Administration Of Neuropeptide FF Research Articles

Pressor and tachycardic responses to intrathecal administration of neuropeptide FF in anesthetized rats

Neuropeptide FF (NPFF) belongs to a neuropeptide family including two precursors (pro-NPFF A and pro-NPFF B) and two receptors (NPFF 1 and NPFF 2). NPFF and NPFF receptor mRNAs have been reported to be highly expressed and localized in the rat and human spinal cord. In the present study, the i.t. action of NPFF system on blood pressure and heart rate were examined using NPFF and two related agonists, NPVF and dNPA, which exhibit highest selectivities for NPFF 1 and NPFF 2 receptors, respectively. In urethane-anesthetized rats, NPFF and related peptides (5–40 nmol, i.t.) produced significant pressor and tachycardic responses at the spinal cord level. These effects were dose-dependent and similar with respect to time-course for the three peptides. Furthermore, i.t. injection of RF9 (20 nmol), a selective NPFF antagonist, significantly antagonized the cardiovascular responses to 20 nmol NPFF and related peptides (i.t.). Moreover, pretreatment of the rats with α-adrenoceptor antagonist phentolamine (1 mg/kg, i.v.) significantly reduced the pressor effects of NPFF. Nevertheless, pretreatment with muscarinic receptor and adrenoceptor antagonists (i.v.) could block the tachycardic effects induced by NPFF. Collectively, our results suggested that i.t. administration of NPFF and related peptides increased MAP and HR which were possibly mediated by the activation of both NPFF 1 and NPFF 2 receptors in the rat spinal cord. In addition, our results showed that the muscarinic receptor and adrenoceptor participated in the tachycardic response to i.t. NPFF, while α-adrenoceptor played an important role in the regulation of pressor effect of NPFF.

The role of neuropeptide FF (NPFF) in the expression of sensitization to hyperlocomotor effect of morphine and ethanol

Neuropeptide FF (NPFF) has been characterized as an endogenous anti-opioid peptide because its intraventricular injection (icv) reversed morphine- and stress-induced analgesia, and precipitates withdrawal syndrome in morphine-dependent rats. The role of NPFF in other aspects of drug dependence is unknown. Therefore, the aim of this study was to determine NPFF influence on the expression of sensitization to the morphine-induced hyperlocomotion. As the opioid system plays a role in ethanol effects, the influence of NPFF on the expression of sensitization to hyperlocomotor effect of ethanol was also investigated. Our study indicated that acute administration of NPFF (5, 10, 20nmol, icv) inhibited the expression of morphine-induced sensitization at doses of 10 (P<0.05) and 20nmol (P<0.01), and also inhibited ethanol-induced sensitization at a dose of 20nmol (P<0.01). Furthermore, NPFF inhibited the acute locomotor effect of morphine (10 and 20nmol) but not that of ethanol. NPFF, given alone, did not change the locomotor activity of mice and did not disturb motor coordination of animals in the rotarod test. In conclusion, our experiments indicated that NPFF attenuated the acute morphine locomotion and the expression of sensitization to locomotion. We anticipate that NPFF may be involved in both of these effects.

Central administration of neuropeptide FF causes activation of oxytocin paraventricular hypothalamic neurones that project to the brainstem.

Neuropeptide FF (NPFF), a morphine modulatory peptide, is emerging as an important neuromodulator in the context of central autonomic and neuroendocrine regulation. NPFF immunoreactivity and receptors have been identified in discrete autonomic regions within the brain and spinal cord, including the hypothalamic paraventricular nucleus (PVN). In this study, we examined the effects of intracerebroventricular (i.c.v.) administration of NPFF on activation of chemically identified PVN neurones that project to the brainstem nucleus of the solitary tract (NTS). In conscious rats, i.c.v. NPFF at a dose of 10 micro g, but not 8 micro g, caused an increase in arterial blood pressure. Immunohistochemical analysis revealed a dose-dependent increase in activated (Fos positive) PVN neurones following i.c.v. NPFF administration compared to controls receiving i.c.v. saline. Activated PVN neurones were located predominantly in the parvocellular compartment of the nucleus with relatively few Fos positive cells in the magnocellular subdivision. Chemical identification of activated neurones revealed significant number of activated cells to be oxytocin positive, whereas only few vasopressin, tyrosine hydroxylase (TH) or corticotrophin-releasing factor (CRF) neurones were double-labelled. Injection of the retrograde tracer fluorogold into the NTS resulted in labelling of significant numbers of parvocellular oxytocin, but not vasopressin, TH or CRF, PVN neurones. We conclude that centrally administered NPFF stimulates brainstem-projecting oxytocin PVN neurones. Oxytocin released from terminals within the NTS oxytocin thus modulate the activity of ascending visceral autonomic pathways that synapse initially within the NTS.

Central administration of neuropeptide FF (NPFF) causes increased neuronal activation and up-regulation of NPFF gene expression in the rat brainstem.

Neuropeptide FF (NPFF) is a morphine modulatory peptide that plays an important role in a wide variety of physiological functions, including those related to nociception and central autonomic regulation. NPFF fibers and cells have been shown to be discretely localized in key autonomic centers within the brain, including the brainstem nucleus of the solitary tract (NTS). Central applications of NPFF evoke a number of important biological effects through activation of central neuronal circuits whose identities remain unknown at present. NPFF administered in this manner may also be capable of up- or down-regulating its own gene expression. In this study, we investigated the effects of intracerebroventricular (i.c.v.) administration of NPFF on the activation and the gene expression of NPFF in NTS neurons. Conscious rats received saline or NPFF (8 or 10 microg i.c.v.), with concomitant monitoring of arterial blood pressure. Brains were prepared for Fos immunohistochemistry to identify neuronal activation and NPFF in situ hybridization to determine cells expressing NPFF mRNA in the NTS. At a dose of 8 microg, i.c.v., NPFF did not evoke alterations in blood pressure, but, at 10 microg, there was an increase in arterial blood pressure of 30-40 mmHg. Image analysis showed a dose-dependent increase in number of NPFF neurons that were activated in rats receiving i.c.v. NPFF compared with saline controls. NPFF gene expression in the NTS showed a similar dose-dependent increase following i.c.v. administration of either 8 or 10 microg of NPFF. Significantly greater numbers of activated neurons expressing the NPFF gene (double labeled) were observed in the NTS at the level of the area postrema in animals receiving i.c.v. NPFF compared with saline controls. These data indicate that centrally administered NPFF is capable of up-regulating its own gene expression in the NTS and that this effect appears in part to be independent of elevations in arterial blood pressure that this peptide can evoke when administered i.c.v. at the higher dose. The up-regulation of NPFF may play a homeostatic role in response to specific cardiovascular challenges, such as hypotension.

Hypothermic Effects of Neuropeptide FF Analogues in Mice

The effects of neuropeptide FF (NPFF) and its analogues on mouse body temperature were examined. In a thermoneutral environment, administration of NPFF (Phe-Leu-Phe-Gln-Pro-Gln-Arg-Phe-NH 2), 1DMe ([D.Tyr 1, (N.Me)Phe 3] NPFF), and 3D ([D.Tyr 1, D.Leu 2, D.Phe 3] NPFF) in the third ventricle produced marked hypothermia. The effect of 1DMe was dose-dependent, and 45 nmol decreased body temperature by 5.6°C. This effect was more pronounced when mice were placed at 4°C. Hypothermia was not reversed by naloxone, an opioid antagonist, and was not modified by morphine. After 5 days of chronic treatment with 1DMe, mice did not became tolerant to the hypothermic effect. These results indicate that central NPFF receptors may control body temperature independently from opioid functions.

Neuropeptide FF in the VTA blocks the analgesic effects of both intra-VTA morphine and exposure to stress

It has been shown previously that i.c.v. administration of neuropeptide FF (NPFF) attenuates the analgesic effects of exogeneous and endogeneous opioids. Here, we report that intra-ventral tegmental area (VTA) NPFF pre-treatment blocks the analgesia induced by either intra-VTA morphine or exposure to footshock stress in the formalin test for tonic pain. These findings suggest that NPFF in the VTA may play an adaptive role in regulating the response to stress.

Downregulation of mu-opioid binding sites following chronic administration of neuropeptide FF (NPFF) and morphine.

The effect of continuous ICV infusion of NPFF (10 micrograms/microliter) and morphine (40 micrograms/microliter) on mu-opioid binding sites was examined in rats using the in vitro radiolabeled techniques of whole-brain homogenate receptor binding and quantitative autoradiography. Mu receptors were labeled with [3H][D-Ala2-MePhe4,Glyol5] enkephalin in the homogenate binding experiments and with [125I][D-Ala2-MePhe4,Gly-ol5]enkephalin in autoradiographic studies. In homogenate binding studies, chronic administration of NPFF or morphine significantly downregulated mu receptors by 20% and 44%, respectively. Quantitative autoradiographic experiments demonstrated downregulation of mu opioid receptors in specific brain nuclei for both NPFF- and morphine-treated animals. Within the striatum and several nuclei of the thalamus, the mu receptors of the NPFF- and morphine-treated animals were decreased by 20-30% and 38-73%, respectively. These results suggest that NPFF may modulate opioid-mediated responses in part by altering the density of mu-opioid receptors.