Faculty Bibliography

Perinatal changes in the uptake of amino acids were measured in slices of fetal (15- and 19-day) and newborn (4-, 24-, and 48-hr-old) mouse brain. Uptake increased with age; smaller changes occurred with basic and neutral amino acid transport systems, and the largest changes occurred in fetal brain with amino acids of putative neurotransmitter function (taurine, glycine, GABA, and the acidic amino acids). The pattern of increase in uptake was similar at high and at low external amino acid concentrations. Developmental changes in tissue content of Na(+), K(+), or ATP were small during this period, and so are unlikely to be responsible for the observed changes in uptake. It appears that by the 15th day of fetal life, the transport systems for essential amino acids are fairly well developed in the brain, and the transport systems for neurotransmitter amino acids are not so well developed, but undergo a rapid increase in the 15-19-day period. From birth to adulthood, the concentrative capacity of slices of mouse brain for nonessential (putative neurotransmitter) amino acids is much greater than for essential amino acids.

Intraperitoneal injection of [14C]tyrosine suspension followed by subcutaneous implantation of a [14C]tyrosine pellet in mice produced a fairly constant specific activity of plasma free tyrosine for 5 days, and for 3-5 days in the tissue free amino acid pool. The specific activity of tyrosine in the tissue (brain, liver, and kidney) free amino acid pool was 75-90% of that in plasma. Incorporation of tyrosine into tissue proteins was followed for 5 days in brain; during this time 33% of tissue proteins were labeled. Incorporation for 68 h in liver and kidney showed labeling of over 70% of the protein of these tissues. These percentages assume a homogeneous tissue free tyrosine pool as the precursor. The rate of incorporation initially was 0.6, 2.8, and 2.0% per h in brain, liver, and kidney protein, respectively. These rates decreased in longer term experiments. The best fit to the incorporation curves was obtained by assuming the following average half-lives for tissue proteins: brain, two compartments, 5.7% with a half-life of 15 h, 94.3% with a half-life of 10 days; liver, a single compartment with a 26-h half-life; kidney, two compartments, 41% with an 18-h half-life, and 59% with a 63-h half-life

The periaqueductal gray was shown to be an important component of morphine analgesia and tolerance. Two-way analgesic cross tolerance was obtained between systemic and intracerebral morphine administrations when the intracerebral site was the periaqueductal gray. Rats were pretreated with intraperitoneal morphine and tested with intracerebral morphine in the periaqueductal gray. A dose-dependent reduction in analgesia as a function of morphine pretreatment level was obtained. Conversely, when rats were pretreated with intracerebral morphine in the periaqueductal gray and tested with intraperitoneal morphine, significant reductions in analgesia were obtained

The dopamine biosynthetic machinery of intact synaptosomes of rat striatum showed a 5-fold increase in development from 3-day-old neonates to adults, and it was fully developed between 2-3 weeks after birth. Concurring with this development was the appearance 2 weeks after birth of a regulatory mechanism(s) through which amphetamine in vivo induced an inhibition of dopamine biosynthesis. The inhibition was not appreciably reversed when haloperidol, in addition to amphetamine, was administered

Changes in protein components of purified myelin were measured following incubation in vitro with purified intra- and extracellular enzymes. Incubation with calf brain cathepsin D did not result in a significant relese of acid-soluble peptides as measured by ninhydrin analysis but was accompanied by a large loss of myelin proteins as determined on SDS-acrylamide gels. After 5 hr at 37°C there was a loss of about 25% for fast and slow basic proteins and the Agrawal proteolipid, but only a 5-10% loss for the Folch-Lees and Wolfgram components. Rat brain cathepsin D prepared by affinity chromatography gave a 30-60% breakdown of basic proteins and proteolipids. In general, breakdown using lyophilized myelin was increased over two-fold as compared to experiments with fresh myelin. Breakdown induced by cathepsin D was completely inhibited by the pentapeptide pepstatin. Incubation of myelin at physiological pH resulted in an endogenous breakdown of about 12% for basic proteins in freshly prepared, and 50% for lyophilized material. Addition of a soluble neutral proteinase that splits hemoglobin did not induce additional breakdown except for a small change in the Folch-Lees component. The extracellular enzymes pepsin and TPCK-treated trypsin resulted in a larger breakdown of all components as compared to brain enzymes. Present results demonstrate that all protein components of myelin are accessible to hydrolases and vulnerable to breakdown to varying extents by brain enzymes. These facts are consistent with the known rates for myelin protein turnover and may have a bearing on changes associated with demyelinating diseases.