The Journal of Neuroscience, July 1, 2002, 22(13):5374-5386
Somatostatin Inhibits Thalamic Network Oscillations In
Vitro: Actions on the GABAergic Neurons of the Reticular
Nucleus
Qian-Quan
Sun,
John R.
Huguenard, and
David A.
Prince
Department of Neurology and Neurological Science, Stanford School
of Medicine, Stanford, California 94305
We examined the effects of somatostatin (SST) on neurons in the
thalamic reticular nucleus (RT) using whole-cell patch-clamp techniques
applied to visualized neurons in rat thalamic slices. SST, acting via
sst5 receptors and pertussis toxin-sensitive G-proteins, activated an inwardly rectifying K+ (GIRK) current
in 20 of 28 recorded cells to increase input conductance 15 ± 3%
above control and inhibited N-type Ca2+ currents in
17 of 24 neurons via voltage-dependent mechanisms. SST reversibly
depressed evoked EPSCs (eEPSCs) to 37 ± 8% of control without
altering their kinetics. SST-mediated inhibition of eEPSCs showed
short-term relief from block during 25 Hz stimulus trains. SST also
reduced the frequency (33 ± 8%) but not the amplitude of
miniature EPSCs (mEPSCs). These data indicate that SST mediates presynaptic inhibition of glutamate release onto RT neurons. In current-clamp recordings, SST preferentially inhibited burst discharges mediated by near-threshold corticothalamic EPSPs and intracellularly applied depolarizing currents. SST had powerful effects on in vitro intrathalamic rhythms, which included a shortening of the duration and a reduction in spike count within each oscillatory event.
Furthermore, there was a paradoxical increase in the synchrony of
epileptiform oscillations, likely mediated by a suppression of the
responses to weak synaptic inputs in RT. We conclude that SST
suppresses discharges in RT neurons, via presynaptic inhibition of
glutamate release and postsynaptic activation of GIRK channels, leading
to the dampening of both spindle-like and epileptiform thalamic network
oscillations. SST may act as an important endogenous regulator of
physiological and pathological thalamocortical network activities.
Key words:
somatostatin; EPSCs; GIRK channels; CA2+ channels; neural network; epilepsy
Copyright © 2002 Society for Neuroscience 0270-6474/02/22135374-13$05.00/0