The auditory brainstem response (ABR) is a test widely used to assess the integrity of the brain stem. Although it is considered to be an auditory-evoked potential that is influenced by the physical characteristics of the stimulus, such as rate, polarity and type of stimulus, it may also be influenced by the change in several parameters. The use of anesthetics may adversely influence the value of the ABR wave latency. One of the anesthetics used for e ABR assessment, especially in animal research, is the ketamine/xylazine combination. Our objective was to determine the influence of the ketamine/xylazine anesthetic on the ABR latency values in adult gerbils. The ABRs of 12 adult gerbils injected with the anesthetic were collected on three consecutive days, or a total of six collections, namely: pre-collection and A, B, C, D, and E collections. Before each collection the gerbil was injected with a dose of ketamine (100 mg/kg)/xylazine (4 mg/kg). For the capture of the ABR, 2000 click stimuli were used with rarefaction polarity and 13 stimuli per second, 80 dBnHL intensity and in-ear phones. A statistically significant difference was observed in the latency of the V wave in the ABR of gerbils in the C and D collections compared to the pre-, A and E collections, and no difference was observed between the pre-, A, B, and E collections. We conclude that the use of ketamine/xylazine increases the latency of the V wave of the ABR after several doses injected into adult gerbils; thus clinicians should consider the use of this substance in the assessment of ABR.

Sepsis is a systemic inflammatory response that can lead to tissue damage and death. In order to increase our understanding of sepsis, experimental models are needed that produce relevant immune and inflammatory responses during a septic event. We describe a lipopolysaccharide tolerance mouse model to characterize the cellular and molecular alterations of immune cells during sepsis. The model presents a typical lipopolysaccharide tolerance pattern in which tolerance is related to decreased production and secretion of cytokines after a subsequent exposure to a lethal dose of lipopolysaccharide. The initial lipopolysaccharide exposure also altered the expression patterns of cytokines and was followed by an 8- and a 1.5-fold increase in the T helper 1 and 2 cell subpopulations. Behavioral data indicate a decrease in spontaneous activity and an increase in body temperature following exposure to lipopolysaccharide. In contrast, tolerant animals maintained production of reactive oxygen species and nitric oxide when terminally challenged by cecal ligation and puncture (CLP). Survival study after CLP showed protection in tolerant compared to naive animals. Spleen mass increased in tolerant animals followed by increases of B lymphocytes and subpopulation Th1 cells. An increase in the number of stem cells was found in spleen and bone marrow. We also showed that administration of spleen or bone marrow cells from tolerant to naive animals transfers the acquired resistance status. In conclusion, lipopolysaccharide tolerance is a natural reprogramming of the immune system that increases the number of immune cells, particularly T helper 1 cells, and does not reduce oxidative stress.