1
|
Bower RL, Eftekhari S, Waldvogel HJ, Faull RLM, Tajti J, Edvinsson L, Hay DL, Walker CS. Mapping the calcitonin receptor in human brain stem. Am J Physiol Regul Integr Comp Physiol 2016; 310:R788-93. [DOI: 10.1152/ajpregu.00539.2015] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2015] [Accepted: 02/05/2016] [Indexed: 11/22/2022]
Abstract
The calcitonin receptor (CTR) is relevant to three hormonal systems: amylin, calcitonin, and calcitonin gene-related peptide (CGRP). Receptors for amylin and calcitonin are targets for treating obesity, diabetes, and bone disorders. CGRP receptors represent a target for pain and migraine. Amylin receptors (AMY) are a heterodimer formed by the coexpression of CTR with receptor activity-modifying proteins (RAMPs). CTR with RAMP1 responds potently to both amylin and CGRP. The brain stem is a major site of action for circulating amylin and is a rich site of CGRP binding. This study aimed to enhance our understanding of these hormone systems by mapping CTR expression in the human brain stem, specifically the medulla oblongata. Widespread CTR-like immunoreactivity was observed throughout the medulla. Dense CTR staining was noted in several discrete nuclei, including the nucleus of the solitary tract, the hypoglossal nucleus, the cuneate nucleus, spinal trigeminal nucleus, the gracile nucleus, and the inferior olivary nucleus. CTR staining was also observed in the area postrema, the lateral reticular nucleus, and the pyramidal tract. The extensive expression of CTR in the medulla suggests that CTR may be involved in a wider range of functions than currently appreciated.
Collapse
Affiliation(s)
- Rebekah L. Bower
- School of Biological Sciences, University of Auckland, Auckland, New Zealand
| | - Sajedeh Eftekhari
- Division of Experimental Vascular Research, Department of Clinical Sciences, Lund University, Lund, Sweden
| | - Henry J. Waldvogel
- Centre for Brain Research, University of Auckland, Auckland, New Zealand
- Department of Anatomy with Medical Imaging, Faculty of Medical and Health Science, University of Auckland, Auckland, New Zealand; and
| | - Richard L. M. Faull
- Centre for Brain Research, University of Auckland, Auckland, New Zealand
- Department of Anatomy with Medical Imaging, Faculty of Medical and Health Science, University of Auckland, Auckland, New Zealand; and
| | - János Tajti
- Department of Neurology, Faculty of Medicine, University of Szeged, Szeged, Hungary
| | - Lars Edvinsson
- Division of Experimental Vascular Research, Department of Clinical Sciences, Lund University, Lund, Sweden
| | - Debbie L. Hay
- School of Biological Sciences, University of Auckland, Auckland, New Zealand
- Centre for Brain Research, University of Auckland, Auckland, New Zealand
| | - Christopher S. Walker
- School of Biological Sciences, University of Auckland, Auckland, New Zealand
- Centre for Brain Research, University of Auckland, Auckland, New Zealand
| |
Collapse
|
2
|
Hindmarch CCT, Ferguson AV. Physiological roles for the subfornical organ: a dynamic transcriptome shaped by autonomic state. J Physiol 2015; 594:1581-9. [PMID: 26227400 DOI: 10.1113/jp270726] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2015] [Accepted: 07/26/2015] [Indexed: 12/15/2022] Open
Abstract
The subfornical organ (SFO) is a circumventricular organ recognized for its ability to sense and integrate hydromineral and hormonal circulating fluid balance signals, information which is transmitted to central autonomic nuclei to which SFO neurons project. While the role of SFO was once synonymous with physiological responses to osmotic, volumetric and cardiovascular challenge, recent data suggest that SFO neurons also sense and integrate information from circulating signals of metabolic status. Using microarrays, we have confirmed the expression of receptors already described in the SFO, and identified many novel transcripts expressed in this circumventricular organ including receptors for many of the critical circulating energy balance signals such as adiponectin, apelin, endocannabinoids, leptin, insulin and peptide YY. This transcriptome analysis also identified SFO transcripts, the expressions of which are significantly changed by either 72 h dehydration, or 48 h starvation, compared to fed and euhydrated controls. Expression and potential roles for many of these targets are yet to be confirmed and elucidated. Subsequent validation of data for adiponectin and leptin receptors confirmed that receptors for both are expressed in the SFO, that discrete populations of neurons in this tissue are functionally responsive to these adipokines, and that such responsiveness is regulated by physiological state. Thus, transcriptomic analysis offers great promise for understanding the integrative complexity of these physiological systems, especially with development of technologies allowing description of the entire transcriptome of single, carefully phenotyped, SFO neurons. These data will ultimately elucidate mechanisms through which these uniquely positioned neurons respond to and integrate complex circulating signals.
Collapse
Affiliation(s)
- Charles Colin Thomas Hindmarch
- School of Clinical Sciences, Dorothy Hodgkin Building, University of Bristol, Bristol, BS1 3NY, UK.,Department of Physiology, Faculty of Medicine, University of Malaya, 50603, Kuala Lumpur, Malaysia
| | - Alastair V Ferguson
- Department of Biomedical and Molecular Sciences, Queen's University, Kingston, ON, Canada, K7L 3N6
| |
Collapse
|
4
|
Smith PM, Ferguson AV. Circulating signals as critical regulators of autonomic state--central roles for the subfornical organ. Am J Physiol Regul Integr Comp Physiol 2010; 299:R405-15. [PMID: 20463185 DOI: 10.1152/ajpregu.00103.2010] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
To maintain homeostasis autonomic control centers in the hypothalamus and medulla must respond appropriately to both external and internal stimuli. Although protected behind the blood-brain barrier, neurons in these autonomic control centers are known to be influenced by changing levels of important signaling molecules in the systemic circulation (e.g., osmolarity, glucose concentrations, and regulatory peptides). The subfornical organ belongs to a group of specialized central nervous system structures, the circumventricular organs, which are characterized by the lack of the normal blood-brain barrier, such that circulating lipophobic substances may act on neurons within this region and via well-documented efferent neural projections to hypothalamic autonomic control centers, influence autonomic function. This review focuses on the role of the subfornical organ in sensing peripheral signals and transmitting this information to autonomic control centers in the hypothalamus.
Collapse
Affiliation(s)
- Pauline M Smith
- Dept. of Physiology, Queen's Univ., Kingston, Ontario, Canada K7L 3N6
| | | |
Collapse
|
5
|
Riediger T, Schmid HA, Lutz T, Simon E. Amylin potently activates AP neurons possibly via formation of the excitatory second messenger cGMP. Am J Physiol Regul Integr Comp Physiol 2001; 281:R1833-43. [PMID: 11705768 DOI: 10.1152/ajpregu.2001.281.6.r1833] [Citation(s) in RCA: 71] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Amylin is secreted with insulin from the pancreas during and after food intake. One of the most potent actions of amylin in vivo is its anorectic effect, which is directly mediated by the area postrema (AP), a circumventricular organ lacking a functional blood-brain barrier. As we recently demonstrated, amylin also stimulates water intake most likely via its excitatory action on subfornical organ (SFO) neurons. Neurons investigated under equal conditions in an in vitro slice preparation of the rat AP were 15-fold more sensitive to amylin than SFO neurons. Amylin (10(-11)-10(-8) M) excited 48% of 94 AP neurons tested; the remaining cells were insensitive. The average threshold concentration of the excitatory response was 10(-10) M and, thus, close to physiological plasma concentrations. Coapplication of the amylin receptor antagonist AC-187 reduced amylin's excitatory effect. Amylin-mediated activation of AP neurons and antagonistic action of AC-187 were confirmed in vivo by c-fos studies. Peripherally applied amylin stimulated cGMP formation in AP and SFO neurons, as shown in immunohistochemical studies. This response was independent of nitric oxide (NO) formation in the AP, while coapplication of the NO synthase inhibitors N-monomethyl-L-arginine (100 mg/kg) and nitro-L-arginine methyl ester (50 mg/kg) blocked cGMP formation in the SFO. In contrast to the SFO, where NO-dependent cGMP formation seems to represent a general inhibitory transduction pathway, cGMP acts as an excitatory second messenger in the AP, since the membrane-permeable analog 8-bromo-cGMP stimulated 65% of all neurons tested (n = 17), including seven of nine amylin-sensitive neurons (77%). The results indicate that the anorectic effect of circulating amylin is based on its excitatory action on AP neurons, with cGMP acting as a second messenger.
Collapse
Affiliation(s)
- T Riediger
- Max Planck Institute for Physiological and Clinical Research, W. G. Kerckhoff Institute, 61231 Bad Nauheim, Germany.
| | | | | | | |
Collapse
|
6
|
Abstract
This review summarizes research on sensory and behavioral aspects of calcium homeostasis. These are fragmented fields, with essentially independent lines of research involving gustatory electrophysiology in amphibians, ethological studies in wild birds, nutritional studies in poultry, and experimental behavioral studies focused primarily on characterizing the specificity of the appetite in rats. Recently, investigators have begun to examine potential physiological mechanisms underlying calcium intake and appetite. These include changes in the taste perception of calcium, signals related to blood calcium concentrations, and actions of the primary hormones of calcium homeostasis: parathyroid hormone, calcitonin, and 1,25-dihydroxyvitamin D. Other influences on calcium intake include reproductive and adrenal hormones and learning. The possibility that a calcium appetite exists in humans is discussed. The broad range of observations documenting the existence of a behavioral limb of calcium homeostasis provides a strong foundation for future genetic and physiological analyses of this behavior.
Collapse
Affiliation(s)
- M G Tordoff
- Monell Chemical Senses Center, Philadelphia, Pennsylvania 19104, USA.
| |
Collapse
|
7
|
Simon E. Interface Properties of Circumventricular Organs in Salt and Fluid Balance. NEWS IN PHYSIOLOGICAL SCIENCES : AN INTERNATIONAL JOURNAL OF PHYSIOLOGY PRODUCED JOINTLY BY THE INTERNATIONAL UNION OF PHYSIOLOGICAL SCIENCES AND THE AMERICAN PHYSIOLOGICAL SOCIETY 2000; 15:61-67. [PMID: 11390880 DOI: 10.1152/physiologyonline.2000.15.2.61] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The "sensory" circumventricular organs, with their leaky blood-brain barriers, permit contact between brain neurons and blood-borne molecules. Body fluid balance and cardiovascular control involve established interface functions of subfornical organs. Their recently identified target functions for hormones released during digestion suggest that they may coordinate fluid and food intake.
Collapse
Affiliation(s)
- Eckhart Simon
- Physiology Department at Max-Planck-Institute for Physiological and Clinical Research, William G. Kerckhoff-Institute, D-61231 Bad Nauheim, Germany
| |
Collapse
|