Excitatory actions of GABA in the suprachiasmatic nucleus.
Neurons in the suprachiasmatic nucleus (SCN) are responsible for the generation of circadian oscillations, and understanding how these neurons communicate to form a functional circuit is a critical issue. The neurotransmitter GABA and its receptors are widely expressed in the SCN where they mediate cell-to-cell communication. Previous studies have raised the possibility that GABA can function as an excitatory transmitter in adult SCN neurons during the day, but this work is controversial. In the present study, we first tested the hypothesis that GABA can evoke excitatory responses during certain phases of the daily cycle by broadly sampling how SCN neurons respond to GABA using extracellular single-unit recording and gramicidin-perforated-patch recording techniques. We found that, although GABA inhibits most SCN neurons, some level of GABA-mediated excitation was present in both dorsal and ventral regions of the SCN, regardless of the time of day. These GABA-evoked excitatory responses were most common during the night in the dorsal SCN region. The Na(+)-K(+)-2Cl(-) cotransporter (NKCC) inhibitor, bumetanide, prevented these excitatory responses. In individual neurons, the application of bumetanide was sufficient to change GABA-evoked excitation to inhibition. Calcium-imaging experiments also indicated that GABA-elicited calcium transients in SCN cells are highly dependent on the NKCC isoform 1 (NKCC1). Finally, Western blot analysis indicated that NKCC1 expression in the dorsal SCN is higher in the night. Together, this work indicates that GABA can play an excitatory role in communication between adult SCN neurons and that this excitation is critically dependent on NKCC1.
Choi
Hee Joo
HJ
Department of Physiology and Neuroscience Research Institute, Korea University College of Medicine, Seoul 136-705, Republic of Korea.
Lee
C Justin
CJ
Schroeder
Analyne
A
Kim
Yoon Sik
YS
Jung
Seung Hoon
SH
Kim
Jeong Sook
JS
Kim
Do Young
DY
Son
Eun Ju
EJ
Han
Hee Chul
HC
Hong
Seung Kil
SK
Colwell
Christopher S
CS
Kim
Yang In
YI
D015763:2-Amino-5-phosphonovalerate / Q000494:pharmacology; D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D001640:Bicuculline / Q000494:pharmacology; D002034:Bumetanide / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology; D004558:Electric Stimulation / Q000379:methods; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects; D018756:GABA Antagonists / Q000494:pharmacology; D066298:In Vitro Techniques; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009474:Neurons / Q000187:drug effects*; D009553:Nimodipine / Q000494:pharmacology; D009900:Optic Nerve / Q000502:physiology / Q000528:radiation effects; D018408:Patch-Clamp Techniques / Q000379:methods; D051381:Rats; D017207:Rats, Sprague-Dawley; D049994:Sodium Potassium Chloride Symporter Inhibitors / Q000494:pharmacology; D028021:Sodium-Potassium-Chloride Symporters / Q000172:deficiency; D064506:Solute Carrier Family 12, Member 2; D013493:Suprachiasmatic Nucleus / Q000166:cytology*; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology*
D002121:Calcium Channel Blockers; D018691:Excitatory Amino Acid Antagonists; D018756:GABA Antagonists; C578878:Slc12a2 protein, mouse; C578879:Slc12a2 protein, rat; D049994:Sodium Potassium Chloride Symporter Inhibitors; D028021:Sodium-Potassium-Chloride Symporters; D064506:Solute Carrier Family 12, Member 2; D002034:Bumetanide; D005680:gamma-Aminobutyric Acid; D009553:Nimodipine; D015763:2-Amino-5-phosphonovalerate; D002118:Calcium; D001640:Bicuculline