Desacyl Ghrelin Decreases Anxiety-like Behavior in Male Mice.

Ghrelin is a 28-amino acid polypeptide that regulates feeding, glucose metabolism, and emotionality (stress, anxiety, and depression). Plasma ghrelin circulates as desacyl ghrelin (DAG) or, in an acylated form, acyl ghrelin (AG), through the actions of ghrelin O-acyltransferase (GOAT), exhibiting low or high affinity, respectively, for the growth hormone secretagogue receptor (GHSR) 1a. We investigated the role of endogenous AG, DAG, and GHSR1a signaling on anxiety and stress responses using ghrelin knockout (Ghr KO), GOAT KO, and Ghsr stop-floxed (Ghsr null) mice. Behavioral and hormonal responses were tested in the elevated plus maze and light/dark (LD) box. Mice lacking both AG and DAG (Ghr KO) increased anxiety-like behaviors across tests, whereas anxiety reactions were attenuated in DAG-treated Ghr KO mice and in mice lacking AG (GOAT KO). Notably, loss of GHSR1a (Ghsr null) did not affect anxiety-like behavior in any test. Administration of AG and DAG to Ghr KO mice with lifelong ghrelin deficiency reduced anxiety-like behavior and decreased phospho-extracellular signal-regulated kinase phosphorylation in the Edinger-Westphal nucleus in wild-type mice, a site normally expressing GHSR1a and involved in stress- and anxiety-related behavior. Collectively, our data demonstrate distinct roles for endogenous AG and DAG in regulation of anxiety responses and suggest that the behavioral impact of ghrelin may be context dependent.

Activation of POMC neurons during general arousal but not sexual behavior in male rats.

Exogenous opioids influence male rat sexual behavior, suggesting that endogenous opioid peptides are released during mating. Supporting this hypothesis, the authors recently showed that mating induced activation of mu opioid receptors. However, it is unknown which ligand(s) is acting on these receptors during mating. The current set of experiments tested the hypothesis that beta-endorphin-producing neurons, that is, proopiomelanocortin (POMC) neurons, are activated during sexual behavior. Mating-induced activation of POMC neurons was investigated during either the dark phase or the light phase, following different components of male rat sexual behavior or following control manipulations that resulted in general arousal. Results show activation of POMC neurons in the mediobasal hypothalamus following general arousal but not specifically related to sexual behavior per se. In addition, mating did not activate the subpopulation of POMC neurons that project to the medial preoptic nucleus. These results suggest that it is unlikely that POMC neurons contribute to the action of endogenous opioids in the brain area during sexual behavior but instead may contribute to the change in arousal state essential for the expression of sexual behavior.

Mast cells can contribute to axon-glial dissociation and fibrosis in peripheral nerve.

Expression of the human epidermal growth factor receptor (EGFR) in murine Schwann cells results in loss of axon-Schwann cell interactions and collagen deposition, modeling peripheral nerve response to injury and tumorigenesis. Mast cells infiltrate nerves in all three situations. We show that mast cells are present in normal mouse peripheral nerve beginning at 4 weeks of age, and that the number of mast-cells in EGFR(+) nerves increases abruptly at 5-6 weeks of age as axons and Schwann cells dissociate. The increase in mast cell number is preceded and accompanied by elevated levels of mRNAs encoding the mast-cell chemoattractants Rantes, SCF and VEGF. Genetic ablation of mast cells and bone marrow reconstitution in W(41) x EGFR(+) mice indicate a role for mast cells in loss of axon-Schwann cell interactions and collagen deposition. Pharmacological stabilization of mast cells by disodium cromoglycate administration to EGFR(+) mice also diminished loss of axon-Schwann cell interaction. Together these three lines of evidence support the hypothesis that mast cells can contribute to alterations in peripheral nerves.

Perinatal epidermal growth factor receptor blockade prevents peripheral nerve disruption in a mouse model reminiscent of benign world health organization grade I neurofibroma.

Benign peripheral nerve tumors called neurofibromas are a major source of morbidity for patients with neurofibromatosis type 1. Some neurofibroma Schwann cells aberrantly express the epidermal growth factor receptor (EGFR). In a mouse model in which the CNPase promoter drives expression of human EGFR in Schwann cells, nerves develop hypertrophy, mast cell accumulation, collagen deposition, disruption of axon-glial interactions, characteristics of neurofibroma and are hypoalgesic. Administration of the EGFR antagonist cetuximab (IMC-C225) for 2 weeks beginning at birth in CNPase-hEGFR mice normalized all pathologies at 3 months of age as evaluated by hotplate testing or histology and by electron microscopy. Mast cell chemoattractants brain-derived neurotrophic factor, monocyte chemoattractant protein-1, and transforming growth factor-beta1, which may account for mast cell accumulation and fibrosis, were reduced by cetuximab. Later treatment was much less effective. A birth to 2-week pulse of cetuximab blocked hEGFR phosphorylation and Schwann cell prolifera-tion in perinatal mutant nerve, so CNPase-hEGFR Schwann cell numbers correlate with the cetuximab effect. A >250-fold enlarged population of EGFR(+)/p75(+) cells was detected in newborn Nf1(+/-) mouse nerves. These results suggest the existence of an EGFR(+) cell enriched in the perinatal period capable of driving complex changes characteristic of neurofibroma formation.

Evidence that dynorphin plays a major role in mediating progesterone negative feedback on gonadotropin-releasing hormone neurons in sheep.

Endogenous opioid peptides (EOP) mediate progesterone-negative feedback in many species, but the specific EOP systems involved remain unresolved. We first addressed this question in sheep by determining the role of different EOP receptor subtypes in the medial basal hypothalamus (MBH) and preoptic area (POA). Local administration of EOP receptor antagonists to luteal phase ewes indicated that kappa-, but not micro- or delta-, receptors mediate the inhibition of LH secretion in the MBH. In contrast, both kappa- and micro-, but not delta-receptor, antagonists increased LH pulse frequency when placed in the POA. We next examined close appositions between dynorphin (kappa ligand) and beta-endorphin (micro ligand) containing varicosities and GnRH perikarya in luteal phase ewes using dual immunocytochemistry and light microscopy. Approximately 90% of MBH GnRH neurons had close associations by dynorphin-containing varicosities, but only 40-50% of GnRH perikarya elsewhere had such close associations. In contrast, the percentage of beta-endorphinergic varicosities close to GnRH neurons was similar among all regions. Electron microscopic analysis demonstrated both dynorphinergic synapses and beta-endorphinergic synapses onto GnRH perikarya. These and other data lead to the hypothesis that dynorphin neurons play a major role in progesterone-negative feedback in the ewe and that this inhibition may be exerted directly on GnRH perikarya within the MBH, whereas dynorphin and beta-endorphin input to GnRH neurons in the POA provide redundancy to this system or are involved in other actions of progesterone or estradiol in the control of the GnRH surge.

Colocalization of progesterone receptors in parvicellular dynorphin neurons of the ovine preoptic area and hypothalamus.

Recent evidence suggests that the dynorphin-kappa receptor opioid system acts to mediate the inhibitory effect of progesterone (P) on GnRH pulse frequency during the luteal phase of the ovine estrous cycle. It is known that progesterone receptors (PRs) are required for the actions of P on GnRH secretion. Therefore, if P acts directly on dynorphin (DYN) neurons, then these neurons should contain PRs. To test this hypothesis, we used a dual-label immunoperoxidase procedure to visualize PRs and DYN in the preoptic area (POA) and hypothalamus of ovary-intact ewes killed during the luteal phase of the estrous cycle. The PR was colocalized in more than 90% of parvicellular DYN neurons in the POA, anterior hypothalamus (AHA), and arcuate nucleus (ARC). By contrast, none of magnocellular DYN cells of the paraventricular and supraoptic nuclei coexpressed immunoreactive PRs. The high percentage of colocalization of PRs in parvicellular DYN cells of the POA, AHA, and ARC suggests that these cells are prime targets of P. In addition, DYN cells in the ARC, but not the POA or AHA, were found to receive synaptic inputs from DYN-positive axon terminals. This observation raises the possibility that an ultrashort feedback loop controls the release of DYN from ARC neurons.