The distinct functions of reticulum and reticular groove are presumably controlled by neurones of the myenteric plexus. Therefore, we analysed neurones according to their neurochemical code in suckling and fattened lambs. Most neurones in the reticulum were cholinergic, additionally expressing substance P and presumably excitatory. Nitrergic neurones were more abundant in the reticular groove. In both, reticulum and reticular groove, the proportion of nitrergic neurones increased with age with the increase to be more pronounced in the reticular groove. We conclude that the increase of inhibitory innervation might enable the forestomach to adapt to large amounts of ingesta during rumination.