ABSTRACT
Title
Functional antagonism between Nociceptin Orphanin FQ (N/OFQ) and Corticotropin-Releasing Factor (CRF) in anxiety-related behaviour in rats: involvement of the central serotonergic system
Authors
C. Novi1, V. Ruggieri1, M. Filaferro1 and G. Vitale1.
1Dept. of Biological Science, Sect. of Pharmacology. University of Modena and Reggio Emilia, Italy.
1Dept. of Biological Science, Sect. of Pharmacology. University of Modena and Reggio Emilia, Italy.
Abstract
Nociceptin/orphanin FQ (N/OFQ) (Reinscheid et al. 1995) influences a variety of central biological responses, including anxiety and stress (Gavioli and Calò 2006). N/OFQ acts as an anxiolytic-like agent in the rat (Vitale et al., 2006) and has been proposed to be a functional antagonist of corticotropin-releasing factor (CRF) in relation to its ability to antagonize other CRF effects (i.e. anorectic one) without exhibiting affinity for CRF receptors (Rodi et al., 2008). In response to stress CRF triggers changes in other neurotransmitter systems such as serotonin (5-HT) (Leonard 2005). The role of 5-HT1A receptor in anxiety has been supported by findings from preclinical and clinical researches (Akimova et al., 2009).
The present study was aimed at investigating the possible functional antagonism between N/OFQ and CRF in anxiety-related conditions in rats by evaluating behavioural parameters and possible changes in the serotonergic system in frontal cortex and pons, areas rich of serotonergic neurons and affected by stress exposure.
Animals were pretreated with N/OFQ (0,5 and 1 nmol/rat i.c.v.) or saline. CRF (1 µg/rat) or saline was i.c.v. injected 10 min after the last treatment. Ten min thereafter rats were subjected to two anxiometric tests: Elevated Plus Maze (EPM) and Conditioned Defensive Burying (CDB).
N/OFQ (1 nmol/rat)displayed anxiolytic-like effects in both tests, as previously demonstrated (Vitale et al., 2006). Conversely, CRF (1 µg/rat) displayed anxiogenic-like effects in the same behavioural parameters in either test. Treatment with N/OFQ 10 min before CRF administration antagonized the anxiogenic-like effects evoked by CRF, restoring the EPM and DB values to those of control rats.
After EPM experiment, rats were sacrificed and frontal cortex and pons processed to evaluate 5-HT, its metabolite 5-hydroxy-indole acetic acid (5-HIAA) levels and their ratio (5-HIAA/5-HT), by high performance liquid chromatography (HPLC) technique, and to assess the 5-HT1A receptor characteristics by means of radioligand saturation binding assay with 3H-8-OH-DPAT.
In the frontal cortex, N/OFQ (1 mol/rat), induced a significant decrease of 5-HT levels, did not modify the 5-HIAA ones with a subsequent increase in 5-HIAA/5-HT ratio. CRF (1 µg/rat) modified neither 5-HT nor 5-HIAA content in the same area but was able to counteract the changes induced by N/OFQ alone.
In the pons, N/OFQ was ineffective in inducing any change in serotonergic activity while CRF significantly decreased 5-HT levels, increased 5-HIAA content, thus inducing a increase in 5-HIAA/5-HT ratio. The combination of the two peptides reinstated the parameters related to serotonin and its metabolite to those of controls.
As regards 5HT1A characteristics, in the frontal cortex, N/OFQ increased the receptor density but reduced its affinity while CRF did not induce any change when given alone. In the pons, CRF decreased 5HT1A maximum number of binding sites while increasing receptor affinity whereas N/OFQ was ineffective. All these biochemical modifications were reverted by N/OFQ following CRF treatment.
The present study shows evidence that N/OFQ may be a functional antagonist of CRF anxiogenic-like effects in the behavioral tests evaluated. These effects may involve the central serotonergic mechanisms since the combination of N/OFQ and CRF induces a reversion of the serontonergic changes provoked by the single peptide dependently on the area investigated. In conclusion, our data provide further support for the hypothesis that N/OFQ may behave as functional antagonist for CRF, this action being of interest for the treatment of stress and anxiety disorders.
Akimova et al. (2009). Biol Psychiatry. 66, 627-35.
Gavioli and Calo' (2006). Naunyn Schmiedebergs Arch Pharmacol. 372, 319-30.
Leonard (2005). Eur Psychatry. 20, 302-6.
Reinscheid et al. (1995). Science. 270, 792-94.
Rodi et al. (2008). Psychopharmacology. 196, 523-31.
Vitale et al. (2006). Peptides. 27, 2193-200.
The present study was aimed at investigating the possible functional antagonism between N/OFQ and CRF in anxiety-related conditions in rats by evaluating behavioural parameters and possible changes in the serotonergic system in frontal cortex and pons, areas rich of serotonergic neurons and affected by stress exposure.
Animals were pretreated with N/OFQ (0,5 and 1 nmol/rat i.c.v.) or saline. CRF (1 µg/rat) or saline was i.c.v. injected 10 min after the last treatment. Ten min thereafter rats were subjected to two anxiometric tests: Elevated Plus Maze (EPM) and Conditioned Defensive Burying (CDB).
N/OFQ (1 nmol/rat)displayed anxiolytic-like effects in both tests, as previously demonstrated (Vitale et al., 2006). Conversely, CRF (1 µg/rat) displayed anxiogenic-like effects in the same behavioural parameters in either test. Treatment with N/OFQ 10 min before CRF administration antagonized the anxiogenic-like effects evoked by CRF, restoring the EPM and DB values to those of control rats.
After EPM experiment, rats were sacrificed and frontal cortex and pons processed to evaluate 5-HT, its metabolite 5-hydroxy-indole acetic acid (5-HIAA) levels and their ratio (5-HIAA/5-HT), by high performance liquid chromatography (HPLC) technique, and to assess the 5-HT1A receptor characteristics by means of radioligand saturation binding assay with 3H-8-OH-DPAT.
In the frontal cortex, N/OFQ (1 mol/rat), induced a significant decrease of 5-HT levels, did not modify the 5-HIAA ones with a subsequent increase in 5-HIAA/5-HT ratio. CRF (1 µg/rat) modified neither 5-HT nor 5-HIAA content in the same area but was able to counteract the changes induced by N/OFQ alone.
In the pons, N/OFQ was ineffective in inducing any change in serotonergic activity while CRF significantly decreased 5-HT levels, increased 5-HIAA content, thus inducing a increase in 5-HIAA/5-HT ratio. The combination of the two peptides reinstated the parameters related to serotonin and its metabolite to those of controls.
As regards 5HT1A characteristics, in the frontal cortex, N/OFQ increased the receptor density but reduced its affinity while CRF did not induce any change when given alone. In the pons, CRF decreased 5HT1A maximum number of binding sites while increasing receptor affinity whereas N/OFQ was ineffective. All these biochemical modifications were reverted by N/OFQ following CRF treatment.
The present study shows evidence that N/OFQ may be a functional antagonist of CRF anxiogenic-like effects in the behavioral tests evaluated. These effects may involve the central serotonergic mechanisms since the combination of N/OFQ and CRF induces a reversion of the serontonergic changes provoked by the single peptide dependently on the area investigated. In conclusion, our data provide further support for the hypothesis that N/OFQ may behave as functional antagonist for CRF, this action being of interest for the treatment of stress and anxiety disorders.
Akimova et al. (2009). Biol Psychiatry. 66, 627-35.
Gavioli and Calo' (2006). Naunyn Schmiedebergs Arch Pharmacol. 372, 319-30.
Leonard (2005). Eur Psychatry. 20, 302-6.
Reinscheid et al. (1995). Science. 270, 792-94.
Rodi et al. (2008). Psychopharmacology. 196, 523-31.
Vitale et al. (2006). Peptides. 27, 2193-200.