Model of Streptococcus pneumoniae meningitis in adult rats.

The purpose of this study was to develop a model of bacterial meningitis in young adult rats for assessing the efficacy of antimicrobial agents. Sixty 200- to 300-g male Sprague Dawley CD rats were inoculated intracisternally with 5.78 log10 CFU of a clinical isolate of Streptococcus pneumoniae in 5% hog gastric mucin. Inoculated rats were assigned to six groups containing 10 animals each. Group-1 rats served as controls and did not receive antibiotics. Rats of groups 2 to 4 received (subcutaneously every 12 h) cefotaxime (25, 6.25, and 1.56 mg/kg of body weight respectively). Rats of groups 5 and 6 received ampicillin (50 and 12.5 mg/kg respectively) and gentamicin (2.0 and 0.5 mg/kg respectively). Five additional Sprague Dawley CD rats were inoculated with only gastric hog mucin and were assigned to group 7. At postinoculation day 4 all animals were euthanized. Cerebral spinal fluid was collected for culturing. Brains were harvested for histologic examination and culturing. Untreated, infected control (group-1) animals were culture-positive for S. pneumoniae in the brain and cerebral spinal fluid. Of the antibiotic regimens evaluated, only cefotaxime (25 mg/kg) eradicated bacteria from the cerebral spinal fluid and brain. Cefotaxime at 25 or 6.25 mg/kg significantly (P < or = 0.05) decreased the bacterial burden of S. pneumoniae, whereas cefotaxime at 1.56 mg/kg and ampicillin/gentamicin combinations did not. There was histopathological evidence of subacute meningitis in infected rats. No meningitis was observed in rats receiving 25 mg of cefotaxime/kg. This model demonstrates the ability to induce bacterial meningitis with S. pneumoniae in adult rats and the ability to clear infection in 90 to 100% of the animals by administration of cefotaxime at dosages of 6.25 and 25 mg/kg given subcutaneously every 12 h.

Audio-motor interface in anurans.

Like males of many anuran species, fire-bellied toads (Bombina orientalis) call antiphonally, which demonstrates an auditory input into the call-generating network. Males produce their calls by an inspiratory airstream, which is generated exclusively by contraction of the muscles of the buccal cavity. The painted frog (Discoglossus pictus) possesses a combined inspiratory and expiratory call mechanism, and also uses only buccal muscles. These muscles are controlled by branchial motoneurons, which receive vocal premotor input mainly from the pretrigeminal nucleus. The interconnections between the auditory pathway and the vocal pathway were examined by neuroanatomical tracing and intracellular recording. Mesencephalic auditory nuclei, laminar and magnocellular nucleus of the torus semicircularis, and tegmental nuclei constitute strong descending efferents, which, in turn, form collaterals that terminate in vocal premotor nuclei. These findings imply fast audio-vocal interfacing, which is a prerequisite for the control of antiphonal calling.