Human brain of preterm infants after hypoxic-ischaemic injuries: no evidence of a substantial role for apoptosis by using a fine-tuned ultrasound-guided neuropathological analysis

Preterm birth may be associated with hypoxic–ischaemic encephalopathy (HIE) showing a well recognised number of patterns, including neuronal karyorrhexis/eosinophilia mostly at the diencephalon and brain stem and leukomalacia at the periventricular white matter. To investigate whether programmed cell death or apoptosis plays a role in HIE, we examined human brains of preterm infants. Brain tissue samples from 12 consecutive infants (24–34 weeks of gestation) were available at post-mortem examination (1998–2000) after approval of the Ethics Committee. Two tissue sections were stereologically localised after brain fixation, slice preparation, and comparison with ultrasound imaging. We studied the periventricular white matter and the corresponding cortical region in each brain. Conventional histological stains were used. In addition, apoptosis was detected using a neuronal-specific terminal deoxynucleotidyl transferase-mediated nick end-labelling (TUNEL) method (NeuroTACS). A semiquantitative evaluation was performed to compare regions close to brain lesions with injury-free areas. Neuronal apoptosis was low in both cortical and in periventricular regions. No glial apoptosis was detected. Apoptosis in neurones was, however, detected in preterm brains with bacterial or mycotic infection. These results point out to the ambiguity of the TUNEL-reactive neurons in the diseased premature infants using fine-tuned ultrasound-guided neuropathological analysis, support the probable coexistence of neuronal TUNEL-reactivity and infection, and suggest that the association between apoptosis and HIE should overall be viewed with more caution.