Hippocampal activity during transient respiratory events in the freely behaving cat

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Poe GR, Kristensen MP, Rector DM, and Harper RM (1996) Hippocampal activity during transient respiratory events in the freely behaving cat. Neuroscience 72:1 39–48.

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Abstract: We measured dorsal hippocampal activity accompanying sighs and apnea using reflectance imaging and electrophysiologic measures in freely behaving cats. Reflected 660-nm light from a 1-mm2 area of CA1 was captured during sighs and apnea at 25 Hz through a coherent image conduit coupled to a charge coupled device camera. Sighs and apnea frequently coincided with state transitions. Thus, state transitions without apnea or sighs were separately assessed to control for state-related activity changes. All dorsal hippocampal sites showed discrete regions of activation and inactivation during transient respiratory events. Imaged hippocampal activity increased 1-3 s before the enhanced inspiratory effort associated with sighs, and before resumption of breathing after apnea. State transitions lacking sighs and apnea did not elicit analogous optical activity patterns. The suprasylvian cortex, a control for site, showed no significant overall reflectance changes during phasic respiratory events, and no discrete regions of activation or inactivation. Spectral estimates of hippocampal electroencephalographic activity from 0-12 Hz showed significantly increased power at 3-4 Hz rhythmical slow activity before sighs and apnea, and increased 5-6 Hz rhythmical slow activity power during apnea, before resumption of breathing. Imaged activity and broadband hippocampal electroencephalogram power decreased during sighs. We propose that increased hippocampal activity before sigh onset and apnea termination indicates a role for the hippocampus in initiating inspiratory effort during transient respiratory events.

Keywords: sleep state, rhythmical slow activity, respiration, imaging, reflectance

Context

  • Animal study in cat. Field potential and intrinsic imaging signals from CA1 hippocampus were analyzed with reference to spontaneous respiratory ‘events,’ i.e., sighs and apneic periods. Another brain region did not show changes during respiratory events. Power in the 3-4 Hz band increased before sighs or apnea. The authors reviewed this topic in Harper et al. As the authors discuss, the intrinsic optical signal is subject to influence from intracranial pressure and blood composition, so the changes seen after periods of apnea may reflect the influence of the apneic period; neural changes preceding respiratory events are free of such confounds.

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