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Endocrine function of neuropeptide Y knockout mice
Regulatory Peptides 70 (1997) 199–202
Rapid communication
Endocrine function of neuropeptide Y knockout mice a b a b a, Jay C. Erickson , Rexford S. Ahima , Gunther Hollopeter , Jeffrey S. Flier , Richard D. Palmiter * a
b
Howard Hughes Medical Institute and Department of Biochemistry, University of Washington, Box 357370, Seattle WA 98195, USA Department of Medicine, Division of Endocrinology, Beth Israel Deaconess Medical Center, Harvard Medical School, 330 Brookline Avenue, Boston MA 02215, USA Received 7 April 1997; received in revised form 1 May 1997; accepted 1 May 1997
Abstract Among its many proposed functions, neuropeptide Y (NPY) is thought to modulate the hypothalamic-pituitary axis. Specifically, increased hypothalamic NPY signaling may be critical in mediating the neuroendocrine response to fasting. To determine the consequences of NPY deficiency on endocrine physiology, multiple hormones were quantitated in wildtype and NPY-knockout mice under fed and fasted conditions. Serum concentrations of leptin, corticosterone, thyroxine, and testosterone were normal in NPY-knockout males fed ad libitum. A 48-hour fast resulted in a 50% reduction in leptin, a 60% reduction in thyroxine, a 75% reduction in testosterone, and a 12-fold increase in corticosterone in both wildtype and NPY-knockout mice. Fasting also increased the estrous cycle length by 3 days in both wildtype and NPY-deficient female mice. We conclude that NPY is not essential for appropriate function of the gonadotropic, thyrotropic, or corticotropic axes under ad lib fed conditions or in response to acute fasting. 1997 Elsevier Science B.V. Keywords: Leptin; Testosterone; Corticosterone; Thyroxine; Starvation; Hypothalamic-pituitary axis
1. Introduction Neuropeptide Y (NPY), a 36 amino acid neuromodulator secreted by neurons throughout the peripheral and central nervous systems, is implicated in the regulation of many physiological processes including appetite, body weight, mood, cardiovascular physiology, sympathetic function, and neuronal excitability [1]. In addition, NPY is thought to modulate the neuroendocrine system. A role for NPY in regulating neuroendocrine function is suggested by the potent effects of intracerebrally-administered NPY on the release of multiple hypothalamic and pituitary hormones [2–4]. For example, central NPY injection can stimulate the corticotropic axis [5] and suppress the gonadotropic, somatotropic, and thyrotropic axes [6–9]. The abundance of NPY-containing neuron terminals and NPY receptors in anatomic sites involved in regulating the hypothalamic*Corresponding author. Tel.: 1 1 206 5436090; fax: 1 1 206 5430858 e-mail: [email protected] 0167-0115 / 97 / $17.00 PII S0167-0115( 97 )01007-0
pituitary axis [2,3,10–14] further supports a physiological role of endogenous NPY in endocrine function. NPY may be especially important in mediating the endocrine response to food deprivation. In support of this hypothesis, fasting results in a selective increase in hypothalamic NPY synthesis and release [15–17]. In addition, the effects of central NPY infusion on endocrine function in normal rodents resembles the changes induced by starvation, including increased activity of the corticotropic axis and decreased activity of the thyrotropic and gonadotropic axes [7–9,18]. More recently, genetic deficiency of NPY was shown to attenuate the endocrine alterations of leptin-deficient ob /ob mice [19], suggesting that NPY might be essential for the endocrine response to starvation, which is elicited by reduced leptin concentrations [20]. To evaluate the role of NPY in basal endocrine function and in the endocrine response to fasting, we measured multiple peripheral hormones and assessed reproductive function of NPY-knockout mice under both fed and fasted conditions.
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J.C. Erickson et al. / Regulatory Peptides 70 (1997) 199 – 202
2. Materials and methods
2.1. Mice The NPY-knockout mice were generated as described [21] and maintained on a C57Bl 3 129Sv background. Wildtype littermates were used as controls. All mice were housed individually in a conventional facility with a 12 h light:12 h dark cycle and fed standard rodent chow (Teklad). Fasting consisted of placing the mouse in a clean cage with no food (water was freely available) for 48 h beginning early in the light phase. To assess fat content, the inguinal, retroperitoneal, reproductive (epididymal in males and uterine in females), and scapular fat pads were removed after death and weighed. Mice were treated in accordance with University of Washington guidelines.
2.2. Hormone assays Serum hormones were measured in 8–10-week-old male mice. Mice were rapidly rendered unconscious by CO 2 inhalation in the early part of the light phase and blood was collected with a syringe by cardiac puncture. Serum levels of leptin, thyroxine (T4), corticosterone, and testosterone were measured by radioimmunoassay as described [20]. Radioimmunoassay kits for corticosterone and thyroxine were purchased from ICN (Costa Mesa, CA), testosterone from DPC (Los Angeles, CA), and murine leptin from Linco Research (St. Charles, MO).
Under fed conditions, body weight and combined fat pad weight of NPY-knockout males (27.4961.05 g and 1.0360.12 g, respectively) were similar to those of wildtype males (27.1560.97 g and 0.7860.04 g, respectively). No differences in serum hormone levels were observed between the two groups of fed mice (Fig. 1). After a 48-h fast, body weights of knockout mice (20.3060.55 g) and wildtype mice (19.4660.44 g) were | 27% lower than those of fed mice. Moreover, combined fat pad weights after fasting were decreased by | 75% in both knockout (0.2060.01 g) and wildtype (0.2260.02 g) mice. Fasting produced a | 50% fall in serum levels of leptin in both groups (Fig. 1). Fasted NPY knockout mice also exhibited significant reductions in both testosterone and thyroxine and a significant elevation in corticosterone, changes closely resembling those observed in fasted wildtype mice (Fig. 1). To further characterize the gonadotropic axis of NPYdeficient mice, the estrous cycle of female mice was assessed by daily cytological evaluation of vaginal smears. Under fed conditions, 58% (11 / 19) of wildtype females and 50% (11 / 22) of NPY-knockout females exhibited regular, predictable estrous cycles, with an average cycle length of | 4.5 days for consistent cyclers of both genotypes (Fig. 2). Over the course of a 48-h fast, both groups of cycling mice lost | 22% of their body weight which
2.3. Estrous cycle length Daily vaginal cytology was used to assess the phase of the estrous cycle in female mice beginning at 9 weeks of age. A saline-moistened toothpick was gently rotated in the vagina in the middle of the light phase and the cells were smeared onto a microscope slide. The slide was allowed to dry prior to fixing and staining with a Diff-Quik Stain Set from Dade Diagnostics (Aguada, Puerto Rica). The phase of the estrous cycle was then determined by microscopic examination [22]. Individually-housed wildtype and NPYknockout mice were screened for regular estrous cycles beginning at 9 weeks of age. If a mouse exhibited 3 or 4 consecutive estrous cycles of similar length it was fasted for 48 h beginning on diestrous I, and daily vaginal smears were evaluated until the next estrous.
3. Results The first experiment involved measuring leptin, testosterone, corticosterone, and thyroxine levels in serum of wildtype and NPY-knockout males that were either fed ad libitum or deprived of food for 48 h. Body weight and the combined weight of four fat depots were also measured to document the effect of fasting on adiposity.
Fig. 1. Hormone levels in wildtype (NPY 1 / 1 ) and NPY-deficient (NPY 2 / 2 ) mice under fed and fasted conditions. (A) Serum concentration of leptin. (B) Serum concentration of thyroxine (T4). (C) Serum concentration of testosterone. (D) Serum concentration of corticosterone. Values are the mean 1 SEM. For leptin measurements, n 5 7 for both groups of fed mice and n 5 6 for both groups of fasted mice. For all other measurements, n 5 8 for both groups of fed mice and n 5 12 for both groups of fasted mice. Serum hormone levels were significantly different in both groups of fasted mice compared to both groups of fed mice (P , 0.05). No significant differences were observed between wildtype and NPY-deficient mice under either fed or fasted conditions.
J.C. Erickson et al. / Regulatory Peptides 70 (1997) 199 – 202
201
References
Fig. 2. Estrous cycle length in wildtype and NPY-deficient mice under fed and fasted conditions. Values are the mean 1 SEM; n 5 11 for both genotypes. Fasting significantly increased the estrous cycle length in both groups (P , 0.01).
they regained 24 h after refeeding (not shown). Starvation significantly delayed the next estrous by | 3 days in both wildtype and NPY-deficient mice (Fig. 2).
4. Discussion Numerous physiological, anatomical, and pharmacological studies support a role for NPY in regulating the hypothalamic-pituitary axis [2–14,18]. We therefore predicted that complete loss of NPY might result in endocrine dysfunction. However, the results indicate that mice congenitally deficient in NPY have normal serum levels of leptin, corticosterone, thyroxine, and testosterone, and exhibit normal estrous cycles. Moreover, NPY-knockout mice do not appear to be impaired in their ability to appropriately alter the level of these peripheral hormones in response to fasting. We therefore conclude that NPY is not essential for regulation of the corticotropic, gonadotropic, and thyrotropic axes under conditions of food abundance or after an acute fast. Several potential explanations could account for the lack of detectable effects of NPY deficiency on endocrine physiology. One possibility is that unique adaptations to congenital NPY deficiency are capable of functionally compensating for the absence of the peptide. Another possibility is that redundant mechanisms normally exist. Consistent with these possibilities, NPY-deficient mice have a normal hyperphagic response and rapidly gain weight following a fast [20], despite considerable evidence that NPY is important in stimulating appetite after weight loss [3,15–17,23]. An additional possibility is that NPY signaling may become critical only after prolonged food restriction, perhaps when decreased leptin levels are sustained for periods longer than 48 h or when leptin levels fall lower than the two-fold reduction we observed.
Acknowledgments This work was supported in part by N.I.H. grants HD09171 to R.D.P. and R37-28082 to J.S.F. J.C.E. is a Merck fellow.
[1] Colmers WF, Wahlestedt C. The Biology of Neuropeptide Y and Related Peptides. New Jersey: Humana Press, 1993. [2] McDonald JK, Koenig JI. Neuropeptide Y actions on reproductive and endocrine functions. In: Colmers WF, Wahlestedt, C, editors. The Biology of Neuropeptide Y and Related Peptides. New Jersey: Humana Press, 1993:419–456. [3] White JD. Neuropeptide Y: a central regulator of energy homeostasis. Regul Pept 1993;49:93–107. [4] Koenig JI. Regulation of the hypothalamic-pituitary axis by neuropeptide Y. Ann New York Acad Sci 1990;611:317–28. [5] Wahlestedt C, Skagerberg G, Ekman R, Helig M, Sundler F, Hakanson R. Neuropeptide Y (NPY) in the area of the hypothalamic paraventricular nucleus activates the pituitary-adrenocortical axis in the rat. Brain Res 1987;417:33–8. [6] Harfstrand A, Eneroth P, Agnati L, Fuxe K. Further studies on the effect of central administration of neuropeptide Y on neuroendocrine function in the male rat: relationship to hypothalamic catecholamines. Regul Pept 1987;17:167–79. [7] Catzeflis C, Pierroz DD, Rohner-Jeanrenaud F, Rivier JE, Sizonenko PC, Aubert ML. Neuropeptide Y administered chronically into the lateral ventricle profoundly inhibits both the gonadotropic and the somatotropic axis in intact adult female rats. Endocrinology 1993;132:224–34. [8] Pierroz DD, Catzeflis C, Aebi AC, Rivier JE, Aubert ML. Chronic administration of neuropeptide Y into the lateral ventricle inhibits both the pituitary-testicular axis and growth hormone and insulinlike growth factor I secretion in intact adult male rats. Endocrinology 1996;137:3–12. [9] McDonald JK, Lumpkin MD, Samson WK, McCann SM. Neuropeptide Y affects secretion of luteinizing hormone and growth hormone in ovariectomized rats. Proc Natl Acad Sci USA 1985;82:561–4. [10] DeQuidt ME, Emson PC. Distribution of neuropeptide Y-like immunoreactivity in the rat central nervous system. II. Immunohistochemical analysis. Neuroscience 1986;18:545–618. [11] Liposits ZL, Paull WK. Neuropeptide Y and ACTH-immunoreactive innervation of corticotropin releasing factor (CRF)-synthesizing neurons in the hypothalamus of the rat. An immunohistochemical study at the light and electron microscopic levels. Histochemistry 1988;88:227–34. [12] Toni R, Jackson IMD, Lechan RM. Neuropeptide Y-immunoreactive innervation of thyrotropin-releasing hormone-synthesizing neurons in the rat hypothalamic paraventricular nucleus. Endocrinology 1990;126:2444–53. [13] Tsuruo Y, Kawano H, Kagotani Y, Hisano S, Daikoku S, Chihara K, Zhang T, Yanaihara N. Morphological evidence for neuronal regulation of luteinizing hormone-releasing hormone-containing neurons by neuropeptide Y in the rat septo-preoptic area. Neurosci Lett 1990;110:261–6. [14] McDonald JK, Koenig JI, Gibbs DM, Collins P, Noe BD. High concentrations of neuropeptide-Y in pituitary portal blood of rats. Neuroendocrinology 1987;46:538–41. [15] Sahu A, Kalra PS, Kalra SP. Food deprivation and ingestion induce reciprocal changes in neuropeptide Y concentrations in the paraventricular nucleus. Peptides 1988;9:83–6. [16] White JD, Kershaw M. Increased hypothalamic neuropeptide Y expression following food deprivation. Mol Cell Neurosci 1990;1:41–8. [17] Kalra SP, Dube MG, Sahu A, Phelps CP, Kalra PS. Neuropeptide Y secretion increases in the paraventricular nucleus in association with increased appetite for food. Proc Natl Acad Sci USA 1991;88:10931–5. [18] Gruaz NM, Pierroz DD, Rohner-Jeanrenaud F, Sizonenko PC, Aubert ML. Evidence that neuropeptide Y could represent a
202
J.C. Erickson et al. / Regulatory Peptides 70 (1997) 199 – 202
neuroendocrine inhibitor of sexual maturation in unfavorable metabolic conditions in the rat. Endocrinology 1993;133:1891–4. [19] Erickson JC, Hollopeter G, Palmiter RD. Attenuation of the obesity syndrome of ob /ob mice by the loss of neuropeptide Y. Science 1996;274:1704–7. [20] Ahima RS, Prabakaran D, Mantzoros C, Qu D, Lowell B, MaratosFlier E, Flier JS. Role of leptin in the neuroendocrine response to fasting. Nature 1996;382:250–2. [21] Erickson JC, Clegg KE, Palmiter RD. Sensitivity to leptin and
susceptibility to seizures of mice lacking neuropeptide Y. Nature 1996;381:415–8. [22] Yuan YD, Carlson RG. Structure, cyclic change, and function, vagina and vulva, rat. In: Jones TC, Mohr U, Hunt RD, editors. Genital System. Berlin:Springer-Verlag, 1987:161–168. [23] Kaiyala KJ, Woods SC, Schwartz MW. New model for the regulation of energy balance and adiposity by the central nervous system. Am J Clin Nutr 1995;62(suppl.):1123S–34S.
Rapid communication
Endocrine function of neuropeptide Y knockout mice a b a b a, Jay C. Erickson , Rexford S. Ahima , Gunther Hollopeter , Jeffrey S. Flier , Richard D. Palmiter * a
b
Howard Hughes Medical Institute and Department of Biochemistry, University of Washington, Box 357370, Seattle WA 98195, USA Department of Medicine, Division of Endocrinology, Beth Israel Deaconess Medical Center, Harvard Medical School, 330 Brookline Avenue, Boston MA 02215, USA Received 7 April 1997; received in revised form 1 May 1997; accepted 1 May 1997
Abstract Among its many proposed functions, neuropeptide Y (NPY) is thought to modulate the hypothalamic-pituitary axis. Specifically, increased hypothalamic NPY signaling may be critical in mediating the neuroendocrine response to fasting. To determine the consequences of NPY deficiency on endocrine physiology, multiple hormones were quantitated in wildtype and NPY-knockout mice under fed and fasted conditions. Serum concentrations of leptin, corticosterone, thyroxine, and testosterone were normal in NPY-knockout males fed ad libitum. A 48-hour fast resulted in a 50% reduction in leptin, a 60% reduction in thyroxine, a 75% reduction in testosterone, and a 12-fold increase in corticosterone in both wildtype and NPY-knockout mice. Fasting also increased the estrous cycle length by 3 days in both wildtype and NPY-deficient female mice. We conclude that NPY is not essential for appropriate function of the gonadotropic, thyrotropic, or corticotropic axes under ad lib fed conditions or in response to acute fasting. 1997 Elsevier Science B.V. Keywords: Leptin; Testosterone; Corticosterone; Thyroxine; Starvation; Hypothalamic-pituitary axis
1. Introduction Neuropeptide Y (NPY), a 36 amino acid neuromodulator secreted by neurons throughout the peripheral and central nervous systems, is implicated in the regulation of many physiological processes including appetite, body weight, mood, cardiovascular physiology, sympathetic function, and neuronal excitability [1]. In addition, NPY is thought to modulate the neuroendocrine system. A role for NPY in regulating neuroendocrine function is suggested by the potent effects of intracerebrally-administered NPY on the release of multiple hypothalamic and pituitary hormones [2–4]. For example, central NPY injection can stimulate the corticotropic axis [5] and suppress the gonadotropic, somatotropic, and thyrotropic axes [6–9]. The abundance of NPY-containing neuron terminals and NPY receptors in anatomic sites involved in regulating the hypothalamic*Corresponding author. Tel.: 1 1 206 5436090; fax: 1 1 206 5430858 e-mail: [email protected] 0167-0115 / 97 / $17.00 PII S0167-0115( 97 )01007-0
pituitary axis [2,3,10–14] further supports a physiological role of endogenous NPY in endocrine function. NPY may be especially important in mediating the endocrine response to food deprivation. In support of this hypothesis, fasting results in a selective increase in hypothalamic NPY synthesis and release [15–17]. In addition, the effects of central NPY infusion on endocrine function in normal rodents resembles the changes induced by starvation, including increased activity of the corticotropic axis and decreased activity of the thyrotropic and gonadotropic axes [7–9,18]. More recently, genetic deficiency of NPY was shown to attenuate the endocrine alterations of leptin-deficient ob /ob mice [19], suggesting that NPY might be essential for the endocrine response to starvation, which is elicited by reduced leptin concentrations [20]. To evaluate the role of NPY in basal endocrine function and in the endocrine response to fasting, we measured multiple peripheral hormones and assessed reproductive function of NPY-knockout mice under both fed and fasted conditions.
200
J.C. Erickson et al. / Regulatory Peptides 70 (1997) 199 – 202
2. Materials and methods
2.1. Mice The NPY-knockout mice were generated as described [21] and maintained on a C57Bl 3 129Sv background. Wildtype littermates were used as controls. All mice were housed individually in a conventional facility with a 12 h light:12 h dark cycle and fed standard rodent chow (Teklad). Fasting consisted of placing the mouse in a clean cage with no food (water was freely available) for 48 h beginning early in the light phase. To assess fat content, the inguinal, retroperitoneal, reproductive (epididymal in males and uterine in females), and scapular fat pads were removed after death and weighed. Mice were treated in accordance with University of Washington guidelines.
2.2. Hormone assays Serum hormones were measured in 8–10-week-old male mice. Mice were rapidly rendered unconscious by CO 2 inhalation in the early part of the light phase and blood was collected with a syringe by cardiac puncture. Serum levels of leptin, thyroxine (T4), corticosterone, and testosterone were measured by radioimmunoassay as described [20]. Radioimmunoassay kits for corticosterone and thyroxine were purchased from ICN (Costa Mesa, CA), testosterone from DPC (Los Angeles, CA), and murine leptin from Linco Research (St. Charles, MO).
Under fed conditions, body weight and combined fat pad weight of NPY-knockout males (27.4961.05 g and 1.0360.12 g, respectively) were similar to those of wildtype males (27.1560.97 g and 0.7860.04 g, respectively). No differences in serum hormone levels were observed between the two groups of fed mice (Fig. 1). After a 48-h fast, body weights of knockout mice (20.3060.55 g) and wildtype mice (19.4660.44 g) were | 27% lower than those of fed mice. Moreover, combined fat pad weights after fasting were decreased by | 75% in both knockout (0.2060.01 g) and wildtype (0.2260.02 g) mice. Fasting produced a | 50% fall in serum levels of leptin in both groups (Fig. 1). Fasted NPY knockout mice also exhibited significant reductions in both testosterone and thyroxine and a significant elevation in corticosterone, changes closely resembling those observed in fasted wildtype mice (Fig. 1). To further characterize the gonadotropic axis of NPYdeficient mice, the estrous cycle of female mice was assessed by daily cytological evaluation of vaginal smears. Under fed conditions, 58% (11 / 19) of wildtype females and 50% (11 / 22) of NPY-knockout females exhibited regular, predictable estrous cycles, with an average cycle length of | 4.5 days for consistent cyclers of both genotypes (Fig. 2). Over the course of a 48-h fast, both groups of cycling mice lost | 22% of their body weight which
2.3. Estrous cycle length Daily vaginal cytology was used to assess the phase of the estrous cycle in female mice beginning at 9 weeks of age. A saline-moistened toothpick was gently rotated in the vagina in the middle of the light phase and the cells were smeared onto a microscope slide. The slide was allowed to dry prior to fixing and staining with a Diff-Quik Stain Set from Dade Diagnostics (Aguada, Puerto Rica). The phase of the estrous cycle was then determined by microscopic examination [22]. Individually-housed wildtype and NPYknockout mice were screened for regular estrous cycles beginning at 9 weeks of age. If a mouse exhibited 3 or 4 consecutive estrous cycles of similar length it was fasted for 48 h beginning on diestrous I, and daily vaginal smears were evaluated until the next estrous.
3. Results The first experiment involved measuring leptin, testosterone, corticosterone, and thyroxine levels in serum of wildtype and NPY-knockout males that were either fed ad libitum or deprived of food for 48 h. Body weight and the combined weight of four fat depots were also measured to document the effect of fasting on adiposity.
Fig. 1. Hormone levels in wildtype (NPY 1 / 1 ) and NPY-deficient (NPY 2 / 2 ) mice under fed and fasted conditions. (A) Serum concentration of leptin. (B) Serum concentration of thyroxine (T4). (C) Serum concentration of testosterone. (D) Serum concentration of corticosterone. Values are the mean 1 SEM. For leptin measurements, n 5 7 for both groups of fed mice and n 5 6 for both groups of fasted mice. For all other measurements, n 5 8 for both groups of fed mice and n 5 12 for both groups of fasted mice. Serum hormone levels were significantly different in both groups of fasted mice compared to both groups of fed mice (P , 0.05). No significant differences were observed between wildtype and NPY-deficient mice under either fed or fasted conditions.
J.C. Erickson et al. / Regulatory Peptides 70 (1997) 199 – 202
201
References
Fig. 2. Estrous cycle length in wildtype and NPY-deficient mice under fed and fasted conditions. Values are the mean 1 SEM; n 5 11 for both genotypes. Fasting significantly increased the estrous cycle length in both groups (P , 0.01).
they regained 24 h after refeeding (not shown). Starvation significantly delayed the next estrous by | 3 days in both wildtype and NPY-deficient mice (Fig. 2).
4. Discussion Numerous physiological, anatomical, and pharmacological studies support a role for NPY in regulating the hypothalamic-pituitary axis [2–14,18]. We therefore predicted that complete loss of NPY might result in endocrine dysfunction. However, the results indicate that mice congenitally deficient in NPY have normal serum levels of leptin, corticosterone, thyroxine, and testosterone, and exhibit normal estrous cycles. Moreover, NPY-knockout mice do not appear to be impaired in their ability to appropriately alter the level of these peripheral hormones in response to fasting. We therefore conclude that NPY is not essential for regulation of the corticotropic, gonadotropic, and thyrotropic axes under conditions of food abundance or after an acute fast. Several potential explanations could account for the lack of detectable effects of NPY deficiency on endocrine physiology. One possibility is that unique adaptations to congenital NPY deficiency are capable of functionally compensating for the absence of the peptide. Another possibility is that redundant mechanisms normally exist. Consistent with these possibilities, NPY-deficient mice have a normal hyperphagic response and rapidly gain weight following a fast [20], despite considerable evidence that NPY is important in stimulating appetite after weight loss [3,15–17,23]. An additional possibility is that NPY signaling may become critical only after prolonged food restriction, perhaps when decreased leptin levels are sustained for periods longer than 48 h or when leptin levels fall lower than the two-fold reduction we observed.
Acknowledgments This work was supported in part by N.I.H. grants HD09171 to R.D.P. and R37-28082 to J.S.F. J.C.E. is a Merck fellow.
[1] Colmers WF, Wahlestedt C. The Biology of Neuropeptide Y and Related Peptides. New Jersey: Humana Press, 1993. [2] McDonald JK, Koenig JI. Neuropeptide Y actions on reproductive and endocrine functions. In: Colmers WF, Wahlestedt, C, editors. The Biology of Neuropeptide Y and Related Peptides. New Jersey: Humana Press, 1993:419–456. [3] White JD. Neuropeptide Y: a central regulator of energy homeostasis. Regul Pept 1993;49:93–107. [4] Koenig JI. Regulation of the hypothalamic-pituitary axis by neuropeptide Y. Ann New York Acad Sci 1990;611:317–28. [5] Wahlestedt C, Skagerberg G, Ekman R, Helig M, Sundler F, Hakanson R. Neuropeptide Y (NPY) in the area of the hypothalamic paraventricular nucleus activates the pituitary-adrenocortical axis in the rat. Brain Res 1987;417:33–8. [6] Harfstrand A, Eneroth P, Agnati L, Fuxe K. Further studies on the effect of central administration of neuropeptide Y on neuroendocrine function in the male rat: relationship to hypothalamic catecholamines. Regul Pept 1987;17:167–79. [7] Catzeflis C, Pierroz DD, Rohner-Jeanrenaud F, Rivier JE, Sizonenko PC, Aubert ML. Neuropeptide Y administered chronically into the lateral ventricle profoundly inhibits both the gonadotropic and the somatotropic axis in intact adult female rats. Endocrinology 1993;132:224–34. [8] Pierroz DD, Catzeflis C, Aebi AC, Rivier JE, Aubert ML. Chronic administration of neuropeptide Y into the lateral ventricle inhibits both the pituitary-testicular axis and growth hormone and insulinlike growth factor I secretion in intact adult male rats. Endocrinology 1996;137:3–12. [9] McDonald JK, Lumpkin MD, Samson WK, McCann SM. Neuropeptide Y affects secretion of luteinizing hormone and growth hormone in ovariectomized rats. Proc Natl Acad Sci USA 1985;82:561–4. [10] DeQuidt ME, Emson PC. Distribution of neuropeptide Y-like immunoreactivity in the rat central nervous system. II. Immunohistochemical analysis. Neuroscience 1986;18:545–618. [11] Liposits ZL, Paull WK. Neuropeptide Y and ACTH-immunoreactive innervation of corticotropin releasing factor (CRF)-synthesizing neurons in the hypothalamus of the rat. An immunohistochemical study at the light and electron microscopic levels. Histochemistry 1988;88:227–34. [12] Toni R, Jackson IMD, Lechan RM. Neuropeptide Y-immunoreactive innervation of thyrotropin-releasing hormone-synthesizing neurons in the rat hypothalamic paraventricular nucleus. Endocrinology 1990;126:2444–53. [13] Tsuruo Y, Kawano H, Kagotani Y, Hisano S, Daikoku S, Chihara K, Zhang T, Yanaihara N. Morphological evidence for neuronal regulation of luteinizing hormone-releasing hormone-containing neurons by neuropeptide Y in the rat septo-preoptic area. Neurosci Lett 1990;110:261–6. [14] McDonald JK, Koenig JI, Gibbs DM, Collins P, Noe BD. High concentrations of neuropeptide-Y in pituitary portal blood of rats. Neuroendocrinology 1987;46:538–41. [15] Sahu A, Kalra PS, Kalra SP. Food deprivation and ingestion induce reciprocal changes in neuropeptide Y concentrations in the paraventricular nucleus. Peptides 1988;9:83–6. [16] White JD, Kershaw M. Increased hypothalamic neuropeptide Y expression following food deprivation. Mol Cell Neurosci 1990;1:41–8. [17] Kalra SP, Dube MG, Sahu A, Phelps CP, Kalra PS. Neuropeptide Y secretion increases in the paraventricular nucleus in association with increased appetite for food. Proc Natl Acad Sci USA 1991;88:10931–5. [18] Gruaz NM, Pierroz DD, Rohner-Jeanrenaud F, Sizonenko PC, Aubert ML. Evidence that neuropeptide Y could represent a
202
J.C. Erickson et al. / Regulatory Peptides 70 (1997) 199 – 202
neuroendocrine inhibitor of sexual maturation in unfavorable metabolic conditions in the rat. Endocrinology 1993;133:1891–4. [19] Erickson JC, Hollopeter G, Palmiter RD. Attenuation of the obesity syndrome of ob /ob mice by the loss of neuropeptide Y. Science 1996;274:1704–7. [20] Ahima RS, Prabakaran D, Mantzoros C, Qu D, Lowell B, MaratosFlier E, Flier JS. Role of leptin in the neuroendocrine response to fasting. Nature 1996;382:250–2. [21] Erickson JC, Clegg KE, Palmiter RD. Sensitivity to leptin and
susceptibility to seizures of mice lacking neuropeptide Y. Nature 1996;381:415–8. [22] Yuan YD, Carlson RG. Structure, cyclic change, and function, vagina and vulva, rat. In: Jones TC, Mohr U, Hunt RD, editors. Genital System. Berlin:Springer-Verlag, 1987:161–168. [23] Kaiyala KJ, Woods SC, Schwartz MW. New model for the regulation of energy balance and adiposity by the central nervous system. Am J Clin Nutr 1995;62(suppl.):1123S–34S.