P38 Hippocampal modulation of respiratory motor output
Ajayi IE[1], Mills PC[2], Balnave R[3]
- Department of Veterinary Anatomy, University of Abuja, Main campus, Abuja, FCT Nigeria.
- The University of Queensland, School of Veterinary Sciences, Gatton campus, QLD, Australia
- Discipline of Biomedical Sciences, University of Sydney, NSW, Australia
Nuclei in the brainstem are responsible for generating the motor rhythm of respiration and, consequently, maintaining homoeostasis. Emotional responses to actual or potential environmental challenges induce significant changes in respiratory motor rhythm through descending synaptic interactions of the limbic areas with brainstem nuclei. Such descending interactions also maintain homeostasis and shape appropriate responses for the emotion. However, the anatomic pathways and synaptic mechanisms involved are unclear. Discrete neurone populations have been identified in the ventral hippocampus of anaesthetised rats that can modulate eupneic breathing, including the motor expression augmented breaths, which periodically interrupts breathing rhythm. This supports the role of the ventral hippocampus in modulating the emotional expression of anxiety (1). Augmented breaths, also known as sighs, mainly appear as a secondary breath superimposed on a basic breath and the phenomena has strong correlations with the emotional expression of anxiety in humans and animals (2), but without a clear understanding of the underlying anatomic and physiologic substrates. Related neuroanatomical studies have identified the medial nucleus of the amygdala as a potential relay of the ventral hippocampus to bulbar rhythm generators (3) since direct projections do not exist. Thus the need for a clearer description of these hippocampal-bulbar connections forms the basis of investigations in the current study. In searching for alternate descending pathways using classical tract-tracing techniques considering the complexity of anxiety as a behaviour, the potential descending pathways were identified and a possible arousal-setting role was suggested for the augmented breaths in respiratory motor control in anxiety.
- Zhang, W.N., Bast, T., Xu, Y., Feldon, J., 2014. Temporary inhibition of dorsal or ventral hippocampus by muscimol: distinct effects on measures of innate anxiety on the elevated plus maze, but similar disruption of contextual fear conditioning. Behavioural brain research 262, 47-56.
- Ajayi, I.E., Mills, P.C., 2017. Effects of the hippocampus on the motor expression of augmented breaths. Plos One 12, e0183619.
- Ajayi, I.E., McGovern, A.E., Driessen, A.K., Kerr, N.F., Mills, P.C., Mazzone, S.B., 2018. Hippocampal Modulation of Cardiorespiratory Function. Respiratory physiology & neurobiology.