Activation of serotonin1A receptors inhibits midbrain periaqueductal gray neurons of the rat.
The midbrain periaqueductal gray (PAG) is involved in a variety of functions including pain modulation, vocalization, autonomic control, fear and anxiety. This area contains serotonin receptors, particularly 5-HT1A that are known to play a role in the above functions. The goals of this study were to characterize the effects of 8-OH-DPAT, a selective 5-HT1A agonist, on the firing characteristics and membrane properties of PAG neurons. Both in vivo and in vitro preparations were used. The effects of 8-OH-DPAT on baseline activity of 91 neurons were tested in the in vivo preparation. In 50/91 cells, 8-OH-DPAT produced a decrease in the firing rate that ranged between 21 and 98% (mean +/- S.E.M. decrease of 49 +/- 1.9%). This inhibitory effect was dose dependent and could be blocked by spiperone. In 10/91 cells, 8-OH-DPAT produced an increase in the firing rate that ranged between 13 and 290%, with mean increase of 83 +/- 7.4%. The baseline firing rate of the remaining 31 cells was not affected by 8-OH-DPAT. In the PAG slice preparation, the effects of 8-OH-DPAT on synaptic and membrane properties of 17 PAG neurons were tested using whole-cell voltage clamp-recording procedures. In 14 cells, application of 8-OH-DPAT produced hyperpolarization that ranged between 6 and 21 mV, with mean of 8.4 +/- 2.0 mV. This hyperpolarization was associated with a decrease in membrane impedance that ranged between 8 and 45%, with mean decrease of 21.6 +/- 4.5%. The remaining three neurons did not respond to 8-OH-DPAT.(ABSTRACT TRUNCATED AT 250 WORDS)
Behbehani
M M
MM
Department of Physiology, College of Medicine, University of Cincinnati, OH 45267-0576.
Liu
H
H
Jiang
M
M
Pun
R Y
RY
Shipley
M T
MT
D017371:8-Hydroxy-2-(di-n-propylamino)tetralin / Q000037:antagonists & inhibitors / Q000494:pharmacology; D000818:Animals; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology; D066298:In Vitro Techniques; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D008636:Mesencephalon / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D010487:Periaqueductal Gray / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D015221:Potassium Channels / Q000187:drug effects; D051381:Rats; D017207:Rats, Sprague-Dawley; D011985:Receptors, Serotonin / Q000187:drug effects / Q000502:physiology*; D013134:Spiperone / Q000494:pharmacology; D013569:Synapses / Q000187:drug effects
D015221:Potassium Channels; D011985:Receptors, Serotonin; D013134:Spiperone; D017371:8-Hydroxy-2-(di-n-propylamino)tetralin