Table 1.

Number (and percent) of apoptotic neurons expressing p75 with or without trk receptors

Treatment	p75+/trk−	p75+/trk+
NGF	63  (88%)	9  (12%)
BDNF	64  (86%)	10  (14%)
NT3	35  (88%)	5  (12%)
NT4	42  (84%)	8  (16%)

Neurons were grown on slide wells for 5 d and treated with the indicated factors for 6 hr. Cultures were stained with antibodies against p75 and the appropriate trk receptor (i.e., anti-pan-Trk for NGF-treated wells, anti-TrkB_in for BDNF- and NT4-treated wells, and anti-TrkC_in2 for NT3-treated wells) and labeled with Hoechst 33342. Apoptotic neurons were identified by chromatin condensation in the nucleus and scored for expression of p75 and/or trk. Few apoptotic neurons were detected in control wells. Neurons were counted in eight fields per well in three independent experiments.