Release of neurotransmitters during sleep and waking states in the fur seal. (A,B) Cortical and subcortical release of histamine (HI), norepinephrine (NE), serotonin (5HT) and acetylcholine (ACh) during bilateral slow wave sleep (BSWS) and unihemispheric slow wave sleep (USWS) in the left (L) and right (R) hemispheres in fur seals. Each point represents the mean of the percent change in neurotransmitter level relative to BSWS which is calculated separately for the probes located in the left and right cortical hemispheres and subcortical structures (Hy, hypothalamus; Th, thalamus; Nc, caudate nucleus). (C,D) Cortical and subcortical release of HI, NE, 5HT, and ACh during waking and sleep states in fur seals. Each point represents the mean of the percent change in neurotransmitter level relative to BSWS. The release of HI, NE, and 5HT were not lateralized during USWS. It is shown as average for all left and right probes. The release of ACh was lateralized during USWS. For USWS it is shown separately for the waking (open circle) and sleeping (closed circle) hemispheres. During USWS, ACh release is higher on the waking side than on the sleeping side. The release of cortical HI, NE, and 5HT as well as subcortical NE and 5HT during USWS are not lateralized and are comparable to the release of ACh on the sleeping side. The data for cortical ACh and 5HT release were collected during the prior studies (reproduced from Lyamin et al., 2016).