Somatostatin inhibits GABAergic transmission in the sensory thalamus via presynaptic receptors.
The action of somatostatin on GABA-mediated transmission was investigated in cat and rat thalamocortical neurons of the dorsal lateral geniculate nucleus and ventrobasal thalamus in vitro. In the cat thalamus, somatostatin (10 microM) had no effect on the passive membrane properties of thalamocortical neurons and on the postsynaptic response elicited in these cells by bath or iontophoretic application of (+/-)baclofen (5-10 microM) or GABA, respectively. However, somatostatin (1-10 microM) decreased by a similar amount (45-55%) the amplitude of electrically evoked GABA(A) and GABA(B) inhibitory postsynaptic potentials in 71 and 50% of neurons in the lateral geniculate and ventrobasal nucleus, respectively. In addition, the neuropeptide abolished spontaneous bursts of GABA(A) inhibitory postsynaptic potentials in 85% of kitten lateral geniculate neurons, and decreased (40%) the amplitude of single spontaneous GABA(A) inhibitory postsynaptic potentials in 87% of neurons in the cat lateral geniculate nucleus. Similar results were obtained in the rat thalamus. Somatostatin (10 microM) had no effect on the passive membrane properties of thalamocortical neurons in this species, or on the outward current elicited by puff-application of (+/-)baclofen (5-10 microM). However, in 57 and 22% of neurons in the rat lateral geniculate and ventrobasal nuclei, respectively, somatostatin (1 microM) reduced the frequency, but not the amplitude, of miniature GABA(A) inhibitory postsynaptic currents by 31 and 37%, respectively. In addition, the neuropeptide (1 microM) decreased the amplitude of evoked GABA(A) inhibitory postsynaptic currents in 20 and 55% of rat ventrobasal neurons recorded in normal conditions and during enhanced excitability, respectively: this effect was stronger on bursts of inhibitory postsynaptic currents(100% decrease) than on single inhibitory postsynaptic currents (41% decrease). These results demonstrate that in the sensory thalamus somatostatin inhibits GABA(A)- and GABA(B)-mediated transmission via a presynaptic mechanism, and its action is more prominent on bursts of GABAergic synaptic currents/potentials.
Leresche
N
N
Neurobiologie Cellulaire, Institut des Neurosciences, UMR CNRS 7624, Université Pierre et Marie Curie, Paris, France.
Asprodini
E
E
Emri
Z
Z
Cope
D W
DW
Crunelli
V
V
D015763:2-Amino-5-phosphonovalerate / Q000494:pharmacology; D018750:6-Cyano-7-nitroquinoxaline-2,3-dione / Q000494:pharmacology; D000818:Animals; D001418:Baclofen / Q000494:pharmacology; D001640:Bicuculline / Q000494:pharmacology; D002415:Cats; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology; D004827:Epilepsy / Q000503:physiopathology; D005071:Evoked Potentials / Q000187:drug effects / Q000502:physiology; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D018755:GABA Agonists / Q000494:pharmacology; D018756:GABA Antagonists / Q000494:pharmacology; D005829:Geniculate Bodies / Q000187:drug effects / Q000378:metabolism*; D006728:Hormones / Q000494:pharmacology*; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009433:Neural Inhibition / Q000187:drug effects / Q000502:physiology; D018408:Patch-Clamp Techniques; D017729:Presynaptic Terminals / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D011963:Receptors, GABA-A / Q000502:physiology; D018080:Receptors, GABA-B / Q000502:physiology; D012890:Sleep / Q000502:physiology; D013004:Somatostatin / Q000494:pharmacology*; D009435:Synaptic Transmission / Q000187:drug effects*; D013779:Tetrodotoxin / Q000494:pharmacology; D020651:Ventral Thalamic Nuclei / Q000187:drug effects / Q000378:metabolism; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
D018691:Excitatory Amino Acid Antagonists; D018755:GABA Agonists; D018756:GABA Antagonists; D006728:Hormones; D011963:Receptors, GABA-A; D018080:Receptors, GABA-B; D013779:Tetrodotoxin; D013004:Somatostatin; D005680:gamma-Aminobutyric Acid; D018750:6-Cyano-7-nitroquinoxaline-2,3-dione; D015763:2-Amino-5-phosphonovalerate; D001418:Baclofen; D001640:Bicuculline