Shock-induced modulation of lymphocyte reactivity: suppression, habituation, and recovery

The present study was designed to evaluate the suppressive effect of different frequencies of signaled-shock presentations on mitogenic reactivity of lymphocytes in Lewis rats, and to assess the recovery of that reactivity at varying times after the shocks. The results showed that the magnitude of decreased reactivity in both the spleen and whole-blood lymphocytes, as determined by mitogenic reactivity to Concanavalin A (Con A), was directly related to the number of shock presentations within a daily session. However, the suppressed reactivity for the spleen cells diminished with repeated sessions of frequent shocks, in contrast to the whole-blood lymphocytes which did not show any habituation. Furthermore, the imposition of different periods of recovery following a single session of frequent shocks showed that the decreased reactivity for the whole-blood lymphocytes extended beyond the immediate period of the shock experience, and took 48 to 96 hours to recover completely. In contrast, the spleen lymphocytes showed complete recovery within 24 hours following the administration of shock. These results establish that the rate of habituation to and recovery from a shock-induced decrease in mitogen reactivity is more rapid for the spleen than whole-blood lymphocytes.     

Developmental delays in exploration and locomotor activity in male rats exposed to low level lead

Delays in the development of exploratory and locomotor behavior in neonatal male rats (up to 21 days of age) are shown to accrue as a consequence of low level lead exposure. Cross fostering experiments indicate that these delays are primarily due to prenatal exposure. These Pb induced behavioral modifications appear to be associated with the delays in synaptogenesis and biochemical development of the cerebral cortex reported previously (4, 18). A new behavioral bioassay for detecting delays in brain development is described.     

Carbamoyl-phosphate synthetases from Neurospora crassa. Immunological relatedness of the enzymes from Neurospora, bacteria, yeast, and mammals

Neurospora crassa contains two carbamoyl-phosphate synthetases: a mitochondrial enzyme (CPS-A) which supplies carbamoyl phosphate for arginine biosynthesis, and a nuclear enzyme whose product is used for the synthesis of pyrimidines. We have prepared antiserum against a highly purified preparation of the large subunit of CPS-A and have used the antiserum to demonstrate that the large subunit is, like most mitochondrially localized proteins, initially synthesized as a higher molecular weight precursor. The CPS-A antiserum cross-reacts with the nuclear enzyme, allowing us to identify the product of the complex N. crassa pyr-3 genetic locus as a protein with a subunit molecular weight of 180,000. Finally, we have found that the CPS-A antiserum also cross-reacts with carbamoyl-phosphate synthetases from bacteria, yeast, and mammals. The immunological relatedness of carbamoyl-phosphate synthetases from such diverse species suggests that the protein sequences required for carbamoyl phosphate production have been highly conserved during the course of evolution.