Age-related reductions in [3H]WIN 35,428 binding to the dopamine transporter in nigrostriatal and mesolimbic brain regions of the fischer 344 rat

In the present study, we used the potent cocaine analog [3H]WIN 35, 428 to map and quantify binding to the dopamine transporter (DAT) within the dorsal striatum, nucleus accumbens, substantia nigra, and ventral tegmental area in young (6-month-old), middle-aged (12-month-old), and aged (18- and 24-month-old) Fischer 344 rats. Quantitative autoradiographic analysis of indirect [3H]WIN 35,428 saturation curves revealed two-site binding for all four brain regions in every age group. The percentage of binding to the high- or low-affinity sites did not differ with age or region and was approximately 50%. However, significant age-related decreases in the overall density (Bmax) of [3H]WIN 35,428-binding sites were observed in the striatum, nucleus accumbens, substantia nigra, and ventral tegmental area. The Bmax within all brain regions declined by more than 15% every 6 months, with the Bmax in the aged (24-month-old) group being approximately half that measured in the young adult (6-month-old) group. Competition experiments indicated that nomifensine also exhibited two-site binding to the DAT in Fischer 344 rats. No consistent age-related differences in binding affinities were noted with either [3H]WIN 35,428 or nomifensine. Taken together, these results support the hypothesis that functional DATs within the nigrostriatal and mesolimbic systems are down-regulated with age, without changing their affinity for ligands.     

Transfusion therapy: improved patient care and resource utilization

Improving the quality of medical care while reducing costs is one of the major challenges facing the health care system in the United States. At a 1020-bed, tertiary-care, teaching hospital, the Transfusion Committee modified transfusion practice by establishing new transfusion guidelines based upon national standards rather than local practices and by implementing educational and monitoring systems. Over a 3-year period, the number of transfusions decreased, the types of transfused components changed, and the waste due to unused components decreased. From the baseline of Fiscal Year (FY) 1989 (89), the number of exposures to components from allogeneic blood donors for the patient population decreased by 11,015 in FY 90, 14,067 in FY 91, and 16,990 in FY 92, thereby decreasing the risk of transfusion-transmitted disease, transfusion reaction, and alloimmunization. As compared to costs in FY 89, the altered transfusion practices resulted in cost savings of $376,269 in FY 90, $566,375 in FY 91, and $684,704 in FY 92. Over the 3- year period, exposures to components from allogeneic blood donors for the patient population were reduced by 42,072, and the total cost savings was $1,627,348. The methodology and results should be reproducible at other hospitals.     

Decreased efficacy of inositol 1,4,5-trisphosphate to elicit calcium mobilization from cerebrocortical microsomes of aged rats

The effects of aging on the ability of brain microsomes to sequester calcium in response to ATP stimulation and to release calcium in response to inositol 1,4,5-trisphosphate (IP3) stimulation were examined. Calcium uptake and release were compared in microsomal preparations from the cerebral cortex, hippocampus, thalamus, and cerebellum of 3-, 16-, and 28-month-old male Fischer 344 rats. No age-related differences were found in the ability of brain microsomes to sequester calcium in response to ATP stimulation. A maximally effective concentration of IP3 (1 microM) released approximately 30% of the calcium sequestered by microsomes. This was observed in all brain regions and age groups studied except in the cerebral cortex, where the amount of calcium released by IP3 was reduced by 50% in the oldest age group. Concentration-response curves for IP3 in this brain region from 3- and 28-month-old rats confirmed that the maximally effective concentrations, the EC50 values, and the Hill coefficients did not differ with aging. These data indicate that the efficacy of IP3 is selectively diminished in the cerebral cortex of aged rats and that this age-related change may contribute to the attenuated responsiveness of neurons in this brain region to activation by phosphoinositide-coupled receptors.     

Dopamine, acting through D-2 receptors, inhibits rat striatal adenylate cyclase by a GTP-dependent process

This report demonstrates that the D-2 dopamine receptors that are present in rat striatum can directly inhibit the activity of adenylate cyclase in a GTP-dependent manner. N-n-propylnorapomorphine evoked a more pronounced inhibition than did dopamine. However, in the presence of the D-1-selective antagonist, SCH 23390, dopamine was also observed to inhibit the enzyme. Forskolin facilitated the detection of D-2 receptor-mediated inhibition by markedly stimulating striatal adenylate cyclase activity. The inhibition was antagonized in a dose-dependent manner by the D-2 receptor antagonist spiperone (Ki value = 70 pM) and was absolutely dependent on the presence of both GTP and sodium ions. Inhibition produced via D-2 receptors was additive with that produced via opiate or adenosine A1 receptors. The nonhydrolyzable GTP analogue, 5'-guanylylimidodiphosphate [Gpp(NH)p], did not substitute for GTP in promoting the D-2 receptor-mediated inhibition. It thus appears that D-2 receptors mediate adenylate cyclase inhibition by processes that have been observed for other neurotransmitters in the striatum and elsewhere. In addition, Gpp(NH)p displayed a Ca2+/calmodulin dependency for its inhibitory effects that was not shared by receptor-mediated, GTP-dependent inhibition.     

Arachidonic acid metabolites do not mediate modulation of neurotransmitter release by adenosine in rat hippocampus or striatum

The possible involvement of arachidonic acid metabolites as mediators of the modulation of neurotransmitter release by adenosine, acetylcholine, and GABA was examined in brain slices of rat hippocampus and striatum. The synaptic modulatory effects of these 3 agents on excitatory transmission in the CA1 region of hippocampus were completely unaffected by a phospholipase inhibitor (p-bromophenacyl bromide, BPB; 10-50 microM), a lipoxygenase inhibitor (nordihydroguaiaretic acid; 5-50 microM), the cyclooxygenase inhibitor indomethacin (10-20 microM), and a cyclooxygenase/lipoxygenase inhibitor (U53059; 5-10 microM). BPB was also found to be ineffective in altering the modulation of transmission by adenosine in the perforant path, and the adenosine inhibition of electrically stimulated release of endogenous dopamine from striatal slices. Arachidonic acid itself also had no effect on synaptic transmission. While these experiments do not rule out such a role for arachidonic acid or its metabolites in mammalian brain, they suggest that in a number of systems the inhibition of transmitter release must occur through an entirely independent mechanism.