Peptide YY Expression Research Articles

P.1.b.009 Switching in bipolar disorder: the role of 3H-imipramine, 3H-paroxetine and 5-HT2 binding sites

Nesfatin-1 is an 82 amino acid secreted peptide encoded in the precursor, nucleobindin-2 (NUCB2). It is an insulinotropic anorexigen abundantly expressed in the stomach and hypothalamus. Post-prandial insulin secretion is predominantly regulated by incretins glucagon-like peptide 1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP). Nesfatin-1 was previously reported to modulate GLP-1 and GIP secretion in vitro in an enteroendocrine (STC-1) cell line. Intestine is a source of additional hormones including cholecystokinin (CCK) and peptide YY (PYY) that regulate metabolism. We hypothesized that nesfatin-1 modulates CCK and PYY secretion. Immunofluorescence histochemistry showed NUCB2/nesfatin-1 co-localizing CCK and PYY in the intestinal mucosa of mice. Static incubation of STC-1 cells with nesfatin-1 upregulated both CCK mRNA expression (1 and 10 nM) and secretion (0.1, 1 and 10 nM) at 1 h post-incubation. In contrast, nesfatin-1 treatment for 1 h downregulated PYY mRNA expression (all doses tested) and secretion (0.01 and 0.1 nM) in STC-1 cells. Continuous infusion of nesfatin-1 using osmotic mini-pumps for 12 h upregulated CCK mRNA expression in large intestine, and downregulated PYY mRNA expression in both large and small intestines of male C57BL/6J mice. In these tissues, Western blot analysis found a corresponding increase in CCK and a decrease in PYY content. Collectively, we provide new information on the cell specific localization of NUCB2/nesfatin-1 in the intestinal mucosa, and a novel function for nesfatin-1 in modulating intestinal CCK and PYY expression and secretion in mice.

Enhanced transcription of pancreatic peptide YY by 1α-hydroxyvitamin D3 administration in streptozotocin-induced diabetic mice

Peptide YY (PYY) is a peptide hormone secreted from L cells in the intestine in response to food intake that regulates appetite and gastrointestinal function. PYY is also produced in the pancreatic islets. The vitamin D receptor (VDR) is a nuclear receptor for the active form of vitamin D3 that regulates numerous physiological processes. VDR is expressed in the pancreatic islets and pharmacological VDR activation increases PYY expression in mouse peripheral islet cells. Although VDR is present in insulin-producing β cells as well as non-β cells, the role of β cell VDR in Pyy transcription remains unknown. We treated mice with streptozotocin to ablate β cells in the pancreas. Pancreatic Vdr mRNA expression was decreased in streptozotocin-induced diabetic mice. Interestingly, streptozotocin-treated mice exhibited increased basal Pyy expression and 1α-hydroxyvitamin D3 treatment further increased expression. Moreover, 1α-hydroxyvitamin D3 increased mRNA expression of pancreatic polypeptide and decreased that of neuropeptide Y in streptozotocin-induced diabetic mice but not in control mice. 1α-Hydroxyvitamin D3 slightly increased mRNA expression of insulin but transcript levels were nearly undetectable in the pancreas of streptozotocin-treated mice. Thus, VDR in non-β islet cells is involved in Pyy expression in the mouse pancreas. The findings from this β cell ablation study suggest a hormone transcription regulatory network composed of β cells and non-β cells.

Short communication: Expression of peptide YY, proglucagon, neuropeptide Y receptor Y2, and glucagon-like peptide-1 receptor in bovine peripheral tissues

The role of distal gut signals in control of feed intake and metabolism in cattle has received scant attention. Peptide YY (PYY) and glucagon-like peptide-1, which are secreted from enteroendocrine cells of the distal gut in monogastrics have several functions, including regulation of energy balance. However, little is known of the tissue expression of these peptides and their receptors in cattle. The aim of the current study was to characterize the tissue distribution of PYY, neuropeptide Y receptor Y2 (Y2), proglucagon (GCG), and glucagon-like peptide-1 receptor (GLP1R) in various peripheral tissues of cattle. Four male 7-wk-old dairy calves were euthanized and 16 peripheral tissues were collected. Conventional PCR and quantitative real-time PCR were performed to confirm tissue expression and quantify the transcript abundance in various tissues. The results of conventional PCR revealed that mRNA for both PYY and Y2 was detectable in the rumen, abomasum, duodenum, jejunum, ileum, and colon but not in other tissues. Quantitative real-time PCR data demonstrated that PYY mRNA was 2- to 3-fold greater in the pancreas, kidney, and heart relative to the liver. By conventional PCR, GCG mRNA was detected in the abomasum, duodenum, jejunum, ileum, and colon and GLP1R mRNA was expressed in all gut segments, pancreas, spleen, and kidney. Quantitative real-time PCR data demonstrated that, relative to transcript abundance in the liver, GCG mRNA was 4- to 40-fold higher from abomasum to colon, and GLP1R mRNA was 50- to 300-fold higher from the rumen to colon, 14-fold greater in the pancreas, 18-fold higher in the spleen, and 166-fold greater in the kidney. The tissue distribution of PYY, GCG, and their receptors observed in the current study is, in general, consistent with expression patterns in monogastrics. The predominant expression of PYY, Y2, and GCG in the gut, and the presence of GLP1R in multiple peripheral tissues suggest a role for PYY in controlling gut functions and for GLP-1 in regulating multiple physiological functions in cattle.

Peptide YY Regulates Bone Remodeling in Mice: A Link between Gut and Skeletal Biology

Background & AimsGastrointestinal peptides are increasingly being linked to processes controlling the maintenance of bone mass. Peptide YY (PYY), a gut-derived satiety peptide of the neuropeptide Y family, is upregulated in some states that also display low bone mass. Importantly, PYY has high affinity for Y-receptors, particularly Y1R and Y2R, which are known to regulate bone mass. Anorexic conditions and bariatric surgery for obesity influence circulating levels of PYY and have a negative impact on bone mass, but the precise mechanism behind this is unclear. We thus examined whether alterations in PYY expression affect bone mass.MethodsBone microstructure and cellular activity were analyzed in germline PYY knockout and conditional adult-onset PYY over-expressing mice at lumbar and femoral sites using histomorphometry and micro-computed tomography.ResultsPYY displayed a negative relationship with osteoblast activity. Male and female PYY knockout mice showed enhanced osteoblast activity, with greater cancellous bone mass. Conversely, PYY over-expression lowered osteoblast activity in vivo, via a direct Y1 receptor mediated mechanism involving MAPK stimulation evident in vitro. In contrast to PYY knockout mice, PYY over expression also altered bone resorption, as indicated by greater osteoclast surface, despite the lack of Y-receptor expression in osteoclastic cells. While evident in both sexes, cellular changes were generally more pronounced in females.ConclusionsThese data demonstrate that the gut peptide PYY is critical for the control of bone remodeling. This regulatory axis from the intestine to bone has the potential to contribute to the marked bone loss observed in situations of extreme weight loss and higher circulating PYY levels, such as anorexia and bariatric obesity surgery, and may be important in the maintenance of bone mass in the general population.

A Beautiful Cell (or Two or Three?)

The intestinal tract is the largest endocrine organ of the body, containing at least 15 different cells types that release more than 100 biologically active peptides and hormones [Fig. 1 (1–3)]. The vast majority of these enteroendocrine cells have been identified using immunohistochemical techniques, an approach that is inherently limited by the specificity of the antisera/antibodies, particularly because they are used in high concentrations with this technique (1). The current study by Habib et al. (4) takes advantage of two newly developed fluorescent enteroendocrine cell models (5, 6) to purify specific cells of interest, thereby permitting deeper interrogation of the gene profiles of these cells. The findings both confirm and extend previous observations that different enteroendocrine cell types have more features in common than originally believed. These findings have important implications for current investigations into the possible use of enteroendocrine cell stimulators for the treatment of diseases such as type 2 diabetes. The enteroendocrine cell of focus in the present study by Habib et al. (4) is the L cell, originally described on the basis of enteroglucagon immunoreactivity, using the K cell that produces glucose-dependent insulinotropic peptide (GIP) as a comparator. Enteroglucagon is a generic term for the intestinal proglucagon-derived peptides, including glucagon-like peptide (GLP)-1, an incretin hormone that stimulates glucose-dependent insulin secretion; both GLP-1 receptor agonists and degradation inhibitors are currently used in the clinic to treat patients with type 2 diabetes (7, 8). The other main L cell proglucagon-derived peptides are the gut growth factor GLP-2 and the anorexigenic hormone oxyntomodulin, whereas GIP also serves a role as an incretin hormone (7). Based on the expression of GIP vs. GLP-1, the highest numbers of K cells are found in the duodenum with decreasing numbers in the aboral direction, whereas L cells demonstrate the opposite gradient, with the greatest numbers in the ileum/colon (9, 10). However, the presence of GLP-1 has been demonstrated in subsets of duodenal K cells, whereas immunoreactive GIP has been detected in subpopulations of proximal L cells (5, 9, 11, 12). To further complicate the issue, numerous studies have also demonstrated the expression of peptide YY (PYY) in some ileal and colonic L cells (5, 10, 13, 14) as well as coexpression of GLP-1 with cholecystokinin (CCK) and with neurotensin (14, 15). Thus, it has long been suspected that different types of K and L cells may exist in the intestine. Studies on enteroendocrine cell development have elucidated the transcription factors required for lineage progression from early stem cells to differentiated enteroendocrine cells (Fig. 1). Thus, the development of related enteroendocrine cell populations requires sequential expression of Math1 (mammalian atonal homolog-1), Ngn3 (neurogenin 3), NeuroD (neurogenic differentiation), followed by the expression of paired box transcription factor (Pax)-4 and/or ARX (aristaless related homeobox) (16– 21). The specific transcription factors required for final differentiation of these progenitor cells into specific enteroendocrine cells are not well characterized but include both Pax6 and pancreatic duodenal homeobox-1 (Pdx1) for K cells as well as Pax6 for L cells: in this regard, expression of Pdx1 in L cells appears to be permissive for their coexpression of GIP (22). Recent findings of Dtx1 (deltex1),Egr2 (earlygrowth responseprotein2),Tbx3 (T box 3) in duodenal but not colonic L cells and Etv1 (ETS translocation variant 1) and Prox1 (prospero-related homeobox 1) in proximal L cells but not in K cells remain of uncertain significance (4). In the current study by Habib et al. (4), intestinal L cells from transgenic mice expressing a fluorescent marker (Ve-

Biliopancreatic diversion induces villi elongation and cholecystokinin and ghrelin increase

IntroductionFactors leading to weight loss and weight stabilization after bariatric surgery are not fully understood. Our aim was to evaluate, in Sprague–Dawley rats, the histological and gut hormonal changes after Larrad-biliopancreatic diversion (Larrad-BPD). Materials and methodsRats randomly underwent the following protocols: Larrad-BPD (n=4) versus pair fed (PF) (n=4). Weight and food intake were measured every day. By immunohistochemistry ghrelin was examined in the stomach, while cholecystokinin (CCK), glucagon-like-peptide-1 (GLP-1), peptide YY (PYY) and serotonin (5-HT) expression were analyzed in alimentary limb and ileum following or not the Larrad-BPD. ResultsLarrad-BPD rats exhibited significant (P<0.05) weight loss compared to PF rats. Villi enlongation was observed in Larrad-BPD rats. In residual stomach, ghrelin was diminished. In the alimentary limb, ghrelin and CCK positive cells were detected more than in the ileum of PF rats. GLP-1 expression was decreased and PYY expression was absent after Larrad-BPD compared with PF rats. DiscussionLarrad-BPD is followed by histological changes and a pleiotropic gut endocrine response aimed to compensate the reduction of intestinal area exposed to food. Until now, the hormones responsible for the intestinal hypertrophy have not been defined.

Postprandial changes in GI‐tract peptide hormones in the teleost Atlantic salmon

The spatial distribution of two isoforms of Ghrelin (Ghrelin‐1 and ‐2), two isoforms of Cholecystokinin (CCK‐L and ‐N) and peptide YY (PYY) was assessed by Q‐PCR in four GI‐tract segments covering stomach, pyloric caeca, midgut and hindgut after feeding a single meal to Atlantic salmon. Both CCK‐L and CCK‐N levels increased within 1.5 hours past feeding (hpf). At this time the stomach was still ca 80% full (the gastric evacuation half‐time was 4.5 hrs), the gallbladder was almost completely empty and chyme had started to be transferred into the midgut. During the 24 hpf there were both temporal and spatial differences between the expression profile of the CCK isoforms. PYY expression increased at 1.5 hpf, and then decreased after 3 hpf. Feeding had only minor effects on the Ghrelin isoforms expression. Taken together this suggests that CCK and PYY have in part similar roles in regulating digestive processes to that observed in higher vertebrates. The two isoforms of CCK appear to have different functions. The data did not identify a role for Ghrelin related to digestion or appetite comparable to the orexigenic role described in humans.

Reduced Ghrelin, Islet Amyloid Polypeptide, and Peptide YY Expression in the Stomach of Gastrin-Cholecystokinin Knockout Mice

The antral hormone gastrin and its intestinal relative, cholecystokinin (CCK), are pivotal in the regulation of gastric functions. Other gastric hormones like ghrelin, peptide YY (PYY), and islet amyloid polypeptide (IAPP), however, also contribute to the regulation of acid secretion, motility, and feeding. Because gastrin and CCK are crucial for gastric homeostasis, we examined how loss of gastrin alone and gastrin plus CCK affected the expression of ghrelin, IAPP, and PYY and ghrelin secretion. The expression of ghrelin, IAPP, and PYY and the CCK-A receptor genes were examined in both gastrin and gastrin-CCK double-knockout (KO) mice using immunocytochemistry and quantitative RT-PCR. Ghrelin concentrations in plasma were measured using RIA. Gastrin and CCK were infused in gastrin-CCK KO mice using osmotic minipumps. The number of ghrelin cells and ghrelin gene expression were unaffected, albeit the ghrelin cells were located closer to the base of the glands in both KO mouse strains when freely fed. However, lack of both gastrin and CCK attenuated fasting-induced ghrelin expression and secretion. Fundic ghrelin cells expressed the CCK-A receptor, and ghrelin expression increased after CCK infusion. Furthermore, gastric IAPP and PYY expression as well as the number of IAPP- and PYY-containing cells were reduced in both gastrin and gastrin-CCK KO mice. Gastrin infusion increased gastric IAPP but not PYY expression. In conclusion, lack of gastrin plus CCK but not gastrin alone reduced ghrelin secretion in response to fasting through both direct and indirect mechanisms. Both gastrin and combined gastrin-CCK deficiency reduced the gastric IAPP and PYY expression.

Energy Homeostasis and Gastrointestinal Endocrine Differentiation Do Not Require the Anorectic Hormone Peptide YY

The gastrointestinal hormone peptide YY is a potent inhibitor of food intake and is expressed early during differentiation of intestinal and pancreatic endocrine cells. In order to better understand the role of peptide YY in energy homeostasis and development, we created mice with a targeted deletion of the peptide YY gene. All intestinal and pancreatic endocrine cells developed normally in the absence of peptide YY with the exception of pancreatic polypeptide (PP) cells, indicating that peptide YY expression was not required for terminal differentiation. We used recombination-based cell lineage trace to determine if peptide YY cells were progenitors for gastrointestinal endocrine cells. Peptide YY(+) cells gave rise to all L-type enteroendocrine cells and to islet partial differential and PP cells. In the pancreas, approximately 40% of pancreatic alpha and rare beta cells arose from peptide YY(+) cells, suggesting that most beta cells and surprisingly the majority of alpha cells are not descendants of peptide YY(+)/glucagon-positive/insulin-positive cells that appear during early pancreagenesis. Despite the anorectic effects of exogenous peptide YY(3-36) following intraperitoneal administration, mice lacking peptide YY showed normal growth, food intake, energy expenditure, and responsiveness to peptide YY(3-36). These observations suggest that targeted disruption of the peptide YY gene does not perturb terminal endocrine cell differentiation or the control of food intake and energy homeostasis.

Impact of Adenoviral Transduction With SREBP1c or AMPK on Pancreatic Islet Gene Expression Profile

Accumulation of triglyceride in islets may contribute to the loss of glucose-stimulated insulin secretion (GSIS) in some forms of type 2 diabetes (Diraison et al., Biochem J 373:769-778, 2004). Here, we use adenoviral vectors and oligonucleotide microarrays to determine the effects of the forced expression of SREBP1c on the gene expression profile of rat islets. Sterol regulatory element binding protein-1c (SREBP1c) overexpression led to highly significant (P <0.1 with respect to null adenovirus) changes in the expression of 1,238 genes or expressed sequence tags, of which 1,180 (95.3%) were upregulated. By contrast, overexpression of constitutively active AMP-activated protein kinase (AMPK), expected to promote lipolysis, altered the expression of 752 genes, of which 702 (93%) were upregulated. To identify specific targets for SREBP1c or AMPK, we eliminated messages that were 1) affected in the same direction by the expression of either protein, 2) changed by less than twofold, or 3) failed a positive false discovery test; 206 SREBP1c-regulated genes (195; 95% upregulated) and 48 AMPK-regulated genes (33; 69% upregulated) remained. As expected, SREBP1c-induced genes included those involved in cholesterol (6), fatty acid (3), and eicosanoid synthesis. Interestingly, somatostatin receptor (sstr1) expression was increased by SREBP1c, whereas AMPK induced the expression of peptide YY, the early endocrine pancreas marker.

Peptide YY and cancer: current findings and potential clinical applications

Peptide YY (PYY) is a naturally occurring gut hormone with mostly inhibitory actions on multiple tissue targets. PYY has been identified in several carcinoid tumors and a decreased expression of PYY may be relevant to the development and progression of colon adenocarcinoma. Treatment with PYY decreases growth in pancreatic and breast tumors, most likely through a reduction in intracellular cAMP. In cancer patients, PYY may also improve malnutrition that results from iatrogenic causes or cachexia associated with advanced disease. PYY plays a significant role in multiple aspects of cancer from regulation of cell growth to potential therapeutic applications.

Immunocytochemical localization of the NPY/PYY Y1 receptor in the developing pancreas.

Neuropeptide Y, peptide YY, and pancreatic polypeptide are structurally related peptides that are considered to play a role in the regulation of pancreatic secretion and blood flow. Several receptor subtypes for these peptides have been identified, and the Y1, Y2, Y4/PP1, Y5, and Y5/PP2/Y2b receptors are cloned. We have prepared polyclonal peptide antibodies that recognize the Y1 receptor and now report on its localization in the adult and developing rat pancreas. In the adult pancreas, Y1 receptors were detected both in some centroacinar and intralobular duct cells and in endothelial cells. In the developing pancreas (E12.5-E16.5), Y1 receptor immunoreactivity was observed in numerous nonendocrine epithelial cells. These cells occurred in the immediate vicinity of peptide YY-positive endocrine cells. At E16.5, a fraction of these Y1 receptor-containing cells co-stored amylase. One day later, Y1 receptor immunoreactivity became restricted to pancreatic duct-like cells that occurred in close proximity to peptide YY cells. In fetal rats, intense Y1 receptor staining was also observed in endothelial cells. These observations, together with the finding of early pancreatic peptide YY expression, suggest that peptide YY produced by fetal endocrine cells may exert an action on exocrine cells, duct cells and endothelial cells during development.

Peptide YY expression is an early event in colonic endocrine cell differentiation: evidence from normal and transgenic mice

The hormone peptide YY is produced by endocrine cells in the pancreas, ileum and colon. We have previously shown that peptide YY is coexpressed in all four islet cell types in the murine pancreas when they first appear, suggesting a common peptide YY-producing progenitor. In the colon, peptide YY has been frequently identified in glucagon-expressing L-type endocrine cells. Characterization of colonic endocrine tumors in transgenic mice expressing simian virus 40 large T antigen under the control of the peptide YY gene 5' flanking region revealed tumor cells producing not only peptide YY and glucagon, but also neurotensin, cholecystokinin, substance P, serotonin, secretin, and gastrin. This suggested that multiple enteroendocrine lineages were related to peptide YY-producing cells. Subsequent examination of the ontogeny of colonic endocrine differentiation in nontransgenic mice revealed that peptide YY was the first hormone to appear during development, at embryonic day 15.5. Between embryonic days 16.5 and 18.5, cells expressing glucagon, cholecystokinin, substance P, serotonin, secretin, neurotensin, gastrin and somatostatin first appeared and peptide YY was coexpressed in each cell type at this time. Peptide YY coexpression continued in a significant fraction of most enteroendocrine cell types throughout fetal and postnatal development and into adulthood, with the exception of serotonin-producing cells. This latter population of cells expanded dramatically after birth with rare coexpression of peptide YY. These studies indicate that expression of peptide YY is an early event in colonic endocrine differentiation and support the existence of a common progenitor for all endocrine cells in the colon.

Pancreatic Peptide YY mRNA Levels Increase during Adaptation after Small Intestinal Resection

Peptide YY (PYY) is a 36-amino-acid peptide known to inhibit pancreatic and gastrointestinal secretion. Immediately following small bowel resection, intestinal PYY mRNA and plasma PYY levels rise. The purpose of this study was to determine whether PYY expression changes in the pancreas during the adaptive period after extensive small bowel resection. Female Sprague-Dawley rats (250 g) underwent 70% small intestinal resection or transection alone as control. Animals were sacrificed at 6 hr, 24 hr, 1 week, or 2 weeks following operation (N = 5/time group). Pancreatic tissue was harvested and RNA was isolated by the guanididium-thiocyanate method. PYY mRNA was analyzed by reverse transcriptase PCR, standardized to glyceraldehyde-3-phosphate dehydrogenase, and semiquantitated by Southern blotting and 32P cpm. Ribonuclease protection assay was used to confirm PCR results. PYY mRNA expression was increased 912-fold beginning 6 hr after resection compared to transection (P < 0.05). PYY mRNA levels remain elevated, 214-fold greater than control after 2 weeks (P < 0.05) as analyzed by reverse transcriptase PCR and ribonuclease protection assay. Quantitation by ribonuclease protection assay reveals a gradual elevation of PYY mRNA levels in transected animals compared to a nonoperated rat starting at 1 and 2 weeks. Pancreatic PYY mRNA levels increase rapidly after extensive intestinal resection and remain elevated 2 weeks postoperatively. These results confirm for the first time that the increase in PYY seen after extensive intestinal resection also occurs in extraintestinal sites. In the pancreas, elevated PYY levels may inhibit exocrine secretion, reducing luminal volume, and thereby facilitating intestinal adaptation.

Evolution of the Neuropeptide Y-Peptide Yy Family

Neuropeptide Y (NPY), peptide YY (PYY) and pancreatic polypeptide (PP) form a family of 36-amino-acid peptides. DNA clones for NPY and PYY from several vertebrate species, including the river lamprey, show that both peptide genes were already present in the early vertebrate ancestor and that they have remained highly conserved during evolution. The PP gene probably arose as a copy of the PYY gene in early tetrapods. In situ hybridization shows that PYY expression is more widespread in the brain of lamprey than of mammals. We have cloned the zebrafish PYY (and NPY) gene to investigate whether this is a common feature among vertebrates. Clones have also been isolated for several NPY/PYY receptors in rat, human, and zebrafish to unravel the evolution of the receptor gene family. The results suggest that there may be at least four distinct receptor genes in bony fish and mammals.

Expression of peptide YY and mRNA for the NPY/PYY receptor of the Y1 subtype in dorsal root ganglia during rat embryogenesis

We have used in situ hybridization to study the distribution of mRNA for neuropeptide Y (NPY), peptide YY (PYY) and the NPY/PYY receptor of the Y1 subtype during ontogenesis in the rat and immunohistochemistry to analyse peptide immunoreactivity for NPY and PYY. We found that mRNA and immunoreactivity for NYY are transiently expressed in dorsal root ganglia (DRG) at embryonic day 16 (E16). In contrast, neither NPY mRNA nor NPY-like immunoreactivity were found in DRG at any developmental stage. The Y1 receptor mRNA is not expressed in DRG at E16 but it appears in these ganglia later in development (E20) and it is present in DRG of adult rats. In sagittal sections of whole embryos at very early stages of development we found that the onset of PYY mRNA expression is around day 11, when mRNA for PYY is found in the foregut. NPY and Y1-receptor mRNA are not detected in whole embryo sections until around day 14. Therefore, PYY mRNA expression precedes by 2–3 days the expression of mRNA for both NPY and the Y1 receptor. At E14, PYY mRNA is present in trigeminal ganglia and stomach. Our results suggest that PYY is not only a gut hormone but may also act as a neuropeptide with roles in the development of sensory neurons.

Differential expression of mRNAs for neuropeptide Y-related peptides in rat nervous tissues: possible evolutionary conservation

Neuropeptide Y (NPY) is the only member of its peptide family that has been isolated from the mammalian CNS. We have recently found that two different NPY-related molecules are present in the CNS of a cyclostome, the river lamprey (Lampetra fluviatilis) (Söderberg et al., 1991). Here we show that this is also true for the rat CNS, by demonstrating expression of peptide YY (PYY) mRNA in brainstem neurons distinct from those neurons that express NPY mRNA. Dissimilar oligonucleotide DNA probes complementary to 3' untranslated regions of the rat PYY, NPY, and pancreatic polypeptide (PP) mRNA were used in in situ hybridization experiments on sections of rat brain and spinal cord, visceral organs, and peripheral nerve ganglia. The PYY probe hybridized with two populations of neurons in the brainstem: one dispersed along the midline in the rostral medulla and another in the lateral caudal medulla (A1 region). No additional labeling was detected in the remainder of the neuraxis. In the periphery, PYY hybridization was seen only in endocrine cells of the colon, and not in sympathetic ganglia or the adrenal gland, suggesting that previous observations of PYY immunoreactivity in these latter structures were due to antibody cross-reactivity with NPY. The NPY probe did not hybridize with cells on the midline region that contains PYY neurons, but it did label large numbers of neurons throughout the neuraxis. No expression of PP mRNA was detected in the CNS. Northern blot analysis failed to detect PYY mRNA in the CNS, further supporting the observation that PYY is only expressed by a discrete collection of CNS neurons. The anatomy of PYY- and NPY-expressing cells in the CNS and gut shows a striking similarity between rat and lamprey (Brodin et al., 1989), vertebrates that diverged evolutionarily about 450 million years ago, suggesting that both peptide systems have been conserved throughout vertebrate evolution.