tongue. But there were some differences in the RF distribution between the SP and non-SP mechanoreceptive neurons. Most of the mechanoreceptive SP neurons (9 of 11) had an RF on the tongue, while ca. half of the mechanoreceptive non-SP neurons (43 of 79) had an RF on the tongue and palate, but the rest had an RF on other tissue. Most of the neurons studied had a small restricted RF, but complex RFs, e.g. two separate RFs on the tongue, were found in a relatively small number of neurons (four taste and five mechanoreceptive neurons). An inhibitory RF, usually in a remote place from the excitatory RFs, was found in four mechanoreceptive neurons but no inhibitory RFs for taste neurons. Electrical stimulation of the epithelium in the RF with a low current of short duration evoked a few spikes in most units. Two of the three units, giving rise to a vigorous response to taste stimulation, but having single restricted RFs on the anterior tongue, produced a train of spikes lasting more than 20 ms in response to electrical stimulation of the RF.(ABSTRACT TRUNCATED AT 250 WORDS)

Responsiveness of solitario-parabrachial relay neurons to taste and mechanical stimulation applied to the oral cavity in rats.

A total of 311 units, responsive to natural stimulation of the oral cavity, were isolated from the rostral part of the solitary tract nucleus (NTS) of rats. Of these, 169 "taste neurons", activated by taste stimulation, and 142 mechanoreceptive units, exclusively sensitive to mechanical stimulation of the oral cavity, were found. Most taste units (62.3%) were also excited by mechanical stimulation. Forty-three (34.1%) of the 126 taste units examined were identified as solitario -parabrachial relay (SP) neurons by antidromic stimulation from the ipsilateral dorsal pons, while only eleven (12.6%) of the 87 mechano-receptive units were SP neurons. Taste SP neurons could be divided into two subgroups according to their antidromic latency; the fast SP units with an antidromic latency shorter than 9 ms and slow SP units with a longer antidromic latency. These two subgroups were not differentiated in any physiological properties except that the fast SP neurons were frequently excited by sucrose. Taste neurons were classified according to the best stimulus of the four basic taste solutions to produce the largest number of discharges in each neuron. All types of taste neurons were found among the SP and non-SP neurons, but only a small number of quinine-best neurons (n = 2) were found in the SP neuron group compared to the number of quinine-best neurons in the non-SP neuron group (n = 10). A histological examination of the recording sites revealed that taste relay neurons were found at the central or dorsal part of the nucleus but mechanoreceptive relay neurons were found at the peripheral part, although relay and non-relay neurons of either class were intermingled in the nucleus.

Verrucous hyperplasia and verrucous carcinoma of the rat oral mucosa. Experimental oral carcinogenesis using 4-nitroquinoline 1-oxide.

Verrucous hyperplasia and carcinoma are recognized entities in the human pathology, but not documented experimentally. During application of the carcinogen 4-nitroquinoline 1-oxide to the oral cavity of rats three times a week for a maximum of 18 weeks an increasing frequency of verrucous hyperplasias and carcinomas were noted. The majority of the carcinomas were localized to the palate and 3/4 of these were verrucous carcinomas, with or without anaplastic transformation to infiltrating squamous cell carcinomas. The oral verrucous lesions have all the histological characteristics of their human counterparts. The present experimental study supports the idea that tobacco consumption may represent an important etiological factor in the development of human, oral verrucous carcinomas.

Dextran degrading bacteria in rat oral cavity (author's transl)

Dextran degrading activity of bacteria in the mouth of Wister rat was studied. Weaning rats were divided into two groups, one was fed cariogenic diet, 6-PMV, and the other fed ordinary diet. After breeding for 2 weeks, dental plaque material was collected, and inoculated into Tryp-tose-Yeast extract broth containing 0.2% Dextran T-2, 000 (Pharmacia, M. W. 2, 000, 000), and incubated at 37C for 24 h aerobically or anaerobically. To the supernatant of the culture was added ethanol to 55% to 60% by volume, and remaining dextran was determined. At the same time, dextran degrading bacteria were isolated from the plaque materials.The results obtained are as follows:1) Dextran degrading activity was observed in both groups, one bred with cariogenic diet and the other with ordinary diet, but the former was more active than the latter.2) Several types of bacteria showed to have dextran degrading activity in the plaque of rats.3) Anerobic culture assumed dextran more than aerobic culture. This result indicated that anaerobes are more predominant in the plaque for degrading dextran than aerobes.4) A representative organism which degrades dextran was anaerobic, gram negative rod, and identified as Bacteroides fragilis by its biochemical and serological characteristics.

Taste-aversion conditioning with expected versus unexpected drug treatment.

Following differential conditioning in which a drug-predictive taste solution (D) infused into the oral cavity of rats was followed by a lithium injection and a no-drug-predictive solution (ND) was not reinforced, animals received a backward pairing between lithium and a novel saccharin flavor. Subjects infused with either the D solution or tap water immediately before backward conditioning learned weaker saccharin aversions than animals infused with the ND solution and animals given no infusion at this time (Experiments 1 and 3). These latter groups did not differ from each other (Experiment 3). The interference with aversion learning produced by water infusion appeared to be due to conditioned excitation that accrued to sensations of the infusion process. Extinction of the infusion sensations eliminated blocking produced by the infusion of water (Experiments 4 and 5). The blocking of saccharin-aversion learning produced by infusion of the D solution was due, to a large extent, to the conditioned aversiveness of the D taste. Extinction of the aversion to the D taste eliminated the interference with saccharin conditioning (Experiment 2), whereas extinction of the excitatory properties of the infusion process did not prevent the blocking of conditioning by infusion of the D solution (Experiment 5). These results are inconsistent with suggestions that taste-aversion learning is a primitive form of conditioning; rather, they demonstrate the influence of informational variables on conditioned taste aversions.

Taste-aversion conditioning with expected versus unexpected drug treatment.

Following differential conditioning in which a drug-predictive taste solution (D) infused into the oral cavity of rats was followed by a lithium injection and a no-drug-predictive solution (ND) was not reinforced, animals received a backward pairing between lithium and a novel saccharin flavor. Subjects infused with either the D solution or tap water immediately before backward conditioning learned weaker saccharin aversions than animals infused with the ND solution and animals given no infusion at this time (Experiments 1 and 3). These latter groups did not differ from each other (Experiment 3). The interference with aversion learning produced by water infusion appeared to be due to conditioned excitation that accrued to sensations of the infusion process. Extinction of the infusion sensations eliminated blocking produced by the infusion of water (Experiments 4 and 5). The blocking of saccharin-aversion learning produced by infusion of the D solution was due, to a large extent, to the conditioned aversiveness of the D taste. Extinction of the aversion to the D taste eliminated the interference with saccharin conditioning (Experiment 2), whereas extinction of the excitatory properties of the infusion process did not prevent the blocking of conditioning by infusion of the D solution (Experiment 5). These results are inconsistent with suggestions that taste-aversion learning is a primitive form of conditioning; rather, they demonstrate the influence of informational variables on conditioned taste aversions.

Inhibition of rat dental caries by dextranase from a strain of Spicaria violacea.

Dextranase AD17 obtained from a culture liquor of a strain of Spicaria violacea was assessed for its ability to inhibit the development of dental caries in conventional Sprague-Dawley rats which had been infected with one of the Streptococcus mutans strains. MT6R (serotype c), OMZ 176R (d), or MT-703R (e). These experiments showed that caries was significantly inhibited when rats were given cariogenic diets No. 2000 and drinking water containing AD17 at a concentration of 10 units/g, as compared to control rats not given dextranase. The inhibitory effects of AD17 were more prominent in smooth surface caries than in total caries. AD17 had a tendency to retard both the establishment of inoculated S. mutans and plaque deposition on tooth surfaces. However, S. mutans could be implanted in the rat oral cavity after repeated inoculation of the bacteria, even in the presence of AD17. These results suggest that the anticaries activity of AD17 is due to not only inhibition of adherence of S. mutans cells on tooth surfaces but also to physiochemical changes of dental plaque formed under the enzymatic action of AD17. Preliminary histophatological examination showed that AD17 had no significant toxicity in rats.

Ultrastructural observations on the keratinization process in rat buccal epithelium

Keratinized epithelium from the buccal region of the rat oral cavity was examined with the electron microscope. The granular layer contained keratohyalin granules and small lamellate bodies as well as cell nuclei and mitochondria. All these organelles disappeared from the cells when they reached the keratinized layer and the plasma membrane became internally thickened; no intermediate stages or transition cells were seen. Only a few cells in the superficial keratinized layer showed a dense fibrillar pattern which could be interpreted as keratin. It is therefore suggested that keratinization in oral epithelium is a less complete process than in the epidermis.

Absorption of fluoride through the oral mucosa of rats

The oral cavity of rats was isolated by means of ligating the oesophagus. Blood was withdrawn from one group of rats via a carotid catheter and the plasma fluoride concentration was determined before and for 2 hr after the application of sodium fluoride or sodium chloride solutions to their oral mucosa. A marked rise in the plasma fluoride level was noted with the maximum concentration reached within 30–60 min. A second group of rats was used for urinary excretion studies. Urine was collected for 24 hr prior to surgery and the application of the test solutions and for 24 hr after. These animals also had their tracheas cannulated. The amount of urinary fluoride for the 24 hr period was 6–7-fold greater in the fluoride-treated rats than that in the saline controls. The study indicated that fluoride ions from sodium fluoride solutions can be absorbed through rat oral mucosa, but probably at a relatively slow rate.