Microinjection Of Muscimol Research Articles

Growth of the prefrontal cortical glioblastoma altered cognitive and emotional behaviors via mediating miRNAs and GABA-A receptor signaling pathways in rats.

The present study investigated the impact of GABAergic signaling and miRNA expression on glioblastoma multiforme (GBM) growth within the medial prefrontal cortex (mPFC) and its associated cognitive and emotional impairments. The implantation of C6 cells into the mPFC induced GBM in this brain region (referred to as the mPFC-GBM) in male Wistar rats via stereotaxic surgery, as confirmed by Magnetic Resonance Imaging (MRI), and Hematoxylin and Eosin (H&E) staining. Repeated microinjections of muscimol, a potent GABAA receptor agonist, directly into the mPFC-GBM (1µg/rat/2.5μl) following tumor induction decreased tumor volume and weight, resulting in an increased survival rate. Conversely, a higher dose of muscimol (6µg/rat/2.5μl) increased tumor size and reduced survival. Behavioral alterations induced by GBM, including anxiety-like responses, exploratory behaviors, locomotor activity, and memory formation, were assessed using anxiety-like behavior task, the hole-board test, and the novel object recognition test. Muscimol treatment dose-dependently affected these behaviors in the animals with the mPFC-GBM, bringing their performance with that of the sham group at the dose of 1µg/rat/2.5μl. Changes in specific miRNAs expressions, including miR-208, -290-295, -345, -743 and -802 were associated with the growth of the mPFC-GBM under muscimol treatment. These findings suggest that GBM growth into the mPFC profoundly impacts cognitive and emotional behaviors which can be improved by muscimol treatment. Considering that the expression levels of targeted miRNAs could be influenced by the growth of the mPFC-GBM, both with or without muscimol treatment, these non-coding RNAs might serve as potential biomarkers for GBM.

Role of GABAA receptors of the dorsomedial periaqueductal grey on blood pressure and heart rate in the anesthetized rat.

The midbrain dorsomedial periaqueductal grey column (dmPAG) is involved in the regulation of cardiovascular responses. Due to the presence of Gamma-Aminobutyric acid (GABA) receptors in the dmPAG, this study aimed to investigate the role of GABAA receptors in the dmPAG on cardiovascular parameters and its possible peripheral mechanisms. The left femoral artery was cannulated, and systolic arterial pressure (SAP), mean arterial pressure (MAP) and heart rate (HR) were recorded using a Power lab system. Microinjection of saline, muscimol and bicuculline (BIC) was done using a stereotaxic device. Also, the peripheral mechanisms dependent on GABAA receptors in the dmPAG were evaluated by intravenous (i.v.) injection of hexamethonium (Hexa) and atropine (Atr) 5min before the BIC. Results showed that BIC significantly increased ∆SAP, ∆MAP and ∆HR than the control group, but muscimol had no significant effect. Injection of Hex significantly attenuates the effect of BIC on ∆SAP and ∆MAP. Atr (i.v) significantly increased the ∆HR, and when injected before BIC microinjection, it did not affect the cardiovascular responses induced by BIC. These findings show that GABAA receptors of the dmPAG have inhibitory effects on the cardiovascular system, which are mostly mediated by the sympathetic system.

Activation of nociception-sensitive ionotropic glutamate receptor-expressing rostroventrolateral medulla neurons by stimulation of cardiac afferents in rats.

Myocardial ischemia causes the release of bradykinin, which activates afferent nerve endings in the ventricular epicardium. This elicits a sympathetically mediated increase in arterial pressure and heart rate, referred to as the cardiogenic sympathetic afferent reflex. The rostroventrolateral medulla (RVLM) is a key sympathetic brain stem site for regulating cardiovascular activity. This study aimed to determine the importance of non-barosensitive nociception sympathetic activity and the role of glutamate receptor activation of RVLM neurons in the cardiogenic sympathetic afferent reflex. We tested the hypothesis that inhibition of barosensitive sympathetic activity attenuates but does not abolish the reflex response to cardiac visceral afferents. Renal sympathetic nerve activity (RSNA), arterial pressure, and heart rate responses to epicardial bradykinin application were recorded in anesthetized rats before and after bilateral RVLM microinjection of either GABAA agonist muscimol, ionotropic glutamate receptor antagonist kynurenic acid, N-methyl-d-aspartate (NMDA) receptor antagonist 2-amino-5- phosphonopentanoic acid (AP5), or non-NMDA antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX). Baroreceptor loading-induced inhibition of barosensitive activity attenuated the bradykinin-induced RSNA response (93 ± 14% increase) and tachycardia (18 ± 3 bpm). While RVLM muscimol microinjection abolished the RSNA response (1.6 ± 4.2% from baseline, 0.49 ± 0.38 μV*s), surprisingly, it did not abolish the tachycardia (27 ± 4 bpm). Kynurenic acid microinjection blocked the arterial pressure and RSNA responses, while AP5 or CNQX only attenuated the responses. These data suggest that nociception-sensitive sympathetic activity that does not appear to be barosensitive is also involved in the cardiogenic sympathetic afferent reflex. Importantly, while muscimol and kynurenic acid abolished the arterial pressure and RSNA response, neither affected the tachycardia, suggesting an alternate cardiac pathway independent of RVLM.

The additive effect between citalopram and muscimol upon induction of antinociceptive effect in male mice

Previous investigations have revealed the role of GABAergic and serotonergic systems in the modulation of pain behavior. This research aimed to examine the effects of intracerebroventricular (i.c.v.) infusion of GABAA receptor agonist and antagonist as well as citalopram on pain behavior in male mice. For i.c.v. microinjection, a guide cannula was surgically implanted in the left lateral ventricle of male mice. Pain behavior was evaluated using a tail-flick test. Tail flick latency was measured in each experimental group of mice every 15 min (for 60 min). I.c.v. microinjection of muscimol (0.5 and 1 µg/mouse; GABAA receptor agonist) into the left lateral ventricle dose-dependently induced an antinociceptive effect. On the other hand, i.c.v. infusion of bicuculline (1 µg/mouse; GABAA receptor antagonist) induced a hyperalgesia response. Moreover, intraperitoneally (i.p.) administration of citalopram (8 mg/kg) produced an antinociceptive effect. Co-treatment of citalopram (8 mg/kg) along with muscimol (0.25 µg/mouse) or bicuculline (0.25 µg/mouse) potentiated the antinociceptive effect produced by citalopram. We found an additive antinociceptive effect of citalopram and muscimol in male mice. In conclusion, our results suggested an interaction between citalopram and GABAergic agents on the modulation of pain behavior in male mice.

Inactivation of face-selective neurons alters eye movements when free viewing faces.

During free viewing, faces attract gaze and induce specific fixation patterns corresponding to the facial features. This suggests that neurons encoding the facial features are in the causal chain that steers the eyes. However, there is no physiological evidence to support a mechanistic link between face-encoding neurons in high-level visual areas and the oculomotor system. In this study, we targeted the middle face patches of the inferior temporal (IT) cortex in two macaque monkeys using an functional magnetic resonance imaging (fMRI) localizer. We then utilized muscimol microinjection to unilaterally suppress IT neural activity inside and outside the face patches and recorded eye movements while the animals free viewing natural scenes. Inactivation of the face-selective neurons altered the pattern of eye movements on faces: The monkeys found faces in the scene but neglected the eye contralateral to the inactivation hemisphere. These findings reveal the causal contribution of the high-level visual cortex in eye movements.

Inactivation of the paraventricular nucleus attenuates the cardiogenic sympathetic afferent reflex in the spontaneously hypertensive rat.

Myocardial ischemia causes the release of bradykinin, which stimulates cardiac afferents, causing sympathetic excitation and chest pain. Glutamatergic activation of the paraventricular hypothalamic nucleus (PVN) in the spontaneously hypertensive rat (SHR) drives elevated basal sympathetic activity. Thus, we tested the hypothesis that inactivation of the PVN attenuates the elevated reflex response to epicardial bradykinin in the SHR and that ionotropic PVN glutamate receptors mediate the elevated reflex. We recorded the arterial pressure and renal sympathetic nerve activity (RSNA) response to epicardial bradykinin application in anesthetized SHR and Wistar Kyoto (WKY) rats before and after PVN microinjection of GABA A agonist muscimol or ionotropic glutamate receptor antagonist kynurenic acid. Muscimol significantly decreased the arterial pressure response to bradykinin from 180.4 ± 5.8 to 119.5 ± 6.9 mmHg in the SHR and from 111.8 ± 7.0 to 84.2 ± 8.3 mmHg in the WKY and the RSNA response from 186.2 ± 7.1 to 142.7 ± 7.3% of baseline in the SHR and from 201.0 ± 11.5 to 160.2 ± 9.3% of baseline in the WKY. Kynurenic acid significantly decreased the arterial pressure response in the SHR from 164.5 ± 5.0 to 126.2 ± 7.7 mmHg and the RSNA response from 189.9 ± 13.7to 168.5 ± 12.7% of baseline but had no effect in the WKY. These results suggest that tonic PVN activity is critical for the full manifestation of the CSAR in both the WKY and SHR. Glutamatergic PVN activity contributes to the augmented CSAR observed in the SHR.

Activation of Beta-adrenergic Receptors Upregulates the Signal-to-Noise Ratio of Auditory Input in the Medial Prefrontal Cortex and Mediates Auditory Fear Conditioning.

Norepinephrine (NE) is involved in auditory fear conditioning (AFC) in posttraumatic stress disorder (PTSD). However, it is still unclear how it acts on neurons. We aimed to investigate whether the activation of the β-adrenergic receptor (β-AR) improves AFC by sensitization of the prelimbic (PL) cortex at the animal, cellular, and molecular levels. In vivo single-cell electrophysiological recording was used to characterize the changes in neurons in the PL cortex after AFC. Then, PL neurons were locally administrated by the β-AR agonist isoproterenol (ISO), the GABAaR agonist muscimol, or intervened by optogenetic method, respectively. Western blotting and immunohistochemistry were finally used to assess molecular changes. Noise and low-frequency tones induced similar AFC. The expression of β-ARs in PL cortex neurons was upregulated after fear conditioning. Microinjection of muscimol into the PL cortex blocked the conformation of AFC, whereas ISO injection facilitated AFC. Moreover, PL neurons can be distinguished into two types, with type I but not type II neurons responding to conditioned sound and being regulated by β-ARs. Our results showed that β-ARs in the PL cortex regulate conditional fear learning by activating type I PL neurons.

Regulation of vagally-evoked respiratory responses by the lateral parabrachial nucleus in the mouse

Vagal sensory inputs to the brainstem can alter breathing through the modulation of pontomedullary respiratory circuits. In this study, we set out to investigate the localised effects of modulating lateral parabrachial nucleus (LPB) activity on vagally-evoked changes in breathing pattern. In isoflurane-anaesthetised and instrumented mice, electrical stimulation of the vagus nerve (eVNS) produced stimulation frequency-dependent changes in diaphragm electromyograph (dEMG) activity with an evoked tachypnoea and apnoea at low and high stimulation frequencies, respectively. Muscimol microinjections into the LPB significantly attenuated eVNS-evoked respiratory rate responses. Notably, muscimol injections reaching the caudal LPB, previously unrecognised for respiratory modulation, potently modulated eVNS-evoked apnoea, whilst muscimol injections reaching the intermediate LPB selectively modulated the eVNS-evoked tachypnoea. The effects of muscimol on eVNS-evoked breathing rate changes occurred without altering basal eupneic breathing. These results highlight novel roles for the LPB in regulating vagally-evoked respiratory reflexes.

Controllable Stress Increases Rapid Eye Movement Sleep in Rats: Regulation by the Central Nucleus of the Amygdala.

Training with inescapable shock (IS; uncontrollable stressor) is followed by significant decreases in rapid eye movement sleep (REM). However, controllability is important in the effects of stress. We examined the effects of escapable shock (ES; controllable stressor) on sleep and whether the central nucleus of the amygdala (CNA) plays a role in regulating these effects. Six Wistar rats implanted with a cannula located in CNA underwent two days of ES training (20 shock presentations; 0.5 mA; 5.0 s maximum duration; 1.0 min interstimulus interval). Five days later, they were re-exposed to the shock context. Following shock training, REM was significantly increased in both light and dark periods. Non-REM (NREM) and total sleep (TS) duration were decreased during the light period. Similar effects on REM and NREM were observed following re-exposure to the training context alone. Microinjections of saline into CNA immediately following ES also produced similar increases in REM, whereas microinjections of muscimol (MUS; GABAA (γ-aminobutyric acid) antagonist) subsequent to ES blocked the increases in REM. These data, along with previous work with ES and IS, demonstrate that stressor controllability is important in determining how stress impacts sleep. Moreover, the results of the microinjection study indicate that the effects of ES on REM are regulated through the CNA.

Pharmacological activation of mediodorsal thalamic GABA-A receptors modulates morphine/cetirizine-induced changes in the prefrontal cortical GFAP expression in a rat model of neuropathic pain

The present study investigated the involvement of mediodorsal thalamic (MD) GABA-A receptors in cetirizine/morphine-induced anti-allodynia using a rat model of neuropathic pain. To assess the importance of the prefrontal cortex (PFC) for chronic pain processing, its expression level changes of glial fibrillary acidic protein (GFAP) were measured following drug treatments. Each animal was subjected to chronic constriction of the sciatic nerve surgery simultaneously with the MD cannulation under stereotaxic surgery. The results showed that the administration of morphine (3–5 mg/kg) or cetirizine (1–3 mg/kg) produced significant analgesia in neuropathic rats. Systemic administration of cetirizine (2.5 and 3 mg/kg) potentiated the analgesic response to a low and intolerance dose of morphine (3 mg/kg). Intra-MD microinjection of muscimol, a selective GABA-A receptor agonist (0.005–0.01 μg/rat), increased the cetirizine/morphine-induced anti-allodynia, while muscimol by itself did not affect neuropathic pain. The neuropathic pain was associated with the increased PFC expression level of GFAP, suggesting the impact of chronic pain on PFC glial management. Interestingly, the anti-allodynia was associated with a decrease in the PFC expression level of GFAP under the drugs' co-administration. Thus, cetirizine has a significant potentiating effect on morphine response in neuropathic pain via interacting with the MD GABA-A receptors. It seems that neuropathic pain affects the prefrontal cortex GFAP signaling pathway. In clinical studies, these findings can be considered to create a combination therapy with low doses of GABA-A receptor agonist plus cetirizine and morphine to manage neuropathic pain.

Effect of pharmacological inhibition of the pontine respiratory group on swallowing interneurons in the dorsal medulla oblongata

ObjectivesTo examine the role of neurons of the pontine respiratory group (PRG) overlapping with the Kölliker-Fuse nucleus in the regulation of swallowing, we compared the activity of swallowing motor activities and interneuron discharge in the dorsal swallowing group in the medulla before and after pharmacological inhibition of the PRG. MethodsIn 23 in situ perfused brainstem preparation of rats, we recorded the activities of the vagus (VNA), hypoglossal (HNA), and phrenic nerves (PNA), and swallowing interneurons of the dorsal medulla during fictive swallowing elicited by electrical stimulation of the superior laryngeal nerve or oral water injection. Subsequently, respiratory- and swallow-related motor activities and single unit cell discharge were assessed before and after local microinjection of the GABA-receptor agonist muscimol into the area of PRG ipsilateral to the recording sites of swallowing interneurons. ResultsAfter muscimol injection, the amplitude and duration of swallow-related VNA bursts decreased to 71.3 ± 2.84 and 68.1 ± 2.76 % during electrically induced swallowing and VNA interburst intervals during repetitive swallowing decreased. Similar effects were observed for swallowing-related HNA. The swallowing motor activity was similarly qualitatively altered during physiologically induced swallowing. All 23 neurons were changed in either discharge duration or frequency after PRG inhibition, however, the general discharge patterns in relation to the motor output remained unchanged. ConclusionDescending synaptic inputs from PRG provide control of the primary laryngeal sensory gate and synaptic activity of the PRG partially determine medullary cell and cranial motor nerve activities that govern the pharyngeal stage of swallowing.

Involvement of GABAA receptors of lateral habenula in the acquisition and expression phases of morphine-induced place preference in male rats.

The lateral habenula (LHb) is a critical brain structure involved in the aversive response to drug abuse. It has been determined that the gamma-aminobutyric acid (GABA)-ergic system plays the main role in morphine dependency. The role of GABA type A receptors (GABAARs) in LHb on morphine-induced conditioned place preference (CPP) remains unknown. In this study, the effect of bilateral intra-LHb microinjection of GABAAR agonist and antagonist on the acquisition and expression phases of CPP, utilizing a 5-day CPP paradigm in male rats, was evaluated. Subcutaneous administration of different doses of morphine caused a dose-dependent CPP. Intra-LHb microinjection of the GABAAR agonist, muscimol, in combination with morphine (5 mg/kg; subcutaneously) enhanced CPP scores in the acquisition phase of morphine CPP, whereas the GABAAR antagonist, bicuculline, significantly reduced the conditioning scores in the acquisition phase. Furthermore, pretreatment with a high dose of bicuculline reversed the additive effect of muscimol during the acquisition phase, yet the low dose of antagonist had no significant effect on agonist-induced CPP scores. On the other hand, muscimol (3 µg/rat) significantly increased CPP scores in the expression phase but bicuculline did not induce a significant effect on CPP scores. Bicuculline and muscimol microinjections did not affect locomotor activity in the testing sessions. Our results confirm that GABAARs in LHb play an active role in morphine reward. In addition, microinjections of bicuculline/muscimol may alter the morphine response through the GABAergic system.

KCl-induced repetitive cortical spreading depression inhibiting trigeminal neuronal firing is mediated by 5-HT1B/1D and opioid receptors.

We aimed to examine the effects of repetitive cortical spreading depression on the responses of nociceptive trigeminal neurons with dural afferents and characterize the role of 5-HT1B/1D and opioid receptors. Trigeminocervical complex neurons (n = 53) responsive to nociceptive activation of the dura mater were studied in rats using electrophysiological techniques. A sub-population (n = 32) showed an average inhibition of dural-evoked responses of 65 ± 14% from baseline with cortical spreading depression. This response was reversed by the selective 5-HT1B/1D receptor antagonist, GR127935 (3 mg/kg; n = 6, iv), and a non-selective opioid receptor antagonist, naloxone (1.5 mg/kg; n = 6, iv), five minutes after injection. To determine the role of the nucleus raphe magnus in the trigeminocervical complex inhibitory effect, microinjection of lidocaine (2%, n = 6) or muscimol (100 mM, n = 5) into the nucleus raphe magnus was performed. There was no effect on cortical spreading depression-induced inhibition of neuronal firing in trigeminocervical complex by either. The data demonstrate that repetitive cortical spreading depression inhibits a subpopulation of dural nociceptive trigeminocervical neurons, an effect mediated by serotonin and opioid receptors. This inhibition does not involve modulation of nucleus raphe magnus neurons.

Pharmacological inactivation of the primate posterior insular/secondary somatosensory cortices attenuates thermal hyperalgesia.

We previously established a macaque model of central post-stroke pain (CPSP) and confirmed the involvement of increased activity of the posterior insular cortex (PIC) and secondary somatosensory cortex (SII) to somatosensory stimuli in mechanical allodynia by a combination of imaging techniques with local pharmacological inactivation. However, it is unclear whether the same intervention would be effective for thermal hyperalgesia. Therefore, using the macaque model, we examined behavioural responses to thermal stimuli following pharmacological inactivation of the PIC/SII. Two CPSP model macaques were established based on collagenase-induced unilateral hemorrhagic lesions in the ventral posterolateral nucleus of the thalamus. To evaluate pain perception, withdrawal latencies to thermal stimuli of 37, 45, 50, 52, and 55 °C to hands were measured. Several weeks after the lesion induction, pharmacological inactivation of the PIC/SII by microinjection of muscimol was performed. The effect of inactivation on withdrawal latency was assessed by comparison with withdrawal latency after vehicle injection. Several weeks after induction of the thalamic lesions, both macaques demonstrated a reduction in withdrawal latencies to thermal stimulation (<50 °C) on the contralesional hand, indicating the occurrence of thermal hyperalgesia. When the PIC/SII were inactivated by muscimol, the withdrawal latencies to thermal stimuli of 50 and 52 °C were significantly increased compared to those after vehicle injection. Our data emphasize that increased activity in the PIC/SII after appearance of thalamic lesions can contribute to abnormal pain of multiple modalities, and the modulation of PIC/SII activity may be a therapeutic approach for thermal hyperalgesia. CPSP is caused by stroke lesions in the sensory system and characterized by mechanical allodynia or thermal hyperalgesia. Inactivation of the PIC/SII has an analgesic effect on mechanical allodynia; however, it is not clear whether the same intervention could reduce thermal hyperalgesia. Here, using the macaque model, we demonstrated that inactivation of these cortices reduces hypersensitivity to thermal stimuli. This result emphasizes that increased PIC/SII activity can contribute to abnormal pain of multiple modalities.

Post-Weaning Treatment with Probiotic Inhibited Stress-Induced Amnesia in Adulthood Rats: The Mediation of GABAergic System and BDNF/c-Fos Signaling Pathways.

The current study aimed to examine the effect of post-weaning treatment with probiotics on memory formation under stress during the adult period in male Wistar rats. Considering GABA is a potential mediator between probiotics and the host, the present study also investigated the involvement of the GABAergic system in the probiotic response. The hippocampal and prefrontal cortical (PFC) expression levels of BDNF and c-Fos were also assessed to show whether the treatments affect the memory-related signaling pathway. Three weeks after birth, the post-weaning rats were fed with probiotic water (PW) or tap water (TW) for 2, 3, 4, or 5weeks. Exposure to acute stress impaired memory formation in a passive avoidance learning task. Feeding the post-weaning animals with probiotic strains (3, 4, or 5weeks) inhibited stress-induced amnesia of the adult period. Post-training intracerebroventricular (ICV) microinjection of muscimol improved stress-induced amnesia in the animals fed with TW. ICV microinjection of muscimol inhibited probiotic treatment's significant effect on the stress response in the memory task. The expression levels of BDNF and c-Fos in the PFC and the hippocampus were significantly decreased in the stress animal group. The levels of BDNF and c-Fos were increased in the PW/stress animal group. The muscimol response was compounded with the decreased levels of BDNF and c-Fos in the PFC and the hippocampus. Thus, the GABA-A receptor mechanism may mediate the inhibitory effect of this probiotic mixture on stress-induced amnesia, which may be associated with the PFC and hippocampal BDNF/c-Fos signaling changes.

Респираторные реакции при стимуляции и блокаде ГАМКА-рецепторов ретротрапециевидного ядра у крыс

The respiratory reactions to microinjections of muscimol and bicuculline solutions into the retrotrapezoid nucleus (RTN) were studied in acute experiments on anesthetized rats breathing ordinary atmospheric air. It was found that the activation of GABAA-receptors of the RTN by muscimol has inhibitory effect on external respiration, reducing its minute volume and volumetric rate of inspiratory flow due to prolongation of inspiration and expiration and a decrease in the tidal volume. The reactions to microinjections of the GABAA-receptors antagonist bicuculline into the RTN were not unambiguous, but in most cases they manifested as an increase in minute lung ventilation with an increase in tidal volume and volumetric inspiration rate. The data obtained indicate that GABAA-receptors are involved in the activity of the RTN, in particular, they are an important link in central mechanisms of respiratory control in adult rats when breathing air of normal composition, which does not cause disruption of gas homeostasis. It is suggested that ionotropic GABA receptors in the RTN region are involved in inhibitory modulation of neurons that regulate both the duration of the respiratory cycle phases and the level of breathing depth.

Synaptic potentiation of anterior cingulate cortex contributes to chronic pain of Parkinson’s disease

Parkinson’s disease (PD) is a multi-system neurodegenerative disorder. Patients with PD often suffer chronic pain. In the present study, we investigated motor, sensory and emotional changes in three different PD mice models. We found that 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treatment caused significant changes in all measurements. Mechanical hypersensitivity of PD model induced by MPTP peaked at 3 days and persisted for at least 14 days. Using Fos transgenic mice, we found that neurons in the anterior cingulate cortex (ACC) were activated after MPTP treatment. Inhibiting ACC by bilateral microinjection of muscimol significantly reduced mechanical hypersensitivity and anxiety-like responses. By contrast, MPTP induced motor deficit was not affected, indicating ACC activity is mostly responsible for sensory and emotional changes. We also investigated excitatory synaptic transmission and plasticity using brain slices of MPTP treated animals. While L-LTP was blocked or significantly reduced. E-LTP was not significantly affected in slices of MPTP treated animals. LTD induced by repetitive stimulation was not affected. Furthermore, we found that paired-pulse facilitation and spontaneous release of glutamate were also altered in MPTP treated animals, suggesting presynaptic enhancement of excitatory transmission in PD. Our results suggest that ACC synaptic transmission is enhanced in the animal model of PD, and cortical excitation may play important roles in PD related pain and anxiety.

GABAergic neurons in the nucleus accumbens regulate hedonic food intake via orexin-A expression in the lateral hypothalamus.

Objective(s):To investigate the regulatory effects of the nucleus accumbens (NAcSh)-lateral hypothalamus (LHA) GABAergic neural pathway on palatable food (PF) intake via orexin-A expression in diet-induced obesity (DIO) rats. Materials and Methods:NAcSh-LHA GABAergic pathways were observed by fluorogold retrograde tracing combined with fluorescence immunohistochemistry, and the regulatory effects of this neural pathway on PF intake were detected after 1) microinjection of GABA-A receptor agonist muscimol (MUS) or antagonist bicuculine (BIC) into LHA, 2) electrical stimulation NAcSh, and 3) blocking the orexin-A receptor by icv SB334867. Results:Compared with rats on a normal diet (ND), NAcSh-LHA GABAergic neurons in the DIO rats were significantly decreased, and orexin-A expression in LHA significantly increased (P<0.05). Microinjection of MUS into LHA significantly decreased the PF intake in both ND and DIO rats (P<0.05), and BIC could markedly increase the PF intake in the ND rats (P<0.05), but not the DIO rats (P>0.05). After NAcSh electrical stimulation or SB334867 ICV injection, the PF intake was significantly decreased in the DIO rats (P<0.05), and there was no significant difference after preadministration of BIC into LHA (P>0.05). Conclusion:This GABAergic pathway could regulate the expression of orexin-A in LHA and PF intake. Orexin-A neurons in LHA of DIO rats might be less sensitive to GABAergic signals and may consequently lead to more hedonic food intake.

Inactivation of the infralimbic cortex decreases discriminative stimulus-controlled relapse to cocaine seeking in rats.

Persistent susceptibility to cue-induced relapse is a cardinal feature of addiction. Discriminative stimuli (DSs) are one type of drug-associated cue that signal drug availability (DS+) or unavailability (DS-) and control drug seeking prior to relapse. We previously established a trial-based procedure in rats to isolate DSs from context, conditioned stimuli, and other drug-associated cues during cocaine self-administration and demonstrated DS-controlled cocaine seeking up to 300 abstinence days. The behavioral and neural mechanisms underlying trial-based DS-control of drug seeking have rarely been investigated. Here we show that following discrimination training in our trial-based procedure, the DS+ and DS- independently control the expression and suppression of cocaine seeking during abstinence. Using microinjections of GABAA + GABAB receptor agonists (muscimol + baclofen) in medial prefrontal cortex, we report that infralimbic, but not prelimbic, subregion of medial prefrontal cortex is critical to persistent DS-controlled relapse to cocaine seeking after prolonged abstinence, but not DS-guided discriminated cocaine seeking or DS-controlled cocaine self-admininstration. Finally, using ex vivo whole-cell recordings from pyramidal neurons in the medial prefrontal cortex, we demonstrate that the disruption of DS-controlled cocaine seeking following infralimbic cortexmicroinjections of muscimol+baclofen is likely a result of suppression of synaptic transmission in the region via a presynaptic mechanism of action.

D2 Receptors in the Periaqueductal Gray/Dorsal Raphe Modulate Peripheral Inflammatory Hyperalgesia via the Rostral Ventral Medulla

Dopamine neurons in the periaqueductal gray (PAG)/dorsal raphe are key modulators of antinociception with known supraspinal targets. However, no study has directly tested whether these neurons contribute to descending pain inhibition. We hypothesized that PAG dopamine neurons contribute to the analgesic effect of D-amphetamine via a mechanism that involves descending modulation via the rostral ventral medulla (RVM). Male C57BL/6 mice showed increased c-FOS expression in PAG dopamine neurons and a significant increase in paw withdrawal latency to thermal stimulation after receiving a systemic injection of D-amphetamine. Targeted microinfusion of D-amphetamine, L-DOPA, or the selective D2 agonist quinpirole into the PAG produced analgesia, while a D1 agonist, chloro APB, had no effect. In addition, inhibition of D2 receptors in the PAG by eticlopride prevented the systemic D-amphetamine analgesic effect. D-amphetamine and PAG D2 receptor-mediated analgesia were inhibited by intra-RVM injection of lidocaine or the GABAA receptor agonist muscimol, indicating a PAG-RVM signaling pathway in this model of analgesia. Finally, both systemic D-amphetamine and local PAG microinjection of quinpirole, inhibited inflammatory hyperalgesia induced by carrageenan. This hyperalgesia was transiently restored by intra-PAG injection of eticlopride, as well as RVM microinjection of muscimol. We conclude that D-amphetamine analgesia is partially mediated by descending inhibition and that D2 receptors in the PAG are responsible for this effect via modulating neurons that project to the RVM. These results further our understanding of the antinociceptive effects of dopamine and elucidate a mechanism by which clinically available dopamine modulators produce analgesia.