DISTRIBUTION OF SP-LIKE AND CGRP-LIKE IMMUNOREACTIVE NERVE-FIBERS IN THE LOWER RESPIRATORY-TRACT OF NEONATAL FOALS - EVIDENCE FOR LOSS DURING DEVELOPMENT

The lungs of neonatal foals contain many nerves immunoreactive for sub stance P and calcitonin gene-related peptide. These nerves are closely associated with the epithelium, bronchial and pulmonary vessels and t he airway smooth muscle of all intrathoracic airways, including non-ca rtilaginous bronchioles. Activation of sensory nerves in the respirato ry epithelium could thus potentially affect, via local axon reflexes, vascular and respiratory smooth muscle in neonatal equine airways. Ner ves immunoreactive for these peptides are much more widely distributed within the lung than in adult horses; they may thus play a trophic ro le before birth, or contribute to the post-natal adaptation to breathi ng.