Effects of median raphe nucleus lesions on hippocampal EEG in the freely moving rat

Maru, Eiichi; Takahashi, Lorey K.; Iwahara, Shinkuro

doi:10.1016/0006-8993(79)90351-2

Cited by 108 publications

(50 citation statements)

References 22 publications

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“…We are not aware of a systematic study of hippocampal EEG after muscimol inactivation of the MR in the behaving rat. Electrolytic lesion of the MR induced persistent hippocampal theta rhythm during immobility (Maru et al, 1979;Yamamoto et al, 1979). We did not see a significant increase of hippocampal theta during walking after muscimol (0.25 mg) infuion in the MR, as compared to baseline walking.…”

Section: Limbic Circuit and General Anesthesiacontrasting

confidence: 62%

Limbic System Participates in Mediating the Effects of General Anesthetics

Leung

2005

Neuropsychopharmacol

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In a previous study, we reported that inactivation of the medial septum or the hippocampus by muscimol, a GABA A receptor agonist, potentiated the effects of a general anesthetic. In this study, we further investigated whether other structures that are connected to the septohippocampal system are involved in mediating general anesthesia. In freely behaving rats, muscimol (0.25 mg) or saline was infused intracerebrally into one of four areasFthe supramammillary area (SUM), nucleus accumbens (NAC), ventral pallidum (VP), and ventral tegmental area (VTA)Fand righting, pain, and EEG responses were recorded following either halothane or sodium pentobarbital, representing inhalational and injectable general anesthetic, respectively. The effect of halothane (2%) or pentobarbital (20 mg/kg i.p.) in abolishing the righting, pain response, or low-voltage neocortical activity was enhanced, and the initial behavioral hyperactivity (delirium) was reduced, after muscimol as compared to after saline infusion in SUM, NAC, VP, and VTA. EEGs in the hippocampus and the sensorimotor cortex following halothane or pentobarbital showed increased delta, and decreased hippocampal theta and gamma waves after muscimol infusion as compared to saline infusion in SUM, NAC, VP, and VTA. By contrast, infusion of muscimol in the median raphe increased locomotion and did not significantly alter the behavioral or EEG effects of halothane or pentobarbital. It is suggested that structures that activate the limbic cortices (MS, SUM, and VTA but not the median raphe) or mediate the output of the hippocampus (NAC and VP) normally participate in maintaining consciousness and inactivation of these structures potentiates the response to a general anesthetic.

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Section: Limbic Circuit and General Anesthesiacontrasting

confidence: 62%

Limbic System Participates in Mediating the Effects of General Anesthetics

Leung

2005

Neuropsychopharmacol

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“…These hypotheses are supported by experimental evidence demonstrating that high-frequency MR stimulation suppresses theta field oscillations (Assaf and Miller 1978;Peck and Vanderwolf 1990;Vertes 1981;Vinogradova et al 1999), whereas MR lesion elicits theta recorded in the hippocampus (Kinney et al , 1995(Kinney et al , 1996Kitchigina et al 1999;Li et al 2005;Maru et al 1979;Varga et al 2002;Vertes et al 1994). As proposed by Vertes et al (2004), MR projections serve to overactivate medial septal GABAergic cells (Alreja 1996;Liu and Alreja 1997), which in turn inhibit GABAergic septohippocampal neurons and therefore decrease the production of hippocampal theta (Leranth and Vertes 1999).…”

Section: Introductionmentioning

confidence: 83%

Median Raphe Stimulation Disrupts Hippocampal Theta Via Rapid Inhibition and State-Dependent Phase Reset of Theta-Related Neural Circuitry

Jackson

Dickson²,

Bland³

2008

Journal of Neurophysiology

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Jackson J, Dickson CT, Bland BH. Median raphe stimulation disrupts hippocampal theta via rapid inhibition and state-dependent phase reset of theta-related neural circuitry. J Neurophysiol 99: 3009 -3026, 2008. First published April 24, 2008 doi:10.1152/jn.00065.2008. Evidence has accumulated suggesting that the median raphe (MR) mediates hippocampal theta desynchronization. However, few studies have evaluated theta-related neural circuitry during MR manipulation. In urethane-anesthetized rats, we investigated the effects of MR stimulation on hippocampal field and cell activity using high-frequency (100 Hz), theta burst (TBS), and slow-frequency electrical stimulation (0.5 Hz). We demonstrated that high-frequency stimulation of the MR did not elicit deactivated patterns in the forebrain, but rather elicited lowvoltage activity in the neocortex and small-amplitude irregular activity (SIA) in the hippocampus. Both hippocampal phasic theta-ON and -OFF cells were inhibited by high-frequency MR stimulation, although MR stimulation failed to affect cells that had neither state or phase relationships with theta field activity. TBS of the MR-induced theta field activity phase locked to the stimulation. Slow-frequency stimulation elicited a state-dependent reset of theta phase through a short-latency inhibition (5 ms) in phasic theta-ON cells. Subpopulations of phasic theta-ON cells responded in either oscillatory or nonoscillatory patterns to MR pulses, depending on their intraburst interval. OFF cells exhibited a state-dependent modulation of cell firing occurring preferentially during nontheta. The magnitude of MRinduced reset varied as a function of the phase of the theta oscillation when the pulse was administered. Therefore high-frequency stimulation of the MR appears to disrupt hippocampal theta through a state-dependent, short-latency inhibition of rhythmic cell populations in the hippocampus functioning to switch theta oscillations to an activated SIA field state.

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“…Electrical stimulation of the MRN desynchronizes the hippocampal EEG in freely behaving as well as in anesthetized rodents (Assaf and Miller 1978;Kitchigina et al 1999;Macadar et al 1974;Vertes 1981;Yamamoto et al 1979), whereas MRN lesions Maru et al 1979;Vinogradova et al 1999;Yamamoto et al 1979), 5-HT depletion (Mushiake et al 1988), or selective inhibition of MRN serotonergic cells through 5-HT 1A autoreceptors ) produce continuous theta rhythm.…”

Section: Gabaergic Suppression Of 5-ht Neurons Drives Hippocampal Thementioning

confidence: 99%

GABAergic Control of the Ascending Input From the Median Raphe Nucleus to the Limbic System

Varga

Sı́k

et al. 2005

Journal of Neurophysiology

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Li, Shaomin, Viktor Varga, Attila Sik, and Bernat Kocsis. GABAergic control of the ascending input from the median raphe nucleus to the limbic system. J Neurophysiol 94: 2561-2574, 2005. First published June 8, 2005 doi:10.1152/jn.00379.2005. The median raphe nucleus (MRN) is the primary source of serotonergic afferents to the limbic system that are generally considered to suppress hippocampal theta oscillations. GABA receptors are expressed in the MRN by serotonergic and nonserotonergic cells, including GABAergic and glutamatergic neurons. This study investigated the mechanisms by which the fluctuating GABA tone in the MRN leads to induction or suppression of hippocampal theta rhythm. We found that MRN application of the GABA A agonist muscimol (0.05-1.0 mM) or GABA B agonist baclofen (0.2 mM) by reverse microdialysis had strong theta promoting effects. The GABA A antagonist bicuculline infused in low concentrations (0.1, 0.2 mM) eliminated theta rhythm. A short period of theta activity of higher than normal frequency preceded hippocampal desynchronization in 46% of rats. Bicuculline in larger concentrations (0.5, 1.0, 2.0 mM) resulted in a biphasic response of an initial short (Ͻ10 min) hippocampal desynchronization followed by stable theta rhythm that lasted as long as the infusion continued. The frequency and amplitude of theta waves were higher than in control recordings and the oscillations showed a conspicuous intermittent character. Hippocampal theta rhythm elicited by MRN administration of bicuculline could be completely (0.5 mM bicuculline) or partially (1.0 mM bicuculline) blocked by simultaneous infusion of the GABA B antagonist CGP35348. Our findings suggest that the GABAergic network may have two opposing functions in the MRN: relieving the theta-generators from serotonergic inhibition and regulating the activity of a theta-promoting circuitry by the fluctuating GABA tone. The two mechanisms may be involved in different functions.

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Effects of median raphe nucleus lesions on hippocampal EEG in the freely moving rat

Cited by 108 publications

References 22 publications

Limbic System Participates in Mediating the Effects of General Anesthetics

Limbic System Participates in Mediating the Effects of General Anesthetics

Median Raphe Stimulation Disrupts Hippocampal Theta Via Rapid Inhibition and State-Dependent Phase Reset of Theta-Related Neural Circuitry

GABAergic Control of the Ascending Input From the Median Raphe Nucleus to the Limbic System

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