New evidence for a gating action of norepinephrine in central neuronal circuits of mammalian brain.
Many previous studies have examined the effects of norepinephrine (NE) on neuronal responsiveness to synaptic inputs and putative transmitter substances and have described differential depressant actions of NE on stimulus evoked versus spontaneous discharge such that the "signal to noise" ratio of threshold responses was increased. In the present studies, similar experimental strategies employing a combination of microiontophoresis, single unit recording and afferent pathway stimulation in intact anesthetized and brain tissue slice preparations have revealed noradrenergic "gating" actions whereby weak or subthreshold synaptic stimuli can evoke threshold neuronal responses in the presence of iontophoretically applied NE or following electrical stimulation of the locus coeruleus. Overall, these results suggest that potentially threshold excitatory and inhibitory synaptic inputs may normally arrive at central neurons but appear weak or absent except during behavioral conditions favoring the synaptic release of NE. As such, these findings provide evidence that signal to noise ratio may not be the only potential modulatory action expressed by NE in noradrenergic target circuits of the mammalian brain.
Waterhouse
B D
BD
Department of Physiology and Biophysics, Hahnemann University, Philadelphia, PA 19102-1192.
Sessler
F M
FM
Cheng
J T
JT
Woodward
D J
DJ
Azizi
S A
SA
Moises
H C
HC
D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D002540:Cerebral Cortex / Q000187:drug effects / Q000502:physiology*; D004558:Electric Stimulation; D005071:Evoked Potentials / Q000187:drug effects; D005260:Female; D007031:Hypothalamus / Q000187:drug effects / Q000502:physiology*; D008125:Locus Coeruleus / Q000502:physiology*; D008297:Male; D009638:Norepinephrine / Q000494:pharmacology*; D051381:Rats; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology
D015124:8-Bromo Cyclic Adenosine Monophosphate; D005680:gamma-Aminobutyric Acid; D009638:Norepinephrine