Simultaneous chemical stimulation of the hypothalamus and dorsal hippocampus in the waking cat

Abstract

The spontaneous behaviour of waking cats was hardly, if at all, influenced by the injection of carbachol or noradrenaline into the dorsal hippocampus. On some occasions in mild sedation and shift of the EEG pattern towards synchronization were observed. Carbachol injection into the anterior hypothalamus evoked a characteristic range reaction with complete EEG arousal and theta-wave dominance in the hippocampal lead. Previous application of either carbachol or noradrenaline, but not nicotine, in the dorsal hippocampus inhibited or fully abolished the carbachol-induced hypothalamic emotional-behavioural reaction. The inhibitory effect of intrahippocampal carbachol on the hypothalamic rage reaction was easily counteracted by previous topical, intra-hippocampal application of a few μg of atropine. Intrahippocampal injection of dopamine or of the alpha-receptor stimulatory drug phenylephrine did not inhibit the carbachol-induced hypothalamic emotional reaction, while the beta-receptor stimulatory agent isoprenaline did. It is concluded that the dorsal hippocampus of the cat contains both a cholinergic and adrenergic receptor system. The cholinergic system presumably consists of muscarinic receptors and the adrenergic of beta-type adrenergic receptors.