Disease-associated prion protein in neural and lymphoid tissues of mink (Mustela vison) inoculated with transmissible mink encephalopathy.

Transmissible spongiform encephalopathies (TSEs) are diagnosed by immunodetection of disease-associated prion protein (PrP(d)). The distribution of PrP(d) within the body varies with the time-course of infection and between species, during interspecies transmission, as well as with prion strain. Mink are susceptible to a form of TSE known as transmissible mink encephalopathy (TME), presumed to arise due to consumption of feed contaminated with a single prion strain of ruminant origin. After extended passage of TME isolates in hamsters, two strains emerge, HY and DY, each of which is associated with unique structural isoforms of PrP(TME) and of which only the HY strain is associated with accumulation of PrP(TME) in lymphoid tissues. Information on the structural nature and lymphoid accumulation of PrP(TME) in mink is limited. In this study, 13 mink were challenged by intracerebral inoculation using late passage TME inoculum, after which brain and lymphoid tissues were collected at preclinical and clinical time points. The distribution and molecular nature of PrP(TME) was investigated by techniques including blotting of paraffin wax-embedded tissue and epitope mapping by western blotting. PrP(TME) was detected readily in the brain and retropharyngeal lymph node during preclinical infection, with delayed progression of accumulation within other lymphoid tissues. For comparison, three mink were inoculated by the oral route and examined during clinical disease. Accumulation of PrP(TME) in these mink was greater and more widespread, including follicles of rectoanal mucosa-associated lymphoid tissue. Western blot analyses revealed that PrP(TME) accumulating in the brain of mink is structurally most similar to that accumulating in the brain of hamsters infected with the DY strain. Collectively, the results of extended passage in mink are consistent with the presence of only a single strain of TME, the DY strain, capable of inducing accumulation of PrP(TME) in the lymphoid tissues of mink but not in hamsters. Thus, mink are a relevant animal model for further study of this unique strain, which ultimately may have been introduced through consumption of a TSE of ruminant origin.

An autoradiographic study of the rubroolivary tract in the rhesus monkey.

Autoradiographic tracing methods were employed to study the course and distribution of the rubroolivary tract following unilateral injections of tritiated leucine into the rostral red nucleus of seven rhesus monkeys. A topographic organization of projections to the ipsilateral principal nucleus of the inferior olivary complex was demonstrated. Lateral and medial portions of the rostral red nucleus projected to medial parts of the dorsal and ventral laminae of the principal inferior olive respectively; neurons in intermediate lateralities emitted fibers which terminated in lateral parts of the principal olive. Injections involving the oral end of the rostral red nucleus elicited label overlying the medial accessory olive in addition to the principal nucleus. Projections to the medial accessory olive may have arisen from the rostral end of the red nucleus and/or the immediately adjacent tegmentum. There were no projections to the dorsal accessory olive. Fibers of rubral origin also were distributed ipsilaterally to several reticular nuclei including the pedunculopontine, pontis oralis, caudalis, and gigantocellularis.

Mechanism and site of small intestinal uptake of vitamin D3 in pharmacological concentrations.

The site and mechanism of initial uptake of 1,2-3H vitamin D3 pharmacological concentrations was investigated using everted rat small bowel sacs incubated in a micellar medium. The mean +/- SE uptake rates of the vitamin at 300 muM incubation solution concentration by proximal, medial, and distal small bowel segments were 6.7 +/- 0.26, 7.8 +/- 0.54, and 3.3 +/- 0.20 nmole/min/100 mg tissue, respectively. Incubation with the addition of 10(-3) M 2,4-dinitrophenol, or 10(-3) M KCN, or under nitrogen atmosphere did not change (P greater than 0.05) the above rates of absorption. Incremental increases in the concentration of vitamin D in the incubation medium up to 1200 muM resulted in a linear increase in the uptake rate indicating lack of saturation kinetics. In all the above experiments, greater rate of uptake of the vitamin occurred in the proximal and medial small bowel than the distal small bowel (P less than 0.01). The above experiments indicate that vitamin D3 in this range of concentrations is taken up by enterocytes by a nonsaturable passive diffusion mechanism showing no evidence for carrier mediation. The rate of intestinal uptake is highest in the proximal and medial segments of the small bowel.

Effects of phenylalanine and 5-hydroxytryptophan on seizure severity in mice.

The degree of audiogenic seizure was measured in DBA/2J (phenylalanine hydroxylase deficient) mice as a function of dietary phenylalanine (Phe) and injected 5-hydroxytryptophan (5-HTP), the precursor of serotonin (5-HT). Phe was shown to exacerbate seizures significantly, and seizure severity was found to be directly related to dietary concentration when animals were not treated with exogenous 5-HTP. 5-htp was observed to significantly ameliorate seizures. The seizure-intensifying effect of Phe was reversible by 5-HTP injection and protection against seizures was directly related to 5-HTP concentration for animals on a high Phe diet. The results of this study indicate that Phe and 5-HTP are mutually antagonistic in modulating audiogenic seizure suceptibility.