Prolactin reduces the kainic acid-induced increase in intracellular Ca2+ concentration, leading to neuroprotection of hippocampal neurons.

The aim of this study was to determine the effect of prolactin (PRL) on intracellular calcium (Ca2+) concentration and its neuroprotective role in a model of kainic acid (KA) excitotoxicity in primary cultures of hippocampal neurons. Cell viability and intracellular Ca2+ concentrations were determined by MTT and Fura-2 assays, respectively, either after induction by KA as an agonist or after treatment with NBQX antagonist alone or in combination with PRL administration. Expression of ionotropic glutamatergic receptors (iGluRs) subunits in neuronal cells was determined by RT-qPCR. Dose-response treatments with KA or glutamate (Glu), the latter used as endogenous agonist control, induced a significant increase in neuronal intracellular Ca2+ concentration followed by a significant decrease in hippocampal neuronal viability. Administration of PRL induced a significant increase in neuronal viability after treatment with KA. Furthermore, administration of PRL decreased intracellular Ca2+ concentrations induced by KA treatment. Independent administration of the AMPAR-KAR antagonist reversed cell death and reduced intracellular Ca2+ concentration in a similar manner as PRL. Additionally, mRNA expression of AMPAR, KAR and NMDAR subtypes were detected in hippocampal neurons; however, no significant changes in iGluRs subunit expression were observed due to excitotoxicity or PRL treatment. The results suggest that PRL inhibits the increase in intracellular Ca2+ concentration induced by KA, leading to neuroprotection.

Fructose ingestion modifies NMDA receptors and exacerbates the seizures induced by kainic acid.

Fructose ingestion elicits a diversity of brain alterations, but it is unknown how it affects N-methyl-D-Aspartate receptors (NMDAr). Here, we analyzed the expression of NMDAr subunits and protein kinases after the long-term dietary fructose intake. Since NMDAr are related to epileptogenesis, we also examined whether fructose increases the susceptibility to seizures after the microinjection of kainic acid (KA) in the rat hippocampus. Wistar rats were randomly divided into water (control) and fructose groups. For twelve weeks, groups had ad libitum access to water or fructose solution (10% w/v). After treatment, hippocampal protein expression of NMDAr subunits and protein kinases involved in NMDAr regulation were analyzed. Additionally, electroencephalographic and behavioral changes related to seizures were evaluated after the microinjection of a sub-convulsive dose of KA in the hippocampus. Fructose induced the decrease of NR1 and, conversely, the increase of NR2A subunits expression in the hippocampus. Also, the phosphorylation of protein kinase C alpha (PKCα) and c-Src increased significantly. No electroencephalographic or behavioral patterns related to convulsive motor seizures were observed in the control group. However, all the rats that ingested fructose showed stage 3 seizures (forelimb clonus) and a significant increase in the number of wet-dog shakes. Moreover, electroencephalographic recordings revealed pronounced epileptiform activity and increased total spectral power at 30 and 60 min after the microinjection of KA. This study shows for the first time that fructose intake exacerbates the seizures induced by KA. Therefore, we propose that this proconvulsant effect could be mediated by changes in NMDAr subunits expression and increased activation of kinases modulating NMDAr function.

Dietary omega-3 fatty acids prevent neonatal seizure-induced early alterations in the hippocampal glutamatergic system and memory deficits in adulthood.

OBJECTIVE: We investigated the influence of dietary omega-3 polyunsaturated fatty acids (n-3 PUFAs) on glutamatergic system modulation after a single episode of neonatal seizures and their possible effects on seizure-induced long-lasting behavioral deficits. METHODS: Male Wistar rats receiving an omega-3 diet (n-3) or an n-3 deficient diet (D) from the prenatal period were subjected to a kainate-induced seizure model at P7. Glutamate transporter activity and immunocontents (GLT-1 and GLAST) were assessed in the hippocampus at 12, 24, and 48 h after the seizure episode. Fluorescence intensity for glial cells (GFAP) and neurons (NeuN) was assessed 24 h after seizure in the hippocampus. Behavioral analysis (elevated-plus maze and inhibitory avoidance memory task) was performed at 60 days of age. RESULTS: The D group showed a decrease in glutamate uptake 24 h after seizure. In this group only, the GLT1 content increased at 12 h, followed by a decrease at 24 h. GLAST increased up to 24 h after seizure. GFAP fluorescence was higher, and NeuN fluorescence decreased, in the D group independent of seizures. In adulthood, the D group presented memory deficits independent of seizures, but short-term memory (1.5 h after a training session) was abolished in the D group treated with kainate. SIGNIFICANCE: N-3 PUFA positively influenced the glutamatergic system during seizure and prevented seizure-related memory deficits in adulthood.

Involvement of medial prefrontal cortex NMDA and AMPA/kainate glutamate receptors in social recognition memory consolidation.

Social recognition memory (SRM) enables the distinction between familiar and strange conspecifics, a fundamental ability for sociable species, such as rodents and humans. There is mounting evidence that the medial prefrontal cortex plays a prominent role both in shaping social behavior and in recognition memory. Glutamate is the major excitatory neurotransmitter in the brain, and activity of its ionotropic receptors is known to mediate both synaptic plasticity and consolidation of various types of memories. However, whether these receptors are required in the medial prefrontal cortex (mPFC) for SRM consolidation remains elusive. To address this issue, we submitted rats to a social discrimination paradigm, administered infusions of NMDA- and AMPA/kainate-receptors antagonists into the prelimbic (PrL) subdivision of the mPFC at different post-encoding time points and evaluated long-term memory retention twenty-four hours later. We found that blocking NMDA receptors immediately after the sample phase, but not 3 h later, impaired SRM consolidation, whereas the blockade of AMPA/kainate receptors immediately and 3 h, but not 6 h after the sample phase, prevented long-term memory consolidation. These results highlight the importance of the mPFC in social cognition and may contribute towards the understanding of the dysfunctional social information processing that underlies multiple neuropsychiatric disorders.

Regulation of the Serotonergic System by Kainate in the Avian Retina.

Serotonin (5-HT) has been recognized as a neurotransmitter in the vertebrate retina, restricted mainly to amacrine and bipolar cells. It is involved with synaptic processing and possibly as a mitogenic factor. We confirm that chick retina amacrine and bipolar cells are, respectively, heavily and faintly immunolabeled for 5-HT. Amacrine serotonergic cells also co-express tyrosine hydroxylase (TH), a marker of dopaminergic cells in the retina. Previous reports demonstrated that serotonin transport can be modulated by neurotransmitter receptor activation. As 5-HT is diffusely released as a neuromodulator and co-localized with other transmitters, we evaluated if 5-HT uptake or release is modulated by several mediators in the avian retina. The role of different glutamate receptors on serotonin transport and release in vitro and in vivo was also studied. We show that L-glutamate induces an inhibitory effect on [3H]5-HT uptake and this effect was specific to kainate receptor activation. Kainate-induced decrease in [3H]5-HT uptake was blocked by CNQX, an AMPA/kainate receptor antagonist, but not by MK-801, a NMDA receptor antagonist. [3H]5-HT uptake was not observed in the presence of AMPA, thus suggesting that the decrease in serotonin uptake is mediated by kainate. 5-HT (10-50 µM) had no intrinsic activity in raising intracellular Ca2+, but addition of 10 µM 5-HT decreased Ca2+ shifts induced by KCl in retinal neurons. Moreover, kainate decreased the number of bipolar and amacrine cells labeled to serotonin in chick retina. In conclusion, our data suggest a highly selective effect of kainate receptors in the regulation of serotonin functions in the retinal cells.

Mechanism of Neuroprotection Against Experimental Spinal Cord Injury by Riluzole or Methylprednisolone.

Any spinal cord injury carries the potential for persistent disability affecting motor, sensory and autonomic functions. To prevent this outcome, it is highly desirable to block a chain of deleterious reactions developing in the spinal areas immediately around the primary lesion. Thus, early timing of pharmacological neuroprotection should be one major strategy whose impact may be first studied with preclinical models. Using a simple in vitro model of the rat spinal cord it is possible to mimic pathological processes like excitotoxicity that damages neurons because of excessive glutamate receptor activation due to injury, or hypoxic/dysmetabolic insult that preferentially affects glia following vascular dysfunction. While ongoing research is exploring the various components of pathways leading to cell death, current treatment principally relies on the off-label use of riluzole (RLZ) or methylprednisolone sodium succinate (MPSS). The mechanism of action of these drugs is diverse as RLZ targets mainly neurons and MPSS targets glia. Even when applied after a transient excitotoxic stimulus, RLZ can provide effective prevention of secondary excitotoxic damage to premotoneurons, although not to motoneurons that remain very vulnerable. This observation indicates persistent inability to express locomotor activity despite pharmacological treatment conferring some histological protection. MPSS can protect glia from dysmetabolic insult, yet it remains poorly effective to prevent neuronal death. In summary, it appears that these pharmacological agents can produce delayed protection for certain cell types only, and that their combined administration does not provide additional benefit. The search should continue for better, mechanism-based neuroprotective agents.

Glutamatergic, GABAergic, and endocannabinoid neurotransmissions within the dorsal hippocampus modulate the cardiac baroreflex function in rats.

The dorsal hippocampus (DH) is involved in the modulation of the cardiac baroreflex function. There is a wide expression of the NMDA and AMPA/Kainate receptors within the DH. Glutamate administration into the DH triggers both tachycardia and pressor responses. Moreover, GABAergic interneurons and endocannabinoid system play an important role in modulation of the activity of glutamatergic neurons within the DH. Therefore, the present work aimed to evaluate the involvement of the glutamatergic, GABAergic, and endocannabinoid neurotransmissions within the DH in cardiac baroreflex function in rats. We have used the technique of vasoactive drugs infusion to build both sigmoidal curves and linear regressions to analyze the cardiac baroreflex function. Bilateral injection into the DH of DL-AP7, a NMDA receptor antagonist (10 or 50 nmol/500 nL), or NBQX, an AMPA/Kainate antagonist (100 nmol/ 500 nL), reduced the cardiac baroreflex function. On the other hand, bilateral injection of Bicuculline, a GABAA receptor antagonist (1 nmol/500 nL), or AM251, a CB1 receptor antagonist (10 or 100 pmol/500 nL), increased the cardiac baroreflex function. Furthermore, 1 nmol/500 nL of the NMDA receptor antagonist, when administrated alone, was ineffective to change baroreflex function, but it was able to inhibit the alteration in the cardiac baroreflex function elicited by the dose of 100 pmol/500 nL of the CB1 receptor antagonist. Taken together, these findings suggest that glutamatergic, GABAergic, and endocannabinoid neurotransmissions interact each other within the DH to modulate the cardiac baroreflex function.

A thermodynamic description for physiological transmembrane transport.

A general formulation for both passive and active transmembrane transport is derived from basic thermodynamical principles. The derivation takes into account the energy required for the motion of molecules across membranes and includes the possibility of modeling asymmetric flow. Transmembrane currents can then be described by the general model in the case of electrogenic flow. As it is desirable in new models, it is possible to derive other well-known expressions for transmembrane currents as particular cases of the general formulation. For instance, the conductance-based formulation for current turns out to be a linear approximation of the general formula for current. Also, under suitable assumptions, other formulas for current based on electrodiffusion, like the constant field approximation by Goldman, can be recovered from the general formulation. The applicability of the general formulations is illustrated first with fits to existing data, and after, with models of transmembrane potential dynamics for pacemaking cardiocytes and neurons. The general formulations presented here provide a common ground for the biophysical study of physiological phenomena that depend on transmembrane transport.

Unravelling cortico-hypothalamic pathways regulating unconditioned fear-induced antinociception and defensive behaviours.

The medial prefrontal cortex can influence unconditioned fear-induced defensive mechanisms organised by diencephalic neurons that are under tonic GABAergic inhibition. The posterior hypothalamus (PH) is involved with anxiety- and panic attack-like responses. To understand this cortical mediation, our study characterised anterior cingulate cortex (ACC)-PH pathways and investigated the effect of ACC local inactivation with lidocaine. We also investigated the involvement of PH ionotropic glutamate receptors in the defensive behaviours and fear-induced antinociception by microinjecting NBQX (an AMPA/kainate receptor antagonist) and LY235959 (a NMDA receptor antagonist) into the PH. ACC pretreatment with lidocaine decreased the proaversive effect and antinociception evoked by GABAA receptor blockade in the PH, which suggests that there may be descending excitatory pathways from this cortical region to the PH. Microinjections of both NBQX and LY235959 into the PH also attenuated defensive and antinociceptive responses. This suggests that the blockade of AMPA/kainate and NMDA receptors reduces the activity of glutamatergic efferent pathways. Both inputs from the ACC to the PH and glutamatergic hypothalamic short links disinhibited by intra-hypothalamic GABAA receptors blockade are potentially implicated. Microinjection of a bidirectional neurotracer in the PH showed a Cg1-PH pathway and PH neuronal reciprocal connections with the periaqueductal grey matter. Microinjections of an antegrade neurotracer into the Cg1 showed axonal fibres and glutamatergic vesicle-immunoreactive terminal boutons surrounding both mediorostral-lateroposterior thalamic nucleus and PH neuronal perikarya. These data suggest a critical role played by ACC-PH glutamatergic pathways and AMPA/kainate and NMDA receptors in the panic attack-like reactions and antinociception organised by PH neurons.

4-phenylselenyl-7-chloroquinoline, a novel multitarget compound with anxiolytic activity: Contribution of the glutamatergic system.

A growing body of evidence demonstrates that quinoline compounds have attracted much attention in the field of drug development. Accordingly, 4-phenylselenyl-7-chloroquinoline (4-PSQ) is a new quinoline derivative containing selenium, which showed a potential antioxidant, antinociceptive and anti-inflammatory effect. The present study was undertaken to evaluate the anxiolytic-like properties of 4-PSQ. Mice were orally pretreated with 4-PSQ (5-50 mg/kg) or vehicle, 30 min prior to the elevated plus-maze (EPM), light-dark (LDT) or open field (OFT) tests. A time-response curve was carried out by administration of 4-PSQ (50 mg/kg) at different times before the EPM test. The involvement of glutamate uptake/release and Na+, K+-ATPase activity in the anxiolytic-like effect was investigated in cerebral cortices. In addition, the effectiveness of acute treatment with 4-PSQ was evaluated in a model of kainate (KA)-induced anxiety-related behavior. Finally, acute toxicity of this compound was investigated. 4-PSQ produced an anxiolytic-like action, both in EPM and LDT. In OFT, 4-PSQ did not affect locomotor and exploratory activities. 4-PSQ anxiolytic-like effect started at 0.5 h and remained significant up to 72 h after administration. Treatment with 4-PSQ reduced [3H] glutamate uptake, but the [3H] glutamate release and Na+, K+-ATPase activity were not altered. KA-induced anxiety-related behavior was protected by 4-PSQ pretreatment. Additionally, 4-PSQ exposure did not alter urea levels, aspartate (AST) and alanine aminotrasferase (ALT) activities in plasma. Parameters of oxidative stress in brain and liver of mice were not modified by 4-PSQ. Taken together these data demonstrated that the anxiolytic-like effect caused by 4-PSQ seems to be mediated by involvement of the glutamatergic system.