Research reportNeuromedin C decreases potassium conductance and increases a non-specific conductance in rat suprachiasmatic neurones in brain slices in vitro
Introduction
Neuromedin C (NMC) is one of three mammalian counterparts to the bombesin-like peptide family, which includes peptides derived from amphibian and mammalian tissues. All three mammalian peptides, which includes gastrin-releasing peptide (GRP) and neuromedin B (NMB), have been isolated from porcine spinal cord and non-antral gastric tissue 18, 19, 24, 25, 26. The peptide NMC is the carboxy terminal decapeptide fragment of the mammalian counterpart gastrin-releasing peptide (GRP). Bombesin and a number of related amphibian peptides were themselves isolated from the skin of a number of species of European and American frogs 2, 10, 11. Both amphibian and mammalian members of the bombesin-like peptide family have been shown to evoke a range of biological responses in vivo which includes effects on feeding, thermoregulation, blood pressure, locomotor activity and circadian rhythms 1, 3, 8, 10, 12, 21. To date, two mammalian bombesin receptor subtypes have been cloned, termed the GRP and NMB receptor subtypes 6, 41. In situ hybridisation studies have shown that each receptor subtype displays a distinct distribution throughout the rat CNS, with overlap in some regions [5].
Evidence supports the view that the biological clock or circadian pacemaker is located within the suprachiasmatic nucleus (SCN), a structure located in the rostral hypothalamus 20, 24, 27, 38. Albers et al. (1991) have recently demonstrated that GRP is able to induce phase shifts in circadian rhythms, noted as delays in the onset of wheel-running activity in hamsters [1]. This evidence supports a role for the mammalian form of bombesin in the re-entrainment of circadian rhythms. In a previous study, we reported the use of the three mammalian counterparts and the selective GRP-receptor antagonist [d-Phe6]bombesin(6–13)ethylamide to examine the pharmacology of the bombesin receptors expressed within the SCN [32]. The data obtained were supportive of the predominant expression of the GRP-preferring bombesin receptor subtype by a subpopulation of suprachiasmatic neurones. In this present study using NMC we have examined the ionic mechanism which underlies the acute excitatory responses to the bombesin-like peptides. The peptide GRP, and the decapeptide fragment NMC, have been shown to be expressed by neurones which appear to be intrinsic to the nucleus 24, 40. This aim has been achieved by application of the whole-cell recording technique to acutely prepared rat brain slices.
Section snippets
Preparation of brain slices
Coronal brain slices containing the suprachiasmatic nuclei were prepared from rats as previously described [30]. Prior to sacrifice, male Wistar rats were housed in a 12-h light–dark cycle. During the subjective day only, rats (50–150 g) lightly anaesthetized with ether were killed by cervical dislocation and the brain was rapidly removed. Coronal slices (350–400 μm) were cut at the level of the rostral hypothalamus in a vibratome (Oxford instruments) filled with artificial cerebrospinal fluid
Results
All whole-cell recordings were made in the dorsal region of the nucleus, on the border of the SCN and periventricular nucleus of the hypothalamus. In our previous report [30]this region was referred to as the PVN/SCN region.
Discussion
Using the whole-cell recording technique we have demonstrated that nanomolar concentrations of NMC can evoke excitatory responses from a subpopulation of suprachiasmatic neurones. A comparison of the present current clamp recordings of the potency, magnitude and duration of the responses to the bombesin related peptides, with our previously reported study [30], suggests that the responses to NMC were little affected by the invasive nature of the whole-cell recording technique. The most notable
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Gastrin-releasing peptide receptor mediates the excitation of preoptic GABAergic neurons by bombesin
2016, Neuroscience LettersCitation Excerpt :More importantly, the data reported here suggests that excitation of GABAergic preoptic neurons may represent a mechanism for inducing hypothermia. Several studies have reported excitatory effects of bombesin on central neurons and the mechanisms involved appear to be cell type-specific including modulation of K+ conductances, activation of a nonselective conductance, and the activation of a Na+/Ca2+ exchanger [15,16,6,23,2,4]. Our data indicate that in GABAergic preoptic neurons GRP activates Ca2+ release from intracellular stores and a Ca2+ −dependent cationic conductance, however the specific ion channel subunits and second messengers involved remain to be established.
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Present address: Merck Sharpe and Dohme Neuroscience Research Center, Terlings Park, Harlow, Essex, UK