Noradrenaline reduces synaptic responses in normal and tottering mouse entorhinal cortex via alpha 2 receptors

The effects of noradrenaline (NA) on synaptic responses in layer II of the entorhinal cortex (EC) were studied in normal and spontaneously epileptic mutant mice tottering using intracellular recording in a slice preparation. Neither the membrane properties of neurones nor the responses to NA differed between normal and tottering mice. NA (50 microM) hyperpolarized most (29/54) of the neurones via alpha 2 adrenergic receptors. Synaptic responses of EC neurones were complex. NA (10-100 microM) reduced all the components of the synaptic response in a concentration-dependent and reversible manner. The pharmacological properties of the inhibitory effect of NA were characterised and quantified on one component of the complex synaptic response, the fast excitatory postsynaptic potential. The effect of NA was mimicked by the alpha 2 agonist UK 14,304 and blocked by the alpha 2 antagonist yohimbine. It is concluded that NA can inhibit via an alpha 2 receptor-mediated action synaptic responses in the superficial layers of the EC.