Long-term infusion of nonphysiologic solutions into brain parenchyma: Effects of pH, osmolarity, and flow rate

The effects of long-term (3-day) infusion of nonphysiologic solutions into brain parenchyma were investigated in male Fischer (F344) 344 rats. Two wee ks prior to infusion, a guide cannula was placed into the striatum, substan tia nigra, or hippocampus. Solutions were infused continually for 3 days at flow rates of 0.03 (129.6 mu l total) or 0.10 (432 mu l total) mu l/min. F our days after infusion, rats were euthanized and the brain was removed and processed for histologic evaluation. Rats that received cannula implants a lone had the usual mechanical damage induced by implantation of the cannula . The brain regions that received 0.9% saline, pH 5.0 or pH 9.0 buffer at t he two aforementioned flow rates had only minor evidence of tissue damage a djacent to the infusion site that was similar to that attributable to mecha nical damage from the cannula implants. Brain tissue infused with distilled water or 1.8% saline also had modest effects of the solutions similar to t he usual mechanical damage induced by the infusion cannulae. In contrast, c ontamination of the infusion sites was seen to induce inflammation. Data fr om these studies support the hypothesis that nonphysiologic solutions can b e used to deliver compounds into brain parenchyma, without the infusion sol utions themselves causing excess damage to brain tissue.