In the dorsal raphe nucleus many inputs converge and interact to modulate serotonergic neuronal activity and the behavioral responses to stress. The effects exerted by two stress-related neuropeptides, corticotropin releasing factor and nociceptin/orphaninFQ, on the outflow of [3H]5-hydroxytryptamine were investigated in superfused rat dorsal raphe nucleus slices. Electrical stimulation (100 mA, 1 msec for 2 min) evoked a frequency-dependent peak of [3H]5-hydroxytryptamine outflow, which was sodium and calcium-dependent. Corticotropin releasing factor (1-100 nM), concentration-dependently inhibited the stimulation (3 Hz)-evoked [3H]5-hydroxytryptamine outflow; the inhibition by 30 nM corticotropin releasing factor (to 68 ± 5.7%) was prevented both by the non selective CRF receptor antagonist alpha-helicalCRF(9-41) (300 nM) and by the CRF1 receptor antagonist antalarmin (100 nM). The CRF2 agonist urocortin II (10 nM) did not modify [3H]5-hydroxytryptamine outflow, ruling out the involvement of CRF2 receptors. Bicuculline, a GABAA antagonist (10 µM), prevented the inhibitory effect of corticotropin releasing factor (30 nM), supporting the hypothesis that the inhibition was mediated by increased -aminobutyric acid release. Nociceptin/orphaninFQ (1 nM - 1 µM) exerted an antalarmin- and bicuculline-insensitive inhibition on [3H]5-hydroxytryptamine outflow, with the maximum at 100 nM (to 63 ± 4.2%), antagonized by the NOP receptor antagonist UFP-101 (1 µM). Dorsal raphe nucleus slices prepared from rats exposed to 15 min of forced swim stress displayed a reduced [3H]5-hydroxytryptamine outflow, in part reversed by antalarmin and further inhibited by nociceptin/orphaninFQ. These findings indicate that (i) both corticotropin releasing factor and nociceptin/orphaninFQ exert an inhibitory control on dorsal raphe nucleus serotonergic neurons; (ii) the inhibition by corticotropin releasing factor involves -aminobutyric acid neurons; (iii) nociceptin/orphaninFQ inhibits dorsal raphe nucleus serotonin system in a corticotropin releasing factor- and -aminobutyric acid-independent manner; iv) nociceptin/orphaninFQ modulation is still operant in slices prepared from stressed rats. The nociceptin/orphaninFQ - NOP receptor system could represent a new target for drugs effective in stress-related disorders.
Inhibition of serotonin outflow by Nociceptin/OrphaninFQ in dorsal raphe nucleus slices from normal and stressed rats: role of Corticotropin Releasing Factor.
NAZZARO, Cristiano;BARBIERI, Mario;SINISCALCHI, Anna
2009
Abstract
In the dorsal raphe nucleus many inputs converge and interact to modulate serotonergic neuronal activity and the behavioral responses to stress. The effects exerted by two stress-related neuropeptides, corticotropin releasing factor and nociceptin/orphaninFQ, on the outflow of [3H]5-hydroxytryptamine were investigated in superfused rat dorsal raphe nucleus slices. Electrical stimulation (100 mA, 1 msec for 2 min) evoked a frequency-dependent peak of [3H]5-hydroxytryptamine outflow, which was sodium and calcium-dependent. Corticotropin releasing factor (1-100 nM), concentration-dependently inhibited the stimulation (3 Hz)-evoked [3H]5-hydroxytryptamine outflow; the inhibition by 30 nM corticotropin releasing factor (to 68 ± 5.7%) was prevented both by the non selective CRF receptor antagonist alpha-helicalCRF(9-41) (300 nM) and by the CRF1 receptor antagonist antalarmin (100 nM). The CRF2 agonist urocortin II (10 nM) did not modify [3H]5-hydroxytryptamine outflow, ruling out the involvement of CRF2 receptors. Bicuculline, a GABAA antagonist (10 µM), prevented the inhibitory effect of corticotropin releasing factor (30 nM), supporting the hypothesis that the inhibition was mediated by increased -aminobutyric acid release. Nociceptin/orphaninFQ (1 nM - 1 µM) exerted an antalarmin- and bicuculline-insensitive inhibition on [3H]5-hydroxytryptamine outflow, with the maximum at 100 nM (to 63 ± 4.2%), antagonized by the NOP receptor antagonist UFP-101 (1 µM). Dorsal raphe nucleus slices prepared from rats exposed to 15 min of forced swim stress displayed a reduced [3H]5-hydroxytryptamine outflow, in part reversed by antalarmin and further inhibited by nociceptin/orphaninFQ. These findings indicate that (i) both corticotropin releasing factor and nociceptin/orphaninFQ exert an inhibitory control on dorsal raphe nucleus serotonergic neurons; (ii) the inhibition by corticotropin releasing factor involves -aminobutyric acid neurons; (iii) nociceptin/orphaninFQ inhibits dorsal raphe nucleus serotonin system in a corticotropin releasing factor- and -aminobutyric acid-independent manner; iv) nociceptin/orphaninFQ modulation is still operant in slices prepared from stressed rats. The nociceptin/orphaninFQ - NOP receptor system could represent a new target for drugs effective in stress-related disorders.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
