Corticotropin releasing factor (CRF) receptor antagonist blocks activating and ‘anxiogenic’ actions of CRF in the rat

The effectiveness of a recently synthesized corticotropin releasing factor (CRF) antagonist, alpha-helical CRF9-41, in reversing the locomotor activating and proconflict effects of CRF was evaluated. The CRF receptor antagonist (50, 100 and 200 micrograms, i.c.v.) produced a dose-related attenuation of the response-suppressing effects of CRF in a conflict model of anxiety. The antagonist also effectively suppressed the marked locomotor activation produced by CRF. No discernible intrinsic effects on behavior were noted when the antagonist was administered alone. These results suggest that the behavioral effects of CRF are receptor-mediated phenomena and point to the potential usefulness of a CRF antagonist in understanding the function of endogenous CRF in mediating responses to stressful stimuli.     

Corticosterone and corticotropin‐releasing factor acutely facilitate gamma oscillations in the hippocampus in vitro

Stressful experiences do not only cause peripheral changes in stress hormone levels, but also affect central structures such as the hippocampus, implicated in spatial orientation, stress evaluation, and learning and memory. It has been suggested that formation of memory traces is dependent on hippocampal gamma oscillations observed during alert behaviour and rapid eye movement sleep. Furthermore, during quiescent behaviour, sharp wave‐ripple (SW‐R) activity emerges. These events provide a temporal window during which reactivation of memory ensembles occur. We hypothesized that stress‐responsive modulators, such as corticosterone (CORT), corticotropin‐releasing factor (CRF) and the neurosteroid 3α, 21‐dihydroxy‐5α‐pregnan‐20‐one (THDOC) are able to modulate gamma oscillations and SW‐Rs. Using in vitro hippocampal slices, we studied acute and subacute (2 h) impact of these agents on gamma oscillations in area cornu ammonis 3 of the ventral hippocampus induced by acetylcholine (10 μm ) combined with physostigmine (2 μm ). CORT increased the gamma oscillations in a dose‐dependent fashion. This effect was mediated by glucocorticoid receptors. Likewise, CRF augmented gamma oscillations via CRF type 1 receptor. Lastly, THDOC was found to diminish cholinergic gamma oscillations in a dose‐dependent manner. Neither CORT, CRF nor THDOC modulated gamma power when pre‐applied for 1 h, 2 h before the induction of gamma oscillations. Interestingly, stress‐related neuromodulators had rather mild effects on spontaneous SW‐R compared with their effects on gamma oscillations. These data suggest that the alteration of hippocampal gamma oscillation strength in vitro by stress‐related agents is an acute process, permitting fast adaptation to new attention‐requiring situations in vivo.     

The CRF1 receptor mediates the excitatory actions of corticotropin releasing factor (CRF) in the developing rat brain: in vivo evidence using a novel, selective, non-peptide CRF receptor antagonist

Corticotropin releasing factor (CRF) is the key coordinator of the neuroendocrine and behavioral responses to stress. In the central nervous system, CRF excites select neuronal populations, and infusion of CRF into the cerebral ventricles of infant rats produces severe age-dependent limbic seizures. These seizures, like other CRF effects, result from activation of specific receptors. Both of the characterized members of the CRF receptor family (CRF₁ and CRF₂), are found in the amygdala, site of origin of CRF-induced seizures, and may therefore mediate these seizures. To determine which receptor is responsible for the excitatory effects of CRF on limbic neurons, a selective, non-peptide CRF₁ antagonist was tested for its ability to abolish the seizures, in comparison to non-selective inhibitory analogues of CRF. Pretreatment with the selective CRF₁ blocker (NBI 27914) increased the latency and decreased the duration of CRF-induced seizures in a dose-dependent manner. The higher doses of NBI 27914 blocked the behavioral seizures and prevented epileptic discharges in concurrent electroencephalograms recorded from the amygdala. The selective CRF₁ blocker was poorly effective when given systemically, consistent with limited blood-brain barrier penetration. Urocortin, a novel peptide activating both types of CRF receptors in vitro, but with preferential affinity for CRF₂ receptors in vivo, produced seizures with a lower potency than CRF. These limbic seizures, indistinguishable from those induced by CRF, were abolished by pretreatment with NBI 27914, consistent with their dependence on CRF₁ activation. In summary, CRF induces limbic seizures in the immature rat, which are abolished by selective blocking of the CRF₁ receptor. CRF₁-messenger RNA levels are maximal in sites of seizure origin and propagation during the age when CRF is most potent as a convulsant. Taken together, these facts strongly support the role of the developmentally regulated CRF₁ receptor in mediating the convulsant effects of CRF in the developing brain.     

CRF1 and CRF2 receptors in the bed nucleus of stria terminalis differently modulate the baroreflex function in unanesthetized rats

The baroreflex is an important blood pressure regulating mechanism. The bed nucleus of stria terminalis (BNST) modulates the baroreflex function. However, the local BNST neurochemical mechanisms involved in control of baroreflex responses are not completely understood. Therefore, in this study, we investigated the involvement of corticotropin‐releasing factor (CRF) receptors within the BNST in baroreflex control of heart rate in unanesthetized rats. For this, we evaluated effects of bilateral microinjection into the BNST of either the selective CRF₁ receptor antagonist CP376395 (5 nmol/100 nL) or the selective CRF₂ receptor antagonist antisauvagine‐30 (5 nmol/100 nL) in bradycardiac response evoked by blood pressure increases caused by intravenous infusion of phenylephrine as well as tachycardiac response to blood pressure decrease caused by intravenous infusion of sodium nitroprusside. Bilateral microinjection of CP376395 into the BNST decreased the baroreflex bradycardiac response without affecting the reflex tachycardia. Conversely, BNST treatment with antisauvagine‐30 decreased heart rate response during blood pressure drop without affecting the reflex bradycardia. Overall, these findings provide evidence of an involvement of CRF neurotransmission within the BNST in baroreflex activity. Nevertheless, data indicate that local CRF₁ and CRF₂ receptors differently modulate the baroreflex control of heart rate.     

Astressin, a corticotropin releasing factor antagonist, reverses the anxiogenic effects of urocortin when administered into the basolateral amygdala

Previous work in our laboratory has shown that Urocortin (Ucn), a peptide related to corticotropin releasing factor (CRF), injected into the basolateral nucleus of the amygdala (BLA) in male Wistar rats would result in an anxiogenic response as measured in the social interaction (SI) test. In addition, it was found that repeated injections of subthreshold doses of Ucn would 'prime' the animal's response. This 'priming' effect induces a sensitivity to sodium lactate infusions that results in a panic-like reaction. Currently, we examined the effects of the CRF(1) and CRF(2) antagonist Astressin (Asn) on the anxiety-like responses produced during 'priming' as well as during a sodium lactate infusion into 'primed' rats. The results showed that Asn (60 pmoles) was able to reverse the anxiogenic effects seen during acute administration of Ucn, but was only able to partially antagonize the same response following 'priming' with Ucn. Furthermore, Asn administered either alone or prior to a sodium lactate infusion had no effect on the primed rat's behavior. Autoradiographic studies, in Ucn primed and sham-primed animals indicated no significant changes in [(125)I]-Sauvagine binding to CRF(1) and CRF(2) receptors in several brain regions. Thus, a 60 pmole dose of Asn blocks the effects of an acute injection of Ucn (100 pmoles), while only partially blocking the behavioral effects after repeated injections of subthreshold doses of Ucn (6 pmoles) are given. Furthermore, Asn has no effect on anxiogenic responses due to sodium lactate infusions in 'primed' rats     

The effect of morphine on MC4 and CRF receptor mRNAs in the rat amygdala and attenuation of tolerance after their blockade

The relationships between the CRF, which enhances the proopiomelanocortin (POMC) biosynthesis, and POMC-derived peptides (opioids and melanocortins) might be a new target for rational treatment of morphine tolerance. In the present study, we investigated the effect of acute and chronic morphine administration on the level of CRF1 and melanocortin 4 receptor (MC4-R) mRNAs in the rat amygdala by quantitative real-time PCR method. Moreover, we investigated the effect of antagonists of melanocortin and CRF receptors, SHU9119 and -helical CRF (h-CRF), respectively, administered bilaterally into the central nucleus of the amygdala, on morphine tolerance using tail-flick and paw withdrawal tests. Our study demonstrated that acute morphine administration decreased the level of MC4-R mRNA in the rat amygdala. This decrease was attenuated following chronic morphine administration, and mRNA level of MC4 receptors was gradually increased and, on 9th day of morphine administration, i.e. in the period when morphine tolerance already developed, the level was significantly increased in comparison with control and with the effect after single morphine dose. In contrast, morphine did not affect the CRF receptor. In behavioral study, we demonstrated that SHU9119 and h-CRF significantly increased the antinociceptive effect of morphine, when they were injected into the amygdala prior to morphine administration in tolerant rats. We have shown for the first time the contribution of amygdalar melanocortin receptors to morphine tolerance, and we conclude that the altered melanocortin receptor function may play an important role in the development of morphine-induced tolerance. CRF and melanocortin peptides can modulate the phenomena in the same direction, in opposition to opioids. Therefore, antagonists of melanocortin receptors may be regarded as possible therapeutic modulators of morphine tolerance.     

Blockade of corticotropin‐releasing hormone receptor 1 attenuates early‐life stress‐induced synaptic abnormalities in the neonatal hippocampus

Adult individuals with early stressful experience exhibit impaired hippocampal neuronal morphology, synaptic plasticity and cognitive performance. While our knowledge on the persistent effects of early‐life stress on hippocampal structure and function and the underlying mechanisms has advanced over the recent years, the molecular basis of the immediate postnatal stress effects on hippocampal development remains to be investigated. Here, we reported that repeated blockade of corticotropin‐releasing hormone receptor 1 (CRHR1) ameliorated postnatal stress‐induced hippocampal synaptic abnormalities in neonatal mice. Following the stress exposure, pups with fragmented maternal care showed retarded dendritic outgrowth and spine formation in CA3 pyramidal neurons and reduced hippocampal levels of synapse‐related proteins. During the stress exposure, repeated blockade of glucocorticoid receptors (GRs) by daily administration of RU486 (100 µg g^?1) failed to attenuate postnatal stress‐evoked synaptic impairments. Conversely, daily administration of the CRHR1 antagonist antalarmin hydrochloride (20 µg g^?1) in stressed pups normalized hippocampal protein levels of synaptophysin, postsynaptic density‐95, nectin‐1, and nectin‐3, but not the N‐methyl‐d ‐aspartate receptor subunits NR1 and NR2A. Additionally, GR or CRHR1 antagonism attenuated postnatal stress‐induced endocrine alterations but not body growth retardation. Our data indicate that the CRH‐CRHR1 system modulates the deleterious effects of early‐life stress on dendritic development, spinogenesis, and synapse formation, and that early interventions of this system may prevent stress‐induced hippocampal maldevelopment. © 2014 Wiley Periodicals, Inc.     

Protective effect of MK-801 on the anoxia-aglycemia induced damage in the fluorocitrate-treated hippocampal slice of the rat

We investigated electrophysiological responses induced by ischemia-like insult (anoxia and aglycemia, AA) in the rat hippocampal CA1 pyramidal cells in an in vitro slice preparation devoid of glial metabolism. In the slice treated with fluorocitrate (100 μM), a glia-specific metabolic inhibitor, 10 min AA induced hyperexcitation as evidenced by an appearance of multiple population spikes evoked by stimulation of the Schaffer collateral/commissural pathway in the CA1 region prior to elimination of the response. Readministration of oxygen and glucose failed to restore the population spike amplitude. Intracellular recordings revealed that 10 min AA induced slow EPSPs with relative long duration. The induction of the slow EPSPs was followed by a rapid membrane depolarization with a large amplitude. When the fluorocitrate-treated slice was exposed to MK-801 (10 μM), a non-competitive N-methyl-

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-aspartate (NMDA) receptor antagonist, 10 min AA failed to induce either the hyperexcitation of synaptic responses or the rapid depolarization. Furthermore, synaptic responses were fully restored after readministration of oxygen and glucose. In contrast, neither the synaptic hyperexcitation nor the rapid depolarization was observed during 10 min AA in the hippocampal CA1 pyramidal cells of the control slice. In addition, an irreversible synaptic failure associated with AA was not induced in the control slice. These results strongly suggest that fluorocitrate increases NMDA receptor-dependent AA-induced damage in the hippocampal slice by interfering glial spatial buffering of K⁺.     

Bed nucleus of the stria terminalis: cytoarchitecture, immunohistochemistry, and projection to the parabrachial nucleus in the rat

The bed nucleus of the stria terminalis (BST) sends a dense projection to the parabrachial nucleus (PB) in the pons. The BST contains many different types of neuropeptidelike immunoreactive cells and fibers, each of which exhibits its own characteristic distribution within cytoarchitecturally distinct BST subnuclei. Corticotropin releasing factor (CRF)-, neurotensin (NT)-, somatostatin (SS)-, and enkephalin (ENK)-like immunoreactive (ir) neurons are particularly numerous within areas of the BST that project to the PB. In this study, we use the combined retrograde fluorescence-immunofluorescence method to determine whether neurons in the BST that project to the PB contain these immunoreactivities. After Fast Blue injections into PB, retrogradely labeled neurons were numerous throughout the lateral part of the BST, particularly in the dorsal lateral (DL) and posterior lateral subnuclei. Retrogradely labeled neurons were also present in the preoptic, ventral lateral, and supracapsular BST subnuclei and in the parastrial nucleus. Many of the CRF-ir, NT-ir, and SS-ir neurons in DL were retrogradely labeled. A few double-labeled cells of each type were also found in the posterior lateral, ventral lateral and supracapsular BST subnuclei ENK-ir neurons were never retrogradely labeled. Our results show that BST neurons that project to the PB stain for the same neuropeptides as those in the central nucleus of the amygdala (CeA) that project to the PB, demonstrating further the close anatomical relations between these two structures.     

Developmental and regional differences in the localization of Na,K-ATPase activity in the rabbit hippocampus

Regional differences in Na,K-ATPase activity, and development of Na,K-ATPase activity were examined in rabbit hippocampus using a histochemical marker of enzyme activity. Stratum lucidum of CA3/CA2, corresponding to the mossy fiber terminal field, showed high Na,K-ATPase activity compared to stratum radiatum of CA1. A significant increase in Na,K-ATPase activity was found between 8 and 15 days postnatal. Tissues with limited Na,K-ATPase activity (immature hippocampus, the mature CA1 region) appear particularly prone to seizure-like abnormalities, perhaps reflecting an inability to regulate extracellular potassium.     

Sex differences in the ontogeny of CRF receptors during adolescent development in the dorsal raphe nucleus and ventral tegmental area

Interactions between corticotropin‐releasing factor (CRF) and monoaminergic systems originating from the dorsal raphe nucleus (DR) and ventral tegmental area (VTA) have been implicated in the etiology and pathophysiology of several stress‐related neuropsychiatric disorders such as depression and substance abuse. Sub‐regions within the DR and VTA give rise to specific projections that have unique roles in limbic‐ and reward‐related behaviors. Given that these disorders typically emerge during adolescence, it is surprising that few studies have examined the age‐, sex‐, and region‐dependent expression of CRF receptors throughout multiple stages of adolescence in these stress‐relevant circuits. To determine the ontogeny of CRF receptors during adolescent development, three regions of the DR (dorsal, caudal, and ventrolateral parts) and the posterior VTA were microdissected from Sprague‐Dawley male and female rats on postnatal day (P) 25, P35, P42, P56, and P90. Tissue was processed and analyzed with qRT‐PCR to measure CRF₁ and CRF₂ receptors. The serotonin and catecholamine enzymes in the DR and VTA, tryptophan hydroxylase 2 (TPH2) and tyrosine hydroxylase, respectively, were also analyzed for maturational differences. This study identified that CRF₁ receptors are lower in males than females within the dorsal, ventrolateral region of the DR (DRVL), which is involved in anxiety‐, stress‐, and panic‐related responses. Females had higher CRF₂ receptors compared to males in the DRVL only. Levels of TPH2 mRNA in the DRVL were overproduced transiently in females before declining into adulthood. These fundamental studies suggest that sex differences in CRF receptors should be considered when examining stress‐related neuropsychiatric disorders and their treatment. Synapse 70:125–132, 2016. © 2016 Wiley Periodicals, Inc.     

Dementia of the Alzheimer type and hypothalamus-pituitary-adrenocortical axis: changes in cerebrospinal fluid corticotropin releasing factor and plasma cortisol levels

The activity of the hypothalamus-pituitary-adrenocortical (HPA) axis was explored in 10 patients with dementia of the Alzheimer type (DAT) and in 11 age-matched controls, by measuring 1) corticotropin-releasing factor (CRF) levels in cerebrospinal fluid (CSF), 2) the circadian changes of plasma cortisol, 3) and 4) the plasma cortisol response to dexamethasone suppression test (DST) and to CRF stimulation test. CSF CRF levels in DAT were significantly higher than in controls and inversely related to the Mini Mental State (MMS) score. The patients also displayed increased morning (0800 h) plasma cortisol values, with higher mesor and amplitude in the circadian pattern. Dexamethasone resistance was shown by 6 of the 10 DAT subjects. Plasma cortisol response to CRF administration was similar in the two groups, except for the peak values, which in DAT patients were reached earlier than in controls. The present data suggest an overactivity of HPA axis in DAT; its possible role in the evolution of the disease is discussed.     

Distribution of corticotropin‐releasing factor (CRF) receptor binding in the mouse brain using a new,high‐affinity radioligand, [125I]‐PD‐Sauvagine

The corticotropin‐releasing factor (CRF) family of peptides includes CRF and three urocortins, which signal through two distinct G‐protein coupled receptors, CRF₁ and CRF₂. Although the cellular distribution of CRF receptor expression has been well characterized at the mRNA level, the localization of receptor protein, and, by inference, of functional receptors, has been limited by a lack of reliable immunohistochemical evidence. Recently, a CRF‐related peptide, termed PD‐sauvagine, was isolated from the skin of the frog, Pachymedusa dacnicolor, and validated as a high‐affinity ligand for CRF receptor studies. A radiolabeled analog, [¹²⁵I]‐PD‐sauvagine, with high signal‐to‐noise ratio, was used in autoradiographic studies to map the distribution of CRF receptor binding sites in the mouse brain. Through the use of receptor‐deficient mice and subtype‐specific antagonists, CRF₁ and CRF₂ binding sites were isolated, and found to be readily reconcilable with regional patterns of mRNA expression. Binding site distributions within a given structure sometimes differed from mRNA patterns, however, particularly in laminated structures of the isocortex, hippocampus, and cerebellum, presumably reflecting the trafficking of receptors to their operational homes on neuronal (mostly dendritic) processes. Binding patterns of [¹²⁵I]‐PD‐sauvagine provided independent assessments of controversial receptor localizations, failing to provide support for CRF₁ expression in central autonomic components of the limbic forebrain, the locus coeruleus and cerebellar Purkinje cells, or for CRF₂ in any aspect of the cerebellar cortex. Though lacking in ideal resolution, in vitro binding of the PD‐sauvagine radioligand currently provides the most sensitive and accurate available tool for localizing CRF receptors in rodent brain.     

LAU-0901, a novel platelet-activating factor antagonist, is highly neuroprotective in cerebral ischemia

Platelet-activating factor (PAF) is a bioactive phospholipid that accumulates during ischemia-reperfusion and is involved in the activation of platelets, neutrophils, and pro-inflammatory signaling. PAF has been suggested to enhance brain ischemia-reperfusion damage. LAU-0901, a novel PAF receptor antagonist, was examined in models of focal cerebral ischemia in rats and mice. Sprague–Dawley rats were anesthetized and received 2-hour middle cerebral artery occlusion (MCAo) by intraluminal suture. LAU-0901 (30, 60, 90 mg/kg; n = 9–11) or vehicle (n = 11) was administered i.p. at 2 h after onset of MCAo. The neurological status was evaluated at 60 min, and on days 1, 2, 3 and 7 after MCAo. In the dose–response study in mice, C57BL/6 mice were anesthetized and received 1 h MCAo by intraluminal suture. LAU-0901 (15, 30, 60 mg/kg; n = 7–9) or vehicle (n = 8) was given i.p. at 1 h after onset of MCAo. Local cerebral blood flow (LCBF) was measured at 1, 2, 4, and 6 h after MCAo in mice. LAU-0901 treated rats showed improved neurological score throughout the 7-day survival period. LAU-0901 treatment (30, 60 and 90 mg/kg) reduced total corrected infarct volume compared to vehicle rats by 76, 88 and 90%, respectively. Mice treated with LAU-0901 (30 and 60 mg/kg) reduced total infarction by 29% and 66%, respectively. LCBF was improved by treatment with LAU-0901 (30 mg/kg) by 77% of baseline at 6 h. In conclusion, we demonstrate for the first time that LAU-0901 improves behavioral scores, LCBF and reduces infarct volume after focal cerebral ischemia in rats and mice. Thus, this PAF receptor antagonist exhibits potent and sustained neuroprotection that may be of value for the design of stroke therapies.     

(76) Br]BMK-152, a nonpeptide analogue, with high affinity and low nonspecific binding for the corticotropin-releasing factor type 1 receptor

Corticotropin-releasing factor (CRF), a neuropeptide, regulates endocrine and autonomic responses to stress through G-protein coupled receptors, CRF(1) or CRF(2) . A PET ligand able to monitor changes in CRF(1) receptor occupancy in vivo would aid in understanding the pathophysiology of stress-related diseases as well as in the clinical development of nonpeptide antagonists with therapeutic value. We have radiolabeled the CRF(1) receptor ligand, [8-(4-bromo-2,6-dimethoxyphenyl)-2,7-dimethylpyrazolo[1,5-α][1,3,5]triazin-4-yl]-N,N-bis-(2-methoxyethyl)amine (BMK-152) (ClogP = 2.6), at both the 3 and 4 position with [(76) Br]. Using in vitro autoradiography saturation studies the 4-[(76) Br]BMK-152 exhibited high affinity binding to both rat (K(d) = 0.23 ± 0.07 nM; n = 3) and monkey frontal cortex (K(d) = 0.31 ± 0.08 nM; n = 3) consistent with CRF(1) receptor regional distribution whereas with the 3-[(76) Br]BMK-152, the K(d) s could not be determined due to high nonspecific binding. In vitro autoradiography competition studies using [(125) I]Tyr(0) -o-CRF confirmed that 3-Br-BMK-152 (K(i) = 24.4 ± 4.9 nM; n = 3) had lower affinity (70-fold) than 4-Br-BMK-152 (K(i) = 0.35 ± 0.07 nM; n = 3) in monkey frontal cortex and similiar studies using [(125) I]Sauvagine confirmed CRF(1) receptor selectivity. In vivo studies with P-glycoprotein (PGP) knockout mice (KO) and their wild-type littermates (WT) showed that the brain uptake of 3-[(76) Br]BMK/4-[(76) Br]BMK was increased less than twofold in KO versus WT indicating that 3-[(76) Br]BMK-152/4-[(76) Br]BMK was not a Pgp substrate. Rat brain uptakes of 4-[(76) Br] BMK-152 from ex vivo autoradiography studies showed regional localization consistent with known published CRF(1) receptor distribution and potential as a PET ligand for in vivo imaging of CRF(1) receptors.     

Enhancement of paired-pulse depression in the dentate gyrus in vivo by the NMDA antagonist, MK-801, and electrical kindling

We have previously demonstrated that late paired-pulse depression of dentate granule cell field potentials decreases when stimulus intensity is increased from moderate to high levels. Voltage-dependent N-methyl-

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-aspartate (NMDA) currents are increasingly activated within this stimulus range, and are enhanced following the development of kindled seizures. The NMDA antagonist, MK-801 (0.25 and 1.0 mg/kg, i.p.), was used in the present experiments to evaluate the contribution of NMDA currents to the loss of late paired-pulse depression at high stimulus intensities in naive and kindled rats. Paired-pulse stimulus intensity functions were obtained from animals prepared with chronic electrodes in the perforant path and dentate gyrus. MK-801 administration had no effect on the stimulus intensity function for early paired-pulse depression (20–30 ms interpulse intervals, IPI) in either preparation. Late paired-pulse depression (150–500 ms IPI) was significantly enhanced in naive rats by MK-801. In contrast, MK-801 had no effect on the potentiation of late paired-pulse depression recorded from kindled animals. These findings suggest that the ability of NMDA currents to reduce the strength of late paired-pulse depression in naive animals is altered following the development of kindled seizures. A decrease in late paired-pulse depression was observed at high stimulus intensities under all experimental conditions. The latter findings indicate that the processes responsible for the reduction in late paired-pulse depression at high stimulus intensities are unaffected by either NMDA or kindling-induced modulation of late paired-pulse depression.     

Perampanel: a novel, orally active, noncompetitive AMPA-receptor antagonist that reduces seizure activity in rodent models of epilepsy

Purpose: To assess the pharmacology of perampanel and its antiseizure activity in preclinical models. Perampanel [2‐(2‐oxo‐1‐phenyl‐5‐pyridin‐2‐yl‐1,2‐dihydropyridin‐3‐yl) benzonitrile] is a novel, orally active, prospective antiepileptic agent currently in development for refractory partial‐onset seizures. Methods: Perampanel pharmacology was assessed by examining changes in intracellular free Ca²⁺ ion concentration ([Ca²⁺]_i) in primary rat cortical neurones, and [³H]perampanel binding to rat forebrain membranes. Antiseizure activity of orally administered perampanel was examined in amygdala‐kindled rats and in mice exhibiting audiogenic, maximal electroshock (MES)–induced, pentylenetetrazole (PTZ) –induced, or 6 Hz‐induced seizures. Key Findings: In cultured rat cortical neurones, perampanel inhibited α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionic acid (AMPA)–induced increases in [Ca²⁺]_i (IC₅₀ 93 nm vs. 2 μm AMPA). Perampanel had a minimal effect on N‐methyl‐d ‐aspartate (NMDA)–induced increases in [Ca²⁺]_i, and only at a high concentration (30 μm ). [³H]Perampanel binding to rat forebrain membranes was not significantly displaced by glutamate or AMPA but was displaced by the noncompetitive AMPA receptor antagonists CP465022 (K_i 11.2 ± 0.8 nm ) and GYKI52466 (K_i 12.4 ± 1 μm ). In mice, perampanel showed protective effects against audiogenic, MES‐induced, and PTZ‐induced seizures (ED₅₀s 0.47, 1.6, and 0.94 mg/kg, respectively). Perampanel also inhibited 6 Hz electroshock‐induced seizures when administered alone or in combination with other antiepileptic drugs (AEDs). In amygdala‐kindled rats, perampanel significantly increased afterdischarge threshold (p < 0.05 vs. vehicle), and significantly reduced motor seizure duration, afterdischarge duration, and seizure severity recorded at 50% higher intensity than afterdischarge threshold current (p < 0.05 for all measures vs. vehicle). Perampanel caused dose‐dependent motor impairment in both mice (TD₅₀ 1.8 mg/kg) and rats (TD₅₀ 9.14 mg/kg), as determined by rotarod tests. In mice, the protective index (TD₅₀ in rotarod test/ED₅₀ in seizure test) was 1.1, 3.8, and 1.9 for MES‐induced, audiogenic, and PTZ‐induced seizures, respectively. In rat, dog, and monkey, perampanel had a half‐life of 1.67, 5.34, and 7.55 h and bioavailability of 46.1%, 53.5%, and 74.5%, respectively. Significance: These data suggest that perampanel is an orally active, noncompetitive, selective AMPA receptor antagonist with potential as a broad spectrum antiepileptic agent.     

The serotonergic and noradrenergic systems of the hippocampus: their interactions and the effects of antidepressant treatments

Previous reviews have well illustrated how antidepressant treatments can differentially alter several neurotransmitter systems in various brain areas. This review focuses on the effects of distinct classes of antidepressant treatments on the serotonergic and the noradrenergic systems of the hippocampus, which is one of the brain limbic areas thought to be relevant in depression: it illustrates the complexity of action of these treatments in a single brain area. First, the basic elements (receptors, second messengers, ion channels, ...) of the serotonergic and noradrenergic systems of the hippocampus are revisited and compared. Second, the extensive interactions occurring between the serotonergic and the noradrenergic systems of the brain are described. Finally, issues concerning the short- and long-term effects of antidepressant treatments on these systems are broadly discussed. Although there are some contradictions, the bulk of data suggests that antidepressant treatments work in the hippocampus by increasing and decreasing, respectively, serotonergic and noradrenergic neurotransmission. This hypothesis is discussed in the context of the purported function of the hippocampus in the formation of memory traces and emotion-related behaviors.