Y.C. Lee

Increased neuropeptide Y concentrations in specific hypothalamic regions of streptozocin-induced diabetic rats

Untreated streptozocin-induced diabetic (STZ-D) rats have previously been shown to have significantly increased hypothalamic concentrations of neuropeptide Y (NPY), a regulatory peptide that powerfully stimulates eating and drinking and inhibits secretion of several pituitary hormones when injected centrally. Tissue NPY concentrations have been measured by radioimmunoassay in selected hypothalamic regions microdissected from fresh, unfixed brain slices to localize diabetes-associated NPY changes precisely within the hypothalamus. Significant (35–200%) increases in NPY concentrations (P < .01 vs. matched nondiabetic controls) were found in specific hypothalamic regions between 3 and 14 wk after induction of STZ-D. These regions included the paraventricular and ventromedial nuclei and lateral hypothalamic area, major appetite-regulating areas that are sensitive to the hyperphagic and polydipsic actions of NPY. Increased NPYergic activity in these areas may, at least partly, drive the increased eating and drinking characteristic of STZ-D. NPY concentrations were also increased in the arcuate nucleus and medial preoptic area. Because both of these regions are important in modulating pituitary hormone secretion, local NPY increases may be involved in the impaired secretion of luteinizing hormone, thyroid-stimulating hormone, growth hormone, and prolactin known to occur in STZ-D. Our finding of NPY increases in specific hypothalamic nuclei associated with functional changes found in STZ-D suggests that this peptide may have a role in the altered metabolic and neuroendocrine regulation of the syndrome.

Reduced cholecystokinin-like and somatostatin-like immunoreactivity in limbic lobe is associated with negative symptoms in schizophrenia

Cholecystokinin-like immunoreactivity (CCK) and somatostatin-like immunoreactivity (SRIF) were determined in fourteen brains from patients dying with a diagnosis of schizophrenia and in twelve brains from control cases. The schizophrenics had been rated during life and were divided into two groups on the basis of the presence or absence of negative symptoms (affective flattening and poverty of speech). CCK was reduced in temporal cortex of the schizophrenics and in hippocampus and amygdala of those patients with negative symptoms. SRIF was reduced in the hippocampus in samples from the latter group. The selectivity of these changes to limbic lobe may reflect the presence of a degenerative process in that area. The association of changes in hippocampus and amygdala with negative symptoms of schizophrenia suggests a separate mechanism underlying these symptoms.

Increased Hypothalamic Neuropeptide Y Concentrations in Diabetic Rat

Central and lateral hypothalamic concentrations of 10 regulatory peptides were measured by radioimmunoassay in streptozocin-induced diabetic (STZ-D) and matched control rats between 1 day and 14 wk after diabetes induction. After 2 wk, both central and lateral hypothalamic neuropeptide Y (NPY) concentrations in STZ-D rats were consistently higher than those found in control rats, with significant 30–50% increases at 4 wk in the central hypothalamus, and at 6 and 14 wk in both central and lateral hypothalamus. Immunocytochemical studies in 4- and 6-wk STZ-D animals showed the appearance of intensely NPY-positive swollen cell bodies in the supraoptic nucleus and a subjective increase in NPY staining of medial hypothalamic nerve fibers. Central hypothalamic concentrations of three other peptides were significantly greater in STZ-D animals than those in control animals at single points (neurotensin, 1 day; calcitonin gene-related peptide, 2 wk; neurokinin, 4 wk). Hypothalamic concentrations of the other six peptides examined (bombesin, galanin, neuromedin B, substance P, somatostatin, and vasoactive intestinal peptide) did not differ significantly between STZ-D and control groups at any time. However, galanin immunostaining in the supraoptic and magnocellular paraventricular nuclei was strikingly concentrated in a reduced number of distended cell bodies. Hypothalamic peptide changes in STZ-D could be related to metabolic disturbance, changes in energy and water balance, altered pituitary function, or other factors. Persistently elevated concentrations of NPY, a very potent central stimulant of eating and drinking, may mediate the hyperphagia and polydipsia characteristic of STZ-D.

Regional distribution of bombesin and seven other regulatory peptides in the human brain

In order to compare within the same brains the quantitative distributions of a range of neuropeptides, bombesin, N- and C-terminal glucagon, cholecystokinin, neurotensin, somatostatin, substance P and vasoactive intestinal polypeptide immunoreactivities were determined by radioimmunoassay in 24 regions of 5 normal adult human brains. Each peptide showed a different distribution pattern. Of the peptides not previously mapped in detail in the human brain, bombesin-like immunoreactivity was present in all regions with the highest concentrations in particular areas of the hypothalamus, septal nuclei, nucleus accumbens, globus pallidus, amygdala, periaqueductal grey and substantia nigra. C- and N-terminal glucagon immunoreactivities were detected only in the ventromedial hypothalamus. The concentrations of the remaining 5 peptide immunoreactivities, and their molecular forms, were in good general agreement with those reported individually by others in both human brains and those of experimental animals. The quantitative mapping of the regulatory peptides in the human brain provides an essential base for further comparative study in diseased postmortem brains.

Content and release of neurotensin in PC12 pheochromocytoma cell cultures: modulation by dexamethasone and nerve growth factor

The production of neurotensin-like immunoreactivity was investigated in cultured PC12 rat pheochromocytoma cells with and without the addition of nerve growth factor (NGF) and dexamethasone. Both monolayer cultures and spinner cultures contained measurable amounts of neurotensin. In the monolayer cultures supplemented with NGF and dexamethasone, cell and medium concentrations of neurotensin increased approx. 100-fold. In the spinner cultures the effect of the additives was less potent and the increase in neurotensin content, while still considerable, was approximately an order of magnitude less. Chromatographic analysis of medium and extracts of the cells from monolayer cultures indicated that the majority of the immunoreactivity coeluted in the same position as synthetic neurotensin, with recoveries of 68 and 85%, respectively. The effect of NGF and dexamethasone on neurotensin production differs significantly from their effect on catecholamine production in PC12 cells, and this suggests the possibility of independent regulation.

REDUCED HYPOTHALAMIC NEUROTENSIN CONCENTRATIONS IN THE GENETICALLY-OBESE DIABETIC (OB/OB) MOUSE - POSSIBLE RELATIONSHIP TO OBESITY

Hypothalamic tissue levels of nine regulatory peptides (bombesin, calcitonin gene-related peptide [CGRP], galanin, neuromedin B, neuropeptide Y [NPY], neurotensin, somatostatin, substance P, and vasoactive intestinal peptide [VIP]) were compared in Aston obese diabetic (ob/ob) and lean (+/?) mice aged 4, 16, and 28 weeks. Neurotensin concentrations were significantly lower in ob/ob mice than in lean mice, with a 20% reduction (P = .03) in the whole hypothalamus at 4 weeks of age, a 24% reduction (P = .009) in the lateral hypothalamus at 16 weeks, and a 50% reduction (P = .0007) in the central hypothalamus at 28 weeks of age. Apart from a 42% increase in vasoactive intestinal peptide concentrations in the central hypothalamus of ob/ob mice at 28 weeks (P = .02), levels of the other eight peptides examined did not differ significantly between obese and lean groups. Neurotensin is known to cause anorexia and increased energy expenditure when injected into the central hypothalamus. Reduced hypothalamic neurotensin concentrations may reflect reduced neurotensinergic activity, which might contribute to hyperphagia and decreased energy expenditure, two major defects that contribute to obesity and diabetes in the ob/ob syndrome.

Neuropeptide Y (NPY) in pc12 phaeochromocytoma cultures: Responses to dexamethasone and nerve growth factor

High concentrations of a novel regulatory peptide, neuropeptide Y, have been identified within the PC12 rat phaeochromocytoma cell line by radioimmunoassay and chromatographic analysis. The cellular concentration of this peptide has been demonstrated to be predominantly influenced by the presence of nerve growth factor. After 14 days in culture in the presence of dexamethasone, NPY concentrations were 0.19 +/- 0.03 pmol/mg protein, whereas following similar exposure to nerve growth factor, concentrations were 3.44 +/- 0.19 pmol/mg protein. Addition of nerve growth factor to the dexamethasone-treated cells resulted in a rise in NPY concentration to 0.90 +/- 0.08 pmol/mg over 7 days, whereas addition of dexamethasone to the cells treated with nerve growth factor resulted in no further rise in NPY concentration. The concentrations of NPY far exceed those previously reported for neurotensin in PC12 cells, under the same culture conditions. These two peptides appear also to be regulated by different mechanisms.

Quantitation and characterization of human plasma neurotensin-like immunoreactivity in response to a meal

The secretion and metabolism of endogeneous neurotensin-like immunoreactivities after a test meal were studied in five healthy human subjects. Intact neurotensin and the N-terminal metabolic fragment, neurotensin 1–8, were quantified by radioimmunoassay with C- and N-terminally directed antisera in conjunction with gel filtration of plasma samples obtained at timed intervals. Both C- and N-terminal neurotensin-like immunoreactivities rose after the meal, reaching a plateau level after 20 and 30 min, respectively. During the plateau phase, which lasted for the rest of the experimental period of 180 min, the molar ratio of intact neurotensin to neurotensin 1–8 remained approximately constant at 1∶4.6. Meal-stimulated immunoreactive neurotensin appeared to be metabolized in a manner comparable to that of exogenously infused neurotensin in man. The results suggest that intact neurotensin is secreted at an approximately constant rate during the plateau phase. The relatively low plateau level of neurotensin 1–8, which has a much longer half-life than intact neurotensin in the circulation, implies that only a fraction of the secreted intact neurotensin is metabolized to neurotensin 1–8, indicating the existence of alternative pathways of neurotensin metabolism.

Adult Cystic stic Fibrosis: Postprandial Response of Gut Regulatory Peptides

Responses of 11 gastrointestinal regulatory peptides to a standard test meal were assessed in 10 adult patients with cystic fibrosis. The basal plasma neurotensin was significantly elevated in patients with cystic fibrosis, being 31.5 ± 6.1 pmollL compared with a control value of 10.3 ± 1.5 pmol/L (p

In vitro degradation of neurotensin in human plasma

To study the degradation of neurotensin in plasma in vitro, fresh human plasma was incubated with neurotensin in the presence and absence of the peptidase inhibitors pepstatin A, EDTA, PMSF and aprotinin. The half-time of disappearance of neurotensin at 37 degrees C was calculated to be 226 min in vitro as opposed to 1.4 min in vivo when measured by radioimmunoassay with a C-terminally directed neurotensin antiserum. Both gel filtration and reversed phase high-pressure liquid chromatography (HPLC) showed that the main degradation product of neurotensin in human plasma in vitro was chromatographically and immunologically identical to neurotensin 1-8 and HPLC also demonstrated the formation of neurotensin 1-11. The loss of neurotensin incubated in human plasma in vitro was greatly reduced by EDTA but not by the other peptidase inhibitors tested. In this respect peptidase(s) responsible for the degradation of neurotensin in plasma differ from those present in brain homogenates. EDTA may be of importance in the preservation of neurotensin in plasma samples.