Extrapulmonary gas exchange enhances brain oxygen in pigeons.

Blood in mouth, nose, and eye tissues of birds cools by evaporation, then flows to a cephalic vascular heat exchanger, the ophthalmic rete. There, acting as a heat sink, blood from the evaporative surfaces cools arterial blood flowing counter-current to it toward the brain. The brain thus remains cooler than the body core. Data for unanesthetized domestic pigeons (Columba livia) suggest that in addition to losing heat, blood perfusing the evaporative surfaces also exchanges oxygen and carbon dioxide with air. In the heat exchanger, this blood apparently gives up oxygen to, and gains carbon dioxide from, arterial blood. The consequent increase in oxygen and decrease in carbon dioxide in the brain's arterial blood enhance diffusion of these gases in, and oxygen supply to, the brain. Such events may help birds maintain the brain's oxygen supply during the high systemic demand of exercise and at the reduced oxygen availability of high altitude.

Site-specific gap-misrepair mutagenesis by O4-ethylthymine.

The mutagenicity of the DNA base O-alkylation adduct, O4-ethylthymine, specifically incorporated into the plasmid vector pUC8 at the unique SalI and HincII recognition sites, was studied in vivo. Escherichia coli, Micrococcus luteus and AMV DNA polymerases catalyze the incorporation of O4-ethylTMP against template adenine and guanine residues, resulting in DNA sequence alteration during subsequent replication in the host E. coli K-12 strain JM83. The greatest mutation frequency was observed with error-prone AMV DNA polymerase. High levels of cognate restriction endonuclease-resistant mutant plasmid isolates were obtained by gap replication repair in the presence of O4-ethylTTP. The yields of mutant isolates were dependent upon the relative concentration of the competing pyrimidine deoxynucleoside triphosphates, TTP and dCTP, in the misreplication reaction. Repair of incorporated O4-ethylTMP of plasmid DNA by in vitro treatment with specific alkyltransferase, prior to transformation in the host, effectively increases the mutagenic efficiency of the adduct. The results obtained are consistent with the high miscoding potential O4-ethylthymine observed in in vitro studies and its ability to base-pair with noncomplementary guanine residues in DNA.

Cerebral tuberculosis with expansion into brainstem tuberculoma. Report of two cases.

There are only scattered case reports of intracranial tuberculosis in industrialized nations; brainstem tuberculoma is even more unusual, accounting for 2.5% to 8% of all intracranial tuberculoma. In developing nations, however, central nervous system tuberculosis (CNS-TB) is not rare and intracranial tuberculoma may account for 5% to 30% of all intracranial masses. The authors present two cases of CNS-TB with expansion to brainstem tuberculoma in patients who were undergoing treatment and had no known prior exposure to Mycobacterium tuberculosis.

Halifax clamps: efficacy and complications in posterior cervical stabilization.

BACKGROUND: Trauma, neoplasia, rheumatoid arthritis, Down's syndrome, and inflammatory conditions are well-known causes of spinal instability. The Halifax clamp is a method of posterior cervical stabilization that is attached to the adjoining laminae and tightened until no movement between involved vertebrae is possible. Our experience with cases that have utilized Halifax interlaminar clamps, their results and complications are presented. METHODS: We conducted a retrospective review of patients with spinal instability in whom Halifax interlaminar clamps were utilized for posterior spinal stabilization. RESULTS: Over a 5-year period, 38 patients in our institution underwent posterior stabilization of the cervical spine utilizing the Halifax interlaminar clamp. The patients represent a mix of motor vehicle- and sports-related traumas, rheumatoid subluxation, and a single cancer patient. Average follow-up has been 29 months (range 3 to 36 months). Thirty (78.9%) patients have had good results (i.e., stable fusion and regression of symptoms) and no complications. Three patients from our institution, and a fourth patient referred to us postoperatively, developed complications related to the Halifax clamps. Four patients died from unrelated causes. CONCLUSIONS: Halifax interlaminar clamps are a safe and effective method for posterior stabilization of various causes of cervical spinal instability.