Electro-oscillographic correlation between dorsal raphe nucleus, neocortex and hippocampus during wakefulness before and after serotoninergic inactivation

Abstract

Theta rhythm in many brain structures characterizes wakefulness and desynchronized sleep in most subprimate mammalian brains. In close relation to behaviors, theta frequency and voltage undergo a fine modulation which may involve mobilization of dorsal raphe nucleus efferent pathways. In the present study we analyzed frequency modulation (through instantaneous frequency variation) of theta waves occurring in three cortical areas, in hippocampal CA1 and in the dorsal raphe nucleus of Wistar rats during normal wakefulness and after injection of the 5-HT 1a receptor agonist 8-OH-DPAT into the dorsal raphe. We demonstrated that in attentive states the variation of theta frequency among the above structures is highly congruent, whereas after 8-OH-DPAT injection, although regular signals are present, the variation is much more complex and shows no relation to behaviors. Such functional uncoupling after blockade demonstrates the influence of dorsal raphe nucleus efferent serotoninergic fibers on the organization of alertness, as evaluated by electro-oscillographic analysis. Electrical potentials from thalamic, olfactory and septal nuclei, hippocampus, amygdala, most cortical areas and many other brain structures oscillate regularly from 6 to 11 Hz as theta rhythm during wakefulness and desynchronized sleep in rats (1). Theta wave amplitude and frequency undergo fine modulation as a function of time and of the kind of behavior occurring in those states (2). Such modulation is followed by a spectrographic correlation between central structures that is higher in attentive wakefulness than in the relaxed state and narrowing of the oscillation band also occurs, disclosing its functional coupling to wakefulness (3,4).The serotoninergic raphe ascending projections are diffuse and reach almost all mammalian brain structures (5,6). The dorsal raphe

Regular theta‐firing neurons in the nucleus incertus during sustained hippocampal activation

“…Through synchronisation, theta waves allow the integration of the activity of a widespread network during hippocampal processing (Colgin & Moser, 2009). Several areas included in the theta circuitry exhibit neuronal firing or rhythmical field activity coupled with hippocampal theta oscillations, including limbic cortices (Mitchell & Ranck, 1980;Alonso & Garc ıa-Austt, 1987a,b), the septal complex (Stewart & Fox, 1990;Barrenechea et al, 1995;Brazhnik & Fox, 1997; Vinogradova Wang, 2002;Nerad & McNaughton, 2006;Hangya & Borhegyi, 2009), and hypothalamic (Kirk et al, 1996) and brainstem sites (Faris & Sainsbury, 1990;Kocsis & Vertes, 1992;Simões et al, 1996;Fonoff et al, 1999;Bassant & Poindessous-Jazat, 2001;Ma et al, 2013).…”

The Dorsal Raphe Modulates Sensory Responsiveness during Arousal in Zebrafish

“…A few studies have also demonstrated that behavioral responses to sensory cues are altered by serotonergic signaling, however these have largely relied on gross lesions or broad acting pharmacological manipulations (Tenen, 1967; Davis et al, 1980). As noted above, DR activity correlates strongly with different arousal states, moreover, suppression of activity disrupts the highly synchronized oscillations in cortex and hippocampus that occur during attentive states (Fonoff et al, 1999; Womelsdorf and Fries, 2007). Together, these findings have suggested the hypothesis that the DR contributes to changes in sensory thresholds that accompany different behavioral states (Hurley et al, 2004; Petzold et al, 2009; Hurley and Hall, 2011) however, there is little work directly linking state-dependent DR activity to sensory modulation (Hall et al, 2010).…”

C-Fos expression in epileptogenic areas of nephropathic rats undergoing star fruit poisoning

“…Theta rhythm is considered abnormal in human adults, but a moderate amount may be acceptable in the temporal lobes 18 . However, wakeful rodents have a theta rhythm (7 -9 Hz) without slow waves of large amplitude, and eventual exhibition of spindles, a characteristic pattern of relaxed wakefulness 19 . During the gavages, grouped theta waves with increased amplitude and an increasing larger number of spicules in pulse volley were demonstrated, showing multifocal epileptiform activity, which when associated with generalized tonic-clonic seizures confirms the effectiveness of this experimental model to mimic the proposed clinical status.…”