Cardiovascular actions of central neuromedin U in conscious rats

Neuromedin U facilitates oxytocin release from the pituitary via β adrenoceptors

Neuromedin U activates noradrenergic neurones in the medulla oblongata and oxytocin neurones in the hypothalamus. Here we examined roles of noradrenergic transmission in oxytocin release from the pituitary after intracerebroventricular administration of neuromedin U in rats. Neuromedin U administration facilitated noradrenaline release in the supraoptic nucleus. Administration of a beta1 adrenoceptor antagonist, metoprolol, or a beta2 antagonist, ICI 118551 but not an alpha1 antagonist, benoxathian, reduced increases in plasma oxytocin concentrations observed after administration of neuromedin U, but plasma ACTH concentrations were not significantly changed. All theses data suggest that neuromedin U stimulates oxytocin release from the pituitary, at least in part, via activation of beta adrenoceptors.

Neuromedin U depolarizes rat hypothalamic paraventricular nucleus neurons in vitro by enhancing IH channel activity

The effect of neuromedin U (NMU) on rat paraventricular nucleus (PVN) neurons was examined using whole cell patch-clamp recordings. Under current-clamp, 31% of PVN parvocellular neurons (n = 243) were depolarized by 100 nM NMU, but magnocellular neurons were not affected. NMU (10 nM to 1 microM) resulted in increased basal firing rate and depolarization in a dose-dependent manner with an EC50 of 70 nM. NMU-induced depolarization was unaffected by co-perfusion with 0.5 microM TTX + 10 microM 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) + 10 microM bicuculline. Extracellular application of 70 microM ZD 7288 completely inhibited NMU-induced depolarization. Under voltage-clamp, 1 microM NMU produced negligible inward current but did increase the hyperpolarization-activated current (IH) at step potentials less than -80 mV. The effects of NMU on IH were voltage-dependent, and NMU shifted the IH conductance-voltage relationship (V1/2) by about 10.8 mV and enhanced IH kinetics without changing the slope constant (k). Extracellular application of 70 microM ZD 7288 or 3 mM Cs+ blocked IH and the effects of NMU in voltage-clamp. These results suggest that NMU selectively depolarizes the subpopulation of PVN parvocellular neurons via enhancement of the hyperpolarization-activated inward current.

A pro-nociceptive role of neuromedin U in adult mice

Although the neuropeptide neuromedin U (NMU) was first isolated from the spinal cord, its actions in this site are unknown. The recent identification of the NMU receptor subtype 2 (NMU2R) in the spinal cord has increased the interest in investigating the role of NMU in this part of the central nervous system. Here, we report a novel function for NMU in spinal nociception in the mouse. Systemic perfusion of NMU (rat, NMU-23) dose-dependently (0.2, 0.5, 1, and 2.5 microM) potentiated both the background activity and noxious pinch-evoked response of nociceptive or wide dynamic range, but not non-nociceptive, dorsal horn neurons. At 2.5 microM, NMU-23 increased the total background activity from 154+/-34 to 1374+/-260 spikes/160 s (P<0.005, n=28) and increased the evoked nociceptive response by 185+/-50% (P<0.01, n=13). Intrathecal administration of NMU-23 (0.4, 1.1, and 3.8 nmol/10 microl) dose-dependently decreased thermal withdrawal latencies and produced a morphine-sensitive behavioral response. These electrophysiological and behavioral results suggest that NMU may be a novel physiological regulator in spinal nociceptive transmission and processing.

Neuromedin U acts in the central nervous system to inhibit gastric acid secretion via CRH system

Neuromedin U (NMU) is a hypothalamic peptide involved in energy homeostasis and stress responses. NMU, when administered intracerebroventricularly, decreases food intake and body weight while increasing body temperature and heat production. In addition, NMU, acting via the corticotropin-releasing hormone (CRH) system, induces gross locomotor activity and stress responses. We studied the effect of intracerebroventricularly administered NMU (0.5-4 nmol) in the regulation of gastric functions in conscious rats. Intracerebroventricular administration of NMU significantly decreased gastric acid output to 30-60% and gastric emptying to 35-70% in a dose-dependent manner. Vagotomy did not abolish the inhibitory effect of NMU on pentagastrin-induced gastric acid secretion. Pretreatment with indomethacin (10 mg/kg), an inhibitor of prostaglandin synthesis, also did not affect NMU-induced acid inhibition. Pretreatment with anti-CRH IgG (1 microg/rat), however, completely blocked NMU-induced acid inhibition (P < 0.01). Administration of yohimbine (4 mg/kg), an alpha(2)-adrenergic receptor antagonist, also abolished NMU-induced acid inhibition (P < 0.01). These findings suggest that NMU is critical in the central regulation of gastric acid secretion via CRH.