Chronic blockade or constitutive deletion of the serotonin transporter reduces operant responding for food reward

The therapeutic effects of chronic selective serotonin reuptake inhibitors (SSRIs) are well documented, yet the elementary behavioral processes that are affected by such treatment have not been fully investigated. We report here the effects of chronic fluoxetine treatment and genetic deletion of the serotonin transporter (SERT) on food reinforced behavior in three paradigms: the progressive ratio operant task, the concurrent choice operant task, and the Pavlovian-to-Instrumental transfer task. We consistently find that chronic pharmacological blockade or genetic deletion of SERT result in similar behavioral consequences: reduced operant responding for natural reward. This is in line with previous studies reporting declines in operant responding for drugs and intracranial self-stimulation with fluoxetine treatment, suggesting that the effect of SERT blockade can be generalized to different reward types. Detailed analyses of behavioral parameters indicate that this reduction in operant responding affect both goal-directed and non-goal-directed behaviors without affecting the Pavlovian cue-triggered excessive operant responding. In addition, both pharmacological and genetic manipulations reduce locomotor activity in the open field novel environment. Our data contrast with the effect of dopamine in increasing operant responding for natural reward specifically in goal-directed behaviors and in increasing Pavlovian cue-triggered excessive operant responding. Serotonin and dopamine have been proposed to serve opposing functions in motivational processes. Our data suggest that their interactions do not result in simple opponency. The fact that pharmacological blockade and genetic deletion of SERT have similar behavioral consequences reinforces the utility of the SERT null mice for investigation of the mechanisms underlying chronic SSRIs treatment.

Detection of invasiveness of mammalian cells by Escherichia coli: collaborative study

In a collaborative study of 2 standard procedures (Procedure I, presented in J. Assoc. Off. Anal. Chem. 60, 546-562 (1977) and Procedure II in the Bacteriological Analytical Manual, 1978), 7 laboratories evaluated the invasive potential of Escherichia coli. Monolayers of HeLa cultures were infected with E. coli (infectivity ratio 100 bacteria/mammalian cell) suspended in 2 menstrua: heat-inactivated fetal bovine serum (Procedure I) and 0.2% bovine albumin Fraction V dissolved in Earle's buffered salts (Procedure II). After uptake of the bacteria, intracellular growth, and differential staining, the percentages of HeLa cells containing a minimum of 5 bacteria were determined microscopically. All laboratories correctly identified invasiveness of E. coli by Procedure I; 5 of 6 laboratories recognized invasiveness by Procedure II. Although Procedure I was more reproducible than Procedure II, repeatability did not differ significantly. Procedure I was adopted official first action for presumptive recognition of invasiveness in E. coli.

Alkali method for rapid recovery of Yersinia enterocolitica and Yersinia pseudotuberculosis from foods

A new culture method employing a potassium hydroxide treatment was compared with the conventional cold enrichment method for efficacy in recovering Yersinia sp. from naturally and artificially contaminated food. The new method increased the yield of Yersinia sp. fourfold and the sensitivity 100-fold, shortened the incubation period, and appreciably decreased the growth of non-Yersinia bacteria from a variety of meats, shellfish, and vegetables.

Methodology for recognition of invasive potential of Escherichia coli

Surveillance for dysentery-related invasive potential in bacteria using the Sereny keratoconjunctivitis test is restricted by expense, time factor, and necessity for confirmation. Primary screening of isolates in a standardized mammalian cell culture system is recommended. Bacteria are grown 20 hr in veal infusion, washed, and resuspended in 20% heat-inactivated fetal bovine serum (FBS) supplemented with 0.12% brain heart infusion and 0.1% bile salts. The HeLa culture is grown 20 hr as a monolayer in chamber slides with 90% minimal essential medium (MEM)-10% FBS. The host culture is infected at a ratio of 10 bacteria/mammalian cell for 3 hr at 35 degrees C. The infection medium is replaced with MEM-FBS supplemented with 300 microng lysozyme and 5 microng gentamycin/ml. The infected monolayer is incubated 5 hr at 35 degrees C to permit intracellular multiplication. Specimens are washed, fixed with methanol, and stained successively with May-Grunwald and Giemsa dyes. Bacteria occur within the cytoplasm if invasion has occurred. The criterion for a positive test is that 1% of the host cells possesses at least 5 bacteria in 2 of 3 trials. Invasiveness is correlated with and possibly preconditioned by cytotoxic principle(s). Infectivity rates vary from 0 to 30%. The cytopathic effect is noted in 5-50% of HeLa cells. Positive results must be confirmed by the Sereny test.

Pathogenicity of Escherichia coli recovered from food

In Western nations, pathogenic biotypes are sporadically encountered in foodborne gastroentetis. Cholera, dysentery, and chronic ulcerative colitis syndromes are recognized. E. coli has been associated on the average with 2% of annual food outbreaks and 5% of total cases. In developing nations, the incidence may be greater. In contrast with Salmonella and Shigella, significance can be assessed only by fulfillment of Koch's postulates. Preliminary studies using vascular permeability reaction for the detection of heart-labile toxin and the Sereny keratoconjunctivities test for demonstration of invasiveness indicate limited incidence of these pathogenicity markers in cultures from foods. Two per cent of isolates from cheeses involved in recent outbreaks were toxigenic; 14% were invasive. Corresponding values for food isolates not associated with illness were 10 and 0, respectively. To facilitate examination of multiple isolates, 10 may be pooled for the detection of heat-labile toxin, and 5 for invasiveness. Present model pathogenicity systems require standardization, estimation of specificity and sensitivity limits, examination by collaborative study, and ascertainment of human equivalence. Supplemental tests include capacity for colonization of intestinal epithelium and intracellular growth. Stereotypes based upon serology, host range, and recognized toxic factors may require modification.

Microbiological methods. Methodology for enteropathogenic Escherichia coli

Pathogenic biotypes of Escherichia coli grow poorly at temperatures greatly different from that of the host. Percentages quantitatively recovered at 42.0, 44.0, 44.5, and 45.5 degrees C in lauryl tryptose broth were 100, 76, 76, and 42, respectively. Corresponding values for 175 strains of varied origin were 98, 89, 82, and 65%. Maximal growth temperature is dependent upon medium. Lauryl tryptose and elevated coliform broths were equivalent in the recovery of small inocula (100 cells/ml) at 41.5-44.5 degrees. MacConkey, enteric enrichment, and Gram-negative broths were inhibitory at corresponding values. Growth at elevated temperature in nutrient broth is enhanced by carbohydrate. Standard lactose enrichment media fail to recover slow lactose fermenters. An acidified glutamic acid medium was unsuitable for recovery of E. coli. The data suggest modification of standard temperatures for the recovery of pathogenic biotypes. Previously recommended analytical methods have been simplified and supplemented. The enhancement of motility in indole-nitrite broth at 35 degrees C is recommended. A 4-tube semiquantitative test is offered for tentative identification of somatic and capsular antigens. Inclusion of Alkalescens-Dispar strains is warranted by their pathogenic behavior. Examination in Shigella and Alkalescens-Dispar sera is required to cover the dysentery-like biotypes. Pathogenic potential cannot be inferred from serotype.