The purpose of this study was to investigate the occurrence of different developmental forms of leishmania promastigotes during growth in vitro and attempt to correlate these with forms that occur in different localities in the gut of infected sandflies. One aim was to identify and characterise biochemical differences between the promastigotes and so provide insights into the adaptations of the promastigotes to the different environments encountered in the sandfly. The study was initiated with

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... . panamensis to enable investigation of the hindgut forms, stages which occur in only a few Leishmania species. A comparative approach was adopted later, however, and involved L. mexicana, a species which does not undergo hindgut development. Several promastigote forms were distinguished on morphological grounds and were investigated biochemically in order to ascertain stage-specific features. Since amastigotes of L. mexicana were readily available pure and in reasonable quantities, these were also included in my studies in an attempt to identify biochemical differences between the sandfly and mammalian stages of the parasite. Three morphologically distinct promastigote forms were identified in in vitro cultures of L. panamensis and L. mexicana. These forms morphologically resembled promastigotes that occur at different localities in and at different times after infection of, the sandfly host. Morphotype 1 promastigotes, which are similar in appearance to those found in the blood meal, occur primarily in early-log phase cultures in vitro. Morphotype 2 promastigotes have longer and more slender cell bodies than the rounded morphotype 1 forms and occur in large numbers in mid- to late-log phase in vitro cultures. They appear to resemble multiplicative mid-gut forms of L mexicana. L. panamensis promastigotes undergo a different developmental route in the sandfly and multiply as spatulate-shaped cells in the hindgut rather than the midgut. The morphotype 2 forms of this species may be equivalent to these developmental forms. S [...]