BETA-ADRENERGIC ENHANCEMENT OF INHIBITORY SYNAPTIC ACTIVITY IN RAT CEREBELLAR STELLATE AND PURKINJE-CELLS

1. Using the tight-seal whole-cell recording technique. we studied the effects of noradrenaline (NA) on the spontaneous inhibitory synaptic currents (IPSCs) of stellate and Purkinje cells in rat cerebellar slic es. 2. In both types of cells, NA (10 muM) induced a marked increase i n the frequency of the IPSCs. This effect was observed both in the abs ence and in the presence of TTX in the saline bathing the cerebellar s lices. 3. The NA-induced increase in frequency of IPSCs and miniature IPSCs (mIPSCs) in the two cell types was mimicked by bath applications of isoprenaline (10 muM) and of the adenylyl cyclase activator forsko lin (20 muM). Neither phenylephrine nor clonidine changed the frequenc y of IPSCs in stellate or Purkinje cells. 4. ln stellate cells, the be ta-agonists and forskolin had variable effects on the amplitudes of bo th IPSCs and mIPSCs. None of these compounds altered the amplitude of mIPSCs in Purkinje cells. 5. The responses to local applications of GA BA to Purkinje cells were unchanged by bath applications of beta-adren ergic agonists or forskolin. A decrease in the response to GABA after treatment with these agents was observed in half the stellate cells ex amined. 6. We conclude that the major effect of NA on stellate and Pur kinje cells is an increase in the frequency of occurrence of spontaneo us inhibitory synaptic currents. This action is exerted through the ac tivation of beta-adrenergic receptors and is probably mediated by an i ntracellular mechanism involving cAMP. The beta-adrenergic modulation of IPSC frequency takes place at the presynaptic level and may involve a change in the process of transmitter release.