Meijun Ye

Study objectives: Recent evidence suggests that certain anesthetics decrease electrical coupling while the stimulant modafinil appears to increase electrical coupling.  Meijun is investigating the potential role of electrical coupling in the cholinergic arm of the reticular activating system (RAS), the pedunculopontine nucleus (PPN), which has been implicated in the modulation of arousal via ascending cholinergic activation of intralaminar thalamus and descending activation of pontine regions to generate some of the signs of rapid eye movement (REM) sleep.

Design:  Meijun uses 6-30 day brainstem slices to perform whole cell patch-clamp recordings.

Measurements and Results:  Recordings from single cells revealed the presence of spikelets, manifestations of action potentials in coupled cells, and of dye coupling of neurons in the PPN.  Recordings in pairs of PPN revealed that some of these were electrically coupled with coupling coefficients ~2%.  After blockade of fast synaptic transmission, the cholinergic agonist carbachol (CAR) was found to induce rhythmic activity in PPN neurons, an effect eliminated by the gap junction blockers carbenoxolone or mefloquine.  The stimulant modafinil was found to decrease resistance in PPN neurons after fast synaptic blockade, indicating that the effect may be due to increased coupling.

Conclusions:  The finding of electrical coupling in specific RAS cell groups supports the concept that this underlying process behind specific neurotransmitter interactions modulates ensemble activity across cell populations to promote changes in sleep-wake state.


Modulation of electrical couplings in the PPN. A. Whole cell patch-clamp recordings from a pair of electrical coupled PPN neurons under voltage-clamp. Hyperpolarizing pulses (top two records show current pulses) injected to one cell induced a current in the other cell in the presence of 1uM TTX to block sodium channels and thus action potential generation. The coupling ratio (CR) was calculated using the current amplitude in the injected cell divided by the response current in the coupled cell. For this pair, the CR of cell 1 to cell 2 was 1.6%, and of cell 2 to cell 1 was 2%. The gray line represents the average of 20 sweeps after 3 min superfusion of TTX. B. No significant activity was present in this cell during superfusion of fast inhibitory and excitatory synaptic blockers [CAGM=CNQX 10uM, APV 10uM, Gabazine 10uM and mecamylamine (MEC) 10uM] (top record). Carbachol (CAR, 50 uM) induced oscillations in this PPN cell in the presence of fast inhibitory and excitatory synaptic blockers (CAGM) (second record), which was blocked by 300uM carbenexolone (CBX), a putative gap junction blocker (bottom record). C. Power spectrum histogram of the oscillations induced by fast synaptic blockers (no discernible synchronization), CAR in the presence of fast synaptic blockers (theta frequency oscillations), and their blockade by CBX in the same cell shown in B. Each histogram was obtained from a 1 min recording sample. D. An example of a PPN cell whose input resistance was decreased by fast synaptic blockers (CAGM), then decreased further by the superfusion of modafinil (MOD, 150 uM) in the presence of fast synaptic blockers (CAGM). The decrease in resistance was partially reversed by the putative gap junction blockers mefloquine (MEF, 25 uM). The cell was recorded under voltage-clamp mode. A ramp protocol was applied in order to test the change of membrane resistance, such that a higher the current was required to compensate for the voltage change in the presence of MOD, indicating a decrease in resistance. E. The ramp protocol used in the recording shown in D. The voltage was held at -60 mV during baseline and then was held at -105 mV for 500 msec to test the compensatory current. A 1000 msec ramp from -105 mV to -35 mV was then applied. F. The membrane resistance change during 50 min recording from the same cell shown in D. The bars indicate the period when drugs were applied (black: 1 uM TTX + 10 uM CAGM; maroon: 150 uM MOD + TTX + CAGM; green: 25