Olfactory bulb glycogen metabolism: noradrenergic modulation in the young rat

The olfactory bulb exhibits high glycogen phosphorylase activity, the rate-limiting enzyme in the mobilization of glycogen. The bulb also receives dense noradrenergic innervation and noradrenaline is known to stimulate glycogen breakdown. We determined the levels of glycogen in the bulb over the course of development and then determined the ability of noradrenaline to mobilize bulb glycogen. At birth, olfactory bulbs have very high levels of glycogen, with levels declining as the pups develop. Picomolar levels of noradrenaline mobilize glycogen in the bulb. Initially, β-noradrenergic receptors mediate the glycogenolysis and subsequently, the α-noradrenergic receptors in the bulb stimulate the breakdown of glycogen. Carnosine is involved in the repletion of bulb glycogen levels. The stimulation of glycogen breakdown by noradrenaline may play a role in allowing the increased activity that accompanies early olfactory stimulation.