Neuropeptide Y potentiates the pressor response evoked by carbachol administration into the posterior hypothalamic nucleus of conscious rat

Corticotropin releasing factor excites neurons of posterior hypothalamic nucleus to produce tachycardia in rats

Corticotropin releasing factor (CRF), a peptide hormone involved in the stress response, holds a key position in cardiovascular regulation. Here, we report that the central effect of CRF on cardiovascular activities is mediated by the posterior hypothalamic nucleus (PH), an important structure responsible for stress-induced cardiovascular changes. Our present results demonstrate that CRF directly excites PH neurons via two CRF receptors, CRFR1 and CRFR2, and consequently increases heart rate (HR) rather than the mean arterial pressure (MAP) and renal sympathetic nerve activity (RSNA). Bilateral vagotomy does not influence the tachycardia response to microinjection of CRF into the PH, while β adrenergic receptor antagonist propranolol almost totally abolishes the tachycardia. Furthermore, microinjecting CRF into the PH primarily increases neuronal activity of the rostral ventrolateral medulla (RVLM) and rostral ventromedial medulla (RVMM), but does not influence that of the dorsal motor nucleus of the vagus nerve (DMNV). These findings suggest that the PH is a critical target for central CRF system in regulation of cardiac activity and the PH-RVLM/RVMM-cardiac sympathetic nerve pathways, rather than PH-DMNV-vagus pathway, may contribute to the CRF-induced tachycardia.

Effect of basal forebrain neuropeptide Y administration on sleep and spontaneous behavior in freely moving rats

Neuropeptide Y (NPY) is present both in local neurons as well as in fibers in the basal forebrain (BF), an area that plays an important role in the regulation of cortical activation. In our previous experiments in anaesthetized rats, significant EEG changes were found after NPY injections to BF. EEG delta power increased while power in theta, alpha, and beta range decreased. The aim of the present experiments was to determine whether NPY infusion to BF can modulate sleep and behavior in freely moving rats. In this study, microinjections were made into the BF. Saline was injected to the control side, while either saline or one of two doses of NPY (0.5 microl, 300-500 pmol) to the treated side. EEG as well as behavioral changes were recorded. Behavioral elements after the NPY injections changed in a characteristic fashion in time and three consecutive phases were defined. In phase I (half hour 2), activated behavioral items (moving, rearing, grooming) appeared frequently. In phase II (half hours 3 and 4) activity decreased, while motionless state increased. Reappearance of activity was seen in phase III (half hours 5 and 6). NPY injections caused sleep-wake changes. The three phases described for behavioral changes were also reflected in the sleep data. During phase I, lower NPY dose increased wakefulness and decreased deep sleep. Reduced behavioral activity seen in phase II was partially reflected in the sleep. In this phase, wakefulness tended to increase in the third half hour, while decreased in the 4th half hour. Deep sleep and total slow wave sleep non-significantly decreased in the third and increased in the 4th half hour. In most cases, wakefulness was elevated again during Phase III, while sleep decreased. Length of single sleep-wake epochs did not change after NPY injections. Our results suggest a role for NPY in the integration of sleep and behavioral stages via the BF.

Peptide YY administration into the posterior hypothalamic nucleus of the rat evokes cardiovascular changes by non-adrenergic, non-cholinergic mechanisms

1 Microinjection of peptide YY (PYY) (0.23-2.3 nmol) into the posterior hypothalamic nucleus (PHN) of conscious rats evokes a dose-dependent pressor response and a bradycardia. 2 The increase in mean arterial pressure evoked by 2.3 nmol of PYY was not blocked by intravenous pretreatment with: (i) the nicotinic ganglionic receptor antagonist pentolinium (PENT, 10 mg kg(-1)) alone, or in combination with the muscarinic receptor antagonist methylatropine (MeATR, 1 mg kg(-1)); (ii) the alpha(1)-adrenoceptor antagonist prazosin (PRAZ, 0.2 mg kg(-1)); (iii) the V(1)-vasopressin receptor antagonist [d(CH(2))(5)Tyr(Me)]AVP (AVPX, 20 microg kg(-1)); (iv) the combination of AVPX, PENT and MeATR; (v) the combination of PRAZ, AVPX, PENT, MeATR, and the alpha(2)-adrenoceptor antagonist yohimbine (0.3 mg kg(-1)); or (vi) the angiotensin II type 1 receptor antagonist ZD 7155 (1 mg kg(-1)). 3 Adrenal demedullation inhibited the PYY-evoked responses of drug-naive rats, and rats pretreated with the combination of PENT, MeATR and AVPX. 4 Transection of the splanchnic nerve innervating the adrenal medullae attenuated the bradycardia, as did ZD 7155, but not the PYY-evoked pressor response. 5 Systemic pretreatment of rats with the neuropeptide Y(1) receptor antagonist BIBP 3226 (1 mg kg(-1)) blocked the PYY-evoked cardiovascular changes, but not those evoked by microinjection of carbachol (5.5 nmol) into the PHN. 6 These results suggest that the cardiovascular changes evoked from the PHN by PYY requires the presence of the adrenal medullae, which are stimulated by: (i) a hormone to release an NPY-like substance that evokes the pressor response, and (ii) the splanchnic nerve to evoke the release of a substance that results in the bradycardia.

The Y1 receptor subtype mediates the cardiovascular changes evoked by NPY administered into the posterior hypothalamic nucleus of conscious rat

An earlier study showed that the neuropeptide Y (NPY) receptor antagonist PYX-2 blocks the enhancement of a carbachol (CCh)-evoked pressor response produced by prior NPY administration into the posterior hypothalamic nucleus (PHN). The Y receptor subtype that mediates this response, and an increase in mean arterial pressure (MAP) and heart rate, remained unknown due to the lack of selectivity of PYX-2 for the Y receptor subtypes. Thus, the present study was undertaken to elucidate the Y receptor subtype responsible for mediating the NPY-evoked cardiovascular responses from the PHN by determining the rank order of potency of several NPY-related peptides for increasing MAP, and by correlating the pressor response evoked by these peptides to reported K(i)'s and IC(50)'s for the Y(1), Y(2), Y(4) and Y(5) receptor subtypes. The pharmacological profile (PYY>or=NPY>or=[Leu(31),Pro(34)]NPY>or=NPY(13-36)>or=hPP) and correlations suggest that the Y(1) and/or Y(5) receptor subtypes mediate these cardiovascular changes. Administration of the relatively non-selective Y receptor antagonist PYX-2 or the selective Y(1) receptor antagonist BIBP 3226 into the PHN prior to NPY completely blocked the cardiovascular responses. BIBP 3226 also blocked the cardiovascular changes evoked by [Leu(31),Pro(34)]NPY, NPY(13-36) and human pancreatic polypeptide (hPP). In contrast, neither BIBP 3226 nor PYX-2 inhibited the cardiovascular changes induced by peptide YY (PYY) or CCh microinjection into the PHN. These results show that NPY and PYY act on different receptors to mediate their respective cardiovascular changes from the PHN with NPY stimulating the Y(1) receptor.