Responses of diencephalic neurons to olfactory bulb stimulation, odor, and arousal

Abstract

Summary Neuron populations in the lateral hypothalamus, medial thalamus, and dorsal periventricular diencephalic region along the projection pathways of the medial forebrain bundle and stria medullaris-inferior thalamic peduncle, were activated by electrical stimulation of the olfactory bulb in urethane-anesthetized rats. Fifty-seven percent of these neuron populations were also activated by xylene vapors. The median response latency of hypothalamic neurons to single pulses was 10 msec (range: 4–16 msec) and that of thalamic neurons was 14 msec (range: 4–21 msec). Stimulus trains activated neuron populations at substantially longer latencies as well as at these short latencies. The most common types of response were excitation, and excitation followed by activity suppression followed by re-excitation. Responses were usually recorded ipsilaterally to the stimulation site, but were also obtained contralaterally. They were blocked by transection of the lateral olfactory tract. The neuronal responses to olfactory bulb stimulation and xylene, even very short latency responses, were strongly modified in relation to arousal level, as monitored by the cortical EEG.