Dichotomy of Tyrosine Hydroxylase and Dopamine Regulation between Somatodendritic and Terminal Field Areas of Nigrostriatal and Mesoaccumbens Pathways

Measures of dopamine-regulating proteins in somatodendritic regions are often used only as static indicators of neuron viability, overlooking the possible impact of somatodendritic dopamine (DA) signaling on behavior and the potential autonomy of DA regulation between somatodendritic and terminal field compartments. DA reuptake capacity is less in somatodendritic regions, possibly placing a greater burden on de novo DA biosynthesis within this compartment to maintain DA signaling. Therefore, regulation of tyrosine hydroxylase (TH) activity may be particularly critical for somatodendritic DA signaling. Phosphorylation of TH at ser31 or ser40 can increase activity, but their impact on L-DOPA biosynthesis in vivo is unknown. Thus, determining their relationship with L-DOPA tissue content could reveal a mechanism by which DA signaling is normally maintained. In Brown-Norway Fischer 344 F1 hybrid rats, we quantified TH phosphorylation versus L-DOPA accumulation. After inhibition of aromatic acid decarboxylase, L-DOPA tissue content per recovered TH protein was greatest in NAc, matched by differences in ser31, but not ser40, phosphorylation. The L-DOPA per catecholamine and DA turnover ratios were significantly greater in SN and VTA, suggesting greater reliance on de novo DA biosynthesis therein. These compartmental differences reflected an overall autonomy of DA regulation, as seen by decreased DA content in SN and VTA, but not in striatum or NAc, following short-term DA biosynthesis inhibition from local infusion of the TH inhibitor α-methyl-p-tyrosine, as well as in the long-term process of aging. Such data suggest ser31 phosphorylation plays a significant role in regulating TH activity in vivo, particularly in somatodendritic regions, which may have a greater reliance on de novo DA biosynthesis. Thus, to the extent that somatodendritic DA release affects behavior, TH regulation in the midbrain may be critical for DA bioavailability to influence behavior

Effect of Microenvironment in Producing a Visible Film on Milk Handling Equipment

Little is known of the chemistry of the build-up of soil resulting from milk handling operations. This study was developed to find the nature of the presoil and its contribution to the fate of the microflora. The microenvironment in soil on milk handling equipment is dependent upon available water as influenced by humidity in the atmosphere. The effect of RH (80, 86, 93, and 100%) was, therefore, studied using milk products as the soiling. Varying combinations of whole, raw milk and other milk constituents were layered on 1 cm2 stainless steel surfaces and studied with exposure to controlled humidities. Varying humidity levels were found to have a selective effect on the microflora of the raw milk film. The lower RH (80%) showed an inhibition of the gram-negative bacteria, while the higher RH (100%) enhanced the growth of gram-negative bacteria. Stacking and clamping of stainless steel squares, to simulate harborages, produced a microflora similar to that found with a single layer of raw milk using 100% RH. By reducing the surface area of the film exposed to the atmosphere, more water was made available to the bacterial cells of the milk-soil film. A similar retardation in loss of moisture was obtained through presoiling. Presoiling, to simulate incomplete cleaning plus a layer of raw milk, followed by incubation at 25 C, resulted in a visible yellow film similar to a type of “milkstone” encountered under field conditions. Key constituents were presoiled on stainless steel squares followed by a subsequent film of raw milk. Phospholipids were found to be necessary in the production of the yellow film. Another necessity for the production of the yellow film was growth of bacteria of the genus Pseudomonas. Evaluation of the yellow film produced in the laboratory found its production to be dependent on the following factors: 1) inadequate cleaning to yield a presoil of phospholipids, 2) growth of Pseudomonas sp., 3) high population density, and 4) available water. Advisor: R. Burt Maxc