Postnatal Changes in ChAT and NGF Expression in Rat Oculomotor Neurons

Acetylcholine acetyltransferase (ChAT) is exclusively expressed in cholinergic neurons, including motor neurons. It is well established that motor neurons depend on neurotrophins for their survival and maturation. Motor neurons of the oculomotor system exhibit remarkable resistance to injury and to several neurodegenerative diseases, a feature attributed to their distinct neurotrophic profile. Notably, unlike vulnerable motor neuron populations, oculomotor neurons constitutively express the nerve growth factor (NGF) receptor TrkA in the adult. The primary aim of this study was to characterize the developmental changes in ChAT and NGF protein expression during postnatal maturation of the rat oculomotor system. To achieve this, animals were examined at five postnatal stages, and immunofluorescence and Western Blot techniques were used to quantify ChAT and NGF expression within these motor neurons. Both techniques revealed a statistically significant and progressive increase in ChAT protein levels in ocular motor neurons throughout postnatal development, reflecting the maturation of the neurotransmitter phenotype of motor neurons. NGF expression also increased during the same developmental window, showing a parallel upregulation. Although functional interactions between NGF and ChAT were not addressed in this study, the well-known ability of NGF to enhance ChAT activity and promote cholinergic differentiation in other neuronal populations provides useful context. The concurrent rise in NGF and ChAT observed here highlights parallel developmental trajectory, suggesting that NGF signalling may accompany, and potentially support, the maturation and long-term stability of these cholinergic motor neurons. These findings further indicate that NGF upregulation accompanies the acquisition of a mature cholinergic phenotype in oculomotor neurons and may contribute to the exceptional resistance of this motor neuron population to degeneration.