Pseudomonas aeruginosa biofilms perturb wound resolution and antibiotic tolerance in diabetic mice.

Diabetic patients are more susceptible to the development of chronic wounds than non-diabetics. The impaired healing properties of these wounds, which often develop debilitating bacterial infections, significantly increase the rate of lower extremity amputation in diabetic patients. We hypothesize that bacterial biofilms, or sessile communities of bacteria that reside in a complex matrix of exopolymeric material, contribute to the severity of diabetic wounds. To test this hypothesis, we developed an in vivo chronic wound, diabetic mouse model to determine the ability of the opportunistic pathogen, Pseudomonas aeruginosa, to cause biofilm-associated infections. Utilizing this model, we observed that diabetic mice with P. aeruginosa-infected chronic wounds displayed impaired bacterial clearing and wound closure in comparison with their non-diabetic littermates. While treating diabetic mice with insulin improved their overall health, it did not restore their ability to resolve P. aeruginosa wound infections or speed healing. In fact, the prevalence of biofilms and the tolerance of P. aeruginosa to gentamicin treatment increased when diabetic mice were treated with insulin. Insulin treatment was observed to directly affect the ability of P. aeruginosa to form biofilms in vitro. These data demonstrate that the chronically wounded diabetic mouse appears to be a useful model to study wound healing and biofilm infection dynamics, and suggest that the diabetic wound environment may promote the formation of biofilms. Further, this model provides for the elucidation of mechanistic factors, such as the ability of insulin to influence antimicrobial effectiveness, which may be relevant to the formation of biofilms in diabetic wounds.

Gallium maltolate treatment eradicates Pseudomonas aeruginosa infection in thermally injured mice.

Gallium (Ga) is a semimetallic element that has demonstrated therapeutic and diagnostic-imaging potential in a number of disease settings, including cancer and infectious diseases. Gallium's biological actions stem from its ionic radius being almost the same as that of ferric iron (Fe(3+)), whereby it can replace iron (Fe) in Fe(3+)-dependent biological systems, such as bacterial and mammalian Fe transporters and Fe(3+)-containing enzymes. Unlike Fe(3+), ionic gallium (Ga(3+)) cannot be reduced, and when incorporated, it inactivates Fe(3+)-dependent reduction and oxidation processes that are necessary for bacterial and mammalian cell proliferation. Most pathogenic bacteria require Fe for growth and function, and the availability of Fe in the host or environment can greatly enhance virulence. We examined whether gallium maltolate (GaM), a novel formulation of Ga, had antibacterial activity in a thermally injured acute infection mouse model. Dose-response studies indicated that a GaM dose as low as 25 mg/kg of body weight delivered subcutaneously was sufficient to provide 100% survival in a lethal P. aeruginosa-infected thermally injured mouse model. Mice treated with 100 mg/kg GaM had undetectable levels of Pseudomonas aeruginosa in their wounds, livers, and spleens, while the wounds of untreated mice were colonized with over 10(8) P. aeruginosa CFU/g of tissue and their livers and spleens were colonized with over 10(5) P. aeruginosa CFU/g of tissue. GaM also significantly reduced the colonization of Staphylococcus aureus and Acinetobacter baumannii in the wounds of thermally injured mice. Furthermore, GaM was also therapeutically effective in preventing preestablished P. aeruginosa infections at the site of the injury from spreading systemically. Taken together, our data suggest that GaM is potentially a novel antibacterial agent for the prevention and treatment of wound infections following thermal injury.

Adolescent cocaine exposure and offensive aggression: involvement of serotonin neural signaling and innervation in male Syrian hamsters.

Repeated low-dose cocaine treatment (0.5 mg/kg/day) during adolescence facilitates offensive aggression in male Syrian hamsters (Mesocricetus auratus). The current study assessed whether adolescent cocaine-facilitated offensive aggression was inhibited by increased serotonin activity and if cocaine exposure during this developmental period influenced serotonin development in the primary aggression areas of hamster brain. In a first experiment, hamsters were treated with low doses of cocaine throughout adolescence and then scored for offensive aggression following the systemic administration of vehicle or fluoxetine, a selective serotonin reuptake inhibitor. Vehicle-treated hamsters showed high levels of offensive aggression, while treatment with fluoxetine inhibited the cocaine-facilitated aggressive response. Only one out of ten fluoxetine-treated animals both attacked and bit intruders, compared to nine out of ten saline-treated animals. In a second experiment, hamsters were administered low doses of cocaine or saline throughout adolescence, tested for offensive aggression, and then examined for differences in serotonin afferent innervation to regions of the hamster brain implicated in aggressive responding. Aggressive cocaine-treated hamsters showed significant reductions (35-50%) in the number of serotonin immunoreactive varicosities and fibers in several aggression areas, including the anterior hypothalamus, lateral septum, medial amygdala, and bed nucleus of the stria terminalis. Together, these results support a role for serotonin innervation and function in adolescent cocaine-facilitated offensive aggression.

Social stress does not alter the expression of sensitization to cocaine.

The effects of chronic social stress on behavioral sensitization to cocaine were investigated in the Syrian hamster. Adolescent animals received either 15 mg/kg i.p. of cocaine or saline twice per day for 7 consecutive days. Two weeks following the last injection (young adulthood), they were given a challenge dose of 5 mg/kg i.p. of cocaine and scored for locomotion. Motor activity was significantly greater in cocaine-treated animals, demonstrating sensitization to this psychostimulant. Following the results of the first study, another group of adolescent animals was exposed to either a novel clean cage (control) or an aggressive resident male hamster (social stress) for 15 min following an injection of cocaine (20 mg/kg i.p. once daily) or saline for 7 consecutive days. The groups were as follows: Social Stress/Cocaine (SSC), No Social Stress/Cocaine (NSSC), Social Stress/Saline (SSS) and No Social Stress/Saline (NSSS). Two weeks following the last injection (Day 21), all animals were given a challenge dose of cocaine (5 mg/kg i.p.) and were rescored for locomotion. At that time, the suppressive effect of stress on locomotion was no longer detectable, as the expression of sensitization was observed in the NSSC but not in the SSC group. These results suggest that chronic social stress administered during adolescence does not cross-sensitize with cocaine in young adult hamsters.

Repeated anabolic-androgenic steroid treatment during adolescence increases vasopressin V(1A) receptor binding in Syrian hamsters: correlation with offensive aggression.

Repeated anabolic-androgenic steroid treatment during adolescence increases hypothalamic vasopressin and facilitates offensive aggression in male Syrian hamsters (Mesocricetus auratus). The current study investigated whether anabolic-androgenic steroid exposure during this developmental period influenced vasopressin V(1A) receptor binding activity in the hypothalamus and several other brain areas implicated in aggressive behavior in hamsters. To test this, adolescent male hamsters were administered anabolic steroids or sesame oil throughout adolescence, tested for offensive aggression, and examined for differences in vasopressin V(1A) receptor binding using in situ autoradiography. When compared with control animals, aggressive, adolescent anabolic steroid-treated hamsters showed significant increases (20-200%) in the intensity of vasopressin V(1A) receptor labeling in several aggression areas, including the ventrolateral hypothalamus, bed nucleus of the stria terminalis, and lateral septum. However, no significant differences in vasopressin V(1A) receptor labeling were found in other brain regions implicated in aggressive responding, most notably the lateral zone from the medial preoptic area to anterior hypothalamus and the corticomedial amygdala. These data suggest that adolescent anabolic steroid exposure may facilitate offensive aggression by increasing vasopressin V(1A) receptor binding in several key areas of the hamster brain.