Aminergic control of neuronal firing rate in thalamic motor nuclei of the rat.
The effects induced on neuronal firing by microiontophoretic application of the biological amines noradrenaline (NA) and 5-hydroxytryptamine (5-HT) were studied "in vivo" in ventral-anterior (VA) and ventrolateral (VL) thalamic motor nuclei of anaesthetized rats. In both nuclei the amines had a mostly depressive action on neuronal firing rate, the percentage of units responsive to NA application (88%) being higher than to 5-HT (72%). Short-lasting (less than 2 min) and long lasting (up to 20 min) inhibitory responses were recorded, the former mostly evoked by NA and the latter by 5-HT ejection. In some cases 5-HT application had no effect on the firing rate but modified the firing pattern. NA-evoked responses were significantly more intense in VL than in VA neurons. Short-lasting inhibitory responses similar to NA-induced effects were evoked by the alpha2 adrenergic receptor agonist clonidine and to a lesser extent by the beta adrenergic receptor agonist isoproterenol. Inhibitory responses to 5-HT were partially mimicked by application of the 5-HT(1A) receptor agonist 8-hydroxy-2(di-n-propylamino)tetralin (8-OH-DPAT) and of the 5-HT2 receptor agonist alpha-methyl-5-hydroxytryptamine (ALPHA-MET-5-HT). The latter evoked excitatory responses in some cases. Both 5-HT agonists were more effective on VA than on VL neurons. The effects evoked by agonists were at least partially blocked by respective antagonists. These results suggest that although both 5-HT and NA depress neuronal firing rate, their effects differ in time course and in the amount of inhibition; besides aminergic modulation is differently exerted on VA and VL.
Grasso
C
C
Department of Physiological Sciences, University of Catania, Catania, Italy.
Li Volsi
G
G
Licata
F
F
Ciranna
L
L
Santangelo
F
F
D000200:Action Potentials / Q000187:drug effects / Q000502:physiology*; D018674:Adrenergic Antagonists / Q000494:pharmacology; D000344:Afferent Pathways / Q000378:metabolism*; D000818:Animals; D001479:Basal Ganglia / Q000502:physiology; D001679:Biogenic Amines / Q000378:metabolism* / Q000494:pharmacology; D002531:Cerebellum / Q000502:physiology; D008125:Locus Coeruleus / Q000378:metabolism; D009044:Motor Cortex / Q000502:physiology; D009068:Movement / Q000502:physiology; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D009638:Norepinephrine / Q000378:metabolism / Q000494:pharmacology; D011903:Raphe Nuclei / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D012701:Serotonin / Q000378:metabolism / Q000494:pharmacology; D012702:Serotonin Antagonists / Q000494:pharmacology; D020651:Ventral Thalamic Nuclei / Q000378:metabolism*
D018674:Adrenergic Antagonists; D001679:Biogenic Amines; D012702:Serotonin Antagonists; D012701:Serotonin; D009638:Norepinephrine