Organization of the Sleep-Related Neural Systems in the Brain of the Minke Whale (Balaenoptera acutorostrata)

The current study analyzed the nuclear organization of theneural systems related to the control and regulation ofsleep and wake in the basal forebrain, diencepha lon, mid-brain, and pons of the minke whale, a mysticete cetacean.While odontocete cetaceans sleep in an unusual manner,with unihemispheric slow wave sleep (USWS) and sup-pressed REM sleep, it is unclear whether the mysticetewhales show a similar sleep pattern. Previously, wedetailed a range of features in the odontocete brain thatappear to be related to odontocete-type sleep, and herepresent our analysis of these features in the minke whalebrain. All neural elements invol ved in sleep regulation andcontrol found in bihemispheric sleeping mammals and theharbor porpoise were present in the minke whale, with nospecific nuclei being absent, and no novel nuclei beingpresent. This qualitative similarity relates to the choliner-gic, noradrenergic, serotonergic and orexinergic systems,and the GABAergic elements of these nuclei. Quantitativeanalysis revealed that the numbers of pontine cholinergic(274,242) and noradrenergic (203,686) neurons, andhypothalamic orexinergic neurons (277,604), are mark-edly higher than other large-brained bihemispheric sleep-ing mammals. Small telencephalic commissures (anterior,corpus callosum, and hippocampal), an enlarged posteriorcommissure, supernumerary pontine choline rgic and nor-adrenergic cells, and an enlarged peripheral division ofthe dorsal raphe nuclear complex of the minke wh ale, allindicate that the suite of neural characteristics thought tobe involved in the control of USWS and the suppression ofREM in the odontocete cetace ans are present in theminke whale.