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To investigate the role of glial cells in the regulation of glucoprivic responses in rats, a chemogenetic approach was used to activate astrocytes neighboring catecholamine (CA) neurons in the ventromedial medulla (VLM) where A1 and C1 CA cell groups overlap (A1/C1). Previous results indicate that activation of CA neurons in this region is necessary and sufficient for feeding and corticosterone release in response to glucoprivation. However, it is not known whether astrocyte neighbors of CA neurons contribute to glucoregulatory responses. Hence, we made nanoinjections of AAV5-GFAP-hM3D(Gq)-mCherry to selectively transfect astrocytes in the A1/C1 region with the excitatory designer receptor exclusively activated by designer drugs (DREADDs), hM3D (Gq). After allowing time for DREADD expression, we evaluated the rats for increased food intake and corticosterone release in response to low systemic doses of the antiglycolytic agent, 2-deoxy-D-glucose (2DG), alone and in combination with the hM3D (Gq) activator clozapine-N-oxide (CNO). We found that DREADD-transfected rats ate significantly more food when 2DG and CNO were coadministered than when either 2DG or CNO was injected alone. We also found that CNO significantly enhanced 2DG-induced FOS expression in the A1/C1 CA neurons, and that corticosterone release also was enhanced when CNO and 2DG were administered together. Importantly, CNO-induced activation of astrocytes in the absence of 2DG did not trigger food intake or corticosterone release. Our results indicate that during glucoprivation, activation of VLM astrocytes cells markedly increases the sensitivity or responsiveness of neighboring A1/C1 CA neurons to glucose deficit, suggesting a potentially important role for VLM astrocytes in glucoregulation. [ABSTRACT FROM AUTHOR]

Byline: Gerlinda E. Hermann (Laboratory of Autonomic Neurosciences, Pennington Biomedical Research Center, Baton Rouge, Louisiana, HermanGE@pbrc.edu); Richard C. Rogers (Laboratory of Autonomic Neurosciences, Pennington Biomedical Research Center, Baton Rouge, Louisiana, [...]

Byline: Gerlinda E. Hermann (Laboratory of Autonomic Neurosciences, Pennington Biomedical Research Center, Baton Rouge, Louisiana, HermanGE@pbrc.edu); Richard C. Rogers (Laboratory of Autonomic Neurosciences, Pennington Biomedical Research Center, Baton Rouge, Louisiana, [...]

Chimeric G proteins made by replacing the COOH-terminal heptapeptide of [G.sub.[alpha]]q with the COOH-terminal heptapeptide of [G.sub.[alpha]]s or [G.sub.[alpha]]i were used to assess the relative coupling of [[beta].sub.3]-adrenergic receptor ([[beta].sub.3]-AR) splice variants ([[beta].sub.3A] and [[beta].sub.3B]) to [G.sub.[alpha]]s and [G.sub.[alpha]]i. The [G.sub.[alpha]]q/s and [G.sub.[alpha]]q/i chimeras transformed the response to receptor activation from regulation of adenylyl cyclase to mobilization of intracellular calcium ([Ca.sup.2+]i). Complementary high-throughput and single-cell approaches were used to evaluate agonist-induced coupling of the receptor to the G protein chimeras. In cells stably transformed with rat [[beta].sub.3]-AR, transfected with the G protein chimeras, and evaluated using a scanning fluorometer, [[beta].sub.3]-AR-induced coupling to [G.sub.[alpha]]q/s produced a rapid eightfold increase in [Ca.sup.2+]i followed by a slow decay to levels 25% above baseline. [G.sub.[alpha]]q/i also linked rat [[beta].sub.3]-AR to mobilization of [Ca.sup.2+]i in a similar time- and agonist-dependent manner, but the net 2.5-fold increase in [Ca.sup.2+]i was only 30% of the response obtained with [G.sub.[alpha]]q/s. Activation of the rat [[beta].sub.3]-AR also increased GTP binding to endogenous [G.sub.[alpha]]i threefold in membranes from CHO cells stably transformed with the receptor. A complementary single-cell imaging approach was used to assess the relative coupling of mouse [[beta].sub.3A]- and [[beta].sub.3B]-AR to [G.sub.[alpha]]i under conditions established to produce equivalent agonist-dependent coupling of the receptor splice variants to [G.sub.[alpha]]q/s and to increases in intracellular cAMP through endogenous [G.sub.[alpha]]s. The [[beta].sub.3A]- and [[beta].sub.3B]-AR coupled equivalently to [G.sub.[alpha]]q/i, but the temporal patterns of [Ca.sup.2+]i mobilization indicated that coupling was significantly less efficient than coupling to [G.sub.[alpha]]q/s. Collectively, these findings indicate less efficient but equivalent coupling of [[beta].sub.3A]- and [[beta].sub.3B]-AR to [G.sub.[alpha]]i vs. [G.sub.[alpha]]s and suggest that differential expression of the splice variants would not produce local differences in signaling networks linked to [[beta].sub.3]-AR activation. [beta]-adrenergic receptor; G proteins; cyclic adenosine monophosphate; signaling plasticity

It has long been known that the esophageal distension produced by swallowing elicits a powerful proximal gastric relaxation. Gastroinhibitory control by the esophagus involves neural pathways from esophageal distension-sensitive neurons in the nucleus tractus solitarius centralis (cNTS) with connections to virtually all levels of the dorsal motor nucleus of the vagus (DMV). We have shown recently that cNTS responses are excitatory and primarily involve tyrosine hydroxylase-immunoreactive cells, whereas the DMV response involves both an [[alpha].sub.1] excitatory and an [[alpha].sub.2] inhibitory response. In the present study, using an esophageal balloon distension to evoke gastric relaxation (esophageal-gastric reflex, EGR), we investigated the peripheral pharmacological basis responsible for this reflex. Systemic administration of atropine methyl nitrate reduced the amplitude of the gastric relaxation to 52.0 [+ or -] 4.4% of the original EGR, whereas [N.sup.G]-nitro-L-arginine methyl ester (L-NAME) reduced it to 26.3 [+ or -] 7.2% of the original EGR. Concomitant administration of atropine methyl nitrate and L-NAME reduced the amplitude of the gastric relaxation to 4.0 [+ or -] 2.5% of control. This reduction in the amplitude of induced EGR is quite comparable (4.3 [+ or -] 2.6%) to that seen when the animal was pretreated with the nicotinic ganglionic blocker hexamethonium. In the presence of bethanechol, the amplitude of the esophageal distension-induced gastric relaxation was increased to 177.0 [+ or -] 10.0% of control; administration of L-NAME reduced this amplitude to 19.9 [+ or -] 9.5%. Our data provide a clear demonstration that the gastroinhibitory control by the esophagus is mediated via a dual vagal innervation consisting of inhibitory nitrergic and excitatory cholinergic transmission. receptive relaxation reflex; nonadrenergic; noncholinergic; vagovagal reflex

The dorsal motor nucleus of the vagus (DMV) receives more noradrenergic terminals than any other medullary nucleus; few studies, however, have examined the effects of norepinephrine (NE) on DMV neurons. Using whole cell recordings in thin slices, we determined the effects of NE on identified gastric-projecting DMV neurons. Twenty-five percent of DMV neurons were unresponsive to NE, whereas the remaining 75% responded to NE with either an excitation (49%), an inhibition (26%), or an inhibition followed by an excitation (4%). Antrum/pylorus- and corpus-projecting neurons responded to NE with a similar percentage of excitatory (49 and 59%, respectively) and inhibitory (20% for both groups) responses. A lower percentage of excitatory (37%) and a higher percentage of inhibitory (36%) responses were, however, observed in fundus-projecting neurons. In all groups, pretreatment with prazosin or phenylephrine antagonized or mimicked the NE-induced excitation, respectively. Pretreatment with yohimbine or UK-14304 antagonized or mimicked the NE-induced inhibition, respectively. These data suggest that NE depolarization is mediated by [[alpha].sub.1]adrenoceptors, whereas NE hyperpolarization is mediated by [[alpha].sub.2]-adrenoceptors. In 16 neurons depolarized by NE, amplitude of the action potential afterhyperpolarization (AHP) and its kinetics of decay ([tau]) were significantly reduced vs. control. No differences were found on the amplitude and [tau] of AHP in neurons hyperpolarized by NE. Using immunohistochemical techniques, we found that the distribution of tyrosine hydroxylase fibers within the DMV was significantly different within the mediolateral extent of DMV; however, distribution of cells responding to NE did not show a specific pattern of localization. brain stem; electrophysiology; gastrointestinal-receptive relaxation

Vago-vagal reflex circuits modulate digestive functions from the oral cavity to the transverse colon. Previous articles in this series have described events at the level of the sensory receptors encoding the peripheral stimuli, the transmission of information in the afferent vagus, and the conversion of this data within the dorsal vagal complex (DVC) to impulses in the preganglionic efferents. The control by vagal efferents of the postganglionic neurons impinging on the glands and smooth muscles of the target organs has also been illustrated. Here we focus on some of the mechanisms by which these apparently static reflex circuits can be made quite plastic as a consequence of the action of modulatory inputs from other central nervous system sources. A large body of evidence has shown that the neuronal elements that constitute these brain stern circuits have nonuniform properties and function differently according to status of their target organs and the level of activity in critical modulatory inputs. We propose that DVC circuits undergo a certain amount of short-term plasticity that allows the brain stem neuronal elements to act in harmony with neural systems that control behavioral and physiological homeostasis. dorsal motor nucleus of the vagus; nucleus of the solitary tract; brain stem; gastrointestinal motility

Our previous studies suggested that the cytokine tumor necrosis factor-[alpha] (TNF-[alpha]) may act within the neural circuitry of the medullary dorsal vagal complex (DVC) to affect changes in gastric function, such as gastric stasis, loss of appetite, nausea, and vomiting. The definitive demonstration that endogenously generated TNF-[alpha] is capable of affecting gastric function via the DVC circuitry has been impeded by the lack of an antagonist for TNF-[alpha]. The present' studies used localized central nervous system applications of the TNF-adsorbant construct (TNFR:Fc; TNF-receptor linked to the Fc portion of the human immunoglobulin IgG1) to attempt to neutralize the suppressive effects of endogenously produced TNF-[alpha]. Gastric motility of thiobutabarbital-anesthetized rats was monitored after systemic administration of lipopolysaccharide (LPS) to induce TNF-[alpha] production. Continuous perfusion of the floor of the fourth ventricle with TNFR:Fc reversed the potent gastroinhibition induced by LPS, i.e., central thyrotropin-releasing hormone-induced increases in motility were not inhibited. This disinhibition of gastric stasis was not seen after intravenous administration of similar doses of TNFR:Fc nor ventricular application of the Fc fragment of human immunoglobulin. These results validate our previous studies that suggest that circulating TNF-[alpha] may act directly within the DVC to affect gastric function in a variety of pathophysiological states. tumor necrosis factor-ex; gastric stasis; nausea

Researchers have investigated the impact of peptide YY (PYY) and the Y2 agonist PYY-(13-36) on neurons of the dorsal motor nucleus of the vagus (DMN), both intact in vivo by gastric antral inflation and in the in vitro slice preparation under synaptic blockade and normal conditions. It was concluded that one of the main ways in which PYY suppresses digestive functions is by directly inhibiting cholinergic vagal efferent neurons of the DMN through acting as a Y2 receptor.

The pancreatic polypeptide hormone induces the secretion of gastric acid through the dorsal vagal complex. Rats injected with 100 parts per mol of pancreatic polypeptide raised their levels of gastric acid significantly above the baseline levels, and this effect was minimized by cutting the cervical vagus bilaterally or by treatment with atropine. In addition, the effective dose of pancreatic polypeptide necessary to induce a response was determined to be between 10 and 100 ppmol.

Specific peptide YY (PYY) mediates gastric motility by interacting with neurons of dorsal vagal complex involved in vagovagal inhibitory modulation of gastric function. Administration of physiological concentration of PYY in DVC of urethananesthetized rats inhibits gastric motility which is further stimulated by thyrotropin-releasing hormone. The activity of PYY is inhibited by unilateral cervical vagotomy. Elevated concentration of PYY may stimulate gastric function.

Rat pancreatic polypeptide (PP) strongly stimulates gastric emptying by rats. In comparison, the effects of bovine PP is small or non-existent, depending on the method of administration. Researchers injected rat PP, bovine PP, or placebo either intracisternally or into the dorsal vagal complex (DVC) of rats. When injected intracisternally, bovine PP had little or no effect, but that of rat PP was marked. Reaction to DVC injection was measurable but smaller for both rat and bovine PP, and the bovine PP response was much smaller. PP probably acts as a circulating hormone by stimulating gastric voiding through a vagal cholinergic-dependent mechanism.

Vagovagal reflex control circuits in the dorsal vagal complex of the brain stem help coordinate gastric small intestinal and pancreatic digestion. Descending neural inputs control the neural components of these circuits and alter the excitability of the different components of the circuit to cause changes in digestion control. Humoral inputs also influence vagovagal reflex circuitry to alter digestive functions by exerting direct action on brain stem neurons.

The gastric function in rats increases with the modulation of central autonomic nuclei, consequent to action of pancreatic polypeptides (PP). The increase in gastric function is dose-dependent and longlasting. Bilateral cervical and atrophine block the gastric response, indicating the stimulation of cholinergic pathways by PP. The mechanism of direct action on vagovagal circuits of the brain stem indicates digestive tract modulation of its autonomic control.

CTP:phosphoethanolamine cytidylyltransferase (ET), encoded by PCYT2, is the rate-limiting enzyme for phosphatidylethanolamine synthesis via the CDP-ethanolamine pathway. Phosphatidylethanolamine is one of the most abundant membrane lipids and is particularly enriched in the brain. We identified five individuals with biallelic PCYT2 variants clinically characterized by global developmental delay with regression, spastic para- or tetraparesis, epilepsy and progressive cerebral and cerebellar atrophy. Using patient fibroblasts we demonstrated that these variants are hypomorphic, result in altered but residual ET protein levels and concomitant reduced enzyme activity without affecting mRNA levels. The significantly better survival of hypomorphic CRISPR-Cas9 generated pcyt2 zebrafish knockout compared to a complete knockout, in conjunction with previously described data on the Pcyt2 mouse model, indicates that complete loss of ET function may be incompatible with life in vertebrates. Lipidomic analysis revealed profound lipid abnormalities in patient fibroblasts impacting both neutral etherlipid and etherphospholipid metabolism. Plasma lipidomics studies also identified changes in etherlipids that have the potential to be used as biomarkers for ET deficiency. In conclusion, our data establish PCYT2 as a disease gene for a new complex hereditary spastic paraplegia and confirm that etherlipid homeostasis is important for the development and function of the brain. [ABSTRACT FROM AUTHOR]

Severe trauma can produce a postinjury “metabolic self-destruction” characterized by catabolic metabolism and hyperglycemia. The severity of the hyperglycemia is highly correlated with posttrauma morbidity and mortality. Although no mechanism has been posited to connect severe trauma with a loss of autonomic control over metabolism, traumatic injury causes other failures of autonomic function, notably, gastric stasis and ulceration (“Cushing’s ulcer”), which has been connected with the generation of thrombin. Our previous studies established that proteinase-activated receptors (PAR1; “thrombin receptors”) located on astrocytes in the autonomically critical nucleus of the solitary tract (NST) can modulate gastric control circuit neurons to cause gastric stasis. Hindbrain astrocytes have also been implicated as important detectors of low glucose or glucose utilization. When activated, these astrocytes communicate with hindbrain catecholamine neurons that, in turn, trigger counterregulatory responses (CRR). There may be a convergence between the effects of thrombin to derange hindbrain gastrointestinal control and the hindbrain circuitry that initiates CRR to increase glycemia in reaction to critical hypoglycemia. Our results suggest that thrombin acts within the NST to increase glycemia through an astrocyte-dependent mechanism. Blockade of purinergic gliotransmission pathways interrupted the effect of thrombin to increase glycemia. Our studies also revealed that thrombin, acting in the NST, produced a rapid, dramatic, and potentially lethal suppression of respiratory rhythm that was also a function of purinergic gliotransmission. These results suggest that the critical connection between traumatic injury and a general collapse of autonomic regulation involves thrombin action on astrocytes. [ABSTRACT FROM AUTHOR]

Vago-vagal reflex circuits in the medulla are responsible for the smooth coordination of the digestive processes carried out from the oral cavity to the transverse colon. In this themes article, we concentrate mostly on electrophysiological studies concerning the extrinsic modulation of these vago-vagal reflex circuits, with a particular emphasis on two types of modulation, i.e., by 'fast' classic neurotransmitters and by 'slow' neuromodulators. These examples review two of the most potent modulatory processes at work within the dorsal vagal complex, which have dramatic effects on gastrointestinal function. The reader should be mindful of the fact that many more different inputs from other central nervous system (CNS) loci or circulating humoral factors add to this complex mix of modulatory inputs. It is likely that similar long-term modulations of synaptic transmission occur with other neurotransmitters and may represent an important mechanism for the integration and regulation of neuronal behavior. Of course, this fact strongly militates against the success of any single drug or approach in the treatment of motility disorders having a CNS component. thyrotropin-releasing hormone; tumor necrosis factor; gastric motility

Guo, Jinfeng J., Kirsteen N. Browning, Richard C. Rogers, and R. Alberto Travagli. Catecholaminergic neurons in rat dorsal motor nucleus of vagus project selectively to gastric corpus. Am J Physiol Gastrointest Liver Physiol 280: G361-G367, 2001.--Nitric oxide synthase-immunoreactive (NOS-IR) neurons in the rat caudal dorsal motor nucleus of the vagus (DMV) project selectively to the gastric fundus and may be involved in vagal reflexes controlling gastric distension. This study aimed to identify the gastric projections of tyrosine hydroxylase-immunoreactive (TH-IR) DMV neurons, whether such neurons colocalize NOS-IR, and if they are activated after esophageal distension. Gastric-projecting neurons were identified after injection of retrograde tracers into the muscle wall of the gastric fundus, corpus, or antrum/pylorus before removal and processing of the brain stems for TH- and NOS-IR. A significantly higher proportion of corpus- compared with fundus- and antrum/pylorus-projecting neurons were TH-IR (14% compared with 4% and 2%, respectively, P [is less than] 0.05). Colocalization of NOS- and TH-IR was never observed in gastric-projecting neurons. In rats tested for c-Fos activation after intermittent esophageal balloon distension, no colocalization with TH-IR was observed in DMV neurons. These findings suggest that TH-IR neurons in the caudal DMV project mainly to the gastric corpus, constitute a subpopulation distinct from that of nitrergic vagal neurons, and are not activated on esophageal distension. stomach; esophagus; receptive relaxation; gastric motility

TNF-[Alpha] activates solitary nucleus neurons responsive to gastric distension. Am J Physiol Gastrointest Liver PhysioL 279: G582-G586, 2000.--Tumor necrosis factor-[Alpha] (TNF-[Alpha]) is liberated as part of the immune response to antigenic challenge, carcinogenesis, and radiation therapy. Previous studies have implicated elevated circulating levels of this cytokine in the gastric hypomotility associated with these disease states. Our earlier studies suggest that a site of action of TNF-[Alpha] may be within the medullary dorsal vagal complex. In this study, we describe the role of TNF-[Alpha] as a neuromodulator affecting neurons in the nucleus of the solitary tract that are involved in vago-vagal reflex control of gastric motility. The results presented herein suggest that TNF-[Alpha] may induce a persistent gastric stasis by functioning as a hormone that modulates intrinsic vago-vagal reflex pathways during illness. cytokines; brain; gastric motility; tumor necrosis factor-[Alpha]