Neuronal damage in the preterm baboon: impact of the mode of ventilatory support

We evaluated the impact of randomized ventilatory strategies on specific neuronal populations of the cerebral cortex of preterm baboons. In the first series, baboons (n = 5) were delivered at 125 days of gestation (dg; term, 185 days) and exposed to 14 days of positive pressure ventilation (PPV) and compared with 140 dg controls (n = 6). In the second series, baboons were delivered at 125 dg and ventilated by either i) PPV for 1 day, followed by 27 days of nasal continuous positive airway pressure (early [EnCPAP]; n = 6) or ii) PPV for 5 days, followed by 23 days of CPAP (delayed [DnCPAP]; n = 4). Gestational controls were delivered at 153 dg (n = 3). The density of immunoreactive neurons for calretinin and somatostatin was assessed in the primary and secondary visual cortices, cingulate and parietal cortices, and subiculum in paraffin sections. Compared with gestational controls, PPV for 14 days resulted in a reduction in the density of calretinin-positive cells in the visual cortex (Areas 17 and 18) but not in the other cortical areas. No effect of PPV was observed on somatostatin-positive cells. DnCPAP, but not EnCPAP, was associated with a reduction in the density of calretinin and somatostatin-positive cells in the visual cortical areas but not in the other cortical areas compared with gestational controls. Taken together, these data demonstrate that ventilatory strategies involving greater than 5 days of PPV have a regionally selective impact on cortical neuronal subpopulations within the visual area but not in areas of association cortex in a nonhuman primate model of prematurity.