Brain Research 887 2000 391–398 www.elsevier.com locate bres
Research report
Effects of long-term infusion of anorexic concentrations of islet amyloid polypeptide on neurotransmitters and neuropeptides in rat
brain
a , a
b d
Urban Arnelo , Margery K. Herrington , Elvar Theodorsson , Thomas E. Adrian ,
d a
c a
d
¨ ¨
Roger Reidelberger , Jorgen Larsson , Jan Marcusson , Lisa Strommer , Xianzhong Ding ,
a
Johan Permert
a
Arvid Wretlind Laboratory for Metabolic Research , Department of Surgery, Karolinska Institutet at Huddinge University Hospital,
S- 14186 Stockholm, Sweden
b
¨ ¨
Department of Clinical Chemistry , University Hospital, Linkoping University, S-58185, Linkoping, Sweden
c
¨ ¨
Department of Geriatric Medicine , University Hospital, Linkoping University, S-58185 Linkoping, Sweden
d
Department of Biomedical Sciences , Creighton University School of Medicine, Omaha, NE 68178, USA
Accepted 3 October 2000
Abstract
Islet amyloid polypeptide IAPP or amylin potently reduces food intake in rats at or near physiological concentrations. Although the mechanisms of action of IAPP are not understood, the brain is a suggested site. Changes in hypothalamic and striatal neurotransmission
have been reported following acute systemic administration of a pharmacological concentration of IAPP. In the current study, we evaluated the effects of chronic administration of low doses of IAPP on satiety-related neurotransmitters and neuropeptides in the
hypothalamus, hippocampus, striatum, left cortex, and right cortex of the rat. Doses of 0, 5 and 25 pmol IAPP kg–min were administered subcutaneously for 2 or 5 days. Food intake was reduced by 27 and 44 both P,0.001 for the 5 and 25 pmol kg–min groups,
respectively, in the 2-day experiment and was decreased by 14 P,0.01 and 24 P,0.001, respectively, in the 5-day experiment. Body weight was significantly decreased in a dose-dependent fashion. In the 2-day experiment, norepinephrine increased in the
hypothalamus in the 5 pmol IAPP kg–min group, and neurotensin increased in the hippocampus in the 25 pmol kg–min rats both P,0.05. In the 5-day, 5 pmol kg–min rats, 5-hydroxyindoleacetic acid 5-HIAA increased in the hypothalmus and cholecystokinin
CCK increased in the striatum both P,0.05. In the 5-day, 25 pmol kg–min group, neuropeptide Y NPY increased in the hypothalamus P,0.01 and CCK increased in the hypothalmus and striatum both P,0.05. The present study confirms that IAPP is a
potent anorectic peptide at low doses and suggests that IAPP not only affects classical neurotransmitters in the brain but also alters concentrations of neuropeptides known to be involved in food intake.
2000 Elsevier Science B.V. All rights reserved.
Theme : Endocrine and autonomic regulation
Topic : Gastrointestinal and urogenital regulation
Keywords : Brain; Islet amyloid polypeptide; Monoamine; Neuropeptide; Satiety; Body weight
1. Introduction into the circulation together with insulin following food
ingestion [5,10]. Although IAPP has been demonstrated to Islet amyloid polypeptide IAPP is a 37-amino-acid
exert several biological effects, including hypocalcemia peptide produced by the b-cells of the pancreatic islets
[41], inhibition of gastric emptying [42], and impairment [40]. Under normal conditions, the peptide is co-released
of glucose metabolism [21,36], a physiologic role for the peptide has not been established. More recently, IAPP has
been shown to be a potent inhibitor of feeding in experi-
Corresponding author. Tel.: 146-8-5858-0000; fax: 146-8-5858-
ments using a number of different models and modes of
3850. E-mail address
: urban.arnelokaro.ki.se U. Arnelo.
treatment [2–6,9,11,12,22–24,26–28]. Because inhibition
0006-8993 00 – see front matter
2000 Elsevier Science B.V. All rights reserved. P I I : S 0 0 0 6 - 8 9 9 3 0 0 0 3 0 7 0 - 5
392 U
has been seen with plasma levels of IAPP that are at or min, n510; 5 pmol kg–min, n59; 25 pmol kg–min,
very close to physiological concentrations, it has been n59 and the other rats were infused for 5 days IAPP
suggested that IAPP may play a hormonal role in the dose: 0 pmol kg–min, n59; 5 pmol kg–min, n59; 25
control of food intake. pmol kg–min, n59. After 2 or 5 days of treatment, the
Although the mechanisms for an endocrine role of the animals were anesthetized again, and a blood sample was
peptide are poorly understood, experimental data suggests taken from the abdominal aorta for measurement of blood
that the central nervous system is a likely target. There is glucose, plasma IAPP, and plasma insulin. The animals
evidence that IAPP can cross the blood brain barrier [7], were then decapitated with a guillotine and the brains
suggesting that the IAPP in the brain enters from the removed and dissected on ice.
circulation. Brain administration appears to be more potent than systemic administration for reducing food intake
2.2. Animals and housing conditions [3,31]. High-affinity binding sites for IAPP have been
demonstrated in scattered areas within the brain, including A total of 55 male Wistar rats BK Universal Ltd.,
parts of the hypothalamus [35]. IAPP-induced anorexia has Sollentuna, Sweden were individually housed in plastic
been observed following injections of pharmacological shoebox cages on aspen-chip bedding Macrolon [3,
doses, administered either intrahypothalamically in rats Scanbur, Køge, Denmark. Water and standard rodent
[6,12] or intracerebroventricularly in rats [9,23,31] or mice pelleted chow R36, Lactamin, Vadstena, Sweden were
[26]. In addition, intrahypothalamic injections of IAPP available ad libitum throughout the experiments. The
have been shown to inhibit feeding induced by neuro- humidity of the air was maintained between 55 and 60,
peptide-Y NPY in rats [6]. and the temperature was kept at 22618C. The room had a
Intrahypothalamic injections of IAPP have been reported 12-h light and dark cycle, with lights out at 1800. The
to cause neurochemical alterations in the rat brain, with animals were weighed each day, and the daily chow intake
increases in dopamine and serotonin neurotransmission was recorded after being corrected for spillage. The
seen in the hypothalamus and corpus striatum [12]. Sys- experiment was approved by the Animal Research Com-
¨ temic administration of IAPP as a single bolus injection
mittee for
Southern Stockholm
Stockholms Sodra
¨ ¨ ¨
increased concentrations of serotonin in the hypothalamus Forsoksdjursetiska Namnd. Rats were handled according
and decreased levels of the dopamine metabolite 3- to guidelines established by the National Board for Labora-
methoxytyramine in the corpus striatum [11]. However, tory Animals CFN in Sweden.
changes in neuropeptides known to be involved in the regulation of feeding have not been studied following
2.3. IAPP preparation and osmotic mini-pump infusion IAPP administration.
We have previously reported markedly elevated plasma The effects of IAPP were studied after 2 days of
IAPP concentrations in patients with pancreatic cancer, a infusion, when peak inhibition of food intake was expected
disease often associated with anorexia [30]. We have also and at 5 days, when the anorectic effects were expected to
demonstrated that chronic IAPP infusion in rats, at a dose have diminished [2,3]. The Alzet Alza Corp., Palo Alto,
producing plasma levels similar to those of pancreatic CA model 1003D mini-pump was used for the 2-day
cancer patients, causes a reduction of food intake but has infusions and model 2001 was used for the 5-day infu-
no effect on glucose metabolism [3–5]. However, these sions. Synthetic rat IAPP Multiple Peptide Systems, San
experiments did not investigate the mechanisms respon- Diego, CA was dissolved in 75 DMSO 25 saline
sible for the anorectic effects of IAPP. 0.15 M. The osmotic mini-pumps were implanted 5 cm
The aim of the present study was, therefore, to use doses behind the base of the skull and just to the right of the
of IAPP that were anorectic but not diabetogenic to midline under aseptic surgical conditions, following induc-
investigate the effects of chronically-elevated plasma tion of anesthesia with ketamine, 40 mg kg IP Ketalar 50
levels of IAPP on neurotransmitters and neuropeptides in mg ml, Park-Davis, Barcelona, Spain. As soon as the
rat brain. animals awoke, they were placed in their regular cages and
had free access to food and water.
2. Materials and methods 2.4. Blood sampling and brain dissection
