Skip to main content

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

  • Article
  • Published:

Mesopontine median raphe regulates hippocampal ripple oscillation and memory consolidation

Nature Neuroscience volume 18, pages 728–735 (2015)Cite this article

Subjects

This article has been updated

Abstract

Sharp wave–associated field oscillations (∼200 Hz) of the hippocampus, referred to as ripples, are believed to be important for consolidation of explicit memory. Little is known about how ripples are regulated by other brain regions. We found that the median raphe region (MnR) is important for regulating hippocampal ripple activity and memory consolidation. We performed in vivo simultaneous recording in the MnR and hippocampus of mice and found that, when a group of MnR neurons was active, ripples were absent. Consistently, optogenetic stimulation of MnR neurons suppressed ripple activity and inhibition of these neurons increased ripple activity. Notably, using a fear conditioning procedure, we found that photostimulation of MnR neurons interfered with memory consolidation. Our results demonstrate a critical role of the MnR in regulating ripples and memory consolidation.

This is a preview of subscription content, access via your institution

Access options

Buy this article

  • Purchase on Springer Link
  • Instant access to full article PDF
Buy now

Prices may be subject to local taxes which are calculated during checkout

Figure 1: MnR neurons display hippocampal ripple correlated activity.
Figure 2: Ripple event frequency in relation to type I neuron firing-frequency.
Figure 3: Ripple event frequency in relation to type I neuron firing synchrony.
Figure 4: Up- and downregulation of hippocampal ripple activity by the MnR.
Figure 5: Subtypes of MnR neurons in regulation of hippocampal ripple activity.
Figure 6: Optical tagging of the MnR serotonergic and GABAergic neurons.
Figure 7: Impairment of fear memory consolidation by MnR photostimulation.

Similar content being viewed by others

Change history

  • 28 April 2015

    In the HTML version of this article initially published, some figures contained lettering errors. The center panel of Figure 1c was entitled Type 1 instead of Type I. The bottom row of Figure 2a was labeled Typel l instead of Type I. The x axes of Figure 4e and Figure 4f referred to photo-inhibition instead of photoinhibition. And the rows of the key in Figure 5e were misaligned with the corresponding diagram. The errors have been corrected in the HTML version of the article.

References

  1. Squire, L.R. Memory and the hippocampus: a synthesis from findings with rats, monkeys, and humans. Psychol. Rev. 99, 195–231 (1992).

    CAS  PubMed  Google Scholar 

  2. Eichenbaum, H. A cortical-hippocampal system for declarative memory. Nat. Rev. Neurosci. 1, 41–50 (2000).

    Article  CAS  PubMed  Google Scholar 

  3. Buzsáki, G. Two-stage model of memory trace formation: A role for 'noisy' brain states. Neuroscience 31, 551–570 (1989).

    Article  PubMed  Google Scholar 

  4. Ylinen, A. et al. Sharp wave-associated high-frequency oscillation (200 Hz) in the intact hippocampus: network and intracellular mechanisms. J. Neurosci. 15, 30–46 (1995).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  5. Stark, E. et al. Pyramidal cell–interneuron interactions underlie hippocampal ripple oscillations. Neuron 83, 467–480 (2014).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  6. Girardeau, G. & Zugaro, M. Hippocampal ripples and memory consolidation. Curr. Opin. Neurobiol. 21, 452–459 (2011).

    Article  CAS  PubMed  Google Scholar 

  7. Wilson, M.A. & McNaughton, B.L. Reactivation of hippocampal ensemble memories during sleep. Science 265, 676–679 (1994).

    Article  CAS  PubMed  Google Scholar 

  8. Pavlides, C. & Winson, J. Influences of hippocampal place cell firing in the awake state on the activity of these cells during subsequent sleep episodes. J. Neurosci. 9, 2907–2918 (1989).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  9. Nadasdy, Z., Hirase, H., Czurko, A., Csicsvari, J. & Buzsaki, G. Replay and time compression of recurring spike sequences in the hippocampus. J. Neurosci. 19, 9497–9507 (1999).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  10. Jadhav, S.P., Kemere, C., German, P.W. & Frank, L.M. Awake hippocampal sharp-wave ripples support spatial memory. Science 336, 1454–1458 (2012).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  11. Ego-Stengel, V. & Wilson, M.A. Disruption of ripple-associated hippocampal activity during rest impairs spatial learning in the rat. Hippocampus 20, 1–10 (2010).

    PubMed  PubMed Central  Google Scholar 

  12. Girardeau, G., Benchenane, K., Wiener, S.I., Buzsáki, G. & Zugaro, M.B. Selective suppression of hippocampal ripples impairs spatial memory. Nat. Neurosci. 12, 1222–1223 (2009).

    Article  CAS  PubMed  Google Scholar 

  13. Buzsáki, G. Hippocampal sharp waves: their origin and significance. Brain Res. 398, 242–252 (1986).

    Article  PubMed  Google Scholar 

  14. Buzsáki, G., Leung, L.W. & Vanderwolf, C.H. Cellular bases of hippocampal EEG in the behaving rat. Brain Res. 287, 139–171 (1983).

    Article  PubMed  Google Scholar 

  15. Logothetis, N.K. et al. Hippocampal-cortical interaction during periods of subcortical silence. Nature 491, 547–553 (2012).

    Article  CAS  PubMed  Google Scholar 

  16. Ikemoto, S. Brain reward circuitry beyond the mesolimbic dopamine system: A neurobiological theory. Neurosci. Biobehav. Rev. 35, 129–150 (2010).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  17. Azmitia, E.C. & Segal, M. An autoradiographic analysis of the different ascending projections of the dorsal and median raphe nuclei in the rat. J. Comp. Neurol. 179, 641–667 (1978).

    Article  CAS  PubMed  Google Scholar 

  18. Vertes, R.P., Fortin, W.J. & Crane, A.M. Projections of the median raphe nucleus in the rat. J. Comp. Neurol. 407, 555–582 (1999).

    Article  CAS  PubMed  Google Scholar 

  19. Varga, V. et al. Fast synaptic subcortical control of hippocampal circuits. Science 326, 449–453 (2009).

    Article  CAS  PubMed  Google Scholar 

  20. Acsády, L., Arabadzisz, D., Katona, I. & Freund, T.F. Topographic distribution of dorsal and median raphe neurons with hippocampal, septal and dual projection. Acta Biol. Hung. 47, 9–19 (1996).

    PubMed  Google Scholar 

  21. Vertes, R.P. & Kocsis, B. Brainstem-diencephalo-septohippocampal systems controlling the theta rhythm of the hippocampus. Neuroscience 81, 893–926 (1997).

    Article  CAS  PubMed  Google Scholar 

  22. Vertes, R.P. Hippocampal theta rhythm: a tag for short-term memory. Hippocampus 15, 923–935 (2005).

    Article  CAS  PubMed  Google Scholar 

  23. Varga, V., Sik, A., Freund, T.F. & Kocsis, B. GABAB receptors in the median raphe nucleus: distribution and role in the serotonergic control of hippocampal activity. Neuroscience 109, 119–132 (2002).

    Article  CAS  PubMed  Google Scholar 

  24. Jackson, J., Bland, B.H. & Antle, M.C. Nonserotonergic projection neurons in the midbrain raphe nuclei contain the vesicular glutamate transporter VGLUT3. Synapse 63, 31–41 (2009).

    Article  CAS  PubMed  Google Scholar 

  25. Köhler, C. & Steinbusch, H. Identification of serotonin and non-serotonin-containing neurons of the mid-brain raphe projecting to the entorhinal area and the hippocampal formation. A combined immunohistochemical and fluorescent retrograde tracing study in the rat brain. Neuroscience 7, 951–975 (1982).

    Article  PubMed  Google Scholar 

  26. Scott, M.M. et al. A genetic approach to access serotonin neurons for in vivo and in vitro studies. Proc. Natl. Acad. Sci. USA 102, 16472–16477 (2005).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  27. Vong, L. et al. Leptin action on GABAergic neurons prevents obesity and reduces inhibitory tone to POMC neurons. Neuron 71, 142–154 (2011).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  28. Girardeau, G., Benchenane, K., Wiener, S.I., Buzsaki, G. & Zugaro, M.B. Selective suppression of hippocampal ripples impairs spatial memory. Nat. Neurosci. 12, 1222–1223 (2009).

    Article  CAS  PubMed  Google Scholar 

  29. Phillips, R.G. & Ledoux, J.E. Differential contribution of amygdala and hippocampus to cued and contextual fear conditioning. Behav. Neurosci. 106, 274–285 (1992).

    Article  CAS  PubMed  Google Scholar 

  30. Kim, J.J. & Fanselow, M.S. Modality-specific retrograde-amnesia of fear. Science 256, 675–677 (1992).

    Article  CAS  PubMed  Google Scholar 

  31. Freund, T.F., Gulyás, A.I., Acsády, L., Görcs, T. & Tóth, K. Serotonergic control of the hippocampus via local inhibitory interneurons. Proc. Natl. Acad. Sci. USA 87, 8501–8505 (1990).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  32. Gras, C. et al. A third vesicular glutamate transporter expressed by cholinergic and serotoninergic neurons. J. Neurosci. 22, 5442–5451 (2002).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  33. Somogyi, J. et al. GABAergic basket cells expressing cholecystokinin contain vesicular glutamate transporter type 3 (VGLUT3) in their synaptic terminals in hippocampus and isocortex of the rat. Eur. J. Neurosci. 19, 552–569 (2004).

    Article  PubMed  Google Scholar 

  34. Szőnyi, A. et al. The ascending median raphe projections are mainly glutamatergic in the mouse forebrain. Brain Struct. Funct. published online, 10.1007/s00429-014-0935-1 (9 November 2014).

  35. Maviel, T., Durkin, T.P., Menzaghi, F. & Bontempi, B. Sites of neocortical reorganization critical for remote spatial memory. Science 305, 96–99 (2004).

    Article  CAS  PubMed  Google Scholar 

  36. Quinn, J.J., Ma, Q.D., Tinsley, M.R., Koch, C. & Fanselow, M.S. Inverse temporal contributions of the dorsal hippocampus and medial prefrontal cortex to the expression of long-term fear memories. Learn. Mem. 15, 368–372 (2008).

    Article  PubMed  PubMed Central  Google Scholar 

  37. Steriade, M. & Timofeev, I. Neuronal plasticity in thalamocortical networks during sleep and waking oscillations. Neuron 37, 563–576 (2003).

    Article  CAS  PubMed  Google Scholar 

  38. Vertes, R.P. Interactions among the medial prefrontal cortex, hippocampus and midline thalamus in emotional and cognitive processing in the rat. Neuroscience 142, 1–20 (2006).

    Article  CAS  PubMed  Google Scholar 

  39. Siapas, A.G. & Wilson, M.A. Coordinated interactions between hippocampal ripples and cortical spindles during slow-wave sleep. Neuron 21, 1123–1128 (1998).

    Article  CAS  PubMed  Google Scholar 

  40. Hoover, W.B. & Vertes, R.P. Anatomical analysis of afferent projections to the medial prefrontal cortex in the rat. Brain Struct. Funct. 212, 149–179 (2007).

    Article  PubMed  Google Scholar 

  41. Assaf, S.Y. & Miller, J.J. The role of a raphe serotonin system in the control of septal unit activity and hippocampal desynchronization. Neuroscience 3, 539–550 (1978).

    Article  CAS  PubMed  Google Scholar 

  42. Macadar, A.W., Chalupa, L.M. & Lindsley, D.B. Differentiation of brain stem loci which affect hippocampal and neocortical electrical activity. Exp. Neurol. 43, 499–514 (1974).

    Article  CAS  PubMed  Google Scholar 

  43. Maru, E., Takahashi, L.K. & Iwahara, S. Effects of median raphe nucleus lesions on hippocampal EEG in the freely moving rat. Brain Res. 163, 223–234 (1979).

    Article  CAS  PubMed  Google Scholar 

  44. Yamamoto, T., Watanabe, S., Oishi, R. & Ueki, S. Effects of midbrain raphe stimulation and lesion on EEG activity in rats. Brain Res. Bull. 4, 491–495 (1979).

    Article  CAS  PubMed  Google Scholar 

  45. Vertes, R.P. An analysis of ascending brain stem systems involved in hippocampal synchronization and desynchronization. J. Neurophysiol. 46, 1140–1159 (1981).

    Article  CAS  PubMed  Google Scholar 

  46. Vertes, R.P. Brain stem generation of the hippocampal EEG. Prog. Neurobiol. 19, 159–186 (1982).

    Article  CAS  PubMed  Google Scholar 

  47. Kinney, G.G., Kocsis, B. & Vertes, R.P. Injections of excitatory amino acid antagonists into the median raphe nucleus produce hippocampal theta rhythm in the urethane-anesthetized rat. Brain Res. 654, 96–104 (1994).

    Article  CAS  PubMed  Google Scholar 

  48. Kinney, G.G., Kocsis, B. & Vertes, R.P. Injections of muscimol into the median raphe nucleus produce hippocampal theta rhythm in the urethane anesthetized rat. Psychopharmacology (Berl.) 120, 244–248 (1995).

    Article  CAS  Google Scholar 

  49. Vertes, R.P., Kinney, G.G., Kocsis, B. & Fortin, W.J. Pharmacological suppression of the median raphe nucleus with serotonin1A agonists, 8-OH-DPAT and buspirone, produces hippocampal theta rhythm in the rat. Neuroscience 60, 441–451 (1994).

    Article  CAS  PubMed  Google Scholar 

  50. Kinney, G.G., Kocsis, B. & Vertes, R.P. Medial septal unit firing characteristics following injections of 8-OH-DPAT into the median raphe nucleus. Brain Res. 708, 116–122 (1996).

    Article  CAS  PubMed  Google Scholar 

  51. Zhao, S. et al. Cell type–specific channelrhodopsin-2 transgenic mice for optogenetic dissection of neural circuitry function. Nat. Methods 8, 745–752 (2011).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  52. Anagnostaras, S.G. et al. Automated assessment of Pavlovian conditioned freezing and shock reactivity in mice using the video freeze system. Front. Behav. Neurosci. 4 (2010).

  53. Mason, P. Physiological identification of pontomedullary serotonergic neurons in the rat. J. Neurophysiol. 77, 1087–1098 (1997).

    Article  CAS  PubMed  Google Scholar 

  54. Hajós, M. et al. Neurochemical identification of stereotypic burst-firing neurons in the rat dorsal raphe nucleus using juxtacellular labelling methods. Eur. J. Neurosci. 25, 119–126 (2007).

    Article  PubMed  Google Scholar 

Download references

Acknowledgements

We thank the National Institute on Drug Abuse (NIDA) Optogenetics and Transgenetic Technology Core for producing AAVs, E. Deneris (Case Western Reserve University) for providing the ePet-Cre mouse line, R. Cachope, J. Cheer, C. Mejias-Aponte, M. Moralas, A. Kesner, A. Ilango, C. Yang, D. Nguyen and M. Vatsan for technical assistance, and S.-C. Lin, Y. Shaham, G. Schoenbaum and A. Saul for reading and critical discussions. This research was supported by the Intramural Research Program of NIDA and the grant MOST 103-2911-I-038-501 from the Ministry of Science and Technology, Taiwan.

Author information

Authors and Affiliations

  1. Intramural Research Program, National Institute on Drug Abuse, National Institutes of Health, Baltimore, Maryland, USA

    Dong V Wang, Hau-Jie Yau, Carl J Broker, Jen-Hui Tsou, Antonello Bonci & Satoshi Ikemoto

Authors
  1. Dong V Wang
    View author publications

    You can also search for this author in PubMed Google Scholar

  2. Hau-Jie Yau
    View author publications

    You can also search for this author in PubMed Google Scholar

  3. Carl J Broker
    View author publications

    You can also search for this author in PubMed Google Scholar

  4. Jen-Hui Tsou
    View author publications

    You can also search for this author in PubMed Google Scholar

  5. Antonello Bonci
    View author publications

    You can also search for this author in PubMed Google Scholar

  6. Satoshi Ikemoto
    View author publications

    You can also search for this author in PubMed Google Scholar

Contributions

D.V.W., H.-J.Y. and S.I. designed the experiments. D.V.W., H.-J.Y., C.J.B. and J.-H.T. performed the experiments. D.V.W. analyzed the data with help from H.-J.Y., C.J.B. and J.-H.T. D.V.W., H.-J.Y., A.B. and S.I. contributed to interpretation of the data. D.V.W. and S.I. wrote the paper.

Corresponding author

Correspondence to Satoshi Ikemoto.

Ethics declarations

Competing interests

The authors declare no competing financial interests.

Integrated supplementary information

Supplementary Figure 1 Miniature microdrive, spike sorting and sleep stage detection.

a, A movable recording probe with 8-tetrodes (32-channels). It weighs ∼1g. b, A mouse implanted with 8 tetrodes in the MnR and 4 tetrodes in the hippocampal CA1. c, An example of four well-isolated units and representative spike-waveforms recorded from one tetrode. Each dot represents one spike waveform. d, An example of the CA1 local field potential (LFP) recorded during active-awake and immobility/sleep states. All the data analyzed for MnR activity with respect to ripples during immobility were collected when mice were in the cardboard box filled with cotton fiber material (NestletsTM), i.e., “bed”, where they exclusively slept. Typically as soon as mice became immobile in their beds, a series of ripple activity and sleep-like LFPs were detected in the CA1. Outside of the bed, the mice walked around, drank water, ate food, and displayed little immobility, accompanied by no sleep. e, Power spectrogram of the CA1 LFP (as shown in d). Notice strong power levels in the theta band (6–10 Hz) during awake and in the delta band (1–4 Hz) during immobility/sleep. Theta/delta ratio was calculated and smoothed with a Gaussian filter in Matlab (top panel).

Supplementary Figure 2 Identification of MnR putative serotoninergic neurons and classification of non-serotoninergic type I and II neurons.

a,b, Electrodes placements in the hippocampal CA1 (a) and the MnR (b) from the dual-site recording mice (n = 6). c, Representative spike-trains of two putative serotoninergic neurons. Note that neuron 1 displayed tonic activity only, while neuron 2 displayed both tonic and high-frequency firing (*). d, Inter-spike interval (ISI) histograms and representative spike waveforms of the neurons shown in c (5000 spikes overlapped; spike width, 1 ms). Arrows indicate the peaks of ISI that were used for neuron identification as shown in f. Seventy-nine percent (23/29) of the classified putative serotonin neurons displayed tonic activity only, while the other 21% displayed both tonic and high-frequency activity. e, Firing rate histograms of the two neurons shown in c,d upon i.p. injection of the serotonin 1A receptor agonist 8-OH-DPAT (0.2 mg/kg; arrows indicate the injection time point, and the mice were freely moving before and after injection). Effects of 8-OH-DPAT were examined on 12 putative serotonergic neurons of freely-moving mice, since serotonergic neurons are known to be inhibited by the autoreceptor agonist. The most of them (11/12) were inhibited for at least 10 min: either completely (4/12) or partially (7/12), strengthening the validity of the ISI procedure in determining serotonergic neurons. f, Log-log plot of the mean firing frequency vs. latency of ISI peak for all the MnR neurons recorded during immobility. g, Mean firing-rate changes of individual type I and type II neurons prior to ripple events (left panel). A histogram showing a distribution pattern of the type I and type II neurons based on firing-rate changes prior to ripple (right panel). Firing-rate change was calculated 1 s prior to ripple compared against a 2-s baseline activity (between 2 and 4 s prior to ripple). A –20% or lower in frequency change was classified as type I; and the rest of the ripple-correlated neurons were classified as type II.

Supplementary Figure 3 Ripple correlated MnR neural activity during immobility and feeding.

a, Firing rates of the 3 types of MnR neurons plotted in relation to the ripple peak during immobile state, most likely asleep (top panels) and during feeding rodent chow or rice (bottom panels). b, Firing rates of individual putative serotonin (5-HT; n = 12), type I (n = 17) and type II (n = 19) neurons during immobility (top panels) and feeding (bottom panels). Neurons were recorded in consecutive sessions and are arranged in the same order for the top and bottom panels. Colour bars represent z-scored firing-frequency.

Supplementary Figure 4 MnR type I neuron firing properties and its relation to ripple events.

a, Histograms (bin = 10 ms) showing probability of inter-spike interval (ISI) of 3 representative type I neurons. ISIs varied extensively among type I neurons. Inserts: histograms with a 1-ms bin. b, Distribution of type I neurons based on their ISI ranges. c, Distribution of type I neurons based on their mean instant firing rates. d,e, Mean auto-correlations (solid line; s.e.m.: dashed line) of the MnR type I neurons (d) and ripple events (e). The inserts of panels d,e, show respective analyses in a finer time resolution.

Supplementary Figure 5 Coordinated activity between MnR 5-HT and type I neurons during immobility.

a,b, Rate histograms (a) and cross-correlation histogram (b) of two simultaneously recorded MnR neurons. Representative tetrode-recorded spike waveforms of the 2 neurons are shown in a (inserted panels, 1000 spikes overlapped; spike width, 1 ms). c, Z-scored cross-correlations for all the simultaneously recorded 5-HT and type I neuron pairs (n = 35 pairs). Type I neurons were used as the reference for cross-correlation analyses in b and c.

Supplementary Figure 6 Ripple cluster termination coincides with high-rate and synchronous firing of MnR type I neurons.

a, Representative hippocampal CA1 LFP and the filtered ripple activity. Ripples tended to occur in clusters (# 1–5), which were defined as 3 or more consecutive ripple events occurring above 1 Hz. b, During immobility, 58.1 ± 1.7% (mean ± s.e.m.; n = 19) of ripple events occurred in clusters. c, e, Mean firing rates (solid line; s.e.m.: dashed line) of type I neurons in relation to the onset (blue lines) and offset (red lines) of ripple clusters during the high-, mid-, low-rate (c), and high-, mid- low-synchrony (e) states. For definition of the above six categories of firing states, see Online Methods. Inserts: mean firing rates and s.e.m. of type I neurons shown in a finer time resolution. d, f, Mean peak frequencies and s.e.m. of the type I neurons immediately after the onset and offset of ripple clusters. Peak frequency was defined as the maximum frequency within 100 ms (bin = 10 ms) after the onset or offset of ripple clusters. P values were derived with Wilcoxon signed rank tests (n = 32 for d and n = 26 for f; Type I neurons with mean frequency above 1 Hz were used for analyses). n.s., P > 0.05; *P < 0.05; ***P ≤ 0.001.

Supplementary Figure 7 Characterization of hippocampal CA1 neurons upon MnR photostimulation.

a, A plot of the mean firing frequency vs. the action potential (AP) width for all the recorded CA1 neurons. Blue and red dots represent individual inhibited and excited CA1 neurons, respectively, upon MnR photostimulation. b, Response latencies of the inhibited (top) and excited (bottom) CA1 neurons upon MnR photostimulation. Response latency was defined as the latency of the first bin from at least 3 consecutive bins (peri-event histogram bin = 2 ms) that exceed the z-score of 1.96.

Supplementary Figure 8 Optical fiber placements for the mice used in the fear conditioning experiment.

The tips of optic fibers are shown by black rectangles, and just below, red colour-filled rectangles indicate zones (0.5 mm) most powerfully affected by photostimulation. ChR2-group mice (n = 11) and EYFP-group control mice (n = 10). One of the control mice was found at the level of bregma –3.88 mm, and its placement is not shown here.

Supplementary Figure 9 Addressing issues involving MnR photostimulation.

a, Mean ripple-event frequencies (error bars: s.e.m.) upon MnR photostimulation delivered on two different interval schedules. We conducted additional experiments to verify that the MnR photostimulation on a fixed-interval schedule of 2 s (FI2; 2-pulse train per 2 s) suppresses ripples activity. Using a group of 5 mice, we compared two schedules of photostimulation: One was the same scheduled described in Fig. 4 a–d, and the mice received photostimulation on a variable interval schedule of 10 s (VI10; ranged between 5 and 15 s). The other was essentially the same as the one used for disrupting ripple after fear conditioning; the mice received photostimulation on a FI2 for 3–4 hours. Compared to photostimulation on the VI10, FI2 photostimulation suppressed ripple activity with a shorter duration, followed by rebound activation (1–2 sec). These results confirm that MnR photostimulation on a FI2 readily suppress ripple activity with the caveat that this frequent suppression schedule triggers a compensatory process. b, Percentages of time spent on slow-wave sleep (SWS) and rapid-eye movement sleep (REM) with/without photostimulation. Sleep stages were determined by hippocampal LFPs, and the amounts of SWS and REM were compared between the session with the FI2 photostimulation and a session with no photostimulation. The photostimulation condition did not alter the amounts of SWS sleep, but slightly increased REM (unpaired t-tests; n = 5). c, Representative coronal sections of glial fibrillary acidic protein (GFAP) staining. GFAP expressions were compared between mice (n = 3) that did not receive photostimulation and mice (n = 3) that received MnR photostimulation (2 pulses with 3-ms pulse duration) on FI2 during immobility over the course of 4 hours (the same procedure as the fear conditioning mice as shown in Fig. 7a). Scale bars, 0.2 mm. d, Quantification of the GFAP fluorescence intensity. Fluorescence intensities were measured in areas below optical fiber placements as shown in the squares, and did not differ between the conditions with/without photostimulation (2group x 3section ANOVA: F1, 4 = 0.70, P = 0.45; n = 3 per group).

Supplementary Figure 10 SWS/ REM cyclic sleeping pattern during MnR photostimulation session.

a, Representative power spectrogram of the CA1 LFP recorded during a 20-min sleep session in a mouse that received no photostimulation. Notice strong power levels in the theta band (6–10 Hz) during REM sleep and in the delta band (1–4 Hz) during SWS. Theta / delta ratio was calculated and smoothed with a Gaussian filter in Matlab (top panel). b, Power spectrogram of the CA1 LFP recorded from the same mouse during MnR photostimulation session (2-pulse train per 2 s; pulse width, 3 ms; 16 mW).

Supplementary information

Rights and permissions

Reprints and permissions

About this article

Check for updates. Verify currency and authenticity via CrossMark

Cite this article

Wang, D., Yau, HJ., Broker, C. et al. Mesopontine median raphe regulates hippocampal ripple oscillation and memory consolidation. Nat Neurosci 18, 728–735 (2015). https://doi.org/10.1038/nn.3998

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI: https://doi.org/10.1038/nn.3998

This article is cited by

Search

Advanced search

Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing