Microinjection Of GABA Research Articles

A regulatory role of the medial septum in the chloroquine-induced acute itch through local GABAergic system and GABAergic pathway to the anterior cingulate cortex

Itch, a common somatic sensation, serves as a crucial protective system. Recent studies have unraveled the neural mechanisms of itch at peripheral, spinal cord as well as cerebral levels. However, a comprehensive understanding of the central mechanism governing itch transmission and regulation remains elusive. Here, we report the role of the medial septum (MS), an integral component of the basal forebrain, in modulating the acute itch processing. The increases in c-Fos+ neurons and calcium signals within the MS during acute itch processing were observed. Pharmacogenetic activation manipulation of global MS neurons suppressed the scratching behaviors induced by chloroquine or compound 48/80. Microinjection of GABA into the MS or pharmacogenetic inhibition of non-GABAergic neurons markedly suppressed chloroquine-induced scratching behaviors. Pharmacogenetic activation of the MS-ACC GABAergic pathway attenuated chloroquine-induced acute itch. Hence, our findings reveal that MS has a regulatory role in the chloroquine-induced acute itch through local increased GABA to inhibit non-GABAergic neurons and the activation of MS-ACC GABAergic pathway.

Withdrawal Notice: The Role of the Central Histaminergic System in Emergence from Propofol Anesthesia

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Intracerebroventricular streptozotocin-induced Alzheimer's disease-like sleep disorders in rats: Role of the GABAergic system in the parabrachial complex.

Sleep disorders are common in Alzheimer's disease (AD) and assumed to directly influence cognitive function and disease progression. This study evaluated sleep characteristics in a rat model of AD that was induced by intracerebroventricular streptozotocin (STZ) administration and assessed the possible underlying mechanisms. Cognition ability was assessed in the Morris water maze in rats. Sleep parameters were analyzed by electroencephalographic and electromyographic recordings. Neuronal activity in brain areas that regulate sleep-wake states was evaluated by double-staining immunohistochemistry. High-performance liquid chromatography with electrochemical detection was used to detect neurotransmitter levels. Fourteen days after the STZ injection, the rats exhibited sleep disorders that were similar to those in AD patients, reflected by a significant increase in wakefulness and decreases in nonrapid eye movement (NREM) sleep and rapid eye movement (REM) sleep. The c-Fos expression analysis indicated that neuronal activity and the number of neurons in the dorsal raphe nucleus and locus coeruleus decreased in STZ-injected rats. In the ventrolateral preoptic nucleus (VLPO), the activity of γ-aminobutyric acid (GABA) neurons was suppressed. In the arousal-driving parabrachial nucleus (PBN), GABAergic activity was suppressed, whereas glutamatergic activity was promoted. The neurotransmitter analysis revealed a reduction in GABA in the VLPO and PBN and elevation of glutamate in the PBN. A direct injection of the GABAA receptor antagonist bicuculline in the PBN in normal rats induced a similar pattern of sleep disorder as in STZ-injected rats. A microinjection of GABA in the PBN improved sleep disorders that were induced by STZ. These results suggest that the reduction in GABAergic inhibition in the PBN and VLPO may be involved in sleep disorders that are induced by STZ. Our novel findings encourage further studies that investigate mechanisms of sleep regulation in sporadic AD.

GABA-ergic neurotransmission in the nucleus of the solitary tract modulates cough in the cat

GABA, muscimol, and baclofen were microinjected into the rostral (rNTS) and caudal solitary tract nucleus (cNTS) in 24 anesthetized cats. Electromyograms (EMGs) of diaphragm (DIA) and abdominal muscles (ABD), blood pressure and esophageal pressure (EP) were recorded and analysed. Bilateral microinjections of 1 mM GABA (total 66 ± 4 nl), 1 mM baclofen (64 ± 4 nl) and unilateral microinjections of 0.5 mM muscimol (33 ± 1 nl) in the rNTS significantly reduced cough number (CN), amplitudes of ABD EMGs, expiratory EP, and prolonged the duration of the cough inspiratory phase. GABA microinjections decreased the amplitudes of cough-related DIA EMGs and inspiratory EP; muscimol microinjections decreased the cough DIA EMG on the contralateral side. Only microinjections of GABA into the cNTS suppressed CN. In some cases, microinjections prolonged the inspiratory phase, lowered respiratory rate, changed the depth of breathing, and increased blood pressure and heart rate. Our results confirm that GABA-ergic inhibitory mechanisms in the rNTS can regulate coughing in the anesthetized cat.

Effects of GABA microinjection into dorsal raphe nucleus on behavior and activity of lateral habenular neurons in mice

The dorsal raphe nucleus (DRN) is a key site for 5-hydroxytryptamine (5-HT) synthesis and release. DRN dysfunction has been implicated in several stress-related disorders, including depression and anxiety. The lateral habenular nucleus (LHb) has been shown to inhibit the activity of DRN 5-HT neurons, and thus the LHb-DRN pathway plays an important role in the pathogenesis of depression. Although it is known that the LHb also receives the projection from the 5-HT neuron in the DRN, whether 5-HT neurons in the DRN can influence activity of the LHb in vivo and whether this effect is related to the induced behavioral changes have not been investigated. In the current study, we determined how injecting γ-aminobutyric acid (GABA) into the DRN to inhibit 5-HT neurons affected behavior and the changes in the activity of LHb neurons in mice. We found that GABA injection into the DRN induced depression-like behavior in mice, as indicated by increased immobility time, and decreased climbing time in the forced swimming test and the tail suspension test, decreased time spent in the center and total distance moved in the open field test. Using extracellular single unit recording, we showed that the firing rate of LHb neurons decreased after GABA microinjection into the DRN. Further, c-Fos expression in LHb neurons was inhibited. Together our results indicate that inhibition of DRN 5-HT neurons can cause decreased LHb activity and depression-like behavior in mice, however this depression-like behavior could be independent of the LHb activity. The observed decrease in LHb activity is probably due to the presence of a negative feedback loop between the DRN and the LHb, which may play a role in maintaining emotional homeostasis.

Neuropeptide glutamic acid-isoleucine (NEI)-induced paradoxical sleep in rats

Neuropeptideglutamic acid-isoleucine (NEI) as well as melanin concentrating hormone (MCH) is cleaved from the 165 amino acid protein, prepro-melanin concentrating hormone (prepro-MCH). Among many physiological roles of MCH, we demonstrated that intracerebroventricular (icv) injection of MCH induced increases in REM sleep episodes as well as in non REM sleep episodes. However, there are no studies on the effect of NEI on the sleep-wake cycle. As for the sites of action of MCH for induction of REM sleep, the ventrolateral periaqueductal gray (vlPAG) has been reported to be one of its site of action. Although MCH neurons contain NEI, GABA, MCH, and other neuropeptides, we do not know which transmitter(s) might induce REM sleep by acting on the vlPAG. Thus, we first examined the effect of icv injection of NEI on the sleep-wake cycle, and investigated how microinjection of either NEI, MCH, or GABA into the vlPAG affected REM sleep in rats. Icv injection of NEI (0.61μg/5μl: n=7) significantly increased the time spent in REM episodes compared to control (saline: 5μl; n=6). Microinjection of either NEI (61ng/0.2μl: n=7), MCH (100ng/0.2μl: n=6) or GABA (250mM/0.2μl: n=7) into the vlPAG significantly increased the time spent in REM episodes and the AUC. Precise hourly analysis of REM sleep also revealed that after those microinjections, NEI and MCH increased REM episodes at the latter phase, compared to GABA which increased REM episodes at the earlier phase. This result suggests that NEI and MCH may induce sustained REM sleep, while GABA may initiate REM sleep. In conclusion, our findings demonstrate that NEI, a cleaved peptide from the same precursor, prepro-MCH, as MCH, induce REM sleep at least in part through acting on the vlPAG.

Interactions between hypocretinergic and GABAergic systems in the control of activity of neurons in the cat pontine reticular formation

Anatomical studies have demonstrated that hypocretinergic and GABAergic neurons innervate cells in the nucleus pontis oralis (NPO), a nucleus responsible for the generation of active (rapid eye movement (REM)) sleep (AS) and wakefulness (W). Behavioral and electrophysiological studies have shown that hypocretinergic and GABAergic processes in the NPO are involved in the generation of AS as well as W. An increase in hypocretin in the NPO is associated with both AS and W, whereas GABA levels in the NPO are elevated during W. We therefore examined the manner in which GABA modulates NPO neuronal responses to hypocretin. We hypothesized that interactions between the hypocretinergic and GABAergic systems in the NPO play an important role in determining the occurrence of AS or W. To determine the veracity of this hypothesis, we examined the effects of the juxtacellular application of hypocretin-1 and GABA on the activity of NPO neurons, which were recorded intracellularly, in chloralose-anesthetized cats. The juxtacellular application of hypocretin-1 significantly increased the mean amplitude of spontaneous EPSPs and the frequency of discharge of NPO neurons; in contrast, the juxtacellular microinjection of GABA produced the opposite effects, i.e., there was a significant reduction in the mean amplitude of spontaneous EPSPs and a decrease in the discharge of these cells. When hypocretin-1 and GABA were applied simultaneously, the inhibitory effect of GABA on the activity of NPO neurons was reduced or completely blocked. In addition, hypocretin-1 also blocked GABAergic inhibition of EPSPs evoked by stimulation of the laterodorsal tegmental nucleus. These data indicate that hypocretin and GABA function within the context of a neuronal gate that controls the activity of AS-on neurons. Therefore, we suggest that the occurrence of either AS or W depends upon interactions between hypocretinergic and GABAergic processes as well as inputs from other sites that project to AS-on neurons in the NPO.

Hypoxia-induced hypothermia mediated by GABA in the rostral parapyramidal area of the medulla oblongata

Hypoxia evokes a regulated decrease in the body core temperature (Tc) in a variety of animals. The neuronal mechanisms of this response include, at least in part, glutamatergic activation in the lateral preoptic area (LPO) of the hypothalamus. As the sympathetic premotor neurons in the medulla oblongata constitute a cardinal relay station in the descending neuronal pathway from the hypothalamus for thermoregulation, their inhibition can also be critically involved in the mechanisms of the hypoxia-induced hypothermia. Here, I examined the hypothesis that hypoxia-induced hypothermia is mediated by glutamate-responsive neurons in the LPO that activate GABAergic transmission in the rostral raphe pallidus (rRPa) and neighboring parapyramidal region (PPy) of the medulla oblongata in urethane–chloralose-anesthetized, neuromuscularly blocked, artificially ventilated rats. Unilateral microinjection of GABA (15nmol) into the rRPa and PPy regions elicited a prompt increase in tail skin temperature (Ts) and decreases in Tc, oxygen consumption rate (VO2), and heart rate. Next, when the GABAA receptor blocker bicuculline methiodide (bicuculline methiodide (BMI), 10pmol) alone was microinjected into the rRPa, it elicited unexpected contradictory responses: simultaneous increases in Ts, VO2 and heart rate and a decrease in Tc. Then, when BMI was microinjected bilaterally into the PPy, no direct effect on Ts was seen; and thermogenic and tachycardic responses were slight. However, pretreatment of the PPy with BMI, but not vehicle saline, greatly attenuated the hypothermic responses evoked by hypoxic (10%O2–90%N2, 5min) ventilation or bilateral microinjections of glutamate (5nmol, each side) into the LPO. The results suggest that hypoxia-induced hypothermia was mediated, at least in part, by the activation of GABAA receptors in the PPy.

Dorsal hippocampus histaminergic and septum GABAergic neurons work in anxiety related behavior: Comparison between GABAA and GABAB receptors

Background: Integration of septum and hippocampus has an important role in anxiety modulation and inhibition. Our previous studies indicated that GABAergic system blockade in the medial septum (MS) attenuates anxiety-like behavior. Herein, we aimed to investigate the histaminergic and GABAergic associations between dorsal hippocampus and MS, respectively. Moreover, the present study compares the power of two kinds GABA receptors, GABA A and GABA B receptors, in MS in anxiety related behavior of male rats. Methods: In the present study we investigated the intrahippocampal CA1 (intra-CA1) microinjection of histamine and intra-septal GABAergic agents on anxiety-related behavior in rats, using elevated plus-maze test of anxiety. Results: Intra-CA1 administration of histamine increased open arm time (%OAT) and open arm entry (%OAE). Intra-septal administration of the GABA A agonist muscimol (10 ng/rat) increased %OAE and %OAT but not locomotor activity. Administration of muscimol (2.5 and 5 ng/rat) had no effect on anxiety, while co-administration of sub-effective dose of histamine (1 µg/rat) into CA1 and sub-effective dose of muscimol (2.5ng/rat) into medial septum area increased %OAE and %OAT. Administration of GABA A receptor antagonist confirmed GABA A function in the medial septum. In contrast, injection of GABA B receptor agonist decreased OAT and OAE percentage. Microinjection of GABA B receptor antagonist revealed that this GABA receptor increased the anxiety in the rats by a different mechanism. Conclusion: The effect of histamine on anxiety in CA1 may be modulating through septal GABAergic system and GABA A receptor is involved in the process

Respiratory Reactions to Microinjection of GABA and Baclofen into the Betzinger and Pre-Betzinger Complexes in Rats

Acute experiments on anesthetized rats were performed to study changes in the pattern of respiration after microinjections of GABA (10–5 M) and baclofen (10–6 M) solutions into the Betzinger (BC) and pre-Betzinger (PBC) complexes. Acting at the level of the BC, GABA was found to decrease inspiration time and increase expiration time, producing a slight reduction in respiratory rate; respiratory volume and pulmonary ventilation increased. Injections of GABA into the PBC had marked inhibitory effects on the respiratory rhythm, with prolongation of inspiration and expiration and a decrease in respiratory volume. Injection of the specific GABAB receptor agonist baclofen into the BC decreased the duration inspiration and respiratory volume but increased respiratory frequency, while injection of baclofen into the PBC had essentially no effect on the duration of inspiration or respiratory frequency, while volume parameters increased. These reactions provide evidence of different contributions of GABAergic mechanisms, including GABAB receptors, in the BC and PBC to controlling the rhythm and volume parameters of respiration.

Features of GABAergic Cardiovascular Control Provided by Medullary Neurons in Rats

In acute experiments on rats anesthetized with urethane, features of the involvement of GABA in medullary cardiovascular control were studied. It was found that microinjections of GABA (10–8 or 10–10 M) into the medullary nuclei (paramedian reticular nucleus, PMn, lateral reticular nucleus, LRN, and nucl. ambiguous, AMB) were accompanied by the development of either hypo- or hypertensive responses in a dose-dependent manner. There were some differences in the structure of GABA-induced hemodynamic responses. In particular, the cardiac and vascular components contributed about equally to the development of the hypotensive responses caused by GABA injections into the PMn (with significant inhibition of the heart’s chronotropic function). However, GABA-induced hypotensive responses evoked from the LRN were mainly based on the vascular component, with the a less pronounced cardiac component. GABA injections into the AMB resulted in significant decreases in the diastolic blood pressure and the heart rate. As for GABA-induced hypertensive responses originated from PMn and LRN neurons, the vascular component was predominant in their development, and chronotropic effects on the cardiac function were less pronounced. Injections of bicuculline (10–7 M), a competitive antagonist of GABAA receptors, into the medullary nuclei under investigation were accompanied by increases in both the systolic and diastolic blood pressure and heart rate. Therefore, bicuculline-sensitive GABAA receptors are involved in GABA-induced hypotensive effects. After inhibition of neuronal NO synthase, injections of GABA into the medullary nuclei did not cause the development of hypotensive responses, and GABA-induced hypertensive responses were weakened, indicating the possibility for GABA interaction with nitric oxide in nervous control of the cardiovascular system. It was also found that the effects of GABA injected into the medullary nuclei depended on the activity of Na+,K+-ATPase, the enzyme of the plasma membrane of cardiovascular neurons.

Endogenous descending facilitation and inhibition differ in control of formalin intramuscularly induced persistent muscle nociception

In conscious rats, intramuscular injection of 2.5% formalin into the gastrocnemius muscle, at volumes between 25 and 200μl, evoked dose-dependent biphasic persistent flinching activities: phase 1 (0–10min) and phase 2 (10–60min). During this intramuscular formalin-induced ipsilateral muscle nociception, bilateral secondary mechanical hyperalgesia and heat hypoalgesia assessed by measuring thresholds of paw withdrawal reflex to noxious mechanical and heat stimuli were observed (P<0.05). Lesion of either the ipsilateral dorsal funiculus (DF) or contralateral thalamic mediodorsal (MD) nucleus significantly alleviated the formalin-induced flinches in both phase 1 and phase 2 of the behavioral response, and blocked the occurrence of secondary mechanical hyperalgesia, but not heat hypoalgesia. By contrast, lesion of the ipsilateral dorsal lateral funiculus (DLF) or contralateral thalamic ventromedial (VM) nucleus markedly enhanced the formalin induced flinching behavior in the late part (30–60min) of phase 2 alone; phase 1 and early part (10–30min) of phase 2 response were unaffected. Heat hypoalgesia, but not mechanical hyperalgesia, was markedly attenuated by this treatment (P<0.05). Microinjection of GABA (0.1μg/0.5μl) into the thalamic MD nucleus significantly depressed the intramuscular formalin-induced biphasic persistent nociception, and the occurrence of bilateral secondary mechanical hyperalgesia was significantly delayed (P<0.05). By contrast, microinjection of GABA into the thalamic VM nucleus significantly enhanced the formalin-induced nociceptive behavior in the late part (30–60min) of phase 2, and the bilateral secondary heat hypoalgesia was temporarily prevented (P<0.05). The present study demonstrates that intramuscular formalin evokes biphasic muscle nociception, and that bilateral secondary mechanical hyperalgesia and heat hypoalgesia are differentially controlled by endogenous descending facilitation and inhibition respectively. It is further suggested that thalamic MD nucleus and VM nucleus constitute an endogenous discriminative, modulatory system that exerts, via pathways in the DF and DLF, descending facilitatory and inhibitory actions on responses to peripheral afferent activity evoked by noxious mechanical and heat stimulation.

Muscimol microinjection into cerebellar fastigial nucleus exacerbates stress-induced gastric mucosal damage in rats

To investigate the effects of microinjection of the GABA(A) receptor agonist muscimol into cerebellar fastigial nucleus (FN) on stress-induced gastric mucosal damage and the underlying mechanism in rats. Stress-induced gastric mucosal damage was induced in adult male SD rats by restraining and immersing them in cold water for 3 h. GABA(A) receptor agonist or antagonist was microinjected into the lateral FN. The decussation of superior cerebellar peduncle (DSCP) was electrically destroyed and the lateral hypothalamic area (LHA) was chemically ablated by microinjection of kainic acid. The pathological changes in the gastric mucosa were evaluated using TUNEL staining, immunohistochemistry staining and Western blotting. Microinjection of muscimol (1.25, 2.5, and 5.0 μg) into FN significantly exacerbated the stress-induced gastric mucosal damage in a dose-dependent manner, whereas microinjection of GABA(A) receptor antagonist bicuculline attenuated the damage. The intensifying effect of muscimol on gastric mucosal damage was abolished by electrical lesion of DSCP or chemical ablation of LHA performed 3 d before microinjection of muscimol. Microinjection of muscimol markedly increased the discharge frequency of the greater splanchnic nerve, significantly increased the gastric acid volume and acidity, and further reduced the gastric mucosal blood flow. In the gastric mucosa, further reduced proliferation cells, enhanced apoptosis, and decreased anti-oxidant levels were observed following microinjection of muscimol. Cerebellar FN participates in the regulation of stress-induced gastric mucosal damage, and cerebello-hypothalamic circuits contribute to the process.

Thermoregulatory responses elicited by microinjection of l-glutamate and its interaction with thermogenic effects of GABA and prostaglandin E2 in the preoptic area

The aim of the present study was to investigate the thermoregulatory effects of neuronal activation with sodium l-glutamate (glutamate) in the preoptic area (POA) of the hypothalamus and to examine its possible interaction with the thermogenic effects of GABA and prostaglandin E2 (PGE2). Unilateral microinjection of glutamate (5nmol) into the lateral POA or its vicinity elicited a prompt increase in tail skin temperature and simultaneous decreases in the O2 consumption rate (VO2), heart rate, and colonic temperature in urethane–chloralose-anesthetized rats. A central subpopulation of these sites at around the level of bregma was also responsive to the thermogenic and tachycardic effects of GABA (30nmol). Although the microinjection of GABA into nearby sites elicited no direct effect, it greatly attenuated the hypothermic effects of glutamate subsequently administered to the same site. These results suggest that activation of the lateral POA elicited heat-loss responses and that its central part provided a tonic inhibitory drive toward heat production and tail vasoconstriction. On the other hand, the microinjection of glutamate elicited initial small decreases and subsequent large increases in VO2 and heart rate in the rostromedial POA. However, no thermoregulatory response was elicited by the microinjection of glutamate at sites where the microinjection of PGE2 (35fmol) elicited thermogenic, tachycardic and hyperthermic responses. These results may suggest that the rostromedial POA contained two glutamate-responsive cell groups that had opposite influences on thermoregulation and that the locus that was highly sensitive to the thermogenic effect of PGE2 was unreactive to glutamate. Collectively, activation of neurons in the lateral POA and rostromedial POA evoked distinct thermoregulatory responses.

Respiratory Response to Microinjections of GABA and Penicillin into Various Parts of the Ventral Respiratory Group

Experiments on rats showed that local injection of GABA (10(-4) M) into the rostral and caudal compartments of the ventral respiratory groups decreased the respiratory rhythm, but increased lung ventilation (especially injection into the rostral part). Penicillin (10(-7) M) injected into the rostral division increased the tidal volume and practically did not change the respiratory rate, but its injection into the caudal part reduced the tidal volume and increased respiratory rate. These results indicate that GABAergic mechanisms including GABA(A) sites play an ambiguous role in the regulation of respiration at the level of the rostral and caudal parts of the ventral respiratory group.

Role for ventral pallidal GABAergic mechanisms in the regulation of ethanol self-administration

The striatopallidal medium spiny neurons have been viewed as a final common path for drug reward, and the ventral pallidum (VP) as a convergent point for hedonic and motivational signaling. The medium spiny neurons are GABAergic, but they colocalize enkephalin. The present study investigated the role of the GABAergic mechanisms of the VP in ethanol consumption. The effects of bilateral microinjections of GABA(A) and GABA(B) receptor agonists and antagonists into the VP on voluntary ethanol consumption were monitored in alcohol-preferring Alko alcohol rats given 90 min limited access to ethanol in their home cages every other day. The influences of coadministration of GABA and opioid receptor modulators were also studied. The GABA(A) receptor agonist muscimol (1-10 ng/site) decreased ethanol intake dose-dependently, while administration of the GABA(A) receptor antagonist bicuculline (10-100 ng) had an opposite effect. The GABA(B) receptor agonist baclofen (3-30 ng) also suppressed ethanol intake, but the GABA(B) receptor antagonist saclofen (0.3-3 μg) failed to modify it. Animals coadministered with bicuculline (30 ng) and baclofen (30 ng) consumed ethanol significantly less than those treated with bicuculline alone. Coadministration of the μ-receptor agonist D-Ala2,N-Me-Phe4,Glyol5-enkephalin (DAMGO, 0.1 μg) with bicuculline counteracted, whereas the μ-receptor antagonist D-Phe-Cys-Tyr-D-Trp-Orn-Thr-Pen-Thr-NH2 (CTOP, 1 μg) enhanced the bicuculline-induced increase of ethanol intake. When given alone, DAMGO decreased while CTOP increased ethanol intake. The study provides evidence for the ventral pallidal GABAergic mechanisms participating in the regulation of ethanol consumption and supports earlier work suggesting a role for pallidal opioidergic transmission in ethanol reward.

The effect of physical (in)activity on blood pressure and splanchnic sympathetic nerve responses to inhibition of the RVLM

A sedentary lifestyle is a major risk factor for cardiovascular disease (CVD). CVD is often associated with enhanced activation of the sympathetic nervous system. The sympathetic nervous system is under tonic and phasic control by the rostral ventrolateral medulla (RVLM). In sedentary rats, there is enhanced sympathoexcitation in response to glutamatergic activation of the RVLM. Since the activity of RVLM is tonically restrained by γ‐amino‐butyric acid (GABA), we hypothesized that sedentary conditions may also lead to decreased responsiveness to GABA in RVLM when compared to physically active conditions. In Inactin anesthetized, sedentary (SED) or physically active (EX) rats, mean arterial pressure (MAP), heart rate (HR) and splanchnic sympathetic nerve activity (sSNA) were recorded during unilateral microinjection of GABA (30 nl, 0.3–600 mM) into the RVLM. Following GABA injections, the contralateral RVLM was inhibited with 90 nl of 2mM Muscimol and the GABA injections were repeated. There were no significant differences between SED or EX conditions for MAP, HR and sSNA responses to GABA both before and after contralateral blockade of the RVLM. Based on our results the enhanced sympathoexcitation seen in our sedentary model is not due to reduced responsiveness to GABA and may be due to enhanced responsiveness to excitatory neurotransmission. (Supported by R01‐HL096787; R01‐HL096787‐S1)

Modulation of Inhibitory Synaptic Transmission in the Cat Motor Cortex Related to Realization of an Operant Reflex Evoked by a Complex of Stimuli

In non-anesthetized cats, we examined the effects of iontophoretic microinjections of GABA, a blocker of GABAergic synaptic transmission, and modulators of noradrenergic transmission on impulse activity (IA) generated by motor cortex neurons in the course of realization of an operant motor reflex to the action of a complex of stimuli (warning and imperative ones). We tried to elucidate the role of different membrane receptors in modulation of spiking of cortical neurons. Microiontophoretic applications of GABA and noradrenaline resulted in decreases in the frequency of background IA of cortical neurons and suppression of their reactions related to realization of the operant reflex. The use of selective adrenoactive substances showed that applications of an α1 agonist, Mezaton, suppressed background spiking and impulsation generated within an interspike interval and in the course of the movement. An α2 blocker, yohimbine, exerted an opposite effect; the neuronal IA was intensified within the background period and other examined time intervals. There are reasons to believe that noradrenergic modulation of IA of cortical neurons is realized via direct effects on pyramidal neurons and also indirectly, through changes in the activity of inhibitory cortical interneurons.

Role of medullary GABA signal transduction on parasympathetic reflex vasodilatation in the lower lip

In the orofacial area, noxious stimulation of the orofacial structure in the trigeminal region evokes parasympathetic reflex vasodilatation, which occurs via the trigeminal spinal nucleus (Vsp) and the inferior/superior salivatory nucleus (ISN/SSN). However, the neurotransmitter involved in the inhibitory synaptic inputs within these nuclei has never been described. This parasympathetic reflex vasodilatation is suppressed by GABAergic action of volatile anesthetics, such as isoflurane, sevoflurane, and halothane, suggesting that medullary GABAergic mechanism exerts its inhibitory effect on the parasympathetic reflex via an activation of GABA receptors. The aim of the present study was to determine the role of GABAA and GABAB receptors in the Vsp and the ISN in regulating the lingual nerve (LN)-evoked parasympathetic reflex vasodilatation in the lower lip. Under urethane anesthesia (1g/kg), change in lower lip blood flow elicited by electrical stimulation of the LN was recorded in cervically vago-sympathectomized rats. Microinjection of GABA (10μM; 0.3μl/site) into the Vsp or the ISN significantly and reversibly attenuated the LN-evoked parasympathetic reflex vasodilatation. Microinjection of the GABAA receptor-selective agonist muscimol (100μM; 0.3μl/site) or the GABAB receptor-selective agonist baclofen (100μM; 0.3μl/site) into the Vsp or the ISN significantly and irreversibly reduced this reflex vasodilatation, and these effects were attenuated by pretreatment with microinjection of each receptor-selective antagonists [GABAA receptor selective antagonist bicuculline methiodide (1mM; 0.3μl/site) or GABAB receptor selective antagonist CGP-35348 (1mM; 0.3μl/site)] into the Vsp or the ISN. Microinjection of these antagonists alone into the Vsp or the ISN had no significant effect on this reflex vasodilatation. In addition, microinjection (0.3μl/site) of the mixture of muscimol (100μM) and baclofen (100μM) into the Vsp or the ISN also significantly reduced this reflex vasodilatation. These results suggest that medullary GABA signal transduction inhibits the parasympathetic reflex vasodilatation in the rat lower lip via GABAA and GABAB receptors in the Vsp and the ISN.

Altered regulation of the rostral ventrolateral medulla in hypertensive obese Zucker rats

Obese Zucker rats (OZR) have elevated sympathetic nerve activity (SNA) and mean arterial pressure (MAP) compared with lean Zucker rats (LZR). We examined whether altered tonic glutamatergic, angiotensinergic, or GABAergic inputs to the rostral ventrolateral medulla (RVLM) contribute to elevated SNA and MAP in OZR. Male rats (14-18 wk) were anesthetized with urethane (1.5 g/kg iv), ventilated, and paralyzed to record splanchnic SNA, heart rate (HR), and MAP. Inhibition of the RVLM by microinjections of muscimol eliminated SNA and evoked greater decreases in MAP in OZR vs. LZR (P < 0.05). Antagonism of angiotensin AT(1) receptors in RVLM with losartan yielded modest decreases in SNA and MAP in OZR but not LZR (P < 0.05). However, antagonism of ionotropic glutamate receptors in RVLM with kynurenate produced comparable decreases in SNA, HR, and MAP in OZR and LZR. Antagonism of GABA(A) receptors in RVLM with gabazine evoked smaller rises in SNA, HR, and MAP in OZR vs. LZR (P < 0.05), whereas responses to microinjections of GABA into RVLM were comparable. Inhibition of the caudal ventrolateral medulla, a major source of GABA to the RVLM, evoked attenuated rises in SNA and HR in OZR (P <0.05). Likewise, inhibition of nucleus tractus solitarius, the major excitatory input to caudal ventrolateral medulla, produced smaller rises in SNA and HR in OZR. These results suggest the elevated SNA and MAP in OZR is derived from the RVLM and that enhanced angiotensinergic activation and reduced GABAergic inhibition of the RVLM may contribute to the elevated SNA and MAP in the OZR.