Subthreshold oscillation of the membrane potential in magnocellular neurones of the rat supraoptic nucleus

Abstract

Electrophysiological properties and ionic basis of subthreshold oscillation of the membrane potential were examined in 104 magnocellular neurones of the rat supraoptic nucleus using intracellular recording techniques in a brain slice preparation. Subthreshold oscillation of the membrane potential occurring in all neurones examined was voltage dependent. Oscillation was initiated 7‐12 mV negative to the threshold of fast action potentials. Oscillation was the result of neither excitatory nor inhibitory synaptic activity nor of electric coupling. Frequency analyses revealed a broad band frequency distribution of subthreshold oscillation waves (range 10‐70 Hz). The frequency band of 15‐33 Hz was observed in neurones depolarized close to the threshold of discharge. Subthreshold oscillation was blocked by TTX (1.25‐2.5 μM) as well as by TEA (15 mM). Subthreshold oscillation was not blocked by low Ca2+‐high Mg2+ superfusate, CdCl2, TEA (1‐4.5 mM), 4‐aminopyridine, apamin, charybdotoxin, iberiotoxin, BaCl2, carbachol and CsCl. During application of TTX, stronger depolarization induced high‐threshold oscillation of the membrane potential at a threshold of about ‐32 mV. These oscillation waves occurred at a mean frequency of about 35 Hz and were blocked by CdCl2. Effects of ion channel antagonists suggest that subthreshold oscillation is generated by the interaction of a subthreshold sodium current and a subthreshold potassium current. The generation of high‐threshold oscillation during TTX involves a high‐threshold calcium current. Subthreshold oscillation of the membrane potential may be important for the inter‐neuronal synchronization of discharge and for the amplification of synaptic events.

Firing Patterns in Coupled Systems of Inhibitory Neurons

“…The key to generating such firing patterns is the existence of neurons with only subthreshold oscillations. Subthreshold neuronal oscillations have been observed in previous experiments [35,36]. Our phenomenon shows the importance of the subthreshold oscillation to connect the neurons with periodic spikes.…”

Participation of Sodium Currents in Burst Generation and Control of Membrane Excitability in Mesencephalic Trigeminal Neurons

“…Historically, sodium channels are characterized as essential for action potential generation, yet it is now well known that there are not only transient sodium currents (I NaT ), but in many neurons, persistent, or slowly inactivating sodium currents (I NaP ) active within the subthreshold region (Chandler et al, 1994;Crill, 1996;Boehmer et al, 2000;Taddese and Bean, 2002;Do and Bean, 2003). More recently, a novel sodium current termed "resurgent sodium current" (I NaR ), which activates during spike repolarization, was described (Raman and Bean, 1997).…”

Electrical properties of neurons in the intact rat major pelvic ganglion

“…SMPOs can involve TTX-sensitive Na + currents as they are completely blocked by TTX (1-1.5 μM) in magnocellular neurons of the rat supraoptic nucleus (Boehmer et al 2000) and rat striatal fast-spiking interneurons (Bracci et al 2003). In the present study, bath application of 1 μM TTX reversibly abolished the SMPOs and the remaining spikes appeared similar to steady state spikes tested in ramp depolarization or prolonged 5-10 sec depolarizing pulses (Fig.…”

“…As has been demonstrated previously in primary sensory neurons (Amir et al 2002;Liu et al 2000;Xing et al 2003), the amplitude and frequency of the SMPOs in MPG neurons were voltage dependent, with the amplitude and duration increasing as the neurons were brought to more depolarized potentials. The rising phase of SMPOs in other types of neurons has been shown to be Na + -dependent, and they are sensitive to TTX (Amir et al 2002;Boehmer et al 2000;Bracci et al 2003). Similarly, in MPG neurons, the SMPOs were greatly attenuated in the presence of TTX and were eliminated when NMG replaced Na + in the bathing solution.…”