Cortico-pontine theta carrier frequency phase shift across sleep/wake states following monoaminergic lesion in rat

University of Belgrade, Department of Neurobiology, Institute for Biological Research-Sinisa Stankovic, 11060, Belgrade, Serbia Abstract. Thisstudywasaimedtoexplorethesleep/wakestatesrelatedcortico-pontinethetacarrierfrequency phase shiftfollowingasystemicallyinducedchemicalaxotomyofthemonoaminergicafferentswithinabrainofthefreelymovingrats.Ourexperimentswereperformedin14adult,male Sprague Dawley rats, chronically implanted for sleep recording. We recorded sleep during baseline condition, following sham injection (saline i.p. 1 ml/kg), and every week for 5 weeks fol-lowing injection of the systemic neurotoxins (DSP-4 or PCA; 1 ml/kg, i.p.) for chemical axotomy of the locus coeruleus (LC) and dorsal raphe (DR) axon terminals. Aftersleep/wakestatesiden-tification, FFT analysis was performed on 5s epochs. Theta carrier frequency phase shift (∆Φ)was calculated for each epoch by averaging theta Fourier component phase shifts, and the ∆Φvalues were plotted for each rat in control condition and 28 days following the monoaminergic lesions, as a time for permanently established DR or LC chemical axotomy. Calculated group averages have shown that ∆Φ increased between pons and cortex significantlyinallsleep/wakestates (Wake, NREM and REM) following the monoaminergic lesions, with respect to controls. Monoaminergic lesions established the pontine leading role in the brain theta oscillations during all sleep/wake states.Key words: Monoaminergic lesion — Sleep/wake states — Theta carrier frequency phase shift— Locus coeruleus — Nucleus dorsalis raphe IntroductionNeuronal network oscillations in the brain functions, and neuronal synchrony within the same network or between interrelated networks, have been extensively investigated on different oscillation bands (Singer 1993). However, theexact mechanisms of brain oscillations and synchroniza-tion of neuronal activity within single or between differentbrain structures are not well understood (Penttonen and Buzsaki 2003). The hippocampal theta rhythm is the most studiedrhythm in rat. Theta oscillations occur across many brain