Adrenergic modulation of a cholinergic emotional reaction in the cat's thalamus.

Direct carbachol stimulation of the intralaminar nuclei of the thalamus evokes an affective defense reaction in the cat. Pretreatment of the region with noradrenaline inhibited the reaction in a dose-related manner. Phenylephrine was ineffective in this respect while isoprenaline exhibited roughly the same inhibitory action as noradrenaline. The alpha-receptor blocking dihydroergotamine left the inhibitory effect of noradrenaline unaffected while the beta-receptor blocking propranolol abolished it. These findings suggest that the inhibitory effect of noradrenaline on the carbachol-induced thalamic emotional reaction is caused by its influence on beta-type adrenergic receptors. Since a similar adrenergic-cholinergic interaction was previously demonstrated also for the hypothalamus and red nucleus, it can be concluded that adrenergic modulation of cholinergic reactions in the central nervous sytem seems to be a principle of more general validity than has been assumed thus far.