The Pharmacological Mechanism of Diabetes Mellitus-Associated Overactive Bladder and Its Treatment with Botulinum Toxin A.

Diabetes mellitus (DM) is an independent risk factor for overactive bladder (OAB). The pathophysiology of DM-associated OAB is multifactorial and time-dependent. Diabetic bladder dysfunction is highly associated with diabetic complications, mainly including diabetic neuropathy and atherosclerosis. Chronic systemic inflammation and bladder urothelial inflammation may contribute to the onset of OAB. Intravesical botulinum toxin A (BoNT-A) injection has proved to be a successful treatment for idiopathic and neurogenic OAB. BoNT-A can inhibit the efferent pathways of the bladder as well as the chronic inflammation and hypersensitivity via the afferent pathways. We conducted a review of the published literature in Pubmed using a combination of two keywords, namely "botulinum toxin A" (BoNT-A) and "overactive bladder", with or without the additional keywords "detrusor overactivity", "diabetes mellitus", "inflammation", and "urodynamic study". We also reviewed the experience of our research teams, who have published several studies of the association between DM and OAB. Since limited data support the effectiveness and safety of BoNT-A for treating patients with DM-associated OAB, a comprehensive evaluation of diabetic complications and urodynamic study is needed before treatment. In the future, it is imperative to explore the clinical characteristics and inflammatory biomarkers of diabetes as determining predictors of the treatment efficacy.

The vagus nerve role in antidepressants action: Efferent vagal pathways participate in peripheral anti-inflammatory effect of fluoxetine.

The mechanisms responsible for the anti-inflammatory effects of antidepressants are only partially understood. Published data indicate that the vagal anti-inflammatory pathway could be involved in mediating this effect. Therefore, we investigated the influence of subdiaphragmatic vagotomy on the anti-inflammatory effect of fluoxetine in rats injected with lipopolysaccharide (LPS) to induce an inflammatory response. The extent of this response was determined by measurement of TNF-α, IL-1ß, and IL-6 plasma levels, along with gene expression of TNF-α, IL-1ß, and IL-6 in the spleen and selected structures of the brain. To evaluate possible central mechanisms, c-fos mRNA levels were determined in the nucleus of the solitary tract, dorsal motor nucleus of the vagus, paraventricular hypothalamic nucleus, basolateral amygdala, central nucleus of the amygdala, hippocampus, and frontal cortex. We found that pretreatment with fluoxetine substantially prevented LPS-induced increases of pro-inflammatory cytokines in plasma and gene expression in the spleen and brain in animals with an intact vagus nerve. However, in vagotomized animals, fluoxetine pretreatment only partially attenuated the LPS-induced increase in these markers of peripheral inflammation. Our data has shown that fluoxetine exerts potent anti-inflammatory effects in both the periphery and brain. Moreover, we found that the peripheral anti-inflammatory action of fluoxetine is mediated, at least partially, by activation of a vagal anti-inflammatory pathway. The role of the vagus nerve in mediating the anti-inflammatory effects of antidepressants has been marginally explored and our findings highlight its potential contribution to this mechanism of action of antidepressants.

Neurochemical effects of motor cortex stimulation in the periaqueductal gray during neuropathic pain.

OBJECTIVE: Motor cortex stimulation (MCS) is a neurosurgical technique used to treat patients with refractory neuropathic pain syndromes. MCS activates the periaqueductal gray (PAG) matter, which is one of the major centers of the descending pain inhibitory system. However, the neurochemical mechanisms in the PAG that underlie the analgesic effect of MCS have not yet been described. The main goal of this study was to investigate the neurochemical mechanisms involved in the analgesic effect induced by MCS in neuropathic pain. Specifically, we investigated the release of γ-aminobutyric acid (GABA), glycine, and glutamate in the PAG and performed pharmacological antagonism experiments to validate of our findings. METHODS: Male Wistar rats with surgically induced chronic constriction of the sciatic nerve, along with sham-operated rats and naive rats, were implanted with both unilateral transdural electrodes in the motor cortex and a microdialysis guide cannula in the PAG and subjected to MCS. The MCS was delivered in single 15-minute sessions. Neurotransmitter release was evaluated in the PAG before, during, and after MCS. Quantification of the neurotransmitters GABA, glycine, and glutamate was performed using a high-performance liquid chromatography system. The mechanical nociceptive threshold was evaluated initially, on the 14th day following the surgery, and during the MCS. In another group of neuropathic rats, once the analgesic effect after MCS was confirmed by the mechanical nociceptive test, rats were microinjected with saline or a glycine antagonist (strychnine), a GABA antagonist (bicuculline), or a combination of glycine and GABA antagonists (strychnine+bicuculline) and reevaluated for the mechanical nociceptive threshold during MCS. RESULTS: MCS reversed the hyperalgesia induced by peripheral neuropathy in the rats with chronic sciatic nerve constriction and induced a significant increase in the glycine and GABA levels in the PAG in comparison with the naive and sham-treated rats. The glutamate levels remained stable under all conditions. The antagonism of glycine, GABA, and the combination of glycine and GABA reversed the MCS-induced analgesia. CONCLUSIONS: These results suggest that the neurotransmitters glycine and GABA released in the PAG may be involved in the analgesia induced by cortical stimulation in animals with neuropathic pain. Further investigation of the mechanisms involved in MCS-induced analgesia may contribute to clinical improvements for the treatment of persistent neuropathic pain syndromes.

Blockade of synaptic activity in the neostriatum and activation of striatal efferent pathways produce opposite effects on panic attack-like defensive behaviours evoked by GABAergic disinhibition in the deep layers of the superior colliculus.

The dorsal periaqueductal grey matter (dPAG) and the deep layers of the superior colliculus (dlSC) have been implicated in the organisation of innate fear-related defensive behaviours. Furthermore, GABAergic neurons from the substantia nigra pars reticulata (SNpr) connected to the dlSC and dPAG receive convergent disinhibitory inputs from the caudate-putamen (CPu), comprising the neostriatum, and modulate defence responses elicited by midbrain tectum stimulation. The purpose of this work was to study the effect of either excitatory cortico-neostriatal input blockade or neostriato-nigral GABAergic disinhibitory output activation on the responsivity of GABAergic nigro-collicular tonic inhibitory pathways during the elicitation of panic attack-like defensive responses produced by bicuculline administration into the dlSC. Thus, we investigated the effects of microinjection of either the synaptic activity blocker cobalt chloride (CoCl2) or the NMDA receptor agonist N-methyl-D-aspartic acid in the CPu on the elaboration of the defensive behaviour elicited by the selective blockade of GABAA receptors in the dlSC. Our findings showed that pretreatment of the neostriatum with CoCl2 caused clear anxiolytic and panicolytic-like effects, reducing the incidence and duration of alertness and diminishing defensive immobility and explosive escape responses. On the other hand, pretreatment of the neostriatum with NMDA (40 nmol) caused a pro-aversive effect, enhancing running and jumping responses elicited by GABAergic disinhibition in the dlSC. We conclude from the data that the neostriato-nigral disinhibitory and nigro-collicular inhibitory GABAergic pathways modulate innate fear and panic attack-like responses organised by dlSC neurons.

ß-eudesmol, an oxygenized sesquiterpene, affects efferent adrenal sympathetic nerve activity via transient receptor potential ankyrin 1 in rats.

The autonomic nervous system innervates various peripheral tissue functions. Various external stimuli affect autonomic nerve activity, however, there is little information about the involvement of sensory receptors in the responses. The TRPA1 is a calcium-permeable non-selective cation channel which plays a crucial role in the susceptibility to various stimuli. ß-Eudesmol, an oxygenated sesquiterpene found in hop essential oil and beer, activates the TRPA1. Intragastric administration of ß-eudesmol decreased efferent adrenal sympathetic nerve activity (ASNA) in rats, whereas subcutaneous administration did not. ASNA suppression by ß-eudesmol was not observed in TRPA1 knockout rats. The ß-eudesmol derived ASNA suppression was partially, but significantly, eliminated by subdiaphragmatic vagotomy in rats, suggesting the afferent vagal nerve from the gastrointestinal tract to the brain is involved in the effect of ß-eudesmol on ASNA. Our results indicate that ß-eudesmol suppresses ASNA, partly through TRPA1 and the afferent vagus nerve. These findings introduce the physiological significance of the TRPA1 in the control of ASNA.

Corticotropin-Releasing Factor in the Brain and Blocking Spinal Descending Signals Induce Hyperalgesia in the Latent Sensitization Model of Chronic Pain.

Latent sensitization is a model of chronic pain in which an injury triggers a period of hyperalgesia followed by an apparent recovery, but in which pain sensitization persists but is suppressed by opioid and adrenergic receptors. One important characteristic of latent sensitization is that hyperalgesia can be triggered by acute stress. To determine whether the effect of stress is mimicked by the activation of corticotropin-releasing factor (CRF) signaling in the brain, rats with latent sensitization induced by injecting complete Freund's adjuvant (CFA, 50 µl) in one hind paw were given an intracerebroventricular (i.c.v.) injection of CRF. The i.c.v. injection of CRF (0.6 µg, 10 µl), but not saline, induced bilateral mechanical hyperalgesia in rats with latent sensitization. In contrast, CRF i.c.v. did not induce hyperalgesia in rats without latent sensitization (injected with saline in the hind paw). To determine whether descending pain inhibition mediates the suppression of hyperalgesia in latent sensitization, rats with CFA-induced latent sensitization received an intrathecal injection of lidocaine (10%, 1 µl) at the cervical-thoracic spinal cord to produce a spinal block. Lidocaine-injected rats, but not rats injected intrathecally with saline, developed bilateral mechanical hyperalgesia. Intrathecal lidocaine did not induce hyperalgesia in rats without latent sensitization (injected with saline in the hind paw). These results show that i.c.v. CRF mimicked the hyperalgesic response triggered by stress during latent sensitization, possibly by blocking inhibitory spinal descending signals that suppress hyperalgesia.

Facilitation of Locomotor Spinal Networks Activity by Buspirone after a Complete Spinal Cord Lesion in Mice.

Despite efforts to potentiate spinal cord lesioned (SCL) patients' functional recovery with multi-targeted therapy combining pharmacological treatment and training, consistent improvements in locomotor control by descending transmission or spinal network facilitation are still eluding clinicians and researchers. Lately, United States Food and Drug Administration-approved buspirone has shown promise and promoted locomotor-like movement occurrence in SCL patients, but evidence on how and where it exerts its effects is lacking. The objective of the present study was, first, to verify buspirone effect on locomotor spinal network and to evaluate if it promoted functional recovery when combined with training. Also, we evaluated buspirone impact on locomotion in mice that had recovered from a previous hemisection before sustaining the spinal transection. This dual lesion paradigm has allowed confirmation of spinal network involvement in recovery after an incomplete SCL. Buspirone acutely increased the number of steps taken, the coupling strength between hindlimbs, angular excursion of the hip joint during locomotion, and improved paw positioning at contact and paw drag (ps < 0.05). Moreover, it induced long-lasting improvements of paw positioning at contact and paw drag when combined with training in mice after a dual lesion paradigm. Altogether, the results indicate that buspirone exerts considerable acute facilitation of spinally mediated locomotion, and could be used in combination with training to promote functional recovery after SCL.

The influence of 5-HT1A receptors in the dorsal raphé nucleus on genioglossus activity.

Genioglossus activity maintains the patency of the upper airway. 5-HT neurons in the raphe nucleus regulate genioglossus activity. In order to study the influence of 5-HT1A receptors in dorsal raphé nucleus (DRN) on genioglossus EMG during normoxia, adult male Wistar rats were randomly divided into four groups: the artificial cerebrospinal fluid group (ACSF group), the low-concentration of 5-HT1A receptors agonist 8-OH-DPAT group (0.1 mM group), the mid-concentration 8-OH-DPAT group (0.4 mM group) and the high-concentration 8-OH-DPAT group (1.0 mM group). Rats received 0.1 µl ACSF/8-OH-DPAT microinjections into the DRN. EMG activity of the genioglossus was recorded at 5 min, 15 min and 30 min after microinjection. In three 8-OH-DPAT groups, genioglossus EMG activity significantly decreased at 5 min after microinjection and persisted for 30 min. The significantly decreased EMG activity was more pronounced in the mid- and high-concentration groups than in the low-concentration group, indicating that 5-HT1A receptors in the DRN could rapidly and continuously inhibit genioglossus EMG activity during normoxia.

Caffeic acid and resveratrol ameliorate cellular damage in cell and Drosophila models of spinocerebellar ataxia type 3 through upregulation of Nrf2 pathway.

Polyglutamine (polyQ)-expanded mutant ataxin-3 protein, which is prone to misfolding and aggregation, leads to cerebellar neurotoxicity in spinocerebellar ataxia type 3 (SCA3), an inherited PolyQ neurodegenerative disease. Although the exact mechanism is unknown, the pathogenic effects of mutant ataxin-3 are associated with dysregulation of transcription, protein degradation, mitochondrial function, apoptosis, and antioxidant potency. In the present study we explored the protective role and possible mechanism of caffeic acid (CA) and resveratrol (Res) in cells and Drosophila expressing mutant ataxin-3. Treatment with CA and Res increased the levels of antioxidant and autophagy protein expression with consequently corrected levels of reactive oxygen species, mitochondrial membrane potential, mutant ataxin-3, and the aggregation of mutant ataxin-3 in SK-N-SH-MJD78 cells. Moreover, in SK-N-SH-MJD78 cells, CA and Res enhanced the transcriptional activity of nuclear factor erythroid-derived-2-like 2 (Nrf2), a master transcription factor that upregulates the expression of antioxidant defense genes and the autophagy gene p62. CA and Res improved survival and motor performance in SCA3 Drosophila. Additionally, the above-mentioned protective effects of CA were also observed in CA-supplemented SCA3 Drosophila. Notably, blockade of the Nrf2 pathway by use of small interfering RNA annulled the health effects of CA and Res on SCA3, which affirmed the importance of the increase in Nrf2 activation by CA and Res. Additional studies are need to dissect the protective role of CA and Res in modulating neurodegenerative progression in SCA3 and other polyQ diseases.

Chemogenetic inhibition reveals midline thalamic nuclei and thalamo-accumbens projections mediate cocaine-seeking in rats.

Drug addiction is a chronic disease that is shaped by alterations in neuronal function within the cortical-basal ganglia-thalamic circuit. However, our understanding of how this circuit regulates drug-seeking remains incomplete, and relapse rates remain high. The midline thalamic nuclei are an integral component of the cortical-basal ganglia-thalamic circuit and are poised to mediate addiction behaviors, including relapse. It is surprising that little research has examined the contribution of midline thalamic nuclei and their efferent projections in relapse. To address this, we expressed inhibitory, Gi/o -coupled DREADDs (Designer Receptors Exclusively Activated by Designer Drugs) in a subset of the midline thalamic nuclei or in midline thalamic nuclei neurons projecting to either the nucleus accumbens or the amygdala. We examined the effect of transiently decreasing activity of these neuronal populations on cue-induced and cocaine-primed reinstatement of cocaine-seeking. Reducing activity of midline thalamic nuclei neurons attenuated both cue-induced and cocaine-primed reinstatement, but had no effect on cue-induced reinstatement of sucrose-seeking or locomotor activity. Interestingly, attenuating activity of efferent projections from the anterior portion of midline thalamic nuclei to the nucleus accumbens blocked cocaine-primed reinstatement but enhanced cue-induced reinstatement. Decreasing activity of efferent projections from either the posterior midline thalamic nuclei to the nucleus accumbens or the midline thalamic nuclei to amygdala had no effect. These results reveal a novel contribution of subsets of midline thalamic nuclei neurons in drug-seeking behaviors and suggest that modulation of midline thalamic nuclei activity may be a promising therapeutic target for preventing relapse.

Activation of the Hypoglossal to Tongue Musculature Motor Pathway by Remote Control.

Reduced tongue muscle tone precipitates obstructive sleep apnea (OSA), and activation of the tongue musculature can lessen OSA. The hypoglossal motor nucleus (HMN) innervates the tongue muscles but there is no pharmacological agent currently able to selectively manipulate a channel (e.g., Kir2.4) that is highly restricted in its expression to cranial motor pools such as the HMN. To model the effect of manipulating such a restricted target, we introduced a "designer" receptor into the HMN and selectively modulated it with a "designer" drug. We used cre-dependent viral vectors (AAV8-hSyn-DIO-hM3Dq-mCherry) to transduce hypoglossal motoneurons of ChAT-Cre+ mice with hM3Dq (activating) receptors. We measured sleep and breathing in three conditions: (i) sham, (ii) after systemic administration of clozapine-N-oxide (CNO; 1 mg/kg) or (iii) vehicle. CNO activates hM3Dq receptors but is otherwise biologically inert. Systemic administration of CNO caused significant and sustained increases in tongue muscle activity in non-REM (261 ± 33% for 10 hrs) and REM sleep (217 ± 21% for 8 hrs), both P < 0.01 versus controls. Responses were specific and selective for the tongue with no effects on diaphragm or postural muscle activities, or sleep-wake states. These results support targeting a selective and restricted "druggable" target at the HMN (e.g., Kir2.4) to activate tongue motor activity during sleep.

Differential regulation of NMDA receptors by d-serine and glycine in mammalian spinal locomotor networks.

Activation of N-methyl-d-aspartate receptors (NMDARs) requires the binding of a coagonist, either d-serine or glycine, in addition to glutamate. Changes in occupancy of the coagonist binding site are proposed to modulate neural networks including those controlling swimming in frog tadpoles. Here, we characterize regulation of the NMDAR coagonist binding site in mammalian spinal locomotor networks. Blockade of NMDARs by d(-)-2-amino-5-phosphonopentanoic acid (d-APV) or 5,7-dichlorokynurenic acid reduced the frequency and amplitude of pharmacologically induced locomotor-related activity recorded from the ventral roots of spinal-cord preparations from neonatal mice. Furthermore, d-APV abolished synchronous activity induced by blockade of inhibitory transmission. These results demonstrate an important role for NMDARs in murine locomotor networks. Bath-applied d-serine enhanced the frequency of locomotor-related but not disinhibited bursting, indicating that coagonist binding sites are saturated during the latter but not the former mode of activity. Depletion of endogenous d-serine by d-amino acid oxidase or the serine-racemase inhibitor erythro-ß-hydroxy-l-aspartic acid (HOAsp) increased the frequency of locomotor-related activity, whereas application of l-serine to enhance endogenous d-serine synthesis reduced burst frequency, suggesting a requirement for d-serine at a subset of synapses onto inhibitory interneurons. Consistent with this, HOAsp was ineffective during disinhibited activity. Bath-applied glycine (1-100 µM) failed to alter locomotor-related activity, whereas ALX 5407, a selective inhibitor of glycine transporter-1 (GlyT1), enhanced burst frequency, supporting a role for GlyT1 in NMDAR regulation. Together these findings indicate activity-dependent and synapse-specific regulation of the coagonist binding site within spinal locomotor networks, illustrating the importance of NMDAR regulation in shaping motor output.NEW & NOTEWORTHY We provide evidence that NMDARs within murine spinal locomotor networks determine the frequency and amplitude of ongoing locomotor-related activity in vitro and that NMDARs are regulated by d-serine and glycine in a synapse-specific and activity-dependent manner. In addition, glycine transporter-1 is shown to be an important regulator of NMDARs during locomotor-related activity. These results show how excitatory transmission can be tuned to diversify the output repertoire of spinal locomotor networks in mammals.

Effects of methylmercury on spinal cord afferents and efferents-A review.

Methylmercury (MeHg) is an environmental neurotoxicant of public health concern. It readily accumulates in exposed humans, primarily in neuronal tissue. Exposure to MeHg, either acutely or chronically, causes severe neuronal dysfunction in the central nervous system and spinal neurons; dysfunction of susceptible neuronal populations results in neurodegeneration, at least in part through Ca2+-mediated pathways. Biochemical and morphologic changes in peripheral neurons precede those in central brain regions, despite the fact that MeHg readily crosses the blood-brain barrier. Consequently, it is suggested that unique characteristics of spinal cord afferents and efferents could heighten their susceptibility to MeHg toxicity. Transient receptor potential (TRP) ion channels are a class of Ca2+-permeable cation channels that are highly expressed in spinal afferents, among other sensory and visceral organs. These channels can be activated in numerous ways, including directly via chemical irritants or indirectly via Ca2+ release from intracellular storage organelles. Early studies demonstrated that MeHg interacts with heterologous TRP channels, though definitive mechanisms of MeHg toxicity on sensory neurons may involve more complex interaction with, and among, differentially-expressed TRP populations. In spinal efferents, glutamate receptors of the N-methyl-D-aspartate (NMDA), α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), and possibly kainic acid (KA) classes are thought to play a major role in MeHg-induced neurotoxicity. Specifically, the Ca2+-permeable AMPA receptors, which are abundant in motor neurons, have been identified as being involved in MeHg-induced neurotoxicity. In this review, we will describe the mechanisms that could contribute to MeHg-induced spinal cord afferent and efferent neuronal degeneration, including the possible mediators, such as uniquely expressed Ca2+-permeable ion channels.

Ventral Pallidum Output Pathways in Context-Induced Reinstatement of Alcohol Seeking.

Ventral pallidum (VP) is a well-established locus for the reinforcing effects of drugs of abuse and reinstatement of drug seeking. However, VP neurons are at the origin of multiple output pathways, with strong projections to ventral tegmental area (VTA), subthalamic nucleus (STN), lateral hypothalamus, among others, and the roles of these VP output pathways in reinstatement of drug seeking remain poorly understood. Here we addressed these issues using a combination of neuroanatomical tracing and chemogenetic approaches. First, using dual-retrograde tracing, we show that VP neurons projecting to either VTA or STN are recruited during context-induced reinstatement of extinguished alcohol seeking in rats. Then, using chemogenetics, we show modulation of context-induced reinstatement and reacquisition of alcohol seeking via designer receptors exclusively activated by designer drugs excitation or inhibition of the VP. To determine the causal roles of VP → VTA and VP → STN pathways in context-induced reinstatement and reacquisition we used a chemogenetic disconnection approach and show that silencing either the VP → VTA or VP → STN pathways is sufficient to reduce both reinstatement and reacquisition of alcohol seeking. Moreover, these disconnections also each reduced responding and motivation during a progressive ratio test but had no effect on locomotor activity. Together, these results show that multiple ventral pallidal output pathways contribute to relapse to alcohol seeking. SIGNIFICANCE STATEMENT: Ventral pallidum (VP) serves important roles in reward and motivation and is a critical node in the neural circuitry for reinstatement of drug seeking. Despite being a common locus for different forms of reinstatement, fundamental aspects of neural circuitry for these VP contributions to reinstatement of drug seeking remain unknown. Here we used a combination of neuroanatomical tracing and chemogenetic approaches to map the VP output pathways for context-induced reinstatement and reacquisition of alcohol seeking. We show that VP output pathways to the subthalamic nucleus and also to the ventral tegmental area are necessary for these forms of reinstatement.

Direct Hepatocyte Insulin Signaling Is Required for Lipogenesis but Is Dispensable for the Suppression of Glucose Production.

During insulin-resistant states such as type II diabetes mellitus (T2DM), insulin fails to suppress hepatic glucose production (HGP) yet promotes lipid synthesis. This metabolic state has been termed "selective insulin resistance" to indicate a defect in one arm of the insulin-signaling cascade, potentially downstream of Akt. Here we demonstrate that Akt-dependent activation of mTORC1 and inhibition of Foxo1 are required and sufficient for de novo lipogenesis, suggesting that hepatic insulin signaling is likely to be intact in insulin-resistant states. Moreover, cell-nonautonomous suppression of HGP by insulin depends on a reduction of adipocyte lipolysis and serum FFAs but is independent of vagal efferents or glucagon signaling. These data are consistent with a model in which, during T2DM, intact liver insulin signaling drives enhanced lipogenesis while excess circulating FFAs become a dominant inducer of nonsuppressible HGP.

The role of efferent cholinergic transmission for the insulinotropic and glucagonostatic effects of GLP-1.

The importance of vagal efferent signaling for the insulinotropic and glucagonostatic effects of glucagon-like peptide-1 (GLP-1) was investigated in a randomized single-blinded study. Healthy male participants (n = 10) received atropine to block vagal cholinergic transmission or saline infusions on separate occasions. At t = 15 min, plasma glucose was clamped at 6 mmol/l. GLP-1 was infused at a low dose (0.3 pmol·kg(-1)·min(-1)) from t = 45-95 min and at a higher dose (1 pmol·kg(-1)·min(-1)) from t = 95-145 min. Atropine blocked muscarinic, cholinergic transmission, as evidenced by an increase in heart rate [peak: 70 ± 2 (saline) vs. 90 ± 2 (atropine) beats/min, P < 0.002] and suppression of pancreatic polypeptide levels [area under the curve during the GLP-1 infusions (AUC45-145): 492 ± 85 (saline) vs. 247 ± 59 (atropine) pmol/l × min, P < 0.0001]. More glucose was needed to maintain the clamp during the high-dose GLP-1 infusion steady-state period on the atropine day [6.4 ± 0.9 (saline) vs. 8.7 ± 0.8 (atropine) mg·kg(-1)·min(-1), P < 0.0023]. GLP-1 dose-dependently increased insulin secretion on both days. The insulinotropic effect of GLP-1 was not impaired by atropine [C-peptide AUCs45-145: 99 ± 8 (saline) vs. 113 ± 13 (atropine) nmol/l × min, P = 0.19]. Atropine suppressed glucagon levels additively with GLP-1 [AUC45-145: 469 ± 70 (saline) vs. 265 ± 50 (atropine) pmol/l × min, P = 0.018], resulting in hypoglycemia when infusions were suspended [3.6 ± 0.2 (saline) vs. 2.7 ± 0.2 (atropine) mmol/l, P < 0.0001]. To ascertain whether atropine could independently suppress glucagon levels, control experiments (n = 5) were carried out without GLP-1 infusions [AUC45-145: 558 ± 103 (saline) vs. 382 ± 76 (atropine) pmol/l × min, P = 0.06]. Our results suggest that efferent muscarinic activity is not required for the insulinotropic effect of exogenous GLP-1 but that blocking efferent muscarinic activity independently suppresses glucagon secretion. In combination, GLP-1 and muscarinic blockade strongly affect glucose turnover.

Increased Efferent Cardiac Sympathetic Nerve Activity and Defective Intrinsic Heart Rate Regulation in Type 2 Diabetes.

Elevated sympathetic nerve activity (SNA) coupled with dysregulated ß-adrenoceptor (ß-AR) signaling is postulated as a major driving force for cardiac dysfunction in patients with type 2 diabetes; however, cardiac SNA has never been assessed directly in diabetes. Our aim was to measure the sympathetic input to and the ß-AR responsiveness of the heart in the type 2 diabetic heart. In vivo recording of SNA of the left efferent cardiac sympathetic branch of the stellate ganglion in Zucker diabetic fatty rats revealed an elevated resting cardiac SNA and doubled firing rate compared with nondiabetic rats. Ex vivo, in isolated denervated hearts, the intrinsic heart rate was markedly reduced. Contractile and relaxation responses to ß-AR stimulation with dobutamine were compromised in externally paced diabetic hearts, but not in diabetic hearts allowed to regulate their own heart rate. Protein levels of left ventricular ß1-AR and Gs (guanine nucleotide binding protein stimulatory) were reduced, whereas left ventricular and right atrial ß2-AR and Gi (guanine nucleotide binding protein inhibitory regulatory) levels were increased. The elevated resting cardiac SNA in type 2 diabetes, combined with the reduced cardiac ß-AR responsiveness, suggests that the maintenance of normal cardiovascular function requires elevated cardiac sympathetic input to compensate for changes in the intrinsic properties of the diabetic heart.

Efferent pathways of the mouse lateral habenula.

The lateral habenula (LHb) is part of the habenula complex of the dorsal thalamus. Recent studies of the LHb have focused on its projections to the ventral tegmental area (VTA) and rostromedial tegmental nucleus (RMTg), which contain γ-aminobutyric acid (GABA)ergic neurons that mediate reward prediction error via inhibition of dopaminergic activity. However, older studies in the rat have also identified LHb outputs to the lateral and posterior hypothalamus, median raphe, dorsal raphe, and dorsal tegmentum. Although these studies have shown that the medial and lateral divisions of the LHb have somewhat distinct projections, the topographic specificity of LHb efferents is not completely understood, and the relative extent of these projections to brainstem targets is unknown. Here we have used anterograde tracing with adeno-associated virus-mediated expression of green fluorescent protein, combined with serial two-photon tomography, to map the efferents of the LHb on a standard coordinate system for the entire mouse brain, and reconstruct the efferent pathways of the LHb in three dimensions. Using automated quantitation of fiber density, we show that in addition to the RMTg, the median raphe, caudal dorsal raphe, and pontine central gray are major recipients of LHb efferents. By using retrograde tract tracing with cholera toxin subunit B, we show that LHb neurons projecting to the hypothalamus, VTA, median raphe, caudal dorsal raphe, and pontine central gray reside in characteristic, but sometimes overlapping regions of the LHb. Together these results provide the anatomical basis for systematic studies of LHb function in neural circuits and behavior in mice. J. Comp. Neurol. 523:32-60, 2015. © 2014 Wiley Periodicals, Inc.

Neuroestrogen signaling in the songbird auditory cortex propagates into a sensorimotor network via an 'interface' nucleus.

Neuromodulators rapidly alter activity of neural circuits and can therefore shape higher order functions, such as sensorimotor integration. Increasing evidence suggests that brain-derived estrogens, such as 17-ß-estradiol, can act rapidly to modulate sensory processing. However, less is known about how rapid estrogen signaling can impact downstream circuits. Past studies have demonstrated that estradiol levels increase within the songbird auditory cortex (the caudomedial nidopallium, NCM) during social interactions. Local estradiol signaling enhances the auditory-evoked firing rate of neurons in NCM to a variety of stimuli, while also enhancing the selectivity of auditory-evoked responses of neurons in a downstream sensorimotor brain region, HVC (proper name). Since these two brain regions are not directly connected, we employed dual extracellular recordings in HVC and the upstream nucleus interfacialis of the nidopallium (NIf) during manipulations of estradiol within NCM to better understand the pathway by which estradiol signaling propagates to downstream circuits. NIf has direct input into HVC, passing auditory information into the vocal motor output pathway, and is a possible source of the neural selectivity within HVC. Here, during acute estradiol administration in NCM, NIf neurons showed increases in baseline firing rates and auditory-evoked firing rates to all stimuli. Furthermore, when estradiol synthesis was blocked in NCM, we observed simultaneous decreases in the selectivity of NIf and HVC neurons. These effects were not due to direct estradiol actions because NIf has little to no capability for local estrogen synthesis or estrogen receptors, and these effects were specific to NIf because other neurons immediately surrounding NIf did not show these changes. Our results demonstrate that transsynaptic, rapid fluctuations in neuroestrogens are transmitted into NIf and subsequently HVC, both regions important for sensorimotor integration. Overall, these findings support the hypothesis that acute neurosteroid actions can propagate within and between neural circuits to modulate their functional connectivity.

Neurophysiological monitoring of the spinal sensory and motor pathways during embolization of spinal arteriovenous malformations--propofol: a safe alternative.

INTRODUCTION: Embolization of a spinal cord arteriovenous malformation (AVM) is considered a high-risk procedure due to the potential risk of spinal cord injury. We present two cases illustrating the benefits of utilizing pharmacologic provocative testing under general anesthesia with continuous neurophysiologic monitoring of somatosensory evoked potentials (SSEPs) and transcranial electrical motor evoked potentials (TCeMEPs) to identify the functional territory of the catheterized vessels prior to embolization. CLINICAL PRESENTATION: Case #1: A 28-year-old male presented with a progressive right lower leg numbness followed by weakness with impaired sphincter control. The MRI and angiogram of the spine showed an arteriovenous malformation (type 4) (subtype 2). Case #2: A 31-year-old male presented with sudden occipital, neck, right shoulder and back pain. He was neurologically intact. MRI and angiogram showed a predominantly right sided arteriovenous malformation. INTERVENTIONAL PROCEDURE: After intubation, bilateral posterior tibial and median nerve SSEPs were recorded. TCeMEP and electromyogram (EMG) were monitored from upper and lower extremity muscles bilaterally. Total intravenous anesthesia was used with propofol and remifentanil infusion. Neuromuscular blockade was used only for initial intubation. A train of four was maintained during the procedure. Pre-incision baselines were obtained with good morphology of waveforms. Selective spinal Wada tests were performed prior to embolization with lidocaine and propofol. Neurophysiological monitoring was performed for any changes. RESULTS: Complete occlusion of the AVM was achieved. As no changes occurred during provocative testing, all branches were treated with Onyx embolization. At six-month post-operative follow-up, both patients had total relief of symptoms. CONCLUSION: Multimodality IONM with continuous SSEP, TCeMEP, and EMG monitoring was utilized effectively during provocative testing with lidocaine and propofol. IONM helped in predicting and preventing post-operative neurological deficits due to ischemia to the spinal cord.