Recent work has shown that certain neurons have axonal GABAA receptors, whose tonic activation modifies their firing properties and neurotransmitter release capability. In addition, results obtained in interneurons of the molecular layer of the cerebellum indicate that action potential-released GABA binds back to the axon that released it, generating an autoreceptor current. In the present paper, we show that in physiological Cl-i concentration (15 mM) and at 34-36 oC, the autoreceptor current generates a large amplitude (up to 21 mV) afterdepolarization that lasts for about 150 ms, and that occasionally leads to double firing. Furthermore we show that elimination of the afterdepolarization, by either blocking GABAA receptors, or eliminating the autoreceptor currents through prolonged whole-cell recording, decreases burst firing. Ih was previously found to be prominent in interneuron axons. We show that blocking Ih leads to an increase in the amplitude of the autoreceptor current as well as of the associated afterdepolarization, suggesting a shunting effect of Ih on autoreceptor mediated afterdepolarization. Conversely, blocking Ih accentuates burst firing. The effects of autoreceptor mediated afterdepolarization on firing are prominent during a period of development when interneuron synapses are stabilized and vanish by postnatal day 17, together with the expression of the autoreceptor current. Altogether, this work reveals a new role for autoreceptors in the regulation of cell excitability and firing pattern, which may contribute to the development and stabilization of the cerebellar network.