Phase-amplitude coupled persistent theta and gamma oscillations in rat primary motor cortex in vitro

Abstract

In vivo, theta (4-7 Hz) and gamma (30-80 Hz) neuronal network oscillations are known to coexist and display phase-amplitude coupling (PAC). However, in vitro, these oscillations have for many years been studied in isolation. Using an improved brain slice preparation technique we have, using co-application of carbachol (10 μM) and kainic acid (150 nM), elicited simultaneous theta (6.6 ± 0.1 Hz) and gamma (36.6 ± 0.4 Hz) oscillations in rodent primary motor cortex (M1). Each oscillation showed greatest power in layer V. Using a variety of time series analyses we detected significant cross-frequency coupling in 74% of slice preparations. Differences were observed in the pharmacological profile of each oscillation. Thus, gamma oscillations were reduced by the GABA receptor antagonists, gabazine (250 nM and 2 μM), and picrotoxin (50 μM) and augmented by AMPA receptor antagonism with SYM2206 (20 μM). In contrast, theta oscillatory power was increased by gabazine, picrotoxin and SYM2206. GABA receptor blockade with CGP55845 (5 μM) increased both theta and gamma power, and similar effects were seen with diazepam, zolpidem, MK801 and a series of metabotropic glutamate receptor antagonists. Oscillatory activity at both frequencies was reduced by the gap junction blocker carbenoxolone (200 μM) and by atropine (5 μM). These data show theta and gamma oscillations in layer V of rat M1 in vitro are cross-frequency coupled, and are mechanistically distinct. The development of an in vitro model of phase-amplitude coupled oscillations will facilitate further mechanistic investigation of the generation and modulation of coupled activity in mammalian cortex.

Dopamine acting at D1-like, D2-like and α1-adrenergic receptors differentially modulates theta and gamma oscillatory activity in primary motor cortex

“…Using an improved brain slice preparation based on a protocol utilising a number of neuro-protectant agents, we have previously reported simultaneous persistent theta and gamma oscillations in M1, which appear mechanistically distinct [22]. In this study we show differential modulation of theta and gamma oscillations by DA acting at both D1 and D2-like receptors, α1 adrenergic receptors and possibly DA/ α1 heteromultimeric receptor complexes.…”

“…Simultaneous oscillations, at theta (6.6 Hz) and gamma (36.6 Hz) which show greatest power in layer V and display significant phase-amplitude coupling have been previously described in our refined in vitro preparation [22]. Furthermore, the results of our pharmacological studies are consistent with theta oscillations being generated as a result of synchronous intrinsic membrane potential activity [45,46,47,48,49], while the generation of gamma oscillations require AMPA mediated EPSP/Cs indicating a mechanistic resemblance to the pyramidal-interneuron gamma (PING) model of oscillation generation which depends upon mutually connected excitatory pyramidal cells and inhibitory interneurons [50,51,52].…”

“…Animals were first anaesthetised using isoflurane (4% in O 2 ) until no heartbeat was detected and then transcardially perfused with ice-cold sucrose-based artificial cerebral spinal fluid (aCSF) containing (in mM): 180 sucrose, KCl 2.5, MgSO 4 10, NaH 2 PO 4 1.25, NaHCO 3 25, glucose 10, CaCl 2 0.5, ascorbic acid 1, N-acetyl cysteine 2, taurine 1, ethyl pyruvate 20 and saturated with 95% O 2 and 5% CO 2 at pH 7.3, 300–310 mOsm. Indomethacin (45 μM), aminoguanidine (200 μM) and uric acid (400 μM) were added to improve slice viability [22]. The brain was quickly removed and placed into the same sucrose-based aCSF.…”

“…For a number of years we have investigated network oscillatory activity in brain slices recording from M1 [18,19,20,21,22] and observed that oscillatory activity can be routinely induced by co-application of the muscarinic receptor agonist carbachol (CCh) and the glutamate receptor agonist kainic acid (KA). Beta and gamma oscillations in M1 are abolished by picrotoxin and modulated by gabazine, tiagabine and zolpidem, indicating dependence on networks of fast spiking (FS) GABAergic interneurons [18,21,22].…”

“…Beta and gamma oscillations in M1 are abolished by picrotoxin and modulated by gabazine, tiagabine and zolpidem, indicating dependence on networks of fast spiking (FS) GABAergic interneurons [18,21,22]. As with gamma (35–80 Hz) oscillations in the hippocampus [23,24] beta oscillatory activity in M1 is generated as a consequence of sustained excitation of networks of inhibitory interneurons [18,20] which are able to entrain each other to fire in a synchronous manner and hence sculpt pyramidal cell activity through repetitive (I phasic ) inhibitory discharges, the frequency of which is dependent upon the kinetics of the inhibitory postsynaptic potentials [23,25,26].…”