The nuclear phenotypes of Malpighian tubule cells in fifth
instar nymphs of
Triatoma infestans
, one of the most important vectors of Chagas disease, were studied following
sequential shocks at 0ºC, separated by intervals of 8 h and 24 h at
30ºC, under conditions of moderate fasting and full nourishment. The
insects pertained to colonies reared in the laboratory and originated from
domestic specimens collected in the Brazilian states of São Paulo (north)
and Minas Gerais (south). Since nuclear phenotypes in this species are affected
by single cold shocks, it was expected that these phenotypes could also
be changed by sequential shocks. Nuclear phenotypes indicative of mechanisms
of cell survival (nuclear fusion and heterochromatin decondensation) and
cell death (apoptosis and necrosis) were observed concomitantly in all the
conditions tested. Nuclear fusion and heterochromatin decondensation were
not found relevant for the presumed acquisition of the cold-hardening response
in
T. infestans
. The decreased frequency of apoptosis and necrosis following sequential
cold shocks including under fasting conditions, indicated that tolerance
to sequential cold shocks occurred in
T. infestans
of the mentioned origin.
