F. Okutani et al., THE BIPHASIC EFFECTS OF LOCUS-COERULEUS NORADRENERGIC ACTIVATION ON DENDRODENDRITIC INHIBITION IN THE RAT OLFACTORY-BULB, Brain research, 783(2), 1998, pp. 272-279
Some forms of olfactory learning require intact noradrenegic terminals
in the olfactory bulb that originate from the locus coeruleus. To cla
rify the action of noradrenergic inputs on the dendrodendritic interac
tion between mitral and granule cells in the rat olfactory bulb, we an
alyzed field potentials in the granule cell layer of the olfactory bul
b evoked by paired-pulse stimulation of the lateral olfactory tract be
fore and after the activation of the locus coeruleus. Locus coeruleus
activation by glutamate injection in the vicinity of the nucleus chang
ed only the test response without any effect on conditioning response.
Paired-pulse inhibition measured from the ratio of test response ampl
itude to conditioning response amplitude was significantly depressed i
mmediately after locus coeruleus activation. Conversely, 2 min later,
paired-pulse inhibition was significantly potentiated. The significant
potentiation of inhibition lasted for several minutes. The depression
-potentiation sequence of paired-pulse inhibition was blocked by infus
ion of timolol, a beta-antagonist, into the olfactory bulb, in a dose-
dependent manner, but not by infusion of phentolamine, an alpha-antago
nist. Infusion of isoproterenol, a beta-agonist, into the bulb mimicke
d the depression of paired-pulse inhibition by locus coeruleus activat
ion. These results suggest that glutamate activation of the locus coer
uleus produces a depression-potentiation sequence in granule cell-medi
ated feedback inhibition onto mitral cells in the olfactory bulb throu
gh beta-adrenergic receptors. (C) 1998 Elsevier Science B.V.