MINIREVIEW
From heart to mind
The urotensin II system and its evolving neurophysiological role
Hans-Peter Nothacker
1
and Stewart Clark
2
1 Department of Pharmacology, University of California, Irvine, CA, USA
2 The Centre for Addiction and Mental Health, Toronto, Ontario, Canada
Introduction
Urotensin II (UII) is a peptide structurally related to
somatostatin ⁄ cortistatin peptides. It contains a carboxy-
terminal cysteine-bridged cyclic hexapeptide sequence
that is conserved across species. UII was originally iso-
lated from fish urophysis, a neuroendocrine gland
located in the caudal part of the spinal cord, using a
trout hindgut contraction assay [1]. For the decade fol-
lowing its discovery UII was regarded as an exclusive
product of the teleost urophysis. Contrary to this
belief, UII peptides have been shown to have a wide
phylogenetic distribution across the vertebrate lineage
(reviewed in [2]) and independent reports touting UII’s
potent cardiovascular effects in rats have dispelled its
mammalian irrelevance [3,4]. These important studies
inferred for the first time that a specific mammalian
UII receptor must exist and hence postulated the exist-
ence of mammalian UII-like peptides. The genes for
the mammalian orthologues coding for the preproform
of UII were finally discovered in 1998 [5,6]. Shortly
after, in the race for the identification of natural lig-
ands for orphan G-protein coupled receptors (GPCRs)

(REM) sleep. Recently, physiological data have provided further evidence
that UII is indeed a modulator of REM sleep. The peptide directly excites
cholinergic mesopontine neurons and increases the rate of REM sleep epi-
sodes. These new results and its emerging behavioral effects establish UII
as a neurotransmitter ⁄ neuromodulator in mammals and should spark fur-
ther interest into the neurobiological role of the peptide.
Abbreviations
CNS, central nervous system; CRF, corticotrophin-releasing factor; ERK, extracellular signal regulated kinase; GPCR, G-protein coupled
receptor; icv, intracerebroventricular; LDT, laterodorsal tegmental nucleus; PC, pro-hormone convertase; PLC, phospholipase C; PKC, protein
kinase C; PPT, pedunculopontine tegmental nucleus; PVN, hypothalamic paraventricular nucleus; REM, rapid eye movement; SENR, sensory
epithelium neuropeptides-like receptor; UII, urotensin II; URP, urotensin II-related peptide.
5694 FEBS Journal 272 (2005) 5694–5702 ª 2005 FEBS
direction was warranted by mounting evidence for a
role of UII in the pathogenesis of cardiac, renal
and hepatic disease (reviewed in [13–16]). In the fervor
of cardiovascular research successes it seemed to be
forgotten that UII was originally identified as a neuro-
peptide and that its major expression sites in mammals
were confined to certain motor nuclei of the central
nervous system (CNS). From the very beginning, these
findings pointed to a possible neuromodulatory role
for UII.
The aim of this review is to provide an overview of
the UII system and to describe the recently accumu-
lated evidence of its association with centrally acting
functions in mammals, particularly with regard to
arousal and sleep.
Molecular constituents of the UII
system
Presently, three molecules are known to form the UII

mammals sequenced to date [17].
The major biologically active part of both molecules
consists of a canonical cysteine bridged hexapeptide
ring with the sequence CFWKYC, also known as core,
which is invariant between species and ⁄ or paralogues.
Destruction of the cysteine bond by covalent modifica-
tion leads to an immediate loss of biological activity
[18]. Conversely, the amino terminus of both UII and
URP from mammals does not seem to carry much bio-
logical information, as it can be chemically modified
without significant loss of activity [19,20]. It is worth-
while to mention that most of the mature mammalian
UII structures have been deduced from genomic
sequences and so far only pig UII and rat URP have
been isolated and directly sequenced from hypothala-
mus and whole brain, respectively [9,17].
All UII isoforms identified so far contain an acidic
amino acid residue (aspartic or glutamic acid) that
directly precedes its cyclic core structure (Fig. 1) [2].
This particular amino acid is absent in URP, but the
peptide is still a potent agonist at the UII receptor
with a pharmacological profile equal to that of UII
[17,20]. Therefore, this residue is not necessary for
receptor activation. However, its stringent evolutionary
conservation in all known UII isoforms implicates a
not yet understood biological function related to this
residue. It can be speculated that a receptor subtype
exists that is able to distinguish between UII and URP
peptides, but in mammalian genomes no homologous
sequences can be found that would clearly provide evi-

endothelial and smooth muscle cells. Direct evidence
has been presented for a UII converting enzyme activ-
ity present in porcine renal tissue [23]. This is an
intriguing finding, as differential expression of this or
similar enzymes would have dramatic influences on
UII functional dynamics in different tissues. The pre-
sent knowledge of UII biosynthesis has been recently
reviewed [14].
The UII receptor belongs to the large family of
GPCRs. It was originally cloned by homology screen-
ing methods as an orphan receptor called GPR14 or
SENR. Human UII receptor is located on chromo-
some 17q25 as an intronless gene that codes for a 389
amino acid long polypeptide. The receptor exhibits the
prototypical GPCR serpentine structure containing
seven transmembrane domains alternately interspersed
by intra- and extracellular loops (Fig. 1). Phylogenetic
analysis of the receptor’s primary sequence shows stri-
king similarities to the somatostatin receptor family,
most notably in the transmembrane domains. The
pharmacological relatedness of somatostatin receptors
is demonstrated by the fact that the UII receptor is
activated by micromolar concentrations of somato-
statin derivatives and can be blocked by somatostatin
antagonists [8,24]. However, it is rather implausible
that somatostatin acts at UII receptor sites in vivo
under normal physiological conditions, because UII is
more than 10 000-fold more potent and acts at pico-
molar concentrations in a quasi irreversible manner.
Initially the receptor expressed in heterologous

elusive. Short-term UII receptor activation examined
by Fura-2 imaging in dissociated rat spinal cord motor
neurons showed an influx of extracellular calcium via
N-type calcium channels that could be prevented by
N-type specific channel blockers [28]. Additional experi-
ments suggested an activation of the channels via
proteinase kinase A dependent phosphorylation and
no involvement of PKC in the process.
While the UII receptor was initially considered to
only couple Ga
q
proteins, the receptor seems to be
involved in an array of interactions with other signa-
ling molecules whose full spectrum remains to be
determined.
Tissue localization of UII receptor and
peptides
Early studies using hybridization techniques revealed
strong mammalian UII expression in only restricted
areas like the spinal cord, medulla oblongata and kid-
ney [6–8]. Recently, more sensitive RT-PCR techniques
have shown a more ubiquitous distribution of UII
mRNA in various tissues and blood vessels. A recent
survey of both UII and URP transcripts in rat and
human showed species specific expression patterns for
both genes [17]. The most common denominator of
UII expression in rat and human seems to be spinal
cord, which constantly exhibits highest expression
independent of the detection technique. URP is also
ubiquitously found, but in rather low expression levels

are also colocalized in the same neurons [22].
UII receptor expression seems rather ubiquitous
when assessed with highly sensitive RT-PCR technol-
ogy. It has to be kept in mind however, that the UII
receptor might be present in microvessels of the inves-
tigated tissue and not directly expressed in the tissue
specific cell populations. That might be one explan-
ation for the sometimes controversial results using
different detection techniques that vary in their
sensitivities. For example, the UII receptor expression
in rat brain seems to be ubiquitous when assessed by
RT-PCR [31]. Those results substantially differ when
less sensitive in situ hybridization methods are used. In
the latter case UII receptor mRNA exclusively local-
izes to brainstem cholinergic neurons of the laterodor-
sal tegmental (LDT) and pedunculopontine tegmental
nuclei (PPT), and no other expression sites could be
found [32]. Further investigation of the receptors’ site
of action using in situ binding techniques revealed a
much broader expression of the receptor. However, the
binding sites matched the projection areas of the
LDT–PPT complex leading to the hypothesis that
the binding sites might represent presynaptic neuro-
nal terminals. Because cholinergic neurons of the
LDT–PPT are functionally associated with sleep and
wake states, it led to the hypothesis that UII receptor
might be involved in the regulation of sleep-wake
cycles. Functional UII receptors are also detected in
cholinergic motor neurons of the spinal cord, possibly
in the same neuronal population that expresses UII

mone and adrenalin providing the first direct evidence
for a role of UII in the activation of the hypothalamic-
pituitary axis [40] although the pathway remains
mysterious. An increase of c-fos immunoreactivity, a
general indicator of neuronal activity, could not be
found in the PVN [41] two hours after UII injections.
Because c-fos expression temporally progresses to
downstream neuronal circuitries, and the latter study
recorded only one time point, it is possible that activa-
tion of PVN neurons could have simply been missed.
In preliminary studies also carried out in rats we have
seen a significant increase of c-fos mRNA levels in
PVN 20 min after intracerebroventricular (icv) admin-
istration. The PVN plays an important role in stress
and arousal related behavioral responses (reviewed
in [42]) and several stress-related responses have
been reported in rodents after central UII injection.
Low doses of icv administered UII into rats led to a
H P. Nothacker and S. Clark Urotensin II and its neurophysiological role
FEBS Journal 272 (2005) 5694–5702 ª 2005 FEBS 5697
dose-dependent increase in locomotion in a familiar
environment and a dose-dependent increase of ambula-
tory movements, although the effects were less pro-
nounced as compared with CRF and orexin, which
are both much stronger inducers of locomotion and
arousal in rats [31].
In mice central UII injections caused anxiety-like
behavior assessed by two different paradigms: the ele-
vated plus maze and the hole-board head-dipping test
[43]. UII acted dose-dependently in an anxiogenic fash-

polysomnography, the simultaneous recording of elec-
trophysiological potentials measured in the cortex and
skeletal musculature of the neck and eye. Sleep exhibits
a distinct architecture that can be basically divided
into three different states; wakefulness, slow wave and
rapid eye movement (REM, also known as paradoxical
sleep). In most laboratory animals such as rodents the
three stages form a cycle that is repeated many times
during the entire sleep period, but occurs less fre-
quently in humans. In waking states, neurotransmitter
systems governed by norepinephrine, serotonin, and
acetylcholine are all activated in the brainstem, while
in slow wave sleep, all are suppressed. Wakefulness is
accompanied by fast, low-voltage electrical activity in
the cortex and the subcortical structures of the brain,
and by a significant amount of tonus in the skeletal
muscles. REM sleep represents a paradox sleep state in
the sense that electrical activity in the cortex is similar
to that seen in wakefulness while electrical activity in
muscles has disappeared.
REM sleep is related to the specific activation of
cholinergic circuits located in the LDT and PPT of the
pons-midbrain transition area (Fig. 2). Lesions of the
cholinergic LDT–PPT complex lead to a loss of REM
sleep without deficits in wakefulness and cortical acti-
vation [46]. The injection of cholinergic agonists into
the medial pontine reticular formation, a target region
of the LDT–PPT induces a REM-like state [47–50].
These and other studies clearly indicate that choliner-
gic neurons in the PPT are important regulators of

encephalogram bands suggest qualitative differences in
cortical activation between the two routes of adminis-
tration. Moreover, icv administered UII also led to an
increase in cortical blood flow, which points to the direct
activation of cerebral vasculature or the activation of
brain areas that are involved in cardiovascular regula-
tion. The noradrenergic A1 area, located in the lower
medulla has been identified as a possible neural sub-
strate of UII’s central cardiovascular action because
microinjections of UII into A1 causes strong systemic
cardiovascular responses in anesthetized rats [34].
At first UII’s ability to increase the number of REM
sleep episodes may seem at odds with the earlier dis-
cussed observations, which point to more anxiogenic
and stress related properties. This apparent contradic-
tion may be due to the time course of the effect, and
the route of administration. The studies describing
increased locomotion and anxiety were measured soon
after UII application (within one hour) and utilize icv
route of administration that is known to increase corti-
cal blood flow [44] within the same period of time.
Huitron-Resendiz et al. [44], reported that when UII
was applied icv, a significant increase in wakefulness
was observed during the first hour postinjection. The
amount of wakefulness returned to control levels after
two hours, whereas, the increase in the number of
REM sleep episodes could be observed for up to five
hours. Local UII application into the PPT did not pro-
duce any effect on wakefulness, nor was there an
increase in cerebral blood flow, suggesting the effect

Preliminary data collected in our laboratory from rats
show only diffuse URP mRNA expression in certain
areas of the medulla oblongata that are not known to
project to the PPT. There will be a need to produce
selective tools (antibodies, UII ⁄ URP transgenic mouse
strains) that distinguish between the two precursors
and that can be used to create a comprehensive map
of the anatomical circuitry of the UII system. An
established UII circuitry will help to build hypothetical
models that can be experimentally tested and that will
aid the understanding of UII’s interaction with other
sleep and wake promoting systems.
Conclusions
The discovery of UII as a direct activator of central
cholinergic neurons and a modulator of REM sleep
features again the power of reverse physiological strat-
egies to gain new insights into little understood physio-
logical processes. It also introduces a novel player in
the neurochemistry and the electrophysiology of the
complex basis of sleep regulation and offers the oppor-
tunity to study the UII system in relation to other
sleep associated neuropeptides. More sleep studies will
be necessary to establish UII’s role in REM sleep
modulation. Besides the sleep data, there is an accu-
mulation of evidence that the UII system might have a
general role in promoting acetylcholine release and act
as an excitatory modulator. The availability of mouse
models devoid of UII receptor or its ligands will pro-
vide a rational approach for the investigation of the
neurophysiological role of the UII system. While our

tion of major artery segments of rat by fish neuropep-
tide urotensin II. Am J Physiol 252, R361–R366.
4 Gibson A, Wallace P & Bern HA (1986) Cardiovascular
effects of urotensin II in anesthetized and pithed rats.
Gen Comp Endocrinol 64 , 435–439.
5 Coulouarn Y, Jegou S, Tostivint H, Vaudry H & Lihr-
mann I (1999) Cloning, sequence analysis and tissue dis-
tribution of the mouse and rat urotensin II precursors.
FEBS Lett 457, 28–32.
6 Coulouarn Y, Lihrmann I, Jegou S, Anouar Y, Tosti-
vint H, Beauvillain JC, Conlon JM, Bern HA & Vaudry
H (1998) Cloning of the cDNA encoding the urotensin
II precursor in frog and human reveals intense expres-
sion of the urotensin II gene in motoneurons of the
spinal cord. Proc Natl Acad Sci USA 95, 15803–15808.
7 Ames RS, Sarau HM, Chambers JK, Willette RN,
Aiyar NV, Romanic AM, Louden CS, Foley JJ, Sauer-
melch CF, Coatney RW, et al (1999) Human urotensin-
II is a potent vasoconstrictor and agonist for the orphan
receptor GPR14. Nature 401, 282–286.
8 Nothacker HP, Wang Z, McNeill AM, Saito Y, Merten
S, O’Dowd B, Duckles SP & Civelli O (1999) Identifica-
tion of the natural ligand of an orphan G-protein-
coupled receptor involved in the regulation of vasocon-
striction. Nat Cell Biol 1 , 383–385.
9 Mori M, Sugo T, Abe M, Shimomura Y, Kurihara M,
Kitada C, Kikuchi K, Shintani Y, Kurokawa T, Onda
H, Nishimura O & Fujino M (1999) Urotensin II is the
endogenous ligand of a G-protein-coupled orphan
receptor, SENR (GPR14). Biochem Biophys Res

M, Ishibashi Y, Kitada C, Miyajima N, Suzuki N, Mori
M & Fujino M (2003) Identification of urotensin II-
related peptide as the urotensin II-immunoreactive
molecule in the rat brain. Biochem Biophys Res Commun
310, 860–868.
18 McMaster D, Kobayashi Y, Rivier J & Lederis K
(1986) Characterization of the biologically and antigeni-
cally important regions of urotensin II. Proc West Phar-
macol Soc 29, 205–208.
19 Coy DH, Rossowski WJ, Cheng BL & Taylor JE (2002)
Structural requirements at the N-terminus of urotensin
II octapeptides. Peptides 23, 2259–2264.
20 Chatenet D, Dubessy C, Leprince J, Boularan C, Carlier
L, Segalas-Milazzo I, Guilhaudis L, Oulyadi H, Dav-
oust D, Scalbert E et al (2004) Structure-activity rela-
tionships and structural conformation of a novel
urotensin II-related peptide. Peptides 25, 1819–1830.
21 Clozel M, Binkert C, Birker-Robaczewska M, Boukha-
dra C, Ding SS, Fischli W, Hess P, Mathys B, Morrison
K, Muller C, et al (2004) Pharmacology of the uroten-
sin-II receptor antagonist palosuran (ACT-058362;
1-[2-(4-benzyl-4-hydroxy-piperidin-1-yl)-ethyl]-3-
(2-methyl-quinolin-4-yl)-urea sulfate salt): first demon-
stration of a pathophysiological role of the urotensin
System. J Pharmacol Exp Ther 311, 204–212.
Urotensin II and its neurophysiological role H P. Nothacker and S. Clark
5700 FEBS Journal 272 (2005) 5694–5702 ª 2005 FEBS
22 Pelletier G, Lihrmann I, Dubessy C, Luu-The V, Vau-
dry H & Labrie F (2005) Androgenic down-regulation
of urotensin II precursor, urotensin II-related peptide

immunohistochemical localization of urotensin II in the
human brainstem and spinal cord. J Neurochem 91,
110–118.
30 Dun SL, Brailoiu GC, Yang J, Chang JK & Dun NJ
(2001) Urotensin II-immunoreactivity in the brainstem
and spinal cord of the rat. Neurosci Lett 305, 9–12.
31 Gartlon J, Parker F, Harrison DC, Douglas SA, Ash-
meade TE, Riley GJ, Hughes ZA, Taylor SG, Munton
RP, Hagan JJ, et al (2001) Central effects of urotensin-
II following ICV administration in rats. Psychopharma-
cology (Berl) 155, 426–433.
32 Clark SD, Nothacker HP, Wang Z, Saito Y, Leslie FM
& Civelli O (2001) The urotensin II receptor is expressed
in the cholinergic mesopontine tegmentum of the rat.
Brain Res 923, 120–127.
33 Brailoiu E, Brailoiu GC, Miyamoto MD & Dun NJ
(2003) The vasoactive peptide urotensin II stimulates
spontaneous release from frog motor nerve terminals.
Br J Pharmacol 138, 1580–1588.
34 Lu Y, Zou CJ, Huang DW & Tang CS (2002) Cardio-
vascular effects of urotensin II in different brain areas.
Peptides 23, 1631–1635.
35 Lin Y, Tsuchihashi T, Matsumura K, Fukuhara M,
Ohya Y, Fujii K & Iida M (2003) Central cardiovascu-
lar action of urotensin II in spontaneously hypertensive
rats. Hypertens Res 26, 839–845.
36 Lin Y, Tsuchihashi T, Matsumura K, Abe I & Iida M
(2003) Central cardiovascular action of urotensin II in
conscious rats. J Hypertens 21, 159–165.
37 Vale W, Spiess J, Rivier C & Rivier J (1981) Characteri-

cholinergic neurons. J Neuroscience 25, 5465–5474.
45 Behm DJ, Harrison SM, Ao Z, Maniscalco K, Pickering
SJ, Grau EV, Woods TN, Coatney RW, Doe CP, Wil-
lette RN et al (2003) Deletion of the UT receptor gene
results in the selective loss of urotensin-II contractile
activity in aortae isolated from UT receptor knockout
mice. Br J Pharmacol 139, 464–472.
46 Webster HH & Jones BE (1988) Neurotoxic lesions of
the dorsolateral pontomesencephalic tegmentum-choli-
nergic cell area in the cat. II. Effects upon sleep-waking
states. Brain Res 458, 285–302.
47 George R, Haslett WL & Jenden DJ (1964) A choliner-
gic mechanism in the brainstem reticular formation:
induction of paradoxical sleep. Int J Neuropharmacol
72, 541–552.
48 Baghdoyan HA, Monaco AP, Rodrigo-Angulo ML,
Assens F, McCarley RW & Hobson JA (1984)
H P. Nothacker and S. Clark Urotensin II and its neurophysiological role
FEBS Journal 272 (2005) 5694–5702 ª 2005 FEBS 5701
Microinjection of neostigmine into the pontine reticu-
lar formation of cats enhances desynchronized sleep
signs. J Pharmacol Exp Ther 231, 173–180.
49 Quattrochi JJ, Mamelak AN, Madison RD, Macklis JD
& Hobson JA (1989) Mapping neuronal inputs to REM
sleep induction sites with carbachol-fluorescent micro-
spheres. Science 245, 984–986.
50 Bourgin P, Escourrou P, Gaultier C & Adrien J (1995)
Induction of rapid eye movement sleep by carbachol
infusion into the pontine reticular formation in the rat.
Neuroreport 6, 532–536.