Effects Of Bicuculline Research Articles

ANXIOLYTIC ACTION OF OROSTACHYS SPINOSA DRY EXTRACT

The study purpose: to evaluate the anxiolytic effect of the Orostachys spinosa dry extract. Material and methods. The studies were carried out on Wistar rats. An aqueous solution of the O. spinosa extract at doses of 50, 100 and 200 mg/kg was administered to the experimental groups animals for 14 days prior to testing. The anxiolytic effect of the O. spinosa extract was evaluated in the tests: "open field", "elevated plus maze", "light/dark chamber", "unmotivated aggression" and "conflict situation" according to Vogel. Results. It was found that the O. spinosa extract at doses of 100 and 200 mg/kg increases the vertical, horizontal activity and the index of the mink reflex in the "open field"; the entries number and the time into the open arms in the elevated plus maze; the transitions number and the time spent in the light section in the "light/dark chamber". Under conditions of "punishable behavior", the O. spinosa extract at a dose of 100 mg/kg exhibits anti-aggressive and anxiolytic effects. The studied extract reduces the anxiogenic effects of bicuculline and picrotoxin in the Vogel test. Conclusion. The O. spinosa dry extract has an anxiolytic effect, which is due to its stimulating effect on the GABAergic system.

Synergistic effects of bicuculline combined with early running on the recovery of brain injury in rats

目的: 评估γ-氨基丁酸(GABA)受体拮抗剂荷包牡丹碱联合早期跑步运动对大鼠脑损伤后运动功能恢复协同效应。方法: Wistar大鼠随机分为Sham组、缺血/再灌注(I/R)组、荷包牡丹碱+I/R组、运动+I/R组和荷包牡丹碱+运动+I/R组(联合处理组),每组10只大鼠。除Sham组外,其余大鼠均行大脑中动脉阻塞(MCAO)诱导I/R。I/R 2 d后,荷包牡丹碱+I/R组和联合处理组大鼠腹腔注射荷包牡丹碱,连续注射5 d;运动+I/R组和联合处理组大鼠在跑步机上连续跑5 d,每次30 min。I/R 7 d后,采用旋转杆试验和错步试验评估各组大鼠运动功能;采用TTC方法评估各组大鼠脑梗死体积;采用ELISA及Western blot方法检测各组大鼠大脑皮层和脊髓中脑源性神经营养因子(BDNF)、GAP-43、突触素和Nogo-A蛋白表达。结果: 与Sham组相比,I/R组大鼠运动功能受损,脑梗死体积增加(所有P＜0.05);与I/R组相比,荷包牡丹碱+I/R组、运动+I/R组和联合处理组大鼠运动功能改善,脑梗死体积减少(所有P＜0.05),而且联合处理组大鼠运动功能改善和脑梗死体积减少优于其他两组(P均＜0.05)。与I/R组相比,荷包牡丹碱+I/R组、运动+I/R组和联合处理组大鼠大脑皮层和脊髓BDNF蛋白表达增加(P均＜0.05);荷包牡丹碱+I/R组和联合处理组大鼠脊髓突触素和GAP-43蛋白表达增加(P均＜0.05)。此外,联合处理组大鼠脊髓Nogo-A蛋白表达高于其他所有组(P均＜0.05)。结论: 荷包牡丹碱联合早期跑步运动可更有效促进脑损伤后运动功能恢复,可能与脊髓中轴突生长和抑制性修饰有关。.

Heterogeneous Responses to Changes in Inhibitory Synaptic Strength in Networks of Spiking Neurons.

How does the dynamics of neurons in a network respond to changes in synaptic weights? Answer to this question would be important for a full understanding of synaptic plasticity. In this article, we report our numerical study of the effects of changes in inhibitory synaptic weights on the spontaneous activity of networks of spiking neurons with conductance-based synapses. Networks with biologically realistic features, which were reconstructed from multi-electrode array recordings taken in a cortical neuronal culture, and their modifications were used in the simulations. The magnitudes of the synaptic weights of all the inhibitory connections are decreased by a uniform amount subjecting to the condition that inhibitory connections would not be turned into excitatory ones. Our simulation results reveal that the responses of the neurons are heterogeneous: while the firing rate of some neurons increases as expected, the firing rate of other neurons decreases or remains unchanged. The same results show that heterogeneous responses also occur for an enhancement of inhibition. This heterogeneity in the responses of neurons to changes in inhibitory synaptic strength suggests that activity-induced modification of synaptic strength does not necessarily generate a positive feedback loop on the dynamics of neurons connected in a network. Our results could be used to understand the effects of bicuculline on spiking and bursting activities of neuronal cultures. Using reconstructed networks with biologically realistic features enables us to identify a long-tailed distribution of average synaptic weights for outgoing links as a crucial feature in giving rise to bursting in neuronal networks and in determining the overall response of the whole network to changes in synaptic strength. For networks whose average synaptic weights for outgoing links have a long-tailed distribution, bursting is observed and the average firing rate of the whole network increases upon inhibition suppression or decreases upon inhibition enhancement. For networks whose average synaptic weights for outgoing links are approximately normally distributed, bursting is not found and the average firing rate of the whole network remains approximately constant upon changes in inhibitory synaptic strength.

Involvement of NMDA and GABA(A) receptors in modulation of spontaneous activity in hippocampal culture: Interrelations between burst firing and intracellular calcium signal

Spontaneous burst firing is a hallmark attributed to the neuronal network activity. It is known to be accompanied by intracellular calcium [Са2+]i oscillations within the bursting neurons. Studying mechanisms underlying regulation of burst firing is highly relevant, since impairment in neuronal bursting accompanies different neurological disorders. In the present study, the contribution of NMDA and GABA(A) receptors to the shape formation of spontaneous burst -was studied in cultured hippocampal neurons. A combination of inhibitory analysis with simultaneous registration of neuronal bursting by whole-cell patch clamp and calcium imaging was used to assess spontaneous burst firing and [Са2+]i level.Using bicuculline and D-AP5 we showed that GABA(A) and NMDA receptors effectively modulate burst plateau phase and [Са2+]i transient spike which can further affect action potential (AP) amplitudes and firing frequency within a burst. Bicuculline significantly elevated the amplitude and reduced the duration of both burst plateau phase and [Са2+]i spike resulting in an increase of AP firing frequency and shortening of AP amplitudes within a burst. D-AP5 significantly decreases the amplitude of both plateau phase and [Са2+]i spike along with a burst duration that correlated with an increase in AP amplitudes and reduced firing frequency within a burst. The effect of bicuculline was occluded by co-addition of D-AP5 revealing modulatory role of GABA(A) receptors to the NMDA receptor-mediated formation of the burst.Our results provide new evidence on importance of NMDA and GABA(A) receptors in shaping burst firing and Ca2+transient spikes in cultured hippocampal neurons.

Excitation-inhibition balance regulates the patterning of spinal and cranial inspiratory motor outputs in rats in situ

Spinal phrenic nerve activity (PNA) drives the diaphragm but cranial hypoglossal nerve activity (HNA) also expresses synchronous activity during inspiration. Here, we investigated the effects of local disinhibition (bilateral microinjections of bicuculline) of the nucleus tractus solitarius (NTS), the pre-Bötzinger complex and Bötzinger complex core circuit (pre-BötC/BötC) and the Kölliker-Fuse nuclei (KFn) on the synchronization of PNA and HNA in arterially-perfused brainstem preparations of rats. To quantitatively analyze the bicuculline effects on a putatively distributed inspiratory central pattern generator (i-CPG), we quantified the phase synchronization properties between PNA and HNA. The analysis revealed that bicuculline-evoked local disinhibition significantly reduced the strength of phase synchronization between PNA and HNA at any target site. However, the emergence of desynchronized HNA following disinhibition was more prevalent after NTS or pre-BötC/BötC microinjections compared to the KFn. We conclude that the primary i-CPG is located in a distributed medullary circuit whereas pontine contributions are restricted to synaptic gating of synchronous HNA and PNA.

Bicuculline Reduces Neuroinflammation in Hippocampus and Improves Spatial Learning and Anxiety in Hyperammonemic Rats. Role of Glutamate Receptors.

Patients with liver cirrhosis may develop minimal hepatic encephalopathy (MHE) with mild cognitive impairment. Hyperammonemia is a main contributor to cognitive impairment in MHE, which is mediated by neuroinflammation. GABAergic neurotransmission is altered in hyperammonemic rats. We hypothesized that, in hyperammonemic rats, (a) enhanced GABAergic tone would contribute to induce neuroinflammation, which would be improved by reducing GABAergic tone by chronic bicuculline treatment; (b) this would improve spatial learning and memory impairment; and (c) modulation of glutamatergic neurotransmission would mediate this cognitive improvement. The aim of this work was to assess the above hypotheses. Bicuculline was administrated intraperitoneally once a day for 4 weeks to control and hyperammonemic rats. The effects of bicuculline on microglia and astrocyte activation, IL-1β content, on membrane expression of AMPA and NMDA glutamate receptors subunits in the hippocampus and on spatial learning and memory as well as anxiety were assessed. Treatment with bicuculline reduces astrocyte activation and IL-1β but not microglia activation in the hippocampus of hyperammonemic rats. Bicuculline reverses the changes in membrane expression of AMPA receptor subunits GluA1 and GluA2 and of the NR2B (but not NR1 and NR2A) subunit of NMDA receptors. Bicuculline improves spatial learning and working memory and decreases anxiety in hyperammonemic rats. In hyperammonemia, enhanced activation of GABAA receptors in the hippocampus contributes to some but not all aspects of neuroinflammation, to altered glutamatergic neurotransmission and to impairment of spatial learning and memory as well as anxiety, all of which are reversed by reducing activation of GABAA receptors with bicuculline.

Synchrony changes on different time-scales during in vitro neuronal network development

Synchrony changes on different time-scales during in vitro neuronal network development

Panicolytic-like effects caused by substantia nigra pars reticulata pretreatment with low doses of endomorphin-1 and high doses of CTOP or the NOP receptors antagonist JTC-801 in male Rattus norvegicus.

Gamma-aminobutyric acid (GABA)ergic neurons of the substantia nigra pars reticulata (SNpr) are connected to the deep layers of the superior colliculus (dlSC). The dlSC, in turn, connect with the SNpr through opioid projections. Nociceptin/orphanin FQ peptide (N/OFQ) is a natural ligand of a Gi protein-coupled nociceptin receptor (ORL1; NOP) that is also found in the SNpr. Our hypothesis is that tectonigral opioid pathways and intranigral orphanin-mediated mechanisms modulate GABAergic nigrotectal connections. Therefore, the aim of this work was to study the role of opioid and NOP receptors in the SNpr during the modulation of defence reactions organised by the dlSC. The SNpr was pretreated with either opioid or NOP receptor agonists and antagonists, followed by dlSC treatment with bicuculline. Blockade of GABAA receptors in the dlSC elicited fear-related defensive behaviour. Pretreatment of the SNpr with naloxone benzoylhydrazone (NalBzoH), a μ-, δ-, and κ1-opioid receptor antagonist as well as a NOP receptor antagonist, decreased the aversive effect of bicuculline treatment on the dlSC. Either μ-opioid receptor activation or blockade by SNpr microinjection of endomorphin-1 (EM-1) and CTOP promoted pro-aversive and anti-aversive actions, respectively, that modulated the defensive responses elicited by bicuculline injection into the dlSC. Pretreatment of the SNpr with the selective NOP receptor antagonist JTC801 decreased the aversive effect of bicuculline, and microinjections of the selective NOP receptor agonist NNC 63-0532 promoted the opposite effect. These results demonstrate that opioid pathways and orphanin-mediated mechanisms have a critical role in modulating the activity of nigrotectal GABAergic pathways during the organisation of defensive behaviours.

Effects of chemical stimulation of the lateral wings of the dorsal raphe nucleus on panic-like defensive behaviors and Fos protein expression in rats

The lateral wings subnucleus of the dorsal raphe nucleus (lwDR) has been implicated in the modulation of panic-like behaviors, such as escape. Infusion of non- excitotoxic doses of the excitatory amino acid kainic acid into this subnucleus promptly evokes a vigorous escape response. In addition, rats exposed to panic-inducing situations show an increase in Fos protein expression in neurons within the lwDR. In the present study, we first investigated whether key structures associated with the mediation of escape behavior are recruited after chemical stimulation of the lwDR with kainic acid. We next investigated whether the infusion of the GABAA receptor antagonist bicuculline into the lwDR also evoked escape responses measured both in a circular arena and in the rat elevated T-maze. The effects of bicuculline in the circular arena were compared to those caused by the infusion of this antagonist into the ventrolateral periaqueductal gray (vlPAG), an area in close vicinity to the lwDR. The results showed that kainic acid infusion into the lwDR increased Fos protein immunostaining in brain structures deeply involved in panic-like defensive behaviors, such as the periaqueductal gray and hypothalamus, but not the amygdala. As observed with kainic acid, bicuculline evoked a pronounced escape response in the circular arena when microinjected in the lwDR, but not in the vlPAG. The escape-promoting effect of bicuculline in the lwDR was also evidenced in the elevated T-maze. These findings strength the view that dysfunction in mechanisms controlling escape in the lwDR is critically implicated in the pathophysiology of panic disorder.

CB1 cannabinoid receptor-mediated anandamide signalling reduces the defensive behaviour evoked through GABAA receptor blockade in the dorsomedial division of the ventromedial hypothalamus

The effects of cannabinoids in brain areas expressing cannabinoid receptors, such as hypothalamic nuclei, are not yet well known. Several studies have demonstrated the role of hypothalamic nuclei in the organisation of behavioural responses induced through innate fear and panic attacks. Panic-prone states are experimentally induced in laboratory animals through a reduction in the GABAergic activity. The aim of the present study was to examine panic-like elaborated defensive behaviour evoked by GABAA receptor blockade with bicuculline (BIC) in the dorsomedial division of the ventromedial hypothalamus (VMHdm). We also aimed to characterise the involvement of endocannabinoids and the CB1 cannabinoid receptor in the modulation of elaborated defence behavioural responses organised with the VMHdm. The guide-cannula was stereotaxicaly implanted in VMHdm and the animals were treated with anandamide (AEA) at different doses, and the effective dose was used after the pre-treatment with the CB1 receptor antagonist AM251, followed by GABAA receptor blockade in VMHdm. The results showed that the intra-hypothalamic administration of AEA at an intermediate dose (5 pmol) attenuated defence responses induced through the intra-VMHdm microinjection of bicuculline (40 ng). This effect, however, was inhibited when applied central microinjection of the CB1 receptor antagonist AM251 in the VMHdm. Moreover, AM251 potentiates de non-oriented escape induced by bicuculline, effect blocked by pre-treatment with the TRPV1 channel antagonist 6-I-CPS. These results indicate that AEA modulates the pro-aversive effects of intra-VMHdm-bicuculline treatment, recruiting CB1 cannabinoid receptors and the TRPV1 channel is involved in the AM251-related potentiation of bicuculline effects on non-oriented escape behaviour.

Exercise training (ET) in treadmill running reduces oxidative stress and inflammatory signaling of the commissural nucleus of the solitary tract (commNTS) and rostral ventrolateral medulla in rats

Renal sympathetic nerve activity (rSNA) at a low frequencyinfluences handling of sodium and water by the kidneys, without changing renal blood flow and glomerular filtration rate. Accordingly, we have previously demonstrated that renal nerve stimulation increases NHE3mediated sodium reabsorption due to an increased intrarenal reninangiotensin-system (RAS), independent of hemodynamic changes. In the present study, we evaluated how sympathoexcitation accompanied by blood pressure elevation would impact renal function and proximal tubule NHE3 regulation. To this end, we disinhibited the paraventricular nucleus of the hypothalamus (PVN) by microinjecting the antagonist GABA receptor bicuculline in anesthetized Wistar rats. We found that bicuculline injected unilaterallywithin the PVN caused a rapid increase in blood pressure compared with the baseline period (± 45%), which was accompanied by a great increase in urinary volume (more than 300%). This increase in urinary volumewas associatedwith an increase onNHE3 phosphorylation levels, suggesting that the diuretic effect of PVN disinhibition and blood pressure elevation are, at least in part, due to a decrease in NHE3 activity. Ongoing experiments from our laboratory are directed toward investigating the effects of bicuculline within the PVN in other apical sodium transporters along the renal tubule and evaluating the possible role of both systemic and intrarenal RAS in mediating these effects. Supported by CAPES, CNPq and FAPESP.

Exercise training (ET) in treadmill running reduces oxidative stress and inflammatory signaling of the commissural nucleus of the solitary tract (commNTS) and rostral ventrolateral medulla in rats

Renal sympathetic nerve activity (rSNA) at a low frequencyinfluences handling of sodium and water by the kidneys, without changing renal blood flow and glomerular filtration rate. Accordingly, we have previously demonstrated that renal nerve stimulation increases NHE3mediated sodium reabsorption due to an increased intrarenal reninangiotensin-system (RAS), independent of hemodynamic changes. In the present study, we evaluated how sympathoexcitation accompanied by blood pressure elevation would impact renal function and proximal tubule NHE3 regulation. To this end, we disinhibited the paraventricular nucleus of the hypothalamus (PVN) by microinjecting the antagonist GABA receptor bicuculline in anesthetized Wistar rats. We found that bicuculline injected unilaterallywithin the PVN caused a rapid increase in blood pressure compared with the baseline period (± 45%), which was accompanied by a great increase in urinary volume (more than 300%). This increase in urinary volumewas associatedwith an increase onNHE3 phosphorylation levels, suggesting that the diuretic effect of PVN disinhibition and blood pressure elevation are, at least in part, due to a decrease in NHE3 activity. Ongoing experiments from our laboratory are directed toward investigating the effects of bicuculline within the PVN in other apical sodium transporters along the renal tubule and evaluating the possible role of both systemic and intrarenal RAS in mediating these effects. Supported by CAPES, CNPq and FAPESP.

Dopamine directly modulates GABAA receptors.

Dopamine is a critical neuromodulator that activates GPCRs in mammals or ligand-gated ion channels in invertebrates. The present study demonstrates that dopamine (0.1-10 mm) exerts novel, opposing effects on different populations of mammalian (rat) GABAA receptors. Using whole-cell patch-clamp electrophysiology, we observed direct dopamine-mediated inhibition of tonic-level (1 μm) GABA-evoked currents in untransfected striatal neurons that could be recapitulated in HEK293 cells containing α1β3 or α1β2γ2 subunits. Surprisingly, direct activation by dopamine was seen in the absence of GABA with α1β2γ2, α5β3γ2, or α1β3γ2 transfections. This activity was also present in α1β3γ2 receptors containing a mutant β3 subunit (H267A [(Z)β3]) insensitive to trace levels of inhibitory Zn(2+). Dopamine activation required β and γ subunits but not α subunits ((Z)β3γ2 EC50 value, 660 μm). Dopamine activity was fully blocked by picrotoxin but not GABAA competitive antagonists, and was strongly correlated with spontaneous receptor activity. We also report opposing effects of bicuculline and gabazine, such that bicuculline surprisingly activated non-α-containing (β3γ2) GABAA receptors, whereas gabazine suppressed spontaneous activity in these receptors. Our results suggest that dopamine may directly inhibit GABAA receptors that are both immediately adjacent to dopamine release sites in the striatum and activated by tonic GABA. Furthermore, synaptic/phasic release of dopamine may directly enhance signaling at some spontaneously active noncanonical GABAA receptors that lack α subunits.

Progesterone Exerts a Neuromodulatory Effect on Turning Behavior of Hemiparkinsonian Male Rats: Expression of 3 α -Hydroxysteroid Oxidoreductase and Allopregnanolone as Suggestive of GABAA Receptors Involvement.

There is a growing amount of evidence for a neuroprotective role of progesterone and its neuroactive metabolite, allopregnanolone, in animal models of neurodegenerative diseases. By using a model of hemiparkinsonism in male rats, injection of the neurotoxic 6-OHDA in left striatum, we studied progesterone's effects on rotational behavior induced by amphetamine or apomorphine. Also, in order to find potential explanatory mechanisms, we studied expression and activity of nigrostriatal 3α-hydroxysteroid oxidoreductase, the enzyme that catalyzes progesterone to its active metabolite allopregnanolone. Coherently, we tested allopregnanolone for a possible neuromodulatory effect on rotational behavior. Also, since allopregnanolone is known as a GABAA modulator, we finally examined the action of GABAA antagonist bicuculline. We found that progesterone, in addition to an apparent neuroprotective effect, also increased ipsilateral expression and activity of 3α-hydroxysteroid oxidoreductase. It was interesting to note that ipsilateral administration of allopregnanolone reversed a clear sign of motor neurodegeneration, that is, contralateral rotational behavior. A possible GABAA involvement modulated by allopregnanolone was shown by the blocking effect of bicuculline. Our results suggest that early administration of progesterone possibly activates genomic mechanisms that promote neuroprotection subchronically. This, in turn, could be partially mediated by fast, nongenomic, actions of allopregnanolone acting as an acute modulator of GABAergic transmission.

Retinal Input Directs the Recruitment of Inhibitory Interneurons into Thalamic Visual Circuits

Inhibitory interneurons (INs) critically control the excitability and plasticity of neuronal networks, but whether activity can direct INs into specific circuits during development is unknown. Here, we report that in the dorsal lateral geniculate nucleus (dLGN), which relays retinal input to the cortex, circuit activity is required for the migration, molecular differentiation, and functional integration of INs. We first characterize the prenatal origin and molecular identity of dLGN INs, revealing their recruitment from an Otx2(+) neuronal pool located in the adjacent ventral LGN. Using time-lapse and electrophysiological recordings, together with genetic and pharmacological perturbation of retinal waves, we show that retinal activity directs the navigation and circuit incorporation of dLGN INs during the first postnatal week, thereby regulating the inhibition of thalamocortical circuits. These findings identify an input-dependent mechanism regulating IN migration and circuit inhibition, which may account for the progressive recruitment of INs into expanding excitatory circuits during evolution.

Effects of Calcium on the GABA<sub>A</sub>-Coupled CI<sup>-</sup>/HCO<sub>3</sub><sup>-</sup> -ATPase from Plasma Membrane of Rat Brain

The work is a study of the influence of Ca2+ (0.01 - 1 mM) on neuronal CI-, HCO3-, -ATPase complex: an enzyme that is a CI--pump which is functionally and structurally coupled to GABAA-receptors. It is found that influence of Ca2+ on the multifunctional complex starts at concentration of 50·M and at concentration of 0.1 mM, it reduces the “basal” one and increases the CI-, HCO3-, -stimulated Mg2+-ATPase activities. GABA (0.1 - 100μM) activates the “basal” Mg2+-ATPase activity in the ab-sence of calcium. The effect of GABA on the enzyme in the presence of 0.01 ·M Ca2+ does not change. At the same time, 1 mM Ca2+eliminates the GABA effect on the “basal” Mg2+-ATPase activity. Competitive blocker of GABAA-receptors bicuculline (5 - 20 μM) in the absence of Ca2+ ions elimi-nates the stimulation of the “basal” Mg2+-ATPase by anions. When 0.25 mM Ca2+ is added to the in-cubation medium the inhibitory bicuculline effect on the enzyme does not appear. We found that 0.1 mM o-vanadate (protein tyrosine phosphatase blocker) reduces the GABA-activated ATPase activity. At the same time, 0.1 mM genistein (a protein tyrosine kinase blocker) has no effect on enzyme activity. In the presence of Ca2+ (0.25 mM), the effect of o-vanadate on the “basal” and CI-, HCO3-, -ATPase activities does not appear. It is shown for the first time that high concentrations of Ca2+prevent the action of GABAA-ergic ligands on the study ATPase. It is assumed that there is the involvement of protein kinases and protein phosphatases in the modulation of the enzyme activity by calcium. The observed effect of calcium on the ATPase may play an important role in the study of the mechanisms of epileptogenesis and seizure activity.

Lunasin-induced behavioural effects in mice: Focus on the dopaminergic system

The present study for the first time is devoted to identify central effects of synthetic lunasin, a 43 amino acid peptide. A markedly expressed neuroleptic/cataleptic effect was observed at low (0.1–10nmol/mouse) centrally administered doses in male C57Bl/6 mice. Lunasin considerably reduced the amphetamine hyperlocomotion but weakly apomorphine climbing behaviour. No influence on ketamine and bicuculline effects was observed. Binding assay studies demonstrated modest affinity of lunasin for the dopamine D1 receptor (Ki=60±15μM). In a functional assay of cAMP accumulation on live cells lunasin antagonised apomorphine effect on D1 receptor activation (pEC50=6.1±0.3), but had no effect in cells expressing D2 receptors. The obtained data suggest that lunasin's action at least in part is provided via dopaminergic D1 receptor pathways. However, other non-identified mechanisms (probably intracellular) may play an important role in lunasin's central action. Nevertheless further studies of lunasin are promising, particularly taking into account a necessity for novel type of antipsychotic drugs.

Characterization of electrically evoked field potentials in the medial prefrontal cortex and orbitofrontal cortex of the rat: Modulation by monoamines

Medial prefrontal cortex (mPFC) and orbitofrontal cortex (OFC) play critical roles in cognition and behavioural control. Glutamatergic, GABAergic, and monoaminergic dysfunction in the prefrontal cortex has been hypothesised to underlie symptoms in neuropsychiatric disorders. Here we characterised electrically-evoked field potentials in the mPFC and OFC. Electrical stimulation evoked field potentials in layer V/VI of the mPFC and layer V of the OFC. The earliest component (approximately 2ms latency) was insensitive to glutamate receptor blockade and was presumed to be presynaptic. Later components were blocked by 6,7-dinitroquinoxaline-2,3-dione (DNQX (20µM)) and were assumed to reflect monosynaptic (latency 4–6ms) and polysynaptic activity (latency 6–40ms) mediated by glutamate via AMPA/kainate receptor. In the mPFC, but not the OFC, the monosynaptic component was also partly blocked by 2-amino-5-phosphonopentanoic acid (AP-5 (50–100µM)) indicating the involvement of NMDA receptors. Bicuculline (3–10µM) enhanced the monosynaptic component suggesting electrically-evoked and/or glutamate induced GABA release inhibits the monosynaptic component via GABAA receptor activation. There were complex effects of bicuculline on polysynaptic components. In the mPFC both the mono- and polysynaptic components were attenuated by 5-HT (10–100µM) and NA (30 and 60µM) and the monosynaptic component was attenuated by DA (100µM). In the OFC the mono- and polysynaptic components were also attenuated by 5-HT (100µM), NA (10–100µM) but DA (10–100µM) had no effect. We propose that these pharmacologically characterised electrically-evoked field potentials in the mPFC and OFC are useful models for the study of prefrontal cortical physiology and pathophysiology.

Requirement of neuronal connexin36 in pathways mediating presynaptic inhibition of primary afferents in functionally mature mouse spinal cord

Electrical synapses formed by gap junctions containing connexin36 (Cx36) promote synchronous activity of interneurones in many regions of mammalian brain; however, there is limited information on the role of electrical synapses in spinal neuronal networks. Here we show that Cx36 is widely distributed in the spinal cord and is involved in mechanisms that govern presynaptic inhibition of primary afferent terminals. Electrophysiological recordings were made in spinal cord preparations from 8- to 11-day-old wild-type and Cx36 knockout mice. Several features associated with presynaptic inhibition evoked by conditioning stimulation of low threshold hindlimb afferents were substantially compromised in Cx36 knockout mice. Dorsal root potentials (DRPs) evoked by low intensity stimulation of sensory afferents were reduced in amplitude by 79% and in duration by 67% in Cx36 knockouts. DRPs were similarly affected in wild-types by bath application of gap junction blockers. Consistent with presynaptic inhibition of group Ia muscle spindle afferent terminals on motoneurones described in adult cats, conditioning stimulation of an adjacent dorsal root evoked a long duration inhibition of monosynaptic reflexes recorded from the ventral root in wild-type mice, and this inhibition was antagonized by bicuculline. The same conditioning stimulation failed to inhibit monosynaptic reflexes in Cx36 knockout mice. Immunofluorescence labelling for Cx36 was found throughout the dorsal and ventral horns of the spinal cord of juvenile mice and persisted in mature animals. In deep dorsal horn laminae, where interneurones involved in presynaptic inhibition of large diameter muscle afferents are located, cells were extensively dye-coupled following intracellular neurobiotin injection. Coupled cells displayed Cx36-positive puncta along their processes. Our results indicate that gap junctions formed by Cx36 in spinal cord are required for maintenance of presynaptic inhibition, including the regulation of transmission from Ia muscle spindle afferents. In addition to a role in presynaptic inhibition in juvenile animals, the persistence of Cx36 expression among spinal neuronal populations in the adult mouse suggests that the contribution of electrical synapses to integrative processes in fully mature spinal cord may be as diverse as that found in other areas of the CNS.

Interaction between Angiotensinergic System and GABAergic System on Thirst in Adult Male Rats

Thirst is a subjective perception that provides the urge for human and animals to drink fluids and it is important for maintaining body fluid homeostasis and may arise from deficits in either intracellular or extracellular fluid volume. Gamma-aminobutyric acid (GABA) and Angiotensin (Ang) receptors in the brain are involved with thirst, water intake and balance of body liquid. The present study investigated the interaction between Angiotensinergic and GABAergic systems on water intake in adult male rats. Intracerebroventricular (i.c.v.) injections were carried out in all experiments after 24 h deprivation of water intake. After deprivation the volume of consumed water was measured for 1 h. Administration of Losartan (45 μg/rat), Muscimol (0.1 μg/rat) significantly decreased water intake while, i.c.v. microinjection of Bicuculline (1 μg/rat) significantly increased it as compared to Saline-treated controls. I.C.V. microinjection of Muscimol 15 min after Losartan administration decreased water intake significantly, while, i.c.v. microinjection of Bicuculline 15min after Losartan administration could attenuate increasing effect of Bicuculline on water intake. It is concluded that Angiotensinergic system have interaction with GABAergic system on water intake.