Activation of Medulla-Projecting Perifornical Neurons Modulates the Adrenal Sympathetic Response to Hypoglycemia: Involvement of Orexin Type 2 (OX2-R) Receptors

Iatrogenic hypoglycemia in response to insulin treatment is commonly experienced by patients with type 1 diabetes and can be life threatening. The body releases epinephrine in an attempt to counterregulate hypoglycemia, but the neural mechanisms underlying this phenomenon remain to be elucidated. Orexin neurons in the perifornical hypothalamus (PeH) project to the rostral ventrolateral medulla (RVLM) and are likely to be involved in epinephrine secretion during hypoglycemia. In anesthetized rats, we report that hypoglycemia increases the sympathetic preganglionic discharge to the adrenal gland by activating PeH orexin neurons that project to the RVLM (PeH-RVLM). Electrophysiological characterization shows that the majority of identified PeH-RVLM neurons, including a subpopulation of orexin neurons, are activated in response to hypoglycemia or glucoprivation. Furthermore, the excitatory input from the PeH is mediated by orexin type 2 receptors in the RVLM. These results suggest that activation of orexin PeH-RVLM neurons and orexin type 2 receptors in the RVLM facilitates epinephrine release by increasing sympathetic drive to adrenal chromaffin cells during hypoglycemia.

Perinatal thiamine restriction affects central GABA and glutamate concentrations and motor behavior of adult rat offspring

The purposes of the present study were to investigate the effects of perinatal thiamine deficiency, from the 11th day of gestation until the 5th day of lactation, on motor behavior and neurochemical parameters in adult rat offspring, using 3-month-old, adult, male Wistar rats. All rats were submitted to motor tests, using the rotarod and paw print tasks. After behavioral tests, their thalamus, cerebellum and spinal cord were dissected for glutamate and GABA quantifications by high performance liquid chromatography. The thiamine-restricted mothers (RM) group showed a significant reduction of time spent on the rotarod at 25 rpm and an increase in hind-base width. A significant decrease of glutamate concentration in the cerebellum and an increase of GABA concentrations in the thalamus were also observed. For the offspring from control mothers (CM) group there were significant correlations between thalamic GABA concentrations and both rotarod performance and average hind-base width. In addition, for rats from the RM group a significant correlation between stride length and cerebellar GABA concentration was found. These results show that the deficiency of thiamine during an early developmental period affects certain motor behavior parameters and GABA and glutamate levels in specific brain areas. Hence, a thiamine deficiency episode during an early developmental period can induce motor impairments and excitatory and inhibitory neurotransmitter changes that are persistent and detectable in later periods of life.

Aldosterone Contributes to Sympathoexcitation in Renovascular Hypertension

BACKGROUND

Although angiotensin II (Ang II) is essential to the development of renovascular hypertension, aldosterone plays a role as well. Recent studies have demonstrated a cross-talk between Ang II type 1 and mineralocorticoid receptors in the brain and kidneys. However, the role of aldosterone in the autonomic and renal dysfunction of renovascular hypertension is not well understood.

AIM

The current study evaluated whether aldosterone contributes to cardiovascular and renal dysfunction in the 2 kidney-1 clip (2K1C) model.

METHODS

Mean arterial pressure (MAP) and baroreceptor reflex for control of the heart rate were evaluated in 2K1C treated or not treated with spironolactone (200mg/kg/day, 7 days). Tonic and reflex control of renal sympathetic nerve activity (rSNA) were assessed in urethane-anaesthetized rats. Plasma renin activity (PRA), kidney renin protein expression, renal injury, and central AT1 receptor protein expression were assessed.

RESULTS

Spiro reduced MAP (198±4 vs. 170±9mm Hg; P < 0.05), normalized rSNA (147±9 vs. 96±10 pps; P < 0.05), and increased renal baroreceptor reflex sensitivity in the 2K1C rats. Spiro reduced α-smooth muscle actin expression in the nonclipped kidney in the 2K1C group (5±0.6 vs. 1.1±0.2%; P < 0.05). There was no change in PRA; however, a decrease in renin protein expression in the nonclipped kidney was found in the 2K1C treated group (217±30 vs. 160±19%; P < 0.05). Spiro treatment decreased AT1 receptor in the central nervous system (CNS) only in 2K1C rats (138±10 vs. 84±12%; P < 0.05).

CONCLUSION

Aldosterone contributes to autonomic dysfunction and intrarenal injury in 2K1C, these effects are mediated by the CNS.

Developmental exposure to paracetamol causes biochemical alterations in medulla oblongata

The effect and safety of prenatal and early life administration of paracetamol - routinely used over-the-counter antipyretic and analgesic medication on monoamines content and balance of amino acids in the medulla oblongata is still unknown. In this study we have determined the level of neurotransmitters in this structure in two-month old Wistar male rats exposed to paracetamol in the dose of 5 (P5, n=10) or 15mg/kg b.w. (P15, n=10) during prenatal period, lactation and till the end of the second month of life. Control group received drinking water (Con, n=10). Monoamines, their metabolites and amino acids concentration in medulla oblongata of rats were determined using high performance liquid chromatography (HPLC) in 60 postnatal day (PND60). This experiment shows that prenatal and early life paracetamol exposure modulates neurotransmission associated with serotonergic, noradrenergic and dopaminergic system in medulla oblongata. Reduction of alanine and taurine levels has also been established.

Injections of Algesic Solutions into Muscle Activate the Lateral Reticular Formation: A Nociceptive Relay of the Spinoreticulothalamic Tract

Although musculoskeletal pain disorders are common clinically, the central processing of muscle pain is little understood. The present study reports on central neurons activated by injections of algesic solutions into the gastrocnemius muscle of the rat, and their subsequent localization by c-Fos immunohistochemistry in the spinal cord and brainstem. An injection (300μl) of an algesic solution (6% hypertonic saline, pH 4.0 acetate buffer, or 0.05% capsaicin) was made into the gastrocnemius muscle and the distribution of immunolabeled neurons compared to that obtained after control injections of phosphate buffered saline [pH 7.0]. Most labeled neurons in the spinal cord were found in laminae IV-V, VI, VII and X, comparing favorably with other studies, with fewer labeled neurons in laminae I and II. This finding is consistent with the diffuse pain perception due to noxious stimuli to muscles mediated by sensory fibers to deep spinal neurons as compared to more restricted pain localization during noxious stimuli to skin mediated by sensory fibers to superficial laminae. Numerous neurons were immunolabeled in the brainstem, predominantly in the lateral reticular formation (LRF). Labeled neurons were found bilaterally in the caudalmost ventrolateral medulla, where neurons responsive to noxious stimulation of cutaneous and visceral structures lie. Immunolabeled neurons in the LRF continued rostrally and dorsally along the intermediate reticular nucleus in the medulla, including the subnucleus reticularis dorsalis caudally and the parvicellular reticular nucleus more rostrally, and through the pons medial and lateral to the motor trigeminal nucleus, including the subcoerulear network. Immunolabeled neurons, many of them catecholaminergic, were found bilaterally in the nucleus tractus solitarii, the gracile nucleus, the A1 area, the CVLM and RVLM, the superior salivatory nucleus, the nucleus locus coeruleus, the A5 area, and the nucleus raphe magnus in the pons. The external lateral and superior lateral subnuclei of the parabrachial nuclear complex were consistently labeled in experimental data, but they also were labeled in many control cases. The internal lateral subnucleus of the parabrachial complex was labeled moderately. Few immunolabeled neurons were found in the medial reticular formation, however, but the rostroventromedial medulla was labeled consistently. These data are discussed in terms of an interoceptive, multisynaptic spinoreticulothalamic path, with its large receptive fields and role in the motivational-affective components of pain perceptions.

Selective C1 Lesioning Slightly Decreases Angiotensin II Type I Receptor Expression in the Rat Rostral Ventrolateral Medulla (RVLM)

Cardiovascular homeostasis is regulated in large part by the rostral ventrolateral medulla (RVLM) in mammals. Projections from the RVLM to the intermediolateral column of the thoracolumbar spinal cord innervate preganglionic neurons of the sympathetic nervous system causing elevation of blood pressure and heart rate. A large proportion, but not all, of the neurons in the RVLM contain the enzymes necessary for the production of epinephrine and are identified as the C1 cell group. Angiotensin II (Ang II) activates the RVLM acting upon AT1 receptors. To assess the proportion of AT1 receptors that are located on C1 neurons in the rat RVLM this study employed an antibody to dopamine-beta-hydroxylase conjugated to saporin, to selectively destroy C1 neurons in the RVLM. Expression of tyrosine hydroxylase immunoreactive neurons in the RVLM was reduced by 57 % in the toxin injected RVLM compared to the contralateral RVLM. In contrast, densitometric analysis of autoradiographic images of (125)I-sarcosine(1), isoleucine(8) Ang II binding to AT1 receptors of the injected side RVLM revealed a small (10 %) reduction in AT1-receptor expression compared to the contralateral RVLM. These results suggest that the majority of AT1 receptors in the rat RVLM are located on non-C1 neurons or glia.

Neuron-to-neuron α-synuclein propagation in vivo is independent of neuronal injury

INTRODUCTION

Interneuronal propagation of α-synuclein has been demonstrated in a variety of experimental models and may be involved in disease progression during the course of human synucleinopathies. The aim of this study was to assess the role that neuronal injury or, vice versa, cell integrity could have in facilitating interneuronal α-synuclein transfer and consequent protein spreading in an in vivo animal model.

RESULTS

Viral vectors carrying the DNA for human α-synuclein were injected into the rat vagus nerve to trigger protein overexpression in the medulla oblongata and consequent spreading of human α-synuclein toward pons, midbrain and forebrain. Two vector preparations sharing the same viral construct were manufactured using identical procedures with the exception of methods for their purification. They were also injected at concentrations that induced comparable levels of α-synuclein transduction/overexpression in the medulla oblongata. α-Synuclein load was associated with damage (at 6 weeks post injection) and death (at 12 weeks) of medullary neurons after treatment with only one of the two vector preparations. Of note, neuronal injury and degeneration was accompanied by a substantial reduction of caudo-rostral propagation of human α-synuclein.

CONCLUSIONS

Interneuronal α-synuclein transfer, which underlies protein spreading from the medulla oblongata to more rostral brain regions in this rat model, is not a mere consequence of passive release from damaged or dead neurons. Neuronal injury and degeneration did not exacerbate α-synuclein propagation. In fact, data suggest that cell-to-cell passage of α-synuclein may be particularly efficient between intact, relatively healthy neurons.

Respiratory calcium fluctuations in low-frequency oscillating astrocytes in the pre-Bötzinger complex

Astrocytes have been found to modulate neuronal activity through calcium-dependent signaling in various brain regions. However, whether astrocytes of the pre-Bötzinger complex (preBötC) exhibit respiratory rhythmic fluctuations is still controversial. Here we evaluated calcium-imaging experiments within preBötC in rhythmically active medullary slices from TgN(hGFAP-EGFP) mice using advanced analyses. 13.8% of EGFP-negative cells, putative neurons, showed rhythmic fluorescent changes that were highly correlated to the respiratory rhythmic fluctuation (cross-correlation coefficient>0.5 and dF/F>0.2%). In contrast, a considerable number of astrocyte somata exhibited synchronized low-frequency (<0.03Hz) calcium oscillations. After band-pass filtering, signals that irregularly preceded the calcium signal of EGFP-negative cells were observed in 10.2% of astrocytes, indicating a functional coupling between astrocytes and neurons in preBötC. A model simulation confirmed that such preinspiratory astrocytic signals can arise from coupled neuronal and astrocytic oscillators, supporting a concept that slow oscillatory changes of astrocytic functions modulate neighboring neuronal activity to add variability in respiratory rhythm.

Cerebral klotho protein as a humoral factor for maintenance of baroreflex

The klotho protein produced by the choroid plexus is known as a humoral factor in central nervous system. Many hormones affecting the baroreflex sensitivity have been introduced in the brain. However, role of klotho in the baroreflex sensitivity is still unknown. Recently, mutations in the klotho gene have been linked to cardiovascular diseases in both animals and human subjects. Also, silencing of brain klotho has been reported to enhance cold-induced elevation of blood pressure. Thus, we investigated the role of klotho in maintenance of central cardiovascular reflex sensitivity. Male Wistar Kyoto (WKY) rats and spontaneously hypertensive rats (SHRs) were used. Either klotho shRNA or scramble shRNA was also ICV-infused into the brains of WKY rats to investigate the role of klotho in brain. Recombinant klotho or rat IgG was infused into the cerebral paraventricle (ICV) of SHRs for further understanding the role of klotho in hypertension. The baroreflex sensitivity was detected using the challenge with a depressor dose of sodium nitroprusside (SNP, 50 μg/kg) or with a pressor dose of phenylephrine (PE, 8 μg/kg). We found that silencing of klotho expression in the brain decreased the baroreflex sensitivity in WKY rats. Also, modulation of the blood pressure for one week altered the cardiovascular homeostasis and resulted in an increased expression of klotho in medulla oblongata. Moreover, the baroreflex sensitivity was restored in SHRs that received recombinant klotho through ICV brain. Thus, klotho is involved in the maintenance of baroreflex sensitivity in the brain.

Absence of TRH receptor 1 in male mice affects gastric ghrelin production

TRH not only functions as a thyrotropin releasing hormone but also acts as a neuropeptide in central circuits regulating food intake and energy expenditure. As one suggested mode of action, TRH expressed in the caudal brainstem influences vagal activity by activating TRH receptor 1 (TRH-R1). In order to evaluate the impact of a diminished medullary TRH signaling on ghrelin metabolism, we analyzed metabolic changes of TRH-R1 knockout (R1ko) mice in response to 24 hours of food deprivation. Because R1ko mice are hypothyroid, we also studied eu- and hypothyroid wild-type (wt) animals and R1ko mice rendered euthyroid by thyroid hormone treatment. Independent of their thyroidal state, R1ko mice displayed a higher body weight loss than wt animals and a delayed reduction in locomotor activity upon fasting. Ghrelin transcript levels in the stomach as well as total ghrelin levels in the circulation were equally high in fasted wt and R1ko mice. In contrast, only wt mice responded to fasting with a rise in ghrelin-O-acyltransferase mRNA expression and consequently an increase in serum levels of acylated ghrelin. Together, our data suggest that an up-regulation of medullary TRH expression and subsequently enhanced activation of TRH-R1 in the vagal system represents a critical step in the stimulation of ghrelin-O-acyltransferase expression upon starvation that in turn is important for adjusting the circulating levels of acylated ghrelin to the fasting condition.

Inhibition of itch-related responses by selectively ablated serotonergic signals at the rostral ventromedial medulla in mice

Descending control of nociceptive processing in the rostral ventromedial medulla (RVM) has been implicated in the inhibition and facilitation of spinal nociceptive transmission. Here we investigated the contribution of serotonergic (5-HT) pathway at the RVM to pruritic behavior. Selective lesion of the descending serotonergic pathway by intra-RVM injection of focal neurotoxin 5,7-dihydroxytryptamine (2 μg/0.5 μl) attenuated pruritic behavior at the 30-min observation period following an intradermal microinjection of compound 48/80 (100 μg/100 μl) in the nape of the neck. Intradermal microinjection of compound 48/80 resulted in a dramatic increase in itch behavior between naive group and saline group. 5,7-DHT-treated mice showed profound scratching deficits after intradermal injection of compound 48/80. 5,7-DHT treatment resulted in a significant decrease in the number of 5-HT positive neurons in the RVM by using intracisternal injection of the serotonin neurotoxin 5,7-DHT. These findings demonstrate that pruritic behavior is dependent in part on descending facilitation via the RVM, and identify a modulatory role of serotonergic pathway at the RVM for pruritic behavior.

Olanzapine-activated AMPK signaling in the dorsal vagal complex is attenuated by histamine H1 receptor agonist in female rats

Weight gain and its related metabolic disorders are major side effects associated with second generation antipsychotic drug treatment. The dorsal vagal complex (DVC) and AMP-activated protein kinase (AMPK) are implicated in the regulation of food intake and body weight. Blocking the histamine H1 receptor contributes to antipsychotic-induced weight gain. The present study investigated the time-dependent effect of olanzapine treatment (8, 16, and 36 d) on DVC AMPK signaling in olanzapine-induced weight gain and whether these changes are associated with olanzapine-induced H1 receptor antagonism. During the 8-day olanzapine treatment, the rats were hyperphagic and rapidly gained weight. The phosphorylation of AMPK (pAMPK) (activated AMPK) as well as its directly downstream phospho-acetyl-coenzyme A carboxylase was significantly increased. The pAMPK/AMPK ratio, an indicator of AMPK activity, was significantly positively correlated with feeding efficiency and weight gain. As treatment was prolonged (16 and 36 d of olanzapine treatment), the rats were no longer hyperphagic, and there were no longer any changes in DVC AMPK signaling. Although the DVC H1 receptor protein expression was not significantly altered by olanzapine, the pAMPK expression was significantly positively correlated with the H1 receptor level after the 8-, 16-, and 36-day olanzapine treatments. Moreover, we showed that an H1 receptor agonist, 2-(3-trifluoromethylphenyl) histamine, significantly inhibited the olanzapine-induced hyperphagia and DVC AMPK activation in a dose-dependent manner. These results suggest a time-dependent role of DVC AMPK in olanzapine-induced obesity. Thus, olanzapine-induced DVC AMPK activation may be at least partially related to olanzapine's antagonistic effect on the H1 receptor.

P2 purinergic receptor activation of neuronal nitric oxide synthase and guanylyl cyclase in the dorsal facial area of the medulla increases blood flow in the common carotid arteries of cats

In the dorsal facial area (DFA) of the medulla, an activation of either P2 purinergic receptor or nitric oxide synthase (NOS) results in the release of glutamate, leading to an increase in blood flow of the common carotid artery (CCA). It is not known whether activation of the P2 receptor by ATP may mediate activation of NOS/guanylyl cyclase to cause glutamate release and/or whether L-Arg (nitric oxide (NO) precursor) may also cause ATP release from any other neuron, to cause an increase in CCA flow. We demonstrated that microinjections of P2 receptor agonists (ATP, α,β-methylene ATP) or NO precursor (L-arginine) into the DFA increased CCA blood flow. The P2-induced CCA blood flow increase was dose-dependently reduced by pretreatment with NG-nitro-arginine methyl ester (L-NAME, a non-specific NOS inhibitor), 7-nitroindazole (7-NI, a relatively selective neuronal NOS inhibitor) or methylene blue (MB, a guanylyl cyclase inhibitor) but not by that with D-NAME (an isomer of L-NAME) or N5-(1-iminoethyl)-L-ornithine (L-NIO, a potent endothelial NOS inhibitor). Involvement of glutamate release in these responses were substantiated by microdialysis studies, in which perfusions of ATP into the DFA increased the glutamate concentration in dialysates, but co-perfusion of ATP with L-NAME or 7-NI did not. Nevertheless, the arginine-induced CCA blood flow increase was abolished by combined pretreatment of L-NAME and MB, but not affected by pretreatment with a selective P2 receptor antagonist, pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid (PPADS). In conclusion, ATP activation of the P2 receptor in the DFA induced activation of neuronal NOS/guanylyl cyclase, which causes glutamate release leading to an increase in CCA blood flow. However, arginine activation of neuronal NOS/guanylyl cyclase, which also caused glutamate release and CCA blood flow increase, did not induce activation of P2 receptors. These findings provide important information for drug design and/or developing therapeutic strategies for the diseases associated with CCA blood flow that supplies intra- and extra-cranial tissues.

Activation of corticotropin-releasing factor receptors in the rostral ventrolateral medulla is required for glucose-induced sympathoexcitation

Energy expenditure is determined by metabolic rate and diet-induced thermogenesis. Normally, energy expenditure increases due to neural mechanisms that sense plasma levels of ingested nutrients/hormones and reflexively increase sympathetic nerve activity (SNA). Here, we investigated neural mechanisms of glucose-driven sympathetic activation by determining contributions of neuronal activity in the hypothalamic paraventricular nucleus (PVN) and activation of corticotropin-releasing factor (CRF) receptors in the rostral ventrolateral medulla (RVLM). Glucose was infused intravenously (150 mg/kg, 10 min) in male rats to raise plasma glucose concentration to a physiological postprandial level. In conscious rats, glucose infusion activated CRF-containing PVN neurons and TH-containing RVLM neurons, as indexed by c-Fos immunofluorescence. In α-chloralose/urethane-anesthetized rats, glucose infusion increased lumbar and splanchnic SNA, which was nearly prevented by prior RVLM injection of the CRF receptor antagonist astressin (10 pmol/50 nl). This cannot be attributed to a nonspecific effect, as sciatic afferent stimulation increased SNA and ABP equivalently in astressin- and aCSF-injected rats. Glucose-stimulated sympathoexcitation was largely reversed during inhibition of PVN neuronal activity with the GABA-A receptor agonist muscimol (100 pmol/50 nl). The effects of astressin to prevent glucose-stimulated sympathetic activation appear to be specific to interruption of PVN drive to RVLM because RVLM injection of astressin prior to glucose infusion effectively prevented SNA from rising and prevented any fall of SNA in response to acute PVN inhibition with muscimol. These findings suggest that activation of SNA, and thus energy expenditure, by glucose is initiated by activation of CRF receptors in RVLM by descending inputs from PVN.

The coexistence of VGluT2 and neurotensin or leu-enkephalin in the medullary dorsal horn: a confocal and electron microscopic immunohistochemical study in the rat

Neuropeptides such as neurotensin (NT), and enkephalin (ENK) in the medullary dorsal horn (MDH) are involved in excitatory synaptic transmission to modulate nociceptive information. However, morphological evidence indicating that NT or ENK coexists with glutamate in the MDH is still meager. Using fluorescent immunohistochemistry, the results showed that double labeling of NT or ENK terminals with VGluT2 is mainly concentrated in the lamina II of the MDH, and many axon terminals exhibiting NT or ENK immunoreactivity in the superficial layers of the MDH showed VGluT2 immunoreactivity. Electron microscopy confirmed the coexpression of NT or ENK and VGluT2 in axon terminals within the laminae I and II of the MDH. These axon terminals make asymmetrical synapses with immunonegative neuronal cell bodies and dendrites. The findings suggest that glutamate is coreleased with NT or ENK from axon terminals of interneurons in the superficial layers of the MDH.

Crypto-rhombomeres of the mouse medulla oblongata, defined by molecular and morphological features

The medulla oblongata is the caudal portion of the vertebrate hindbrain. It contains major ascending and descending fiber tracts as well as several motor and interneuron populations, including neural centers that regulate the visceral functions and the maintenance of bodily homeostasis. In the avian embryo, it has been proposed that the primordium of this region is subdivided into five segments or crypto-rhombomeres (r7-r11), which were defined according to either their parameric position relative to intersomitic boundaries (Cambronero and Puelles, in J Comp Neurol 427:522-545, 2000) or a stepped expression of Hox genes (Marín et al., in Dev Biol 323:230-247, 2008). In the present work, we examine the implied similar segmental organization of the mouse medulla oblongata. To this end, we analyze the expression pattern of Hox genes from groups 3 to 8, comparing them to the expression of given cytoarchitectonic and molecular markers, from mid-gestational to perinatal stages. As a result of this approach, we conclude that the mouse medulla oblongata is segmentally organized, similarly as in avian embryos. Longitudinal structures such as the nucleus of the solitary tract, the dorsal vagal motor nucleus, the hypoglossal motor nucleus, the descending trigeminal and vestibular columns, or the reticular formation appear subdivided into discrete segmental units. Additionally, our analysis identified an internal molecular organization of the migrated pontine nuclei that reflects a differential segmental origin of their neurons as assessed by Hox gene expression.

Spinally projecting preproglucagon axons preferentially innervate sympathetic preganglionic neurons

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Spinal GLP-1 axons target primarily sympathetic preganglionic neurons.

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Spinal GLP-1 axons innervate interneurons that may regulate sympathetic outflow.

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Many GLP-1 neurons in the medulla are spinally-projecting.

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The lumbar cord contains YFP-expressing neurons that do not innervate the brain.

Glucagon-like peptide-1 (GLP-1) affects central autonomic neurons, including those controlling the cardiovascular system, thermogenesis, and energy balance. Preproglucagon (PPG) neurons, located mainly in the nucleus tractus solitarius (NTS) and medullary reticular formation, produce GLP-1. In transgenic mice expressing glucagon promoter-driven yellow fluorescent protein (YFP), these brainstem PPG neurons project to many central autonomic regions where GLP-1 receptors are expressed. The spinal cord also contains GLP-1 receptor mRNA but the distribution of spinal PPG axons is unknown.

Here, we used two-color immunoperoxidase labeling to examine PPG innervation of spinal segments T1–S4 in YFP-PPG mice. Immunoreactivity for YFP identified spinal PPG axons and perikarya. We classified spinal neurons receiving PPG input by immunoreactivity for choline acetyltransferase (ChAT), nitric oxide synthase (NOS) and/or Fluorogold (FG) retrogradely transported from the peritoneal cavity. FG microinjected at T9 defined cell bodies that supplied spinal PPG innervation.

The deep dorsal horn of lower lumbar cord contained YFP-immunoreactive neurons. Non-varicose, YFP-immunoreactive axons were prominent in the lateral funiculus, ventral white commissure and around the ventral median fissure. In T1–L2, varicose, YFP-containing axons closely apposed many ChAT-immunoreactive sympathetic preganglionic neurons (SPN) in the intermediolateral cell column (IML) and dorsal lamina X. In the sacral parasympathetic nucleus, about 10% of ChAT-immunoreactive preganglionic neurons received YFP appositions, as did occasional ChAT-positive motor neurons throughout the rostrocaudal extent of the ventral horn. YFP appositions also occurred on NOS-immunoreactive spinal interneurons and on spinal YFP-immunoreactive neurons. Injecting FG at T9 retrogradely labeled many YFP-PPG cell bodies in the medulla but none of the spinal YFP-immunoreactive neurons.

These results show that brainstem PPG neurons innervate spinal autonomic and somatic motor neurons. The distributions of spinal PPG axons and spinal GLP-1 receptors correlate well. SPN receive the densest PPG innervation. Brainstem PPG neurons could directly modulate sympathetic outflow through their spinal inputs to SPN or interneurons.

Physical activity correlates with glutamate receptor gene expression in spinally-projecting RVLM neurons: a laser capture microdissection study

Physical inactivity is an important risk factor in the development of cardiovascular disease. The rostral ventrolateral portion of the medulla (RVLM) is composed of heterogeneous populations of neurons that are involved in the regulation of the cardiovascular system. Because of functional heterogeneity, studying the changes in the gene expression of this specific population of neurons within the RVLM is challenging. In the present study, a fluorescent retrograde tracer was injected into the spinal cord to specifically label bulbospinal RVLM neurons in sedentary and active rats. Laser capture microdissection (LCM) was then employed to collect the fluorescently labeled neurons from sections encompassing the rostrocaudal extent of the RVLM. RNA extracted from the neurons was used in qRT-PCR analysis. Changes in gene expression levels of glutamate and GABA receptor subunits were compared between sedentary and physically active rats. GLUR3 subunit showed a significant negative correlation between total running distance and its relative gene expression in active rats. There were no significant difference in the gene expression of NMDA (NR1, NR2A, NR2B, NR2C and NR2D), AMPA (GLUR1, GLUR2 and GLUR3) and GABAA (GABAA1 and GABAA2) receptor subunits. Overall, the present study demonstrates the feasibility of utilizing LCM to investigate the gene expression changes in a specific population of neurons in the RVLM. Correlation studies suggest that physical activity could contribute to neuroplasticity in the RVLM.

RVLM-IML pathway may implicate controlling peripheral airways by melanocortinergic-sympathetic signaling: a transneuronal labeling study using pseudorabies virus

Pseudorabies virus (PRV)-614 was injected into the tracheal wall of male MC4R-GFP transgenic mice, resulting in retrograde infections in spinal cord and autonomic premotor areas of the brain including the rostroventrolateral medulla (RVLM). This polysynaptic pathway to the airway may form the substrate underlying the impact of IML and RVLM on airway function. The neurochemical phenotype of MC4R-GFP-positive neurons was identified using fluorescence immunocytochemical labeling. PRV-614/MC4R-GFP dual labeled neurons were detected in spinal IML and the rostral ventrolateral medulla (RVLM). These data demonstrate the RVLM-IML pathway of synaptically connected neurons extending to the airway through melanocortinergic-sympathetic signaling.

Chronic infusion of lisinopril into hypothalamic paraventricular nucleus modulates cytokines and attenuates oxidative stress in rostral ventrolateral medulla in hypertension

The hypothalamic paraventricular nucleus (PVN) and rostral ventrolateral medulla (RVLM) play a critical role in the generation and maintenance of sympathetic nerve activity. The renin-angiotensin system (RAS) in the brain is involved in the pathogenesis of hypertension. This study was designed to determine whether inhibition of the angiotensin-converting enzyme (ACE) in the PVN modulates cytokines and attenuates oxidative stress (ROS) in the RVLM, and decreases the blood pressure and sympathetic activity in renovascular hypertensive rats. Renovascular hypertension was induced in male Sprague-Dawley rats by the two-kidney one-clip (2K1C) method. Renovascular hypertensive rats received bilateral PVN infusion with ACE inhibitor lisinopril (LSP, 10μg/h) or vehicle via osmotic minipump for 4weeks. Mean arterial pressure (MAP), renal sympathetic nerve activity (RSNA), and plasma proinflammatory cytokines (PICs) were significantly increased in renovascular hypertensive rats. The renovascular hypertensive rats also had higher levels of ACE in the PVN, and lower level of interleukin-10 (IL-10) in the RVLM. In addition, the levels of PICs, the chemokine MCP-1, the subunit of NAD(P)H oxidase (gp91(phox)) and ROS in the RVLM were increased in hypertensive rats. PVN treatment with LSP attenuated those changes occurring in renovascular hypertensive rats. Our findings suggest that the beneficial effects of ACE inhibition in the PVN in renovascular hypertension are partly due to modulation cytokines and attenuation oxidative stress in the RVLM.

Divergent motor projections from the pedunculopontine nucleus are differentially regulated in Parkinsonism

The pedunculopontine nucleus (PPN) is composed of neurons with different connectivity patterns that express different neurochemical markers, display distinct firing characteristics and are topographically organized in functional domains across its rostro-caudal axis. Previous reports have shown that the caudal region of the PPN is interconnected with motor regions of both the basal ganglia and brainstem/medulla. The co-distribution of ascending and descending motor outputs raises the question as to whether the PPN provides a coordinated or differential modulation of its targets in the basal ganglia and the medulla. To address this, we retrogradely labeled neurons in the two main PPN pathways involved in motor control and determined whether they project to one or both structures, their neurochemical phenotype, and their activity in normal and dopamine depleted rats, as indicated by Egr-1 expression. We show that ascending and descending motor pathways from the PPN arise largely from separate neurons that intermingle in the same region of the PPN, but have a distinct neurochemical composition and are differentially regulated in the Parkinsonian state. Thus, neurons projecting to the subthalamic nucleus consist of cholinergic, calbindin- and calretinin-expressing neurons, and Egr-1 is upregulated following a 6-hydroxydopamine lesion. In contrast, a larger proportion of neurons projecting to the gigantocellular nucleus are cholinergic, none express calbindin and the expression of Egr-1 is not changed by the dopamine lesion. Our results suggest that ascending and descending motor connections of the PPN are largely mediated by different sets of neurons and there are cell type-specific changes in Parkinsonian rats.

Nitric oxide signaling modulates synaptic inhibition in the superior paraolivary nucleus (SPN) via cGMP-dependent suppression of KCC2

Glycinergic inhibition plays a central role in the auditory brainstem circuitries involved in sound localization and in the encoding of temporal action potential firing patterns. Modulation of this inhibition has the potential to fine-tune information processing in these networks. Here we show that nitric oxide (NO) signaling in the auditory brainstem (where activity-dependent generation of NO is documented) modulates the strength of inhibition by changing the chloride equilibrium potential. Recent evidence demonstrates that large inhibitory postsynaptic currents (IPSCs) in neurons of the superior paraolivary nucleus (SPN) are enhanced by a very low intracellular chloride concentration, generated by the neuronal potassium chloride co-transporter (KCC2) expressed in the postsynaptic neurons. Our data show that modulation by NO caused a 15 mV depolarizing shift of the IPSC reversal potential, reducing the strength of inhibition in SPN neurons, without changing the threshold for action potential firing. Regulating inhibitory strength, through cGMP-dependent changes in the efficacy of KCC2 in the target neuron provides a postsynaptic mechanism for rapidly controlling the inhibitory drive, without altering the timing or pattern of the afferent spike train. Therefore, this NO-mediated suppression of KCC2 can modulate inhibition in one target nucleus (SPN), without influencing inhibitory strength of other target nuclei (MSO, LSO) even though they are each receiving collaterals from the same afferent nucleus (a projection from the medial nucleus of the trapezoid body, MNTB).

RNA interference of GluN1 inhibits neuronal rhythmogenesis in the adult inferior olive

RNA interference (RNAi) to knockdown N-methyl-D-aspartate receptor (NMDAR) function is being investigated to address disorders associated with pathological brain rhythms. A motivating finding has been that pharmacological block of NMDARs inhibited oscillations in neuronal membrane potential that entrain rhythmic bursts of action potentials. To determine whether transient effects of NMDAR antagonist drugs to inhibit neuronal rhythmicity can be stably induced with genetic specificity, we examined the effects of RNAi of GluN1 protein on the subthreshold oscillations (STOs) of neurons in the inferior olive (IO), a pacemaking nucleus necessary for motor and cognitive timing. Western blot of dissociated neurons demonstrated 90% knockdown of GluN1 after a strong in vivo transduction by a dual-microRNA lentiviral vector. GluN1 RNAi in whole-cell-patched IO neurons blocked both membrane depolarization and STOs typically induced by NMDAR activation for up to 54 days without affecting input resistance, membrane capacitance, action potential firing, high-threshold Ca(2+) spikes, the hyperpolarization-activated current Ih, or the activation of the low-threshold Ca(2+) current I(T). Although an off-target effect on Cav3 expression was ruled out also by BlastN query, we found that GluN1 RNAi chronically eliminated I(T)-dependent STOs at resting membrane potential, well below the activation threshold of the NMDAR channel. In the context of a recent report showing that NMDAR activation induces STOs as it strengthens electrical coupling, the long-term block of STOs by GluN1 RNAi may relate to the loss of an essential support mechanism. Lentivector-mediated RNAi of GluN1 provides a novel technique for future investigations of NMDAR involvement in electrical oscillations and behavior.

Severe diffuse axon injury in chronic alcoholic rat medulla oblongata following a concussion blow

AIMS

We investigated the axonal morphological changes and expression of both tau protein and β-APP following concussion to the medulla oblongata, in a rat model of chronic alcoholism.

METHODS

Fifty-nine male Sprague-Dawley rats were randomly divided into EtOH, EtOH-TBI and control groups (water group, water-TBI group). To establish chronic alcoholic rats, rats were intragastrically given edible spirituous liquor twice daily. Rats also received a blow on the occipital tuberosity with an iron pendulum. Morphological changes and expression of tau and β-APP proteins in the medulla oblongata were examined.

RESULTS

(a) Nerve fibre thickening and twisting were observed in alcoholic rats, with nerve fibre changes becoming more significant following a concussion blow, which leads to some nerve fibres fracturing. (b) Transmission electron microscopy revealed that the nerve fibre myelin became loosened and displayed lamellar separation, which became more significant following concussion. (c) The integral optical density (IOD) sum value of β-APP of the EtOH-TBI group was lower than that in the EtOH group (P < 0.05); the Tau IOD sum value of the EtOH-TBI group was higher than that in the EtOH group (P < 0.05).

CONCLUSION

(a) Chronic alcoholism caused nerve fibre and neuronal morphology damage in the rat medulla oblongata, with structural damage becoming more significant following concussion. (b) Concussion changed the expression of β-APP and tau protein in chronic alcoholic rat medulla oblongata, suggesting that chronic alcoholism can lead to severe axonal injury following a concussion blow. (c) The effect of chronic alcoholism may be synergistic the concussion blow to promote animal injury and death.

Glutamate requires NMDA receptors to modulate alpha2 adrenoceptor in medulla oblongata cultured cells of newborn rats

α2 Adrenoceptors (α2-ARs) are important in regulating the central control of blood pressure in medulla oblongata. However, it is unclear how this receptor is modulated by different receptors, especially the glutamatergic. In the present study, we studied the influence of ionotropic glutamatergic receptors over the α2-ARs in cultured cells of the medulla oblongata of newborn rats. For this purpose, the protein level of the α2-ARs was assessed after administration to the cultured cells of glutamate (glu), the agonists NMDA and kainate (KA), the NMDA receptor antagonist MK801 and the KA receptor antagonist DNQX. Results indicate that the α2-AR protein levels were increased after the treatments with glu and NMDA, and the addition of MK801 to this treatment thwarted this increase. Notwithstanding the fact that KA did not alter the receptor protein level, the combined treatment of DNQX with glu prevented the α2-AR protein modulation. In conclusion, the present study suggests that ionotropic glutamatergic receptors could be related to the α2-AR protein regulation in the medulla oblongata.