5-MeO-DMT induces sleep-like LFP spectral signatures in the hippocampus and prefrontal cortex of awake rats

5-methoxy-N,N-dimethyltryptamine (5-MeO-DMT) is a potent classical psychedelic known to induce changes in locomotion, behaviour, and sleep in rodents. However, there is limited knowledge regarding its acute neurophysiological effects. Local field potentials (LFPs) are commonly used as a proxy for neural activity, but previous studies investigating psychedelics have been hindered by confounding effects of behavioural changes and anaesthesia, which alter these signals. To address this gap, we investigated acute LFP changes in the hippocampus (HP) and medial prefrontal cortex (mPFC) of freely behaving rats, following 5-MeO-DMT administration. 5-MeO-DMT led to an increase of delta power and a decrease of theta power in the HP LFPs, which could not be accounted for by changes in locomotion. Furthermore, we observed a dose-dependent reduction in slow (20–50 Hz) and mid (50–100 Hz) gamma power, as well as in theta phase modulation, even after controlling for the effects of speed and theta power. State map analysis of the spectral profile of waking behaviour induced by 5-MeO-DMT revealed similarities to electrophysiological states observed during slow-wave sleep (SWS) and rapid-eye-movement (REM) sleep. Our findings suggest that the psychoactive effects of classical psychedelics are associated with the integration of waking behaviours with sleep-like spectral patterns in LFPs

Developmental disruption of recurrent inhibitory feedback results in compensatory adaptation in the Renshaw cell - motor neuron circuit

Enjin A, Perry S, Hilscher MM, Nagaraja C, Larhammar M, Gezelius H, Eriksson A, Leão KE, Kullander K (2017) Developmental disruption of recurrent inhibitory feedback results in compensatory adaptation in the Renshaw cell - motor neuron circuit. J Neurosci. May 8. pii: 0949-16. doi: 10.1523/JNEUROSCI.0949-16.2017.When activating muscles, motor neurons in the spinal cord also activate Renshaw cells, which provide recurrent inhibitory feedback to the motor neurons. The tight coupling with motor neurons suggests that Renshaw cells have an integral role in movement, a role that is yet to be elucidated. Here we used the selective expression of the nicotinic cholinergic receptor alpha 2 (Chrna2) in mice to genetically target the vesicular inhibitory amino acid transporter (VIAAT) in Renshaw cells. Loss of VIAAT from Chrna2Cre expressing Renshaw cells did not impact any aspect of drug-induced fictive locomotion in the neonatal mouse, nor did it change gait, motor coordination or grip strength in adult mice of both sexes. However, motor neurons from neonatal mice lacking VIAAT in Renshaw cells received spontaneous inhibitory synaptic input with a reduced frequency, showed lower input resistance and had an increased number of proprioceptive glutamatergic and calbindin labeled putative Renshaw cell synapses on their soma and proximal dendrites. Concomitantly, Renshaw cells developed with increased excitability and a normal number of cholinergic motor neuron synapses indicating a compensatory mechanism within the recurrent inhibitory feedback circuit. Our data suggest an integral role for Renshaw cell signaling in shaping the excitability and synaptic input to motor neurons

Synchronisation through nonreciprocal connections in a hybrid hippocampus microcircuit

Synchronisation among neurons is thought to arise from the interplay between excitation and inhibition; however, the connectivity rules that contribute to synchronisation are still unknown. We studied these issues in hippocampal CA1 microcircuits using paired patch clamp recordings and real time computing. By virtually connecting a model interneuron with two pyramidal cells (PCs), we were able to test the importance of connectivity in synchronising pyramidal cell activity. Our results show that a circuit with a nonreciprocal connection between pyramidal cells and no feedback from PCs to the virtual interneuron produced the greatest level of synchronisation and mutual information between PC spiking activity. Moreover, we investigated the role of intrinsic membrane properties contributing to synchronisation where the application of a specific ion channel blocker, ZD7288 dramatically impaired PC synchronisation. Additionally, background synaptic activity, in particular arising from NMDA receptors, has a large impact on the synchrony observed in the aforementioned circuit. Our results gives new insights to the basic connection paradigms of microcircuits that lead to coordination and the formation of assemblies

Chrna2-Martinotti Cells Synchronize Layer 5 Type A Pyramidal Cells via Rebound Excitation

Martinotti cells are the most prominent distal dendrite-targeting interneurons in the cortex, but their role in controlling pyramidal cell ( PC) activity is largely unknown. Here, we show that the nicotinic acetylcholine receptor alpha 2 subunit (Chrna2) specifically marks layer 5 (L5) Martinotti cells projecting to layer 1. Furthermore, we confirm that Chrna2-expressing Martinotti cells selectively target L5 thick-tufted type A PCs but not thin-tufted type B PCs. Using optogenetic activation and inhibition, we demonstrate how Chrna2-Martinotti cells robustly reset and synchronize type A PCs via slow rhythmic burst activity and rebound excitation. Moreover, using optical feedback inhibition, in which PC spikes controlled the firing of surrounding Chrna2-Martinotti cells, we found that neighboring PC spike trains became synchronized by Martinotti cell inhibition. Together, our results show that L5 Martinotti cells participate in defined cortical circuits and can synchronize PCs in a frequency-dependent manner. These findings suggest that Martinotti cells are pivotal for coordinated PC activity, which is involved in cortical information processing and cognitive control

MCs^α2 connect to local type A PCs but not type B PCs.

<p>(A) <i>Left</i>: The reconstruction of a typical type A PC showing a thick-tufted dendrite (scale bar = 40 μm) and its response to a 500-ms-long depolarizing (100 pA) and hyperpolarizing (−60 pA) stimulus. <i>Right</i>: A representative type B PC with a thin-tufted apical dendrite (scale bar = 40 μm) and its current clamp response (as for <i>left</i>). Note the deeper AHP (following a depolarizing current pulse), the more prominent sag (during a hyperpolarizing current pulse), as well as the pronounced rebound ADP (following a hyperpolarizing current pulse) in the type A PC compared to type B PC (see arrows). (B) Type A PCs can excite postsynaptic MCs^α2 (<i>inset</i>) and generate facilitating EPSPs (<i>left</i>, <i>n</i> = 7/9 pairs, 12 repetitions from one example pair are shown) when stimulated with high frequency (70 Hz), whereas type B PCs do not trigger EPSPs in MCs^α2 (<i>right</i>, <i>n</i> = 0/9 pairs, 12 repetitions). <i>Inset</i> shows experimental setup. (C) Typical MC^α2 discharges (<i>top</i>) to a 500-ms-long (25 pA) stimulus are shown. <i>Inset</i> shows experimental setup. MC^α2 spikes cause inhibition in postsynaptic type A PCs (<i>inset</i>) displaying synaptic depression (<i>middle left</i>, <i>n</i> = 7/9 pairs), whereas type B PCs do not receive MC^α2 inhibition (<i>middle right</i>, <i>n</i> = 0/9 pairs). Grey dashed lines highlight timing of presumably individually generated IPSPs for type A PCs, whereas for type B PCs, dashed line shows the lack of response. Example IPSP responses of 12 repetitions are shown in grey, mean response in black (<i>bottom</i>).</p

Type A PCs auto-synchronize via MC^α2 inhibition.

<p>(A) Coupling one PC (black) out of two unconnected type A PCs to the light source/optical feedback inhibition system shows unsynchronized activity before and synchronized APs during optical feedback inhibition. A total of 24 PC discharges pairwise aligned to the first PC AP with optical feedback inhibition are shown (<i>n</i> = 24 cells; 12 black and 12 grey spike trains). Kernel density estimates (orange) highlight increased (peaks) and decreased (valleys) co-occurrence of APs. Note that the time points of the blue light depend on the PC APs during the optical feedback inhibition and therefore vary between PC pairs. (B) <i>Top</i>: One pair of simultaneously recorded unconnected type A PCs (black and grey) showing discharges before and during the optical feedback inhibition. <i>Bottom</i>: Pairwise mutual information index versus time lag from recordings in (A) showing low mutual information for unconnected PCs and high mutual information around 0-ms lag for PCs coupled by optical feedback inhibition (<i>n</i> = 12 dual recordings, 24 cells). <i>Inset</i>: Amount of overlap in Venn diagrams (black and grey circles) shows low mutual information for unconnected (<i>left</i>) and significantly higher mutual information for coupled (<i>right</i>) PCs (<i>p</i> < 0.05, two-tailed Student’s paired <i>t</i> test). Values are shown in <a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.2001392#pbio.2001392.s017" target="_blank">S9 Data</a>.</p

MC–PC inhibition is frequency dependent.

<p>(A) Expression of AAV-DIO-ChR2-EYFP (green) in MCs^α2 (red) in a primary auditory cortical slice used for optogenetic stimulation, with inset on L5 showing overlap of membrane expression in yellow (scale bars 50 μm). (B) Optogenetic activation (3-ms light pulses, 488 nm) of a group of MCs^α2 induced IPSPs in type A PCs (<i>left</i>) but not type B PCs (<i>right</i>) (<i>n</i> = 12 cells, single examples in grey, mean in black). (C) Example traces show MCs^α2 responses to blue light stimulation at various frequencies (3-ms blue light pulses at 2, 5, 15, 25, 40, and 70 Hz) and the corresponding IPSPs in a nearby type A PC (<i>n</i> = 12 cells, single examples in grey, mean in black). At higher frequencies (≥15Hz), the MC^α2–PC synapse showed depression. Note that MCs^α2 could not follow 70-Hz light stimulation for prolonged time. (D) <i>Top</i>: Continuous light stimulation of MCs^α2 (500 ms) generated large type A IPSP amplitudes (<i>middle</i>; <i>n</i> = 12 cells, single examples in grey, mean in black) similar in magnitude to IPSPs generated by high-frequency stimulation at 70 Hz. <i>Bottom</i>: Spike-frequency adaptation of MCs^α2 is shown as a function of time (see also <a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.2001392#pbio.2001392.s003" target="_blank">S3B–S3D Fig</a>). (E) Mean IPSP amplitudes in type A PCs following stimulation of MCs^α2 at different frequencies (from (C) and (D); 2 Hz: −1.57 ± 0.13 mV, 5 Hz: −1.70 ± 0.08 mV, 15 Hz: −3.05 ± 0.12 mV, 25 Hz: −3.20 ± 0.13 mV, 40 Hz: −3.76 ± 0.10 mV, 70 Hz: −4.37 ± 0.10 mV, 500 ms: −4.41 ± 0.07 mV; 2, 5 Hz versus 15, 25 Hz <i>p</i> < 0.0001; 15, 25 Hz versus 40 Hz <i>p</i> < 0.0001; 40 Hz versus 70 Hz, 500 ms <i>p</i> < 0.001; mean ± SEM, ANOVA, <i>n</i> = 12 cells, <a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.2001392#pbio.2001392.s011" target="_blank">S3 Data</a>).</p

L5 Chrna2-Cre/<i>R26</i>^<i>tom</i> cells show Martinotti cell morphology and are low-threshold, slow accommodating firing.

<p>(A) Confocal image (20 μm, coronal slice) of primary auditory cortex of a <i>Chrna2-Cre/R26</i>^<i>tom</i> mouse showing tdTomato+ somas (red) in L5 with dense axonal arborizations in layer 1 (arrow in corner, scale bar = 100 μm). (B) Confocal image and tracing of a biocytin-filled tdTomato+ neuron (green). Reconstruction of soma and dendrites (black) and axon (red; scale bar = 20 μm) shows long axonal projections to layer 1. (C) Confocal images of a biocytin-filled (green) tdTomato+ neuron among several tdTomato+ neurons (red) show that cells have an ovoid cell body in L5, bipolar dendritic morphology, and proximal axonal arborizations. (D) Image illustrating how the <i>Chrna2-Cre/R26</i>^<i>tom</i> axons emerge from the main dendrite (circle). Scale bars = 50 μm. (E) Image showing the long axonal arborizations (arrows) from one biocytin-filled <i>Chrna2-Cre/R26</i>^<i>tom</i> cell (yellow) to layer 1 and the dense axonal ramifications (asterisk) in layer 1 from all <i>Chrna2-Cre/R26</i>^<i>tom</i> cells expressing tdTomato (red). Scale bars = 50 μm. (F) Example from another biocytin-filled <i>Chrna2-Cre/R26</i>^<i>tom</i> cell to emphasize axonal arborization extending laterally in layer 1, seen as a thin yellow axon at the border of the axonal plexus of <i>Chrna2-Cre/R26</i>^<i>tom</i> cell in layer 1. (G) <i>Top</i>: Example current clamp traces from a tdTomato+ cell showing low-threshold, accommodating firing (20 pA response in red, 100 pA in black, 500 ms) and rebound APs (−20 to −80 pA, 500 ms) typical for Martinotti cells. <i>Bottom</i>: Current clamp trace in response to a 200-pA, 1,000-ms-long stimulus used for analysis in (H). (H) <i>Left</i>: The frequency/current (f/I) curve of MCs^α2 shows an average firing rate around 20 Hz (at 200 pA, 1,000 ms) indicating slow spiking properties. <i>Middle</i>: Difference in maximum frequency and steady-state frequency for each neuron to a 200 pA, 1,000-ms-long current step highlights an accommodating discharge. The black line depicts the mean adaptation. <i>Right</i>: Spike-frequency adaptation is shown as a function of time. Data (<i>n</i> = 36 cells) are presented as mean ± standard error of the mean (SEM) and shown in <a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.2001392#pbio.2001392.s009" target="_blank">S1 Data</a>.</p

MCs^α2 contribute to FDDI, and MC^α2 burst firing can reset type A PC spikes.

<p>(A) High-frequency stimulation (70 Hz, see arrow) of a presynaptic PC (▲) generates delayed IPSPs on a neighboring PC () via intermediate MCs^α2 (О). A mixed excitation (due to a monosynaptic PC–PC connection) followed by a disynaptic inhibition is shown (<i>n</i> = 12 cells, single examples in grey, mean in black). (B) An example of disynaptic inhibition alone (<i>top</i>) is shown (<i>n</i> = 12 cells, single examples in grey, mean in black). Silencing of HaloR-expressing MCs^α2 via green light (555 nm) prevents FDDI, although IPSPs are generated following termination of green light stimulation (<i>bottom</i>, <i>n</i> = 12 cells, single examples in grey, mean in black). (C) Mean IPSP amplitudes with (white) and without (green) FDDI at two different time points. (D) Responses from HaloR-expressing MCs^α2 (<i>top</i>) and local type A PCs (single-spiking and burst-spiking; <i>middle</i>) and type B PCs (<i>bottom</i>) are shown in presence of carbachol (10 μM). Green light stimulation (500 ms) hyperpolarizes HaloR-expressing MCs^α2 and upon termination MC^α2 rebound APs are triggered. This burst of APs generates robust inhibition in local postsynaptic type A PCs that synchronizes the timing of PC (rebound) APs. Kernel density estimates (orange) highlight increased (peaks) and decreased (valleys) co-occurance of APs. (E) Example of voltage clamp responses for type A (<i>top</i>) and type B (<i>bottom</i>) PCs in response to MCs^α2 burst firing (single examples in grey, mean in black). Values are shown in <a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.2001392#pbio.2001392.s012" target="_blank">S4 Data</a>.</p