The physiological role of orexins.

Abstract

Orexins/hypocretins are recently discovered neuropeptides synthetized mainly by neurons located in the posterolateral hypothalamus. Hypocretin-1 and -2 are the same peptides as orexin-A and orexin-B. Orexin A is a 33 amino acid peptide with N-terminal pyroglutamyl residue and two intrachain disulphide bonds. Orexin B is a linear peptide of 28 amino acids. These two peptides are potent agonists at both the orexin-1 (OxR1) and orexin-2 (OxR2) receptors. Orexin-A is selective ligand for OxR1 and OX2 binds both orexins. The structure of orexins and their receptors is highly conservative in mammals. Orexin A sequence is identical in several mammalian species (human, mouse, rat, bovine and porcine). Intracerebroventricular administered orexin-A stimulates food intake and energy expenditure. Orexins are also involved in the regulation of neurohormones and pituitary hormones secretion as well as in the control of cardiovascular and sleep-wake function. Orexins also play a role in the pathogenesis of narcolepsy. Mutation in the gene coding preproorexin or OxR2 receptor gene results in narcolepsy in mice and canine. In patients with narcolepsy orexin neurotransmission was altered and orexin level in cerebrospinal fluid was undetectable.

Full text

Page 1

Neuroendocrinology Letters No.4 August Vol.26, 2005
Copyright © 2005 Neuroendocrinology Letters ISSN 0172–780X www.nel.edu
R E V I E W A R T I C L E
The physiological role of orexins
Lidia Martynska, Ewa Wolinska-Witort, Magdalena Chmielowska, Wojciech Bik &
Boguslawa Baranowska
Department of Clinical Neuroendocrinology Medical Centre of Postgraduate Education,
Marymoncka 99, 01-813 Warsaw, Poland.
Correspondence to:
Lidia Martynska
Department of Clinical Neuroendocrinology,
Medical Centre of Postgraduate Education,
Marymoncka 99, 01-813 Warsaw, POLAND
TEL/FAX: +48228344712
EMAIL: zncmkp@polbox.com
Submitted: October 12, 2004 Accepted: November 3, 2004
Key words:
orexins; control of appetite; hormones; narcolepsy
Neuroendocrinol Lett 2005; 26(3):289–292 PMID: 16135995 NEL260405R02 © Neuroendocrinology Letters www.nel.edu
Abstract
Orexins/hypocretins are recently discovered neuropeptides synthetized mainly by
neurons located in the posterolateral hypothalamus. Hypocretin-1 and -2 are the
same peptides as orexin-A and orexin-B. Orexin A is a 33 amino acid peptide with
N-terminal pyroglutamyl residue and two intrachain disulphide bonds. Orexin
B is a linear peptide of 28 amino acids. These two peptides are potent agonists at
both the orexin-1 (OxR1) and orexin-2 (OxR2) receptors. Orexin-A is selective
ligand for OxR1 and OX2 binds both orexins. The structure of orexins and their
receptors is highly conservative in mammals. Orexin A sequence is identical in
several mammalian species (human, mouse, rat, bovine and porcine). Intracere-
broventricular administered orexin-A stimulates food intake and energy expendi-
ture. Orexins are also involved in the regulation of neurohormones and pituitary
hormones secretion as well as in the control of cardiovascular and sleep-wake
function. Orexins also play a role in the pathogenesis of narcolepsy. Mutation in
the gene coding preproorexin or OxR2 receptor gene results in narcolepsy in mice
and canine. In patients with narcolepsy orexin neurotransmition was altered and
orexin level in cerebrospinal fluid was undetectable.
Introduction
Orexins/hypocretins are recently discovered
neuropeptides synthetized by neurons located in
the posterolateral hypothalamus. Hypocretin-1
and -2 are essentially the same peptides as orexin A
and B. Orexins/hypocretins are derived from 131
amino acid human (130 aa in the rat) precursor
prepro-orexin/hypocretin.
Orexin A/hypocretin 1 is 33 an amino acids
peptide with N-terminal pyroglutamyl residue
and two intrachain disulphide bonds. The human
orexin A/hypocretin 1 sequence is identical to the
mouse, rat, bovine and porcine orexin/hypocre-
tin.
Orexin B is a linear peptide of 28 amino acids.
There is 46% amino acid sequence identity between
orexin B (OxB) and orexin A (OxA) [1]. It has
been reported that Ox A, but not Ox B crosses the
blood-brain barrier [2].
Orexins (Oxs) action is mediated via G protein-
coupled receptors of two different subtypes (OxR1
and OxR2). OxR2 binds both orexin A and B and
OxR1 is highly selective for orexin A [3]. Orexin
immunoreactivity is widely distributed in the cen-
tral nervous system (in the hypothalamus, septum,
thalamus, brainstem and spinal cord [4, 5]. Orexin
fibres innervating neurons in the locus coeruleus

Page 2

290
Neuroendocrinology Letters No.4 August Vol.26, 2005 Copyright © Neuroendocrinology Letters ISSN 0172–780X www.nel.edu
represented the great peptidergic input in the pontine
region [6].
The role of orexins in the control of food
intake and energy expenditure
Immunohistochemical methods showed interaction
between orexin axon terminales and neuropeptide Y
(NPY) and proopiomelanocortin (POMC) –neurons in
the arcuate nucleus (ARC) of the rats [7, 8, 9]. Muroya
et al. [7] demonstrated that orexins directly regulated
NPY, POMC and glucose-responsive neurons in the
ARC and ventromedial hypothalamus (VMH) and
these results may indicate on the orexigenic action of
orexins.
It has been known that the lateral hypothalamus has
classically been considered to be the “feeding” centre
whereas the VMH is known as the “satiety” centre.
Orexin neurons in lateral hypothalamus have connec-
tions with NPY and agouti-releated peptide (AgRP)-
neurons in the ARC [6, 8]. The anatomical location of
orexins and interaction with orexigenic peptides may
indicate that the orexins play an important role in the
control of food intake.
Orexins are neuropeptides present in hypothalamic
nuclei involved in feeding, sleep-wakefulness, neuroen-
docrine homeostasis and autonomic regulation [10].
Orexins receptors are also expressed in peripheral
tissues. The expression of orexin receptors as well as
their biological role in the hypothalamus-pituitary axis,
gastrointestinal tract, endocrine pancreas, gonadal tis-
sues and other peripheral tissues was revealed [10, 11,
12].
There is some evidence that both NPY- and POMC-
containing neurons are regulated simultaneously by
both leptin and orexins [13]. The stimulatory effects of
ghrelin and orexin and inhibitory effect of leptin play a
role in the regulation of the activity of NPY neurons in
feeding behavior [14]. However, melanin-concentrated
hormone (MCH) effects on feeding is independent of
NPY and orexins [9].
Neurons expressing orexins are stimulated by starva-
tion and by hypoglycemia. Orexin neurons are activated
by low level of glucose but inhibited by visceral feed-
ing system mediated via vagal sensory pathway and the
nucleus of the solitary tract [15].
It has been published that intracerebroventricular
(icv) administration of orexin stimulate food intake in a
dose-depended manner in young rats [16]. However, no
effects were observed in old rats. The lack of response
to orexin administration in old rats may be connected
with the decrease in the OXR1 protein level in the hypo-
thalamus in old rats [16].
Sweet et al [17] suggested that functional opioid
pathways are necessary for orexin A-induced feeding.
Orexins play an important role in the regulation of
metabolic rate [18]. The orexins like galanin are “fat-
responsive” peptides that respond to circulating lipid
[19].
Dalal et al [20] and Arihara et al [21] showed for
the first time that orexin A can be detected in human
plasma. Adam et al [22] showed that orexin levels were
decreased in obese subjects and they correlated nega-
tively with leptin plasma level. Matsumura et al [23] and
Tomasik et al [24] demonstrated that orexin A concen-
tration significantly correlated with body mass index
(BMI) in normal subjects. Our previous data indicated
that plasma orexin A were significantly lower, however
plasma leptin and NPY were significantly higher in
obese patients as compared with the control group of
lean people [25]. Plasma orexin and leptin concentra-
tions inversely change during fasting and significantly
correlate with energy metabolism in non obese subjects
[26].
It has been reported that orexins are not only
involved in the regulation of energy balance but also
play an important role in the control of pituitary hor-
mones release.
The role of orexins in the regulation of
hormones release
Orexin fibers innervated hypothalamic regions
important for regulation of pituitary hormones release.
Hagan et al [27] showed that orexin A activates neurons
in the locus coeruleus. Orexin A releases neuropeptides
from hypothalamic explants in vitro [28]. Intracerebro-
ventricular administration of orexin A inhibited prolac-
tin (PRL) release and this effect is partially dependent of
dopamine [28]. A decrease of preproorexin expression
during pregnancy and lactation is involved in the adap-
tation of homeostatic mechanism and in mechanism of
elevated of PRL levels in these states [29].
On the other hand the high hypothalamic orexin
concentration may contribute to the LH and PRL surges
in the proestrus [30].
Centrally administred orexin A altered adrenocorti-
cotropin (ACTH) and corticosterone release. Orexin A
activates pituitary-adrenal axis [31]. It has been dem-
onstrated increased c-fos mRNA in the paraventricular
nucleus (PVN) of hypothalamus where corticotropin
releasing hormone (CRH) neurons are located [27, 31].
Intracerebroventricular injection of orexin A increased
ACTH and corticosterone and significantly increased
CRH mRNA expression in PVN in normal rats but the
response of pituitary-adrenal axis to orexin injection
was inhibited in pregnant rats [32]. These results may
indicate that orexin is involved in an anabolic adap-
tation in pregnancy. The existence of both OX1 and
OX2 receptor subtypes in the adrenal cortex has been
described [33]. This finding suggests that orexins may
also affect directly on glucocorticoids release.
Lopez et al [34] in experiments “in situ hybridisa-
tion” showed that growth hormone releasing hormone
(GHRH) mRNA in PVN is decreased after orexin
A treatment. The effects of icv injection of OxA on
hypothalamic somatostatin and GHRH mRNA levels
demonstrated interaction among the systems involved
in the control of food intake and GH secretion [34].
Chen and Xu [35] showed the increase of GH release
in vitro in response to alone injection of OxB and to
co-administration of OxA and GHRH. In experiments
Lidia Martynska, Ewa Wolinska-Witort Magdalena Chmielowska, Wojciech Bik & Boguslawa Baranowska

Page 3

291
Neuroendocrinology Letters No.4 August Vol.26, 2005 Copyright © Neuroendocrinology Letters ISSN 0172–780X www.nel.edu
The physiological role of orexins
in vivo icv injection of OxA inhibited GH release, and
GH responses to ghrelin. However, orexin A failed to
modify in vivo GH response to GHRH [36]. Orexin
plays an inhibitory role in GH secretion and may be
involved in regulatory mechanism nutritional status
and GH release.
Campbell et al [37] found that 75–85% of GnRH
neurons were contacted by orexin fibers and about
85% of GnRH neurons were co-localized with OxR1
and OxR2 – expressing GnRH neurons. These authors
showed co-expression of NPY Y4 receptor and orexin
fibers in relation to GnRH neurons. Stimulation of Y4
receptors leads to increase of LH release. These results
may suggest that orexin modulates GnRH neurons
directly via OxR1 or by stimulation Y4 receptor. Orexin
A stimulates GnRH release from hypothalamic explants
in vitro. Orexin stimulates LH secretion in steroid-
primed ovariectomized (OVX) female rats and sup-
presses LH secretion in non-primed OVX rats [38].
The results of Kok et al [39] indicate that orexins are
involved in the regulation of hypothalamo-pituitary-
gonadal (HPG) axis in humans. Reduction of basal LH
levels and normal LH release to GnRH stimulation in
narcoleptic men suggests that orexin may play a role
in the GnRH secretion [39]. Russell et al [40] demon-
strated in the rat OxA interaction with hypothalamo-
pituitary-gonadal axis. An interaction between orexin
and NPY was confirmed because a specific NPY Y1
antagonist abolished in vitro release GnRH by orexin
A [40].
The long form of leptin receptor is also found in
orexin cells [41] and leptin treatment regulated orexin
mRNA level [42].
Orexins – the role in the pathogenesis of
narcolepsy
It has been observed that orexins deficiency play a
role in the pathogenesis of narcolepsy [43]. Narcolepsy
is the neurological disease, characterized by excessive
daytime sleepiness, catalepsy, hypnagogic hallucina-
tions and sleep paralysis. Deficiencies of orexins neuro-
transmission may be the cause of narcolepsy. Mutation
in OxR2 in canine model and mice with a targeted dele-
tion of preproorexin gene display a phenotype similar
to that of human narcolepsy [44].
Orexins produced by the neuronal cell body located
in the lateral hypothalamus and parafornical nucleus
are important regulators of wakefulness, autonomic
nervous system tone, neuroendocrinal secretion, feed-
ing behavior and energy expenditure [8]. Plasma leptin
concentration and its circadian pulsatility are altered in
narcoleptic humans. In patients with narcolepsy orexin
neurotransmission is altered and orexin level in cere-
brospinal fluid is undetectable [46]. Genetic studies in
autosonal recessive canine model and in gene-targeted
mice have identified the hypothalamic orexin system
is very important to evaluation of human narcolepsy
[47, 48, 49].
Orexins – other physiological effects
Sakurai et al [50] observed very low orexin A con-
centration in patients with obstructive sleep apnea
hypopnea syndrome (OSAHS). These results suggest
that orexin may play a role in the pathogenesis of this
syndrome.
Orexins are involved in the regulation of cardiovas-
cular and autonomic functions. Samson et al [51] found
that OxA and B injected into lateral cerebral ventricle
stimulated the sympathetic function and resulted in an
increase in blood pressure and heart rate [51]. Orexin
containing fibres and receptors are associated with
regulation of cardiovascular and autonomic function
[52].
Orexin A may play a role in the thermoregulation
[53] and hypothermic effects of OxA are mediated by
NPY [53]. The role of OXR1 in mediating appoptosis
was also demonstrated [54].
REFERENCES
1 Taheri S, Bloom S. Orexins/hypocretins: waking up the scientific
world. Clin Endocrinol 2001; 54:421–429.
2 Kastin AJ, Akerstrom V. Orexin A but not orexin B rapidly en-
ters brain from blood by simple diffusion. J Pharmacol Exp Ther
1999; 289:219–222.
3 Sakurai T, Amemiya A, Ishii M, Matsuzaki I, Chemelli RM, Tanaka
H, et al. Orexins and orexin receptors: a family of hypothalamic
neuropeptides and G protein-coupled receptors that regulate
feeding behaviour. Cell 1998; 92:573–585.
4 Peyron C, Tighe DK, van Den Pol AN, Lecea L, Heller HC, Sutcliffe
JG, et al. Neurons containing hypocretin (orexin) project to mul-
tiple neuronal systems. J Neurosci 1998; 18:9996–10015.
5 Nambu T, Sakurai T, Mizukami K, Hosoya Y, Yanagisawa M, Goto
K. Distribution of orexin neurons in the adult rat brain. Brain Res
1999; 827:243–260.
6 Horvath TL, Peyron C, Diano S, Ivanov A. Aston-Jones G, Kilduff
TS, et al. Hypocretin (orexin) activation and synaptic innerva-
tion of the locus coeruleus noradrenergic system. J Comp Neu-
rol 1999; 415:145–159.
7 Muroya S, Funahashi H, Yamanaka A, Kohno D, Uramura K,
Nambu T, et al. Orexins (hypocretins) directly interact with
neuropeptide Y, POMC and glucose-responsive neurons to regu-
late Ca 2+ signaling in a reciprocal manner to leptin: orexigenic
neuronal pathways in the mediobasal hypothalamus. Eur J Neu-
rosci 2004; 19:1524–1534.
8 Broberger C, De Lecea L, Sutcliffe JG, Hokfelt T. Hypocretin/
orexin- and melanin-concentrating hormone-expressing cells
from distinct populations in the rodent lateral hypothalamus:
relationship to the neuropeptide Y and agouti gene-related
protein systems. J Comp Neurol 1998; 402:460–474.
9 Sahu A. Interactions of neuropeptide Y, hypocretin-I (orexin A)
and melanin-concentrating hormone on feeding in rats. Brain
Res 2002; 19:944: 232–238.
10 Voisin T, Rouet-Benzineb P, Reuter N, Laburthe M. Orexins and
their receptors: structural aspects and role in tissues. Cell Mol
Life Sci 2003; 60:72–87.
11 Karteris E, Chen J, Randeva HS. Expression of human prepro-
orexin and signaling characteristics of orexin receptors in the
male reproductive system. J Clinical Endocrinol Metab 2004;
89:1957–1962.
12 Johren O, Neidert SJ, Kummer M, Dendorfer A, Dominiak
P. Prepro-orexin and orexin receptor mRNAs are differen-
tially expressed in peripheral tissues of male and female rats.
Endocrinology 2001; 142 (8):3324–3331.
13 Funahashi H, Yamada S, Kageyama H, Takenoya F, Guan JL, Sh-
ioda S. Co-existence of leptin- and orexin-receptors in feeding-
regulating neurons in the hypothalamic arcuate nucleus-a triple
lebeling study. Peptides 2003; 24:687–694.

Page 4

292
Neuroendocrinology Letters No.4 August Vol.26, 2005 Copyright © Neuroendocrinology Letters ISSN 0172–780X www.nel.edu
14 Kohno D, Gao HZ, Muroya S, Kikuyama S, Yada T. Ghrelin directly
interacts with neuropeptide-Y-containing neurons in the rat
acuate nucleus: Ca2+ signaling via protein kinase A and N-type
channel-dependent mechanisms and cross-talk with leptin and
orexin. Diabetes 2003; 52:948–956.
15 Williams G, Cai XJ, Elliott JC, Harrold JA. Anabolic neuropeptides.
Physiol Behav 2004; 81:211–222.
16 Takano S, Kanai S, Hosoya H, Ohta M, Uematsu H, Miyasaka K.
Orexin-A does not stimulate food intake in old rats. Am J Physiol
Gastrointest Liver Physiol 2004; in press
17 Sweet DC, Levine AS, Kotz CM. Functional opioid pathways are
necessary for hypocretin-1 (orexin-A)- induced feeding. Peptides
2004; 25:307–314.
18 Lubkin M and Stricker-Krongrad A. Independent feeding and
metabolic actions of orexins in mice. Biochem Biophys Res Com-
muni 1998; 253:241–245.
19 Wortley KE, Chang GQ, Davydova Z, Leibowitz SF. Peptides that
regulate food intake: orexin gene expression is increased during
states of hypertrigliceridemia. Am J Regul Comp Physiol 2003;
284:R1454–1465.
20 Dalal MA, Schuld MD, Haack M, Uhr M, Geisler P, Eisensehr I, et al.
Normal plasma levels orexin A (hypocretin-1) in narcoleptic pa-
tients. Neurology 2001; 56:1749–1751.
21 Arihara Z, Tokahashi K, Murakami O, Totsume K, Sone M, Saton
IS, et al. Immunoreactive orexin – A in human plasma. Peptides
2001; 22:139–142.
22 Adam JA, Meuheere PPCA, Van Dielen FMH, Soeters PB, Baurman
WA, Greve JWM. Decreased plasma orexin – A levels in obese in-
dividuals. Intern J Ob 2002; 26:274–276.
23 Matsumura T, Nakayama M, Satoh H, Naito A, Kamahara K,
Sekizawa K. Plasma orexin A levels and body compasition in
COPD. Chest 2003; 123:1060–1065.
24 Tomasik PJ, Spodaryk M, Sztefko K. Plasma concentrations of
orexins in children. Ann Nutr Metab 2004; 48:215–220.
25 Baranowska B, Wolińska-Witort E, Martyńska L, Chmielowska
M, Baranowska-Bik A. Plasma orexin A, orexin B, leptin,
neuropeptide Y ( NPY) and insulin in obese women. Neuro-
endocrinol Lett 2005 in press.
26 Komaki G, Matsumoto Y, Nishikata H, Kawai K, Nozaki T, Takii M,
et al. Orexin-A and leptin change inversely in fasting non-obese
subjects. Eur J Endocrinol 2001; 144:654–651.
27 Hagan JJ, Leslie RA, Patel S, Evans ML, Wattam TA, Holmes S, et
al. Orexin A activates locus coeruleus cell firing and increase
arousal in the rat. Proc Natl Acad Sci USA. 1999; 99:10911–
10916.
28 Russell SH, Kim MS, Small CJ, Abbott CR, Morgan DGA, Taheri S,
et al. Central administration of orexin A suppresses basal and
domperidone stimulated plasma prolactin. J Neuroendocrinol
2000; 12:1213–1218.
29 Garcia MC, Lopez M, Gualillo O, Seoane LM, Dieguez C, Senaris
RM. Hypothalamic levels of NPY, MCH, and prepro-orexin mRNA
during pregnancy and lactation in the rat: role of prolactin.
FASEB J 2003; 15:1392–1400.
30 Porkka-Heiskanen T, Kalinchuk A, Alanko L, Huhtaniemi I, Sten-
berg D. Orexin A and B levels in the hypothalamus of female
rats: the effects of the estrous cycle and age. Eur J Endocrinol
2004; 150:737–742.
31 Kuru M, Ueta Y, Serino R, Nakazato M, Yomaoto Y, Shibuya I, et al.
Centrally administered orexin/hypocretin activates HPA axis in
rats. Neuroreport 2000; 11:1977–1980.
32 Brunton PJ, Russell JA. Hypothalamic-pituitary-adrenal re-
sponses to centrally administered orexin-A are suppressed in
pregnant rats. J Neuroendocrinol 2003; 15:633–637.
33 Johren O, Bruggemann N, Dominiak P. Orexins (hypocretins) and
adrenal function. Horm Metab Res 2004; 36:370–375.
34 Lopez M, Seoane LM, Tovar S, Nogueiras R, Dieguez C, Senaris R.
Orexin-A regulates growth hormone-releasing hormone mRNA
content in a nucleus-specific manner and somatostatin mRNA
content in a growth hormone-dependent fashion in the rat hy-
pothalamus. Eur J Neurosci 2004; 19:2080–2088.
35 Chen C, Xu R. The in vitro regulation of growth hormone secre-
tion by orexins. Endocrine 2003; 22:57–66.
36 Seoane LM, Tovar S.A., Perez D, Mallo F, Lopez M, Senaris R, et al.
Orexin A suppresses in vivo GH secretion. Eur J Endocrinol 2004;
150:731–736.
37 Campbell RE, Grove KL, Smith MS. Gonadotropin-releasing hor-
mone neurons coexpress orexin 1 receptor immunoreactiv-
ity and receive direct contacts by orexin fibers. Endocrinology
2003; 144:1542–1548.
38 Small CJ, Goubillon ML, Murray JF, Siddiqui A, Grimshaw SE,
Young H, et al. Central orexin A has site specific effects on lu-
teinizing hormone release in female rats. Endocrinology 2003;
144:3225–3236.
39 Kok SW, Roelfsema F, Overeem S, Lammers GJ, Frolich M, Mei-
nders AE, et al. Pulsatile LH release is diminished, while FSH se-
cretion is normal in hypocretin deficient narcoleptic men. Am J
Physiol Endocrinol Metab 2004; 287(4):E630–636.
40 Russell SH, Small CJ, Kennedy AR, Stanley S.A., Seth A, Murphy
KG, et al. Orexin A interactions in the hypothalamo-pituitary go-
nadal axis. Endocrinology 2001; 142(12):5294–5302.
41 Hakansson M, de Lecea L, Sutcliffe JG,Yanagisawa M, Meister B.
Leptin receptor – and STAT3-immunoreactivities in hypocretin/
orexin neurones of the lateral hypothalamus. J Neuroendocrinol
1999; 11:653–663.
42 Lopez M, Seoane L, Garcia MC, Lago F, Casanueva FF, Senaris
R, et al. Leptin regulation of prepro-orexin and orexin receptor
mRNA levela in the hypothalamus. Biochem Biophys Res Com-
mun 2000; 269:41–45.
43 Kok SW, Meinders AE, Overeem S, Lammers GJ, Roelfsema F, Frol-
ich M, et al. Reduction of plasma leptin levels and loss of its cir-
cadian rhythmicity in hypocretin (orexin)-deficient narcoleptic
humans. J Clin Endocrin Metab 2002; 87:805–809.
44 Chemelli RM, Willie JT, Sinton CM, Elmquist JK, Scammell T, Lee
C, et al. Narcolepsy in orexin knokout mice: molecular genetics
of sleep regulation. Cell 1999; 98:437–451.
45 Schuld A, Blum WF, Uhr M, Haack M, Kraus T, Holsboer F, et al. Re-
duced leptin levels in human narcolepsy. Neuroendocrinology
2000; 72:195–198.
46 Baumann C, Bassetti C. The neurotransmitter, hypocretin. An
overview. Nervenarzt 2004; 75:317–323.
47 Taheri S. The genetics of sleep disorders. Minerva Med 2004;
95:203–212.
48 John J, Wu MF, Maidment NT, Lam HA, Boehmer LN, Patton M, et
al. Developmental changes in CSF hypocretin-1 (orexin-A) level
in normal and genetically norcoleptic Doberman pinschers. J
Physiol 2004; in press
49 Wieczorek S, Jagiello P, Arning L, Dahmen N, Epplen JT. Screen-
ing for candidate gene regions in narcolepsy using a microsatel-
lite based approach and pooled DNA. J Mol Med 2004; in press
50 Sakurai S, Nishijima T, Takahashi S, Yamauchi K, Arihara Z, Taka-
hashi K. Clinical significance of daytime plasma orexin-A-like
immunoreactivity concentrations in patients with obstructive
sleep apnea hypopnea syndrome. Respiration 2004; 71:380–
384.
51 Samson WK, Gosnell B, Chang JK, Resch ZT, Murphy TC. Cardio-
vascular regulatory actions of the hypocretins in brain. Brain Res
1999; 831:248–258.
52 Shirasaka T, Takasaki M, Kannan H. Cardiovascular effects of
leptin and orexins. Am J Physiol Regul Integr Comp Physiol 2003;
284:R639–651.
53 Jaszberenyi M, Bujdoso E, Kiss E, Pataki I, Telegdy G. The role of
NPY in the mediation of orexin-induced hypothermia. Regul
Pept 2002; 104:55–59.
54 Rouet-Benzineb P, Rouyer-Fessard C, Jarry A, Avondo V, Pouzet
C, Yanagisawa M, et al. Orexins acting at native OX1 receptor in
colon cancer and neuroblastoma cells or at recombinant OX1 re-
ceptor suppress cell growth by inducing apoptosis. J Biol Chem
2004; in press

Lidia Martynska, Ewa Wolinska-Witort Magdalena Chmielowska, Wojciech Bik & Boguslawa Baranowska