ABSTRACT
Title
Effects of the continuous delivery of a potent NOP receptor antagonist, [Nphe1, Arg14, Lys15] N/OFQ-NH2 (UFP-101), on molecular, cellular and behavioral alterations in a chronic model of stress.
Authors
M. Filaferro1, S. Zucchini2, V. Ruggieri1, G. Vitale1, C. Novi1, C. Cifani3, M. Massi3 and M. Simonato2.
1 Dept. Biomedical Sciences, University of Modena and RE, Italy; 2 Dept. Experimental and Clinical Medicine, Laboratory for Technologies of Advanced Therapies (LTTA), University of Ferrara, Italy; 3 Dept Pharmacological Sciences and Experimental Medicine, University of Camerino, Italy.
1 Dept. Biomedical Sciences, University of Modena and RE, Italy; 2 Dept. Experimental and Clinical Medicine, Laboratory for Technologies of Advanced Therapies (LTTA), University of Ferrara, Italy; 3 Dept Pharmacological Sciences and Experimental Medicine, University of Camerino, Italy.
Abstract
Chronic stress is associated with the development of depression and may trigger neurobiological changes, including plastic alterations in key limbic regions implicated in depressive diseases. The present study investigated the effect of UFP-101, a selective and high affinity NOP receptor antagonist, in the chronic mild stress (CMS) paradigm in male Wistar rats. The nociceptin/orphanin FQ (N/OFQ)-NOP receptor system has been widely studied in the modulation of several central functions and, in particular, NOP antagonists have been reported to elicit antidepressant-like effects in rodents (Gavioli et al., 2004).
Animals were exposed to CMS for at least seven weeks, to induce a condition of anhedonia (measured as reduced consumption of a sucrose solution). UFP-101 (10 nmol/rat i.c.v., continuously infused by means of minipumps for 24 days) did not influence sucrose intake in non-stressed animals, but reinstated basal sucrose consumption in stressed animals (+40% vs. non treated stressed rats), beginning from the second week of treatment. The reference drug fluoxetine (FL, 10 mg/kg i.p.) produced identical effects. Moreover, repeated co-administration of N/OFQ (5 nmol/rat i.c.v., from day 15 to 24) completely prevented the behavioral effects of UFP‑101.
In previousanimal studies the stress/depression condition has been associated to plastic alterations of neuronal networks, including reduced hippocampal volume, neuronal atrophy, cell death and alterations in cell proliferation and cell survival of newly generated neurons in the hippocampus (Gould & Tanapat, 1999; Kempermann, 2002; Warner-Schmidt & Duman, 2006). Neurotrophic factors (NTFs) such as BDNF and FGF-2 may be involved in the modulation of activity-dependent plasticity associated with mood pathologies (Castren, 2007). Therefore, we have investigated if the CMS procedure associated with the continuous delivery of UFP-101 can affect NTFs expression, as well as hippocampal cell proliferation and neurogenesis. After in vivo BrdU labelling, all rats were sacrificed on day 24 and their brains were collected for immunohistochemical analysis. Our data confirm that CMSreduced proliferation of neural stem cells and neurogenesis in the adult rat hippocampus, respectively evaluated as number of BrdU and doublecortin (Dcx) positive cells. The 21-day UFP-101 treatment, which did not produce any primary effect on cell proliferation, also did not affect the reduced proliferation observed in stressed animals. However, UFP-101 was able to increase the number of Dcx positive cells, restoring neurogenesis to the physiological levels.The expression pattern of FGF-2 in the stressed animals displayed a reduction in the number of positive cells and in the protein levels. The continuous delivery of UFP-101 increased significantly the FGF-2 expression.
These findings support the view that blockade of NOP receptor signaling in the brain produces antidepressant-like effects in the CMS protocol, and indicate that the behavioral efficacy of the NOP receptor antagonist UFP-101 as well as the positive effect on neurogenesis and FGF-2 expression are comparable with those of classical antidepressants. Further studies are needed to better elucidate the antidepressant-like activity of UFP-101, but the present findings support the hypothesis that NOP receptors may represent a candidate target for innovative antidepressant drugs.
Animals were exposed to CMS for at least seven weeks, to induce a condition of anhedonia (measured as reduced consumption of a sucrose solution). UFP-101 (10 nmol/rat i.c.v., continuously infused by means of minipumps for 24 days) did not influence sucrose intake in non-stressed animals, but reinstated basal sucrose consumption in stressed animals (+40% vs. non treated stressed rats), beginning from the second week of treatment. The reference drug fluoxetine (FL, 10 mg/kg i.p.) produced identical effects. Moreover, repeated co-administration of N/OFQ (5 nmol/rat i.c.v., from day 15 to 24) completely prevented the behavioral effects of UFP‑101.
In previousanimal studies the stress/depression condition has been associated to plastic alterations of neuronal networks, including reduced hippocampal volume, neuronal atrophy, cell death and alterations in cell proliferation and cell survival of newly generated neurons in the hippocampus (Gould & Tanapat, 1999; Kempermann, 2002; Warner-Schmidt & Duman, 2006). Neurotrophic factors (NTFs) such as BDNF and FGF-2 may be involved in the modulation of activity-dependent plasticity associated with mood pathologies (Castren, 2007). Therefore, we have investigated if the CMS procedure associated with the continuous delivery of UFP-101 can affect NTFs expression, as well as hippocampal cell proliferation and neurogenesis. After in vivo BrdU labelling, all rats were sacrificed on day 24 and their brains were collected for immunohistochemical analysis. Our data confirm that CMSreduced proliferation of neural stem cells and neurogenesis in the adult rat hippocampus, respectively evaluated as number of BrdU and doublecortin (Dcx) positive cells. The 21-day UFP-101 treatment, which did not produce any primary effect on cell proliferation, also did not affect the reduced proliferation observed in stressed animals. However, UFP-101 was able to increase the number of Dcx positive cells, restoring neurogenesis to the physiological levels.The expression pattern of FGF-2 in the stressed animals displayed a reduction in the number of positive cells and in the protein levels. The continuous delivery of UFP-101 increased significantly the FGF-2 expression.
These findings support the view that blockade of NOP receptor signaling in the brain produces antidepressant-like effects in the CMS protocol, and indicate that the behavioral efficacy of the NOP receptor antagonist UFP-101 as well as the positive effect on neurogenesis and FGF-2 expression are comparable with those of classical antidepressants. Further studies are needed to better elucidate the antidepressant-like activity of UFP-101, but the present findings support the hypothesis that NOP receptors may represent a candidate target for innovative antidepressant drugs.