Leptin injected into the fourth ventricle inhibits gastric emptying.

The effect of leptin on gastric emptying of glucose was studied in freely moving rats bearing intragastric fistulas. Leptin (0.39 microg and 3.9 microg) injected into the fourth ventricle inhibited gastric emptying significantly, whereas s.c. administration of leptin (10 microg/kg) had no effect. Leptin receptor immunoreactivity, revealed by an antiserum that recognizes all leptin receptor isoforms, was demonstrated in choline acetyltransferase (ChAT)-containing neurones of the dorsal motor nucleus of the vagus nerve (DMX). The data indicate that leptin acts centrally to suppress gastric emptying possibly via leptin receptors located on cholinergic DMX neurones.

Leptin receptor immunoreactivity in chemically defined target neurons of the hypothalamus.

The adipose tissue-derived hormone leptin regulates body weight homeostasis by decreasing food intake and increasing energy expenditure. The weight-reducing action of leptin is thought to be mediated primarily by signal transduction through the leptin receptor (LR) in the hypothalamus. We have used immunohistochemistry to localize LR-immunoreactive (LR-IR) cells in the rat brain using an antiserum against a portion of the intracellular domain of LR that is common to all LR isoforms. The antiserum recognized the short and long isoforms of LR in transfected hematopoietic BaF3 cells. To examine the chemical nature of target cells for leptin, direct double-labeling immunofluorescence histochemistry was applied. The results show extensive distribution of LR-like immunoreactivity (LR-LI) in the brain with positively stained cells present, e.g., in the choroid plexus, cerebral cortex, hippocampus, thalamus, and hypothalamus. In the hypothalamus, strongly LR-IR neurons were present in the supraoptic nucleus (SON) and paraventricular nucleus (PVN), periventricular nucleus, arcuate nucleus, and lateral hypothalamus. Weaker LR-IR neurons were also demonstrated in the lateral and medial preoptic nuclei, suprachiasmatic nucleus, ventromedial and dorsomedial nuclei, and tuberomammillary nucleus. Confocal laser scanning microscopy showed LR-LI in the periphery of individual cells. In magnocellular neurons of the SON and PVN, LR-LI was demonstrated in vasopressin- and oxytocin-containing neurons. In parvocellular neurons of the PVN, LR-LI was demonstrated in many corticotropin-releasing hormone-containing neurons. LR-IR neurons were mainly seen in the ventromedial aspect of the arcuate nucleus, where LR-LI co-localized with neuropeptide Y. In the ventrolateral part of the arcuate nucleus, LR-LI was present in many large adrenocorticotropic hormone-IR proopiomelanocortin-containing neurons and in a few galanin-, neurotensin-, and growth hormone-releasing hormone-containing neurons. In the dorsomedial arcuate nucleus, few tyrosine hydroxylase (dopamine)-containing neurons were seen to have LR-LI. Melanin-concentrating hormone-containing neurons in the lateral hypothalamus had LR-LI. Based on the immunohistochemical results, possible interactions of leptin with brain mechanisms are discussed.

Transcription factor STAT3 in leptin target neurons of the rat hypothalamus.

Leptin is an adipose tissue-derived hormone that regulates body weight via interactions with hypothalamic neuronal circuitries expressing specific leptin receptors (Ob-R). The Ob-Rs act via the JAK-STAT (Janus kinase-signal transducers and activators of transcription) pathway of signal transduction. Recent evidence suggests that primarily the transcription factor STAT3 mediates leptin's action in the hypothalamus. We have investigated the presence and cellular localization of STAT3 protein in the rat hypothalamus by means of indirect immunofluorescence histochemistry using a rabbit polyclonal STAT3 antiserum. The antiserum identified a 92-kDa protein using Western blotting on rat hypothalamic homogenates, corresponding to the expected size of STAT3. STAT3 immunoreactivity was demonstrated in Ob-R-containing neurons of the paraventricular nucleus (parvocellular part), periventricular nucleus, arcuate nucleus and in the lateral hypothalamic area. Direct double-labeling showed presence of STAT3 immunoreactivity in neuropeptide Y (NPY)-containing neurons of the ventromedial part of the arcuate nucleus and in proopiomelanocortin (POMC)-containing neurons of the ventrolateral part of the arcuate nucleus. The results provide an anatomical basis for a leptin action mediated by STAT3 in Ob-R-containing NPY and POMC neurons of the arcuate nucleus, as well as by Ob-R-containing neurons of the parvocellular paraventricular nucleus and lateral hypothalamic area.

[Orexins--new hypothalamic peptides that stimulate appetite]. / Orexiner--nya hypotalamiska peptider som stimulerar aptit.

A family of novel hypothalamus-specific peptides called orexins have recently been discovered and characterized. The orexins stimulate appetite (the greek word orexis means appetite) when given intraventricularly to rats. Their genes are expressed bilaterally in the lateral hypothalamus, a region previously known to regulate food intake. The two peptides, orexin A (33 amino-acids) and orexin B (28 amino acids), are derived from a common prepro-orexin precursor. The peptides bind to specific G-protein-coupled orexin receptors termed OX-1R and OX-2R. The identification of the orexins will increase our understanding on how the brain regulates food intake.

Botulinum neurotoxin F, a VAMP-specific endopeptidase, inhibits Ca(2+)-stimulated GH secretion from rat pituitary cells.

Botulinum neurotoxin F (BoNTx F) is a zinc-dependent endopeptidase that causes proteolytic cleavage of the vesicle protein VAMP (vesicle-associated membrane protein). VAMP is an important component of the molecular machinery regulating docking and fusion of secretory vesicles with the target membrane. We have investigated presence of VAMP protein in cultured rat anterior pituitary cells. Confocal laser microscopy revealed presence of VAMP-like immunoreactivity in secretory granules of GH-containing cultured rat anterior pituitary cells. Using BoNTx F, we have investigated whether VAMP is involved in growth hormone (GH) secretion. Treatment of streptolysin-O permeabilized GH-secreting cells with BoNTx F (2.0 and 20 nM) significantly inhibited Ca(2+)-induced GH release. The results show that the secretory granules of rat anterior pituitary cell contain VAMP protein and suggest that VAMP is of importance in regulating Ca(2+)-mediated GH secretion.

Expression of leptin receptor mRNA in the hypothalamic arcuate nucleus--relationship with NPY neurones.

The obese phentotype of ob/ob mice is linked to a mutation in the ob gene that results in expression of a truncated inactive protein. The ob gene product, leptin, is synthesized in adipose tissue and is a circulating factor that regulates body weight. Leptin receptors were recently cloned and a mutation in the leptin receptor gene in obese db/db mice was identified. Leptin receptor mRNA has been detected in brain, including hypothalamus, but the cellular localization has so far not been clarified. Here we report on the cellular localization of leptin receptor mRNA in the mouse brain using in situ hybridization. Strong hybridization was observed in the choroid plexus and hypothalamic arcuate nucleus. Weaker hybridization was detected in the hippocampal formation and in the cerebral cortex. Within the arcuate nucleus, cell bodies expressing leptin receptor mRNA were distributed in its ventromedial subdivision. Hybridization of semiadjacent sections with a probe to neuropeptide Y (NPY) showed a co-distribution of labelled cell bodies, suggesting the presence of leptin receptors on NPY-containing neurones.