Neuropeptide FF and prolactin-releasing peptide decrease cortical excitability through activation of NPFF receptors

An Inhibitory Circuit From Brainstem to GnRH Neurons in Male Mice: A New Role for the RFRP Receptor

RFamide-related peptides (RFRPs, mammalian orthologs of gonadotropin-inhibitory hormone) convey circadian, seasonal, and social cues to the reproductive system. They regulate gonadotropin secretion by modulating gonadotropin-releasing hormone (GnRH) neurons via the RFRP receptor. Mice lacking this receptor are fertile but exhibit abnormal gonadotropin responses during metabolic challenges, such as acute fasting, when the normal drop in gonadotropin levels is delayed. Although it is known that these food intake signals to the reproductive circuit originate in the nucleus tractus solitarius (NTS) in the brainstem, the phenotype of the neurons conveying the signal remains unknown. Given that neuropeptide FF (NPFF), another RFamide peptide, resides in the NTS and can bind to the RFRP receptor, we hypothesized that NPFF may regulate GnRH neurons. To address this question, we used a combination of techniques: cell-attached electrophysiology on GnRH-driven green fluorescent protein-tagged neurons in acute brain slices; calcium imaging on cultured GnRH neurons; and immunostaining on adult brain tissue. We found (1) NPFF inhibits GnRH neuron excitability via the RFRP receptor and its canonical signaling pathway (Gi/o protein and G protein-coupled inwardly rectifying potassium channels), (2) NPFF-like fibers in the vicinity of GnRH neurons coexpress neuropeptide Y, (3) the majority of NPFF-like cell bodies in the NTS also coexpress neuropeptide Y, and (4) acute fasting increased NPFF-like immunoreactivity in the NTS. Together these data indicate that NPFF neurons within the NTS inhibit GnRH neurons, and thus reproduction, during fasting but prior to the energy deficit.

Effects of RFamide-related peptide-1 (RFRP-1) microinjections into the central nucleus of amygdala on passive avoidance learning in rats

The amygdaloid body (AMY) plays an important role in memory, learning and reward-related processes. RFRP-1 immunoreactive fibers and NPFF receptors were identified in the AMY, and previously we verified that RFRP-1 infused into the central nucleus of AMY (CeA) induced place preference. The aim of the present study was to examine the possible effects of RFRP-1 in the CeA on passive avoidance learning. Male Wistar rats were examined in two-compartment passive avoidance paradigm. Animals were shocked with 0.5mA current and subsequently were microinjected bilaterally with 50ng or 100ng RFRP-1 in volume of 0.4μl, or 20ng NPFF receptor antagonist RF9 (ANT) alone, or antagonist 15min before 50ng RFRP-1 treatments into the CeA. Fifty nanogram dose of RFRP-1 significantly increased the step-through latency time, the 100ng RFRP-1 and the ANT alone were ineffective. The effect of 50ng RFRP-1 was eliminated by the ANT pretreatment. Our results suggest that intraamygdaloid RFRP-1 enhances learning processes and memory in aversive situations and this effect can specifically be prevented by ANT pretreatment.

The effect of neuropeptide FF in the amygdala kindling model

OBJECTIVE

Neuropeptide FF (NPFF) and its receptors (NPFF1 R and NPFF2 R) are differentially distributed throughout the central nervous system. NPFF reduces cortical excitability in rats when administered intracerebroventricularly (i.c.v.), and both NPFF and NPFF1 R antagonists attenuate pilocarpine-induced limbic seizures. In this study, our aim was to determine whether NPFF exerts anticonvulsant or anti-epileptogenic effects in the rat amygdala kindling model for temporal lobe seizures.

METHODS

Male Wistar rats were implanted with a recording/stimulation electrode in the right amygdala and a cannula in the left lateral ventricle. In a first group of animals, the afterdischarge threshold (ADT) was determined after a single i.c.v. infusion of saline (n = 8) or NPFF (1 nmol/h for 2 h; n = 10). Subsequently, daily infusion of saline (n = 8) or NPFF (1 nmol/h for 2 h; i.c.v.; n = 9) was performed, followed by a kindling stimulus (ADT+200 μA). Afterdischarge duration and seizure severity were evaluated after every kindling stimulus. A second group of rats (n = 7) were fully kindled, and the effect of saline or a high dose of NPFF (10 nmol/h for 2 h, i.c.v.) on ADT and the generalized seizure threshold (GST) was subsequently determined.

RESULTS

In naive rats, NPFF significantly increased the ADT compared to control (435 ± 72 μA vs 131 ± 23 μA [P < 0.05]). When rats underwent daily stimulations above the ADT, NPFF did not delay or prevent kindling acquisition. Furthermore, a high dose of NPFF did not alter ADT or GST in fully kindled rats.

CONCLUSIONS

I.c.v. administration of NPFF reduced excitability in the amygdala in naive, but not in fully kindled rats, and had no effect on kindling acquisition.