Depolarizing responses to capsaicin in a subpopulation of rat dorsal root ganglion cells

Microelectrode recordings from the somata of rat dorsal root ganglion (DRG) cells were used to correlate their electrophysiological characteristics with sensitivity to locally applied capsaicin. Of the 80 cells tested, 17 responded to capsaicin by a rapid depolarization. These cells had low axonal conduction velocities (less than 1.4 m/s) and long duration action potentials, characteristic of C-cells. Some C-cells did not respond to capsaicin, and no A-cells, which had high conduction velocities and brief action potentials, did so. The effect of capsaicin on the current-voltage curve of C-cells suggested that it produced a conductance increase as well as a change in delayed rectification.     

Lung infection caused by Pseudomonas aeruginosa in a CD26/DPP4 deficient F344 rat model

Background

Pseudomonas aeruginosa (PA) is the most important opportunistic pathogen in causing nosocomial infections and, furthermore, poses a permanent threat for severe chronic infections in patients with cystic fibrosis or COPD. The transmembrane protein CD26 with dipeptidyl peptidase-4 (DPP4) activity shows an increased expression in inflamed tissue. We tested whether CD26/DPP4 deficiency leads to reduced inflammation and decreased structural damage when infected with PA.

Methods

CD26/DPP4⁺ and CD26/DPP4^? rats were instilled intratracheally with NaCl (controls) or with PA. Six hours later, bacterial distribution was detected with the in vivo imaging system 200 (IVIS). Lungs were then processed for molecular biology, light and electron microscopy and analyzed qualitatively, quantitatively and stereologically. Bacterial numbers were determined in homogenized lungs.

Results

Compared to saline treated controls, in both infected groups (1) the acinar airspace was significantly increased, (2) the volume density of the alveolar epithelium was significantly decreased, (3) the septal thickness was significantly reduced, (4) more than 40% of the alveolar epithelial surface was damaged, and up to 36% of the epithelial surface was covered with edema. In infected CD26^? rats, the increase in lung weight was significantly less pronounced, the portion of edematous alveolar airspace was significantly lower and the part of edema interspersed with PA was decreased significantly.

Conclusions

CD26/DPP4 deficiency resulted in reduced pulmonary edema under sublethal PA infection, implicating a role for CD26 in infection progression. The partly pronounced structural damage may mask further possible influences of CD26 on the inflammatory response.

     

辣椒素致幼鼠特应性皮炎模型的建立

目的探讨应用辣椒素建立一种新的特应性皮炎幼鼠动物模型。方法新生Wistar大鼠出生48h内背部皮下注射辣椒素(50mg/kg),3w后观察记录幼鼠的搔抓行为和皮损表现,苏木精-伊红染色观察病损皮肤组织病理变化,应用ELISA技术测定幼鼠血清中白介素(IL)-13和免疫球蛋白(Ig)E的水平,同时采用蛋白印迹法研究病损皮肤组织中丝聚合蛋白和神经生长因子的表达变化。结果与对照相比,新生鼠辣椒素皮下注射不仅引起严重瘙痒和皮损表现,而且有明显表皮增生和肥大细胞浸润等病理变化,ELISA结果显示模型鼠血清中IL-13和IgE水平增高,皮损组织中神经生长因子表达显著增加,而丝聚合蛋白表达明显降低,说明皮肤屏障功能受损。结论辣椒素皮下注射的幼鼠模型具有人类特应性皮炎患儿类似的临床表现和病理生理变化,该模型可以为研究儿童特应性皮炎的发病机制和治疗打下基础。     

Different manifestations of Toxoplasma gondii infection in F344 and LEW rats

There is evidence that not only the immune status, but also the genetic predisposition of certain hosts influence the clinical outcome of Toxoplasma gondii infection. By far the majority of our knowledge on genetic and immunological mechanisms involved in control of T. gondii infection has been obtained by studying mouse models, which in terms of clinical outcome of infection differ considerably from humans. Rats which show a rather similar course of infection in comparison to humans have not so far been investigated for effects of genetic differences on course of the infection. In this study we show that, like mice, different strains of rats exhibit a remarkable variation in the number of brain cysts arising from chronic infection. LEW rats seem to be highly resistant to cyst formation, in contrast to F344 rats that are susceptible. In addition, F344 rats express high numbers of γδ T cells during the acute phase of infection, whereas LEW rats express elevated but comparably low numbers of γδ T cells. The RT1 (rat MHC) haplotypes of both strains are identical in the RT1A and RT1B/D regions, which encode the restriction elements for conventional peptide antigens. Consequently, rat strain-specific differences may be useful to define MHC-independent mechanisms of resistance against T. gondii, which may also act in humans. Received: 24 July 1998     

The effects of capsaicin on emotional responses to odors in the rat

Capsaicin is described as disturbing the autonomic responses to stress-inducing environments. The effects of capsaicin (130 mg/kg in 2 series of subcutaneous injections) on emotionality responses were studied in 19 Sprague-Dawley male rats using the open-field test. Eleven rats treated with isotonic saline served as controls. Emotionality (E) measured before capsaicin treatment in the open-field ventilated with deodorized air was similar in the 2 groups of rats. Nine out of the 19 treated rats survived. Their E was significantly higher than that of there 10 rats that died from capsaicin. When a frightening odor (fox feces) was added to the open-field E increased in the controls but remained unchanged in the capsaicin-surviving rats. The ability to discriminate palatable food or female odor was similar in the two groups. The results suggest that; 1) Highly emotional rats survived subcutaneous capsaicin injections; 2) Reaction to an emotionality-inducing environment was decreased in the capsaicin-surviving rats; 3) Olfactory discrimination was not impaired by capsaicin treatment.     

Age-related effects on eyeblink conditioning in the F344 x BN F1 hybrid rat

Young, middle-aged, old, and senescent Fischer 344 x Brown Norway F1 hybrid rats were trained in either the trace or delay eyeblink conditioning task in order to investigate how aging affects associative learning and memory over the life span. Senescent rats at 34-35 months showed severe impairments in acquisition of the trace task with a 250 msec trace interval, which is hippocampally-dependent, and were mildly impaired in the simple delay eyeblink conditioning task. Middle aged animals, varying in age from 18-24 months, acquired the trace and delay eyeblink paradigms as well as young rats (6 months). However, at 28-29 months, approximately 50% of the old animals showed impairments in the trace 250 msec eyeblink task. Our results show that trace eyeblink conditioning is an age-sensitive task useful for studying the neural substrates underlying associative learning and memory in rats, as has been previously shown in humans and rabbits.     

Early capsaicin intervention for neurogenic bladder in a rat model of spinal cord injury

We explored capsaicin pretreatment, prior to spinal trauma, as a method to prevent the development of neurogenic detrusor overactivity (NDO) and urethral-bladder dyssynergia reflex after spinal cord injury (SCI). In addition, the duration of effect of capsaicin therapy on NDO in a rat model of SCI was investigated. Two sets of experiments were performed on female Sprague Dawley rats transected at the T9-T10 spinal level. First, SCI rats received capsaicin (125 mg/kg s.q.) 3-4 days before and 4-5 days after SCI. Cystometrograms (CMG) was performed 4 weeks after injury. In the second set of experiments, serial CMG in the same SCI animal was performed after one time injection of capsaicin (125 mg/kg s.q.) 4 weeks after spinalization. There were no differences in intercontraction intervals, voiding efficiency, or voiding pressure between the capsaicin pretreated and control SCI rats. However, the number of uninhibited detrusor contractions decreased 4 weeks after injury. We found that a single dose of capsaicin suppressed uninhibited detrusor contractions for 34 days in the chronic SCI animals. Early therapy with capsaicin was able to prevent/reduce detrusor hyperreflexia in spinal cord injured animals 4 weeks after injury. Early vanilloid therapy may prevent development of urologic sequelae after SCI.     

Age-related changes in orolingual motor function in F344 vs F344/BN rats

Normal aging is associated with both locomotor and orolingual motor deficits. Preclinical studies of motor function in normal aging, however, have focused primarily on locomotor activity. The purpose of this study was to measure age-related changes in orolingual motor function and compare these changes between two rat strains commonly used in aging studies: Fischer 344 (F344) and Fischer 344/Brown Norway hybrid (F344/BN) rats. Rats (6-, 12-, 18- and 24-months of age) were trained to lick water from an isometric force-sensing operandum so that the number of licks per session, licking rhythm (licks/second) and lick force could be measured. In both strains, the number of licks per session was greatest in the oldest group, while this measure was greater for F344/BN rats at all ages. Peak tongue force increased with age in F344/BN rats, did not change with age in the F344 rats, and was greater for the F344/BN rats at all ages. Both strains exhibited an age-related slowing of licking rhythm beginning with the 18-month-old group. These findings suggest that despite lifespan differences between these two rat strains, diminished tongue motility emerges at the same age.     

N-methyl-D-aspartate mediated responses decrease with age in Fischer 344 rat brain.

N-Methyl-D-aspartate (NMDA) receptor-mediated responses were studied in hippocampus, cortex, and striatum of Fischer 344 rats of various ages (3-5, 12-14, or 24-28 months old; young, middle-aged, and senescent or old, respectively) to determine whether aging alters the function of NMDA receptors. NMDA-induced inhibition of muscarinic-stimulated phosphoinositide hydrolysis in hippocampus, and NMDA-stimulated release of [3H]norepinephrine (NE) or [3H]dopamine (DA) were used as indices of NMDA receptor function. The muscarinic agonist carbachol (1 mM) stimulated PI hydrolysis in hippocampi from all three age groups with no significant differences between the groups. NMDA inhibited the carbachol-evoked PI response in a concentration-dependent manner (10-100 microM) in all age groups. However, the NMDA-induced (100 microM) inhibition of the carbachol-stimulated response was markedly reduced in an age-dependent manner with losses of 25% and 53% in middle-aged and senescent rats compared to young. Concentration-effect curves for NMDA-stimulated [3H]NE release were determined using hippocampal and cortical slices from rats of the three age groups. In the hippocampus the maximal response for NMDA was significantly decreased from 6.55 fractional [3H]NE release in young to 4.51 and 4.18 in middle-aged and old rats, respectively, with no age-related changes in the potency of NMDA or slope of the curves. In cortical slices the maximal response was significantly reduced in an age-dependent manner by 23% in the senescent rats compared to the young rats. NMDA-stimulated [3H]DA release from striatal slices was significantly lower in the senescent rats at concentrations of NMDA from 500-2000 microM.(ABSTRACT TRUNCATED AT 250 WORDS)     

A case report of a spontaneous gastrointestinal stromal tumor (GIST) occurring in a F344 rat

We report a case of gastrointestinal stromal tumor (GIST) that developed in a male F344 rat at week 101 of an experiment in a carcinogenicity study. Macroscopically, the primary tumor, which measured 1 cm in diameter, involved the submucosal tissue of the forestomach at the lesser curvature extending to the glandular stomach and esophagus. Histopathologically, the tumor was composed of neoplastic cells with small- to medium-sized spindle-shaped single nuclei and fibrillary cytoplasm lacking distinct cell borders. It invaded extensively into the tunica muscularis and subserosa, further extending to the lamina propria mucosa and serosal surface. A few densely proliferating portions showed a tendency to storiform pattern. Metastatic tumor nodules were found in the liver, spleen, and femur bone marrow, with multiple nodules, up to 1 cm in diameter, apparent in the liver. Immunohistochemically, diffuse, but weak cytoplasmic immunoreactivity for KIT was evident, and most neoplastic cells also exhibited strong immunoreactivity for a -smooth muscle actin and vimentin. Sparse nuclear S-100-immunoreactive cells were further observed, but none of neoplastic cells were immunoreactive for CD34, caldesmon, desmin, cytokeratin, or synaptophysin. Collectively, these features meet the criteria for a GIST, with limited potential for differentiation to smooth muscle and neural cells.     

Renal lesions induced by ochratoxin A exposure in the F344 rat.

Groups of 80 male and female F344 rats were exposed by gavage to ochratoxin A, a naturally occurring mycotoxin, at levels of 21, 70, and 210 micrograms/kg body weight for up to 2 years. Ochratoxin A induced non-neoplastic renal tubular epithelial changes consisting of cytoplasmic alteration, karyomegaly, degeneration, and cysts. Exposure-related renal tubular proliferative lesions included focal hyperplasia, tubular cell adenoma, and tubular cell carcinoma. Renal tubular cell adenoma occurred as early as 9 months in 1 high-dose male rat, and both adenomas and carcinomas were seen in males by 15 months. At the terminal sacrifice, renal tubular cell tumors were found in both male and female rats, but the response was more pronounced in the males. The incidence of renal tumors in the high-dose rats was the highest of any National Toxicology Program (NTP) study completed to date. In the high-dose males approximately one-third of the renal carcinomas developed metastases. This study demonstrates that ochratoxin A is a potent renal carcinogen in the F344 rat and suggests that contamination of feedstuff by this mycotoxin may pose a potential hazard to domestic animals and man.     

Sarcopenia-related apoptosis is regulated differently in fast- and slow-twitch muscles of the aging F344/N x BN rat model

Age-related decreases in muscle mass have been associated with the loss of myonuclei, possibly through a mechanism involving mitochondria. It is unclear if age-related apoptotic mechanisms vary by fiber type. Here we investigate indices of apoptosis along with the regulation of apoptotic mediators in the extensor digitorum longus (EDL) and soleus of adult (6 month), old (30 month), and very old (36 month) Fischer 344/NNiaHSD x Brown Norway/BiNia (F344/N x BN) rats. Compared to 6-month muscles, aged muscles exhibited decreases in muscle mass along with increases in the number of nuclei staining positively for DNA fragmentation. The expression of Bax, Bcl-2, caspase-3 and caspase-9 was regulated differently with aging between muscle types and in a manner not consistent with mitochondria-mediated apoptosis. To investigate the potential of calpain involvement in age-related myonuclear loss, the calpain-dependent cleavage of alpha-fodrin was examined. The proteolytic cleavage of alpha-fodrin by calpains was increased in both muscles with only the 36-month soleus exhibiting increased caspase-dependent alpha-fodrin cleavage. Taken together, these data suggest that apoptotic regulatory events differ between fiber types in the aging F344/N x BN and that mitochondrial-dependent apoptosis pathways may not play a primary role in the loss of muscle nuclei with aging.     

Dandy-Walker like malformation in a Fischer-344 rat

A spontaneous cerebellar malformation was found in a 32-day-old male Fischer 344 rat. The cerebellar malformation was composed of a vermis defect and markedly dilated fourth ventricle. The cerebellar hemispheres were separated, with the left hemisphere being smaller than the right one. Degenerative/inflammatory lesions consisting of macrophage/lymphocyte infiltration, spheroidal calcium depositions, and astrocytic gliosis were seen adjacent to the cerebral aqueduct. Abnormally arranged hyperplastic ependymal cells were observed beneath the fourth ventricle in the medulla oblongata. The gross findings of the present case resemble those of the human Dandy-Walker malformation. While a precise mechanism remains to be elucidated, degenerative/inflammatory lesions in the present rat may be involved in the pathogenesis of this malformation.     

Effects of chronic adult dietary restriction on spatial learning in the aged F344 x BN hybrid F1 rat

Dietary restriction (DR) has been shown to increase life span and reduce disease incidence across a variety of species. Recent research suggests that chronic adult DR may also alter age-related cognitive decline. The purpose of this study was twofold: (1) to examine the potential deficits in spatial learning ability in the aged F344 x BN hybrid F1 rat with specific attention to the contributory effects of motoric impairments and (2) to determine the influence of chronic adult DR on any such impairments. The Morris water maze (MWM) task was employed with a 1.8 m diameter tank, 10 cm2 escape platform, 28 degrees C water, and an automated collapsing central starting platform. Spatial learning impairments in the aged rats were evident on all dependent measures during training and the probe test. Motoric function, as reflected in measures of strength and locomotion demonstrated profound age-related performance impairments that were attenuated by chronic adult DR. The present data also replicate previous reports, indicating that DR attenuates the age-related impairments of performance in the MWM as indexed by the latency measure in acquisition, but critically was dissociated from any DR effect on measures of preference and, more critically, accuracy in the probe test. Collectively, the most parsimonious interpretation of DR effects on MWM performance would appear to be the preservation of motoric, and not cognitive, function.     

Accumulation of K-Ras codon 12 mutations in the F344 rat distal colon following azoxymethane exposure

Azoxymethane (AOM) administration to F344 male rats is a widely used model of human colon carcinogenesis. The current study investigates quantitatively the accumulation of K-Ras codon 12 mutations following AOM exposure. Male, 6-week-old F344 rats were treated subcutaneously with 30 mg/kg body weight of AOM, and colon tissue was collected at 1, 8, 24, and 32 weeks after treatment. The K-Ras codon 12 GGT to GAT and GGT to GTT mutant fractions (MFs) were measured using allele-specific competitive blocker polymerase chain reaction (ACB-PCR). Between 1 and 32 weeks after AOM treatment, the K-Ras codon 12 GGT to GAT geometric mean MF in the rat colon increased significantly from 12.9 × 10(-5) to 145 × 10(-5) , and the GGT to GTT geometric mean MF increased significantly from 5.26 × 10(-5) to 180 × 10(-5) . K-Ras codon 12 GGT to GAT MF also increased significantly in AOM-treated rat colon tissue at 1 week compared to controls (4.44 × 10(-5) ). The accumulation of the GGT to GAT MF long after the DNA adduct repair phase suggests that a portion of cells containing this mutation have a proliferative advantage, allowing them to accumulate as nascent tumors progress. Also, the GGT to GAT background MF increased in untreated rats, indicating that there is accumulation with age. The ACB-PCR assay generates quantitative data of cancer-related mutations and thus provides insight into pathological processes following carcinogen exposure.     

Serum antibody and cellular responses in LEW and F344 rats after immunization with Mycoplasma pulmonis antigens

Mycoplasma pulmonis causes a chronic respiratory disease in rats which is more severe in LEW than in F344 rats. This study compared the ability of each of these rat strains to produce specific immune responses to M. pulmonis antigens. By an enzyme-linked immunosorbent assay, LEW rats were found to produce approximately 10 times lower levels of specific immunoglobulin G (IgG) after immunization with M. pulmonis antigens than F344 rats, while no significant difference was found in the levels of IgM. The difference in IgG levels was due to much greater levels of specific IgG2b (about 50 times) in F344 rats; no differences were found in other subclasses. Nonimmune LEW rats were found to have as much total IgG2b in their sera as unimmunized F344 rats by a single radial immunodiffusion test; thus, the difference was not due to the inability of LEW rats to produce IgG2b. In contrast to the antibody response to M. pulmonis antigens, anti-keyhole limpet hemocyanin IgG responses in LEW and F344 rats were similar, but F344 rats produced significantly more (about 21 times) IgG2b than was found in M. pulmonis responses. Antisera from F344 rats recognized several additional M. pulmonis antigens than antisera from LEW rats; however, this could not explain the differences in the level of IgG2b in LEW and F344 rats. In vitro stimulation of splenic lymphocytes with M. pulmonis antigens from immunized F344 rats produced much greater proliferative responses than in LEW and nonimmune F344 cells. Thus, the susceptible rat strain LEW produced lower cellular and humoral immune responses to M. pulmonis antigens than the resistant rat strain F344 after immunization.     

Comparative localization of carboxylesterase in F344 rat,Beagle dog,and human nasal tissue

Background. Carboxylesterases (CE) exhibit high activity in the nasal mucosae and produce acid metabolites toxic to the olfactory epithelium following exposures to inhaled esters. The regional distribution and activity of CE have been studied in rodents, but no comparative studies have examined regional localization or activity in dog or human nasal tisses. Methods. We determined the immunohistochemical distributions of CE in the nasal respiratory and olfactory mucosae of Beagle dogs, and the nasal respiratory mucosa of the human nose and compared these distributions to those in the F344 rat. Results. In the dog respiratory mucosa, the greatest CE immunoreactivity was in the subepithelial glands and surface epithelial cells. In the olfactory mucosa, immunoreactivity was observed in the apical portion of the sustentacular cells, and in duct cells and acinar cells of Bowman's glands. This distribution is similar to that found in rat, except the subepithelial glands of the rat respiratory mucosa showed little to no immunoreactive CE. The human respiratory mucosa showed immunostaining in surface epithelial cells as well as glandular cells. Immunostaining in the human tissue samples was dramatically reduced in the presence of hyperplastic lesions and virtually eliminated in samples with squamous metaplasia. Conclusions. The data indicate that the distribution of CE is very similar in healthy nasal mucosae across the three species studied. However, the loss of CE immunoreactivity correlated with nasal epithelial lesions in the human samples suggests enzymatic activity may be compromised by insults to nasal tissues. Further studies of CE activity in animals following nasal insult could improve the ability to predict human responses to inhaled esters. © 1994 Wiley-Liss, Inc.