Direct demonstration of interactions between substance P immunoreactive terminals and tyrosine hydroxylase immunoreactive neurons in the substantia nigra of the rat: an ultrastructural study

The results of many anatomical, physiological, and pharmacological studies suggest that substance P-containing neurons of the striatum project to the substantia nigra, and that substance P influences the activity of dopaminergic nigrostriatal neurons. The purpose of the present ultrastructural study was to employ dual immunocytochemical labeling to determine the morphological basis for the observed actions of substance P on nigral dopaminergic neurons. Substance P-like and tyrosine hydroxylase-like immunoreactivities were localized simultaneously at the ultrastructural level in the substantia nigra of the rat. A double label method was utilized which relied on a combination of the peroxidase-antiperoxidase method (Sternberger, 1979) for substance P, and immunogold or silver enhanced immunogold labeling for tyrosine hydroxylase. The present results indicate that tyrosine hydroxylase immunoreactive (THLI) dendrites in the substantia nigra receive synaptic input from terminals exhibiting substance P-like immunoreactivity. These findings support the idea that substance P is a major neurotransmitter in the striatonigral loop, and suggest that striatal substance P neurons act directly upon nigral dopaminergic cells.     

Control of feeding and sexual behaviors by neuropeptide Y: physiological implications

Recent evidence suggests that a variety of hypothalamic neuropeptides may mediate interneuronal communication to coordinate diverse neuroendocrine and behavioral functions. In this work, we describe the effects of neuropeptide Y (NPY) on feeding and sexual behaviors. We observed that central administration of bolus NPY stimulated a robust, dose-related feeding response in satiated male and female rats. Continuous NPY receptor activation also evoked dose-related, intermittent feeding in a manner normally observed during nocturnal feeding. It appears that the paraventricular nucleus in the hypothalamus may be the primary site of NPY action because the anticipated reciprocal changes in NPY concentrations, in response to food deprivation followed by ad libitum food intake, occurred only in this site. Additional findings revealed that NPY-induced feeding may follow either substantial reduction or complete restraint of an inhibitory influence on feeding mediated by alpha 2-adrenoreceptor systems in satiated rats. Further, NPY was found to suppress male and female sexual behaviors. The suppressive effects on sexual behavior were apparent prior to or at the time of the onset of feeding after NPY administration. These observations may provide a neurochemical basis for clinical and animal studies on disorders of feeding associated with diminished reproductive functions.     

Orthogonal solid-phase synthesis of a monobiotinylated analog of Neuropeptide Y

Analogs of Neuropeptide Y (NPY) were synthesized with conventional Boc/benzyl protective group strategy. Instead of Asn⁷ in the native scquence, Boc-Lys(Alloc)-OH was incorporated. At the end of the synthesis the Alloc group was selectively removed by palladium-catalyzed hydrostannolysis and biotin coupled to the e-amino group of Lys⁷. After cleavage and characterization with plasma desorption mass spectrometry the N^e-7-biotinyl-[Lys⁷]-NPY and the nonbiotinylated analog [Lys⁷]-NPY were investigated as ligands to the NPY receptor from rat cerebral cortex. Both analogs were found to be high affinity ligands to the NPY receptor and bound with essentially the same affinity as unmodified NPY.     

β-Endorphin serum levels in patients with vitiligo

Aim The aim of this study is to correlate the β-endorphin levels at the early and more chronic stages of the disease in an attempt to find or confirm an etiological factor of vitiligo. Background The exact pathogenesis of vitiligo is still unclear. The most important theories are the self destruction, the autoimmune and the neural theories. Methods Patients with vitiligo (n= 28) were divided into two groups according to the duration of their disease. A group of 15 members of medical staff was the control group. β-endorphin levels were determined with a radioimmunoassay (¹²⁵I-β-endorphin IncstarCo). Results The mean β-endorphin levels (11.88 ± 2.25 pmol/l) in patients at the early years of the disease (Group A) were statistically elevated compared to those of patients with ‘chronic’ vitiligo (9.27 ± 2.73 pmol/l) and to those of controls (8.53 ± 2.53) pmol/l). Conclusion We suggest that high β-endorphin levels play a role in the pathogenesis of vitiligo as well as in the prognosis of the disease.     

Neonatal exposure to estradiol prevents the expression of ovarian hormone-induced luteinizing hormone and prolactin surges in adulthood but not antecedent changes in neuropeptide Y or adrenergic transmitter activity: Implications for sexual differentiation of gonadotropin secretion

Sex differences in adult patterns of mating behavior and gonadotropin secretion in rats are determined in part by the presence or absence of gonadal steroids during a perinatal critical period. For example, male rats and female rats exposed neonatally to androgen do not exhibit LH surge patterns when treated appropriately with ovarian hormones in adulthood, and there is evidence that this may be due to a failure of ovarian hormones to activate the hypothalamic neuronal systems that stimulate LH secretion in such animals. Because considerable evidence suggests that estradiol formed centrally from testosterone is responsible for the permanent defeminization of mating behavior and gonadotropin secretion, the present studies compared normal females with normal males and with females treated neonatally with estradiol on the ability of ovarian hormones to induce several important neurochemical changes antecedent to the LH surge, including changes in neuropeptide Y (NPY) and LH-releasing hormone (LHRH) concentrations in the median eminence, as well as changes in turnover rates for catecholamine transmitters in the medial basal hypothalamus and medial preoptic area. Normal ovariectomized female rats responded to sequential treatment with estradiol followed by progesterone with afternoon LH and prolactin (PRL) surges, and with sequential accumulation followed by decline in concentrations of LHRH and NPY in the median eminence prior to the LH surge. In addition, administration of progesterone increased the turnover rates of norepinephrine (NE) and epinephrine (EPI) in the arcuate-median eminence region of normal females. Gonadectomized male rats receiving the same ovarian hormone treatment failed to exhibit LH or PRL surges and displayed none of the changes in neurotransmitter turnover or peptide concentrations characteristically seen in the normal female. Unexpectedly however, when females that were treated with estradiol benzoate on days 1–3 postpartum were ovariectomized and treated with ovarian hormones in adulthood, they showed the same accumulation/decline in median eminence NPY concentrations and the same activation of NE and EPI turnover in the arcuate-median eminence region as normal females, even though they showed no LH or PRL surges or changes in median eminence LHRH concentrations. These results suggest that estradiol may not mediate all of the defeminizing actions of androgen exerted during the early neonatal period, and particularly those actions that result in a lack of responsiveness in central noradrenergic, adrenergic and NPY systems in adulthood. However, an action of neonatal estradiol may result in uncoupling of the LHRH neurosecretory system from normal excitatory neurochemical influences.     

Increased feeding and neuropeptide Y (NPY) but not NPY mRNA levels in the hypothalamus of the rat following central administration of the serotonin synthesis inhibitorp-chlorophenylalanine

Neurons containing serotonin (5-HT), a potent anorexic agent, come into contact with neuropeptide Y-ergic neurons, that project from the arcuate nucleus (ARC) to the paraventricular nucleus (PVN). NPY powerfully stimulates feeding and induces obesity when injected repeatedly into the PVN. We hypothesize that 5-HT tonically inhibits the ARC-PVN neurons and that balance between the two systems determines feeding and energy homeostasis. This study aimed to determine whether central injection of the 5-HT synthesis inhibitor p-chlorophenylalanine (pCPA), which increases feeding, increased hypothalamic NPY and NPY mRNA levels. pCPA (10 mg/kg in 3 μl) was administered into the third ventricle either as a single injection (n = 8) or daily for 7 days (n = 8). Control rats received a similar injection of saline. pCPA significantly increased food intake compared with controls after both single and repeated injections (P < 0.05). NPY levels were measured by radioimmunoassay in microdissected hypothalamic extracts. NPY levels in the acutely treated group were significantly increased in the paraventricular nucleus (PVN; by 41%,P = 0.01), anterior hypothalamic area (AHA; by 34%,P < 0.01) and lateral hypothalamic area (LHA; by 41%,P < 0.02). In the 7-day-treated group, NPY levels were also increased in the same areas, i.e. PVN (by 24%,P < 0.01), AHA (by 30%,P < 0.01) and LHA (by 38%,P = 0.01). There were no significant changes in the ARC or any other region or in hypothalamic NPY mRNA levels. pCPA administration increased NPY levels in several regions notably the PVN. This is a major site of NPY release, where NPY injection induces feeding. We suggest that the hyperphagia induced by pCPA is mediated by increased NPY levels and secretion in the PVN. This is further evidence for interactions between NPY and 5-HT in the control of energy homeostasis.     

[I]Vasoactive intestinal peptide binding in rodent suprachiasmatic nucleus: Developmental and circadian studies

The suprachiasmatic nucleus (SCN) of rat and hamster have been studied extensively and shown to play critical roles in circadian rhythmicity. [¹²⁵I]Vasoactive intestinal peptide (VIP) binding levels are high in the rat SCN, suggesting that VIP receptors may be an important component of SCN function. In contrast to previously demonstrated diurnal variations in VIP immunoreactivity and VIP mRNA, the present study found [¹²⁵I]VIP binding to be stable across the light-dark cycle in both rat and hamster SCN. High [¹²⁵I]VIP labeling appeared to be coextensive with the rat SCN but extended somewhat beyond the cytoarchitectonic boundaries of the hamster SCN. Binding density in hamster SCN was slightly higher than in rat. In the developing rat SCN, [¹²⁵I]VIP binding levels distinguished the SCN on embryonic day 18, and appeared to increase to postnatal day 10 before declining to adult levels. The early presence of [¹²⁵I]VIP binding suggests possible involvement of VIP receptors in fetal entrainment of circadian rhythms.     

Immunohistochemical Localization of Neuropeptide Y in Nerves of the Male Genital Tract of the Photoperiodically Responsive Djungarian Hamster, Phodopus Sungoras/Immunhistochemische Lokalisation von Neuropeptid Y in Nerven der männlichen Genitalorgane des photoperiodisch sensiblen Djungarischen Zwerghamsters, Phodopus sungorus

Neuropeptide Y (NPY) was demonstrated by immunohistochemistry in nerves of the male genital tract of Phodopus sungorus at long (LD 16:8) und short (LD 8:16) photoperiods. No immunoreactive nerve fibres could be demonstrated in the testis, caput and corpus epididymidis and the ventral prostate gland. Dense networks of NPY-containing nerve fibers were demonstrated in the smooth muscle layer of the sperm-transporting duct, beginning in the cauda epididymidis with increasing density towards the distal part of the ductus deferens, and in the smooth muscle layer of the seminal vesicles. At short photoperiods, the density of the NPY-containing nerve plexus decreased only in the smooth muscle layer of the ductus deferens. A "trophic" influence of the large smooth muscle cells of the ductus deferens on their nerves not only in regard to their noradrenaline, but also on their NPY content is discussed.     

Differential increases in brain levels of neuropeptide Y and vasoactive intestinal polypeptide after kainic acid-induced seizures in the rat

Summary Changes in immunoreactivities of neuropeptide Y (NPY) and vasoactive intestinal polypeptide (VIP) were investigated in the brain of rats after severe kainic acid (KA, 10 mg/kg, i.p.) induced limbic seizures. Decreased levels of both neuropeptides were observed in the frontal cortex, striatum, dorsal hippocampus and amygdala/pyriform cortex subsequently to the period of acute seizures (3 h after injection of the toxin). Then NPY increased consistently in the frontal cortex, hippocampus and amygdala/pyriform cortex. Highest levels (290% of controls) were found in the frontal cortex after two months. Anticonvulsant therapy with phenobarbital (20 mg/kg, i.p., twice daily for three weeks) partially suppressed the rise in NPY levels. Immunoreactivity of VIP increased (to 150%) in the frontal cortex only transiently 3 days after injection of kainic acid. At the subsequently examined time intervals (10–60 days after kainic acid) it declined to control values. Levels decreasing subsequently to acute seizures reflect increased release and degradation of the respective peptide. Increased NPY levels suggest upregulation of NPY/ somatostatin/GABA neurons due to the decreased seizure threshold of the animals. The early, reversible rise of VIP in the cortex points to a short-lasting activation of this peptide system contained in local cholinergic neurons. This may be a consequence either of the acute seizures or subsequent neuropathological changes. Send offprint requests to G. Sperk at the above address