Initiation of development in vitro of third-stage Nippostrongylus brasiliensis.

Third-stage larvae of Nippostrongylus brasiliensis were maintained in vitro in 5 different culture systems at 25 C and 37 C, and initiation of development to the parasitic phase was evaluated at the morphological and biochemical levels. A few larvae grown in Krebs-Ringer-Tris solution at 25 C showed minimal development of the anterior region and intestinal cells. The amount of development was enhanced with an increase in medium complexity. At 25 C the greatest development was obtained in NCTC-135 : calf serum (8 : 2/v : v). Temperature elevation from 25 C to 37 C had a more significant effect on development than increasing the complexity of the culture medium. The number of L3 showing development in Krebs-Ringer-Tris at 37 C was significantly greater than the number maintained at 25 C in NCTC-135 : calf serum. Likewise, RNA biosynthesis was greatest in those larvae grown in NCTC-135 : calf serum at 37 C. These results support the idea that an elevation of temperature and certain nutritional components stimulate the transcription of that portion of the genome coding for development into the parasitic phase of the life-history.