The nucleus tractus solitarius (NTS) receives dense terminations from cranial visceral afferents

No abstract

Proopiomelanocortin (POMC) neurons in the hypothalamus are direct targets of the adipostatic hormone leptin and contribute to energy homeostasis by integrating peripheral and central information. The melanocortin and beta-endorphin neuropeptides are processed from POMC and putatively coreleased at axon terminals. Melanocortins have been shown by a combination of pharmacological and genetic methods to have inhibitory effects on appetite and body weight. In contrast, pharmacological studies have generally indicated that opioids stimulate food intake. Here we report that male mice engineered to selectively lack beta-endorphin, but that retained normal melanocortin signaling, were hyperphagic and obese. Furthermore, beta-endorphin mutant and wild-type mice had identical orexigenic responses to exogenous opioids and identical anorectic responses to the nonselective opioid antagonist naloxone, implicating an alternative endogenous opioid tone to beta-endorphin that physiologically stimulates feeding. These genetic data indicate that beta-endorphin is required for normal regulation of feeding, but, in contrast to earlier reports suggesting opposing actions of beta-endorphin and melanocortins on appetite, our results suggest a more complementary interaction between the endogenously released POMC-derived peptides in the regulation of energy homeostasis.

. Cranial visceral afferents enter the brain at the solitary tract nucleus (NTS). GABAergic neurons are scattered throughout the NTS, but their relation to solitary tract (ST) afferent pathways is imprecisely known. We hypothesized that most GABAergic NTS neurons would be connected only indirectly to the ST. We identified GABAergic neurons in brain stem horizontal slices using transgenic mice in which enhanced green fluorescent protein (EGFP) expression was linked to glutamic acid decarboxylase expression (GAD ϩ ). Finely graded electrical shocks to ST recruit STsynchronized synaptic events with all-or-none thresholds and individual waveforms did not change with greater suprathreshold intensities-evidence consistent with initiation by single afferent axons. Most (ϳ70%) GAD ϩ neurons received ST-evoked excitatory postsynaptic currents (EPSCs) that had minimally variant latencies (jitter, SD of latency Ͻ200 s) and waveforms consistent with single, direct ST connections (i.e., monosynaptic). Increasing stimulus intensity evoked additional ST-synchronized synaptic responses with jitters Ͼ200 s including inhibitory postsynaptic currents (IPSCs), indicating indirect connections (polysynaptic). Shocks of suprathreshold intensity delivered adjacent (50 -300 m) to the ST failed to excite non-ST inputs to second-order neurons, suggesting a paucity of axons passing near to ST that connected to these neurons. Despite expectations, we found similar ST synaptic patterns in GAD ϩ and unlabeled neurons. Generally, ST information that arrived indirectly had small amplitudes (EPSCs and IPSCs) and frequency-dependent failures that reached Ͼ50% for IPSCs to bursts of stimuli. This ST afferent pathway organization is strongly use-dependent-a property that may tune signal propagation within and beyond NTS.

Classical mechanisms through which brain-derived molecules influence behavior include neuronal synaptic communication and neuroendocrine signaling. Here we provide evidence for an alternative neural communication mechanism that is relevant for food intake control involving cerebroventricular volume transmission of the neuropeptide melanin-concentrating hormone (MCH). Results reveal that the cerebral ventricles receive input from approximately one-third of MCH-producing neurons. Moreover, MCH cerebrospinal fluid (CSF) levels increase prior to nocturnal feeding and following chemogenetic activation of MCH-producing neurons. Utilizing a dual viral vector approach, additional results reveal that selective activation of putative CSF-projecting MCH neurons increases food intake. In contrast, food intake was reduced following immunosequestration of MCH endogenously present in CSF, indicating that neuropeptide transmission through the cerebral ventricles is a physiologically relevant signaling pathway for energy balance control. Collectively these results suggest that neural-CSF volume transmission signaling may be a common neurobiological mechanism for the control of fundamental behaviors.

Non-dioxin-like (NDL) polychlorinated biphenyls (PCBs) are widespread environmental contaminants linked to neuropsychological dysfunction in children. NDL PCBs increase spontaneous Ca 2ϩ oscillations in neurons by stabilizing ryanodine receptor (RyR) calcium release channels in the open configuration, which results in CREB-dependent dendritic outgrowth. In this study, we address the question of whether activation of CREB by NDL PCBs also triggers dendritic spine formation. Nanomolar concentrations of PCB 95, a NDL congener with potent RyR activity, significantly increased spine density and the frequency of miniature EPSCs in primary dissociated rat hippocampal cultures coincident with upregulation of miR132. Inhibition of RyR, CREB, or miR132 as well as expression of a mutant p250GAP cDNA construct that is not suppressed by miR132 blocked PCB 95 effects on spines and miniature EPSCs. PCB 95 also induced spine formation via RyR-and miR132-dependent mechanisms in hippocampal slice cultures. These data demonstrate a novel mechanism of PCB developmental neurotoxicity whereby RyR sensitization modulates spine formation and synaptogenesis via CREB-mediated miR132 upregulation, which in turn suppresses the translation of p250GAP, a negative regulator of synaptogenesis. In light of recent evidence implicating miR132 dysregulation in Rett syndrome and schizophrenia, these findings identify NDL PCBs as potential environmental risk factors for neurodevelopmental disorders.

No abstract

We used the Xenopus oocyte expression system to examine the regulation of rat opioid receptor (rKOR) function by G protein receptor kinases (GRKs). agonists increased the conductance of G protein-activated inwardly rectifying potassium channels in oocytes coexpressing KOR with Kir3.1 and Kir3.4. In the absence of added GRK and ␤-arrestin 2, desensitization of the agonist-induced potassium current was modest. Co-expression of either GRK3 or GRK5 along with ␤-arrestin 2 significantly increased the rate of desensitization, whereas addition of either ␤-arrestin 2, GRK3, or GRK5 alone had no effect on the KOR desensitization rate. The desensitization was homologous as co-expressed ␦ opioid receptor-evoked responses were not affected by KOR desensitization. The rate of GRK3/␤-arrestin 2-dependent desensitization was reduced by truncation of the C-terminal 26 amino acids, KOR(Q355⌬). In contrast, substitution of Ala for Ser within the third intracellular loop [KOR(S255A,S260A,S262A)] did not reduce the desensitization rate. Within the C-terminal region, KOR(S369A) substitution significantly attenuated desensitization, whereas the KOR(T363A) and KOR(S356A,T357A) point mutations did not. These results suggest that co-expression of GRK3 or GRK5 and ␤-arrestin 2 produced homologous, agonist-induced desensitization of the opioid receptor by a mechanism requiring the phosphorylation of the serine 369 of rKOR. In support of this hypothesis, agonist-induced desensitization of the opioid-evoked response was blocked by the expression of a dominant negative G protein-coupled receptor kinase in transfected cells (7). In addition, over-expression of ␤-arrestin 1 attenuated the opioid receptor-mediated response (8). However, the effects of specific G protein receptor kinases, the contribution of ␤-arrestins, and the regions of KOR required for agonist-induced desensitization remains to be elucidated. In this study, we used the Xenopus oocyte expression system to further characterize the potential mechanisms underlying agonist-induced desensitization of KOR. A better definition of the desensitization process is critical for a clearer understanding of the mechanisms underlying opioid tolerance.