BDNF enhancement of postsynaptic NMDA receptors is blocked by ethanol

The neurotrophin brain-derived neurotrophic factor (BDNF) modulates several distinct aspects of synaptic transmission. Physiological and biochemical evidence implicates the NMDA glutamate receptor as one of the targets for BDNF modulation. In the present studies, murine brain slices containing hippocampus and neocortex were used to study the effects of BDNF on excitatory neurotransmission. Acute exposure to BDNF rapidly and reversibly enhanced the magnitude of NMDA-mediated, but not AMPA receptor-mediated, synaptic currents, specifically enhancing the activity of NMDA receptors containing the NR2B subunit. This effect of BDNF was dependent on activation of trkB neurotrophin receptors because similar effects were not seen with the related neurotrophins NT-3 or NGF. Furthermore, activation of trkB receptors in the postsynaptic neuron was required, as BDNF-induced potentiation was blocked by postsynaptic injection of a trk tyrosine kinase inhibitor. Interestingly, the effect of BDNF was also completely blocked by pretreatment with ethanol, even at concentrations of ethanol that had minimal direct effects on NMDA-mediated responses. These results provide a potential mechanism for the proposed role for BDNF in activity-dependent synaptic plasticity and, potentially, learning and memory processes.     

Norepinephrine and serotonin-induced antinociception are blocked by naloxone with different dosages

The effects of intrathecally (IT) administered naloxone (Nal) on the antinociception produced by IT norepinephrine (NE), serotonin (5-HT), or morphine (Mor) were observed and compared in rats using the tail-flick (TF) assay. The results show that: a) NE, 5-HT, and Mor in doses of 1 nmol, 240 nmol, and 0.5 nmol, respectively, produce similar increases in amplitude and time in TF latency (TFL); b) Nal treatment of 240 and 360 nmol has no effects on TFL; c) the antinociception produced by NE (1 nmol) can be blocked by Nal (240 nmol); d) antinociception produced by Mor (0.5 nmol) can also be blocked by Nal (240 nmol); e) 240 nmol of Nal does not affect the 5-HT (120 nmol)-produced antinociception, while 360 nmol of Nal show a delayed blockade to the 5-HT (120 nmol)-produced antinociception. The results suggest that endogenous opiate-like substances may be involved in both NE- or 5-HT-produced antinociception at the spinal level, and these effects may be mediated through different types of opiate receptors.     

Involvement of amygdala pathways in the influence of post-training intra-amygdala norepinephrine and peripheral epinephrine on memory storage

These experiments examined the role of two major amygdala afferent-efferent pathways--the stria terminalis (ST) and the ventral amygdalofugal pathway (VAF)--in mediating the effects, on memory storage, of post-training intra-amygdala injections of norepinephrine (NE) and subcutaneous (s.c.) injections of epinephrine (E). Rats with either ST lesions or VAF transections and sham-operated rats were trained on a one-trial step-through inhibitory avoidance task and immediately after training received intra-amygdala injections of NE or a buffer solution. Other groups of VAF-transected animals received post-training s.c. injections of E or saline. ST lesions blocked the memory-enhancing effect of intra-amygdala injections of a low dose of NE (0.2 microgram) as well as the amnestic effect of a high dose of NE (5.0 microgram). In contrast, VAF transections did not block the memory-enhancing effect of NE (0.2 microgram). However, VAF transections attenuated the memory-enhancing effect of s.c. injections of E: the effective dose of E was shifted from 0.1 to 0.5 mg/kg. These findings, considered together with previous evidence that ST lesions block the memory-enhancing effect of peripheral E injections, suggest that the VAF is involved in mediating the central influence of peripheral E on amygdala functioning, while the ST is involved in mediating amygdala influences on memory storage elsewhere in the brain.     

Glucocorticoid enhancement of memory consolidation in the rat is blocked by muscarinic receptor antagonism in the basolateral amygdala

Glucocorticoid-induced memory enhancement is known to depend on beta-adrenoceptor activation in the basolateral amygdala (BLA). Additionally, inactivation of muscarinic cholinergic receptors in the rat amygdala blocks memory enhancement induced by concurrent beta-adrenergic activation. Together, these findings suggest that glucocorticoid-induced modulation of memory consolidation requires cholinergic as well as adrenergic activation in the BLA. Two experiments investigated this issue. The first experiment examined whether blockade of muscarinic cholinergic receptors in the BLA with atropine alters the memory-enhancing effects of the systemically administered glucocorticoid dexamethasone. Dexamethasone (0.3, 1.0 or 3.0 mg/kg, s.c.) administered to rats immediately after inhibitory avoidance training produced dose-dependent enhancement of 48-h retention. Concurrent bilateral infusions of the muscarinic cholinergic antagonist atropine (0.5 microg in 0.2 microL per side) into the BLA blocked the memory enhancement. The second experiment investigated whether the BLA is a locus of interaction between glucocorticoid and muscarinic activation. The specific glucocorticoid receptor (GR or type II) agonist RU 28362 (1.0, 3.0 or 10 ng) was infused into the BLA either alone or together with atropine immediately after training. The GR agonist produced dose-dependent memory enhancement and atropine blocked the memory enhancement. These findings indicate that muscarinic cholinergic activation within the BLA is critical for enabling glucocorticoid enhancement of memory consolidation and that enhancement of memory induced by GR activation in the BLA requires cholinergic activation within the BLA.     

Hepatocyte growth factor-induced enhancement of dendritic branching is blocked by inhibitors of N-methyl-D-aspartate receptors and calcium/calmodulin-dependent kinases

Hepatocyte growth factor (HGF) and its receptor, Met, are clustered at excitatory synapses and can enhance N-methyl-D-aspartate (NMDA) receptor current and promote formation of neurites and dendrites. In this study, we examine the effects of HGF on dendritic arborization in mature cultures of dissociated hippocampal neurons. Exogenous HGF treatment caused a dose-dependent increase in total dendritic branch tip number, total dendritic branch length, and dendritic complexity in these neurons. NMDA receptor activity has been linked to changes in dendritic structure, so we tested the effects of HGF on the dendritic arbor in the presence of DL-2-amino-5-phosphonopentanoic acid (APV), an NMDA receptor inhibitor. APV blocked the HGF-induced enhancement of the dendritic arbor in a dose-dependent manner. Similarly, pretreatment of neurons with KN62, an inhibitor of calcium-dependent kinases, suppressed changes in dendritic branching induced by HGF. These results suggest that HGF initiates Ca2+-dependent processes, so we examined the effect of HGF on intracellular calcium levels and autophosphorylation of the calcium/calmodulin-dependent protein kinase II (CaMKII). HGF caused a persistent increase in fluorescence in clusters along dendrites of neurons preloaded with the Ca2+ indicator Fluo-4. HGF treatment also enhanced autophosphorylation of CaMKII. The increases in Fluo-4 fluorescence and autophosphorylation of CaMKII were blocked by pretreatment of neurons with APV. These results indicate that HGF stimulates Ca2+ influx into dendrites through the NMDA receptor and that this effect is necessary for the changes in dendritic morphology induced by HGF.     

BDNF mRNA expression in rat hippocampus following contextual learning is blocked by intrahippocampal IL-1beta administration

The present study examined the modulating effects of an intrahippocampal injection of interleukin-1beta (IL-1beta) on brain-derived neurotrophic factor (BDNF) mRNA expression 0.5, 2, 4, and 6 h following contextual fear conditioning, a task known to increase BDNF mRNA, in rats. Contextual fear conditioning produced a time-dependent increase in BDNF mRNA that varied by region of hippocampus. IL-1beta blocked or reduced these increases in BDNF mRNA in the CA1, CA2, and dentate gyrus regions of the hippocampus, but had no effect in cortical regions. These data support the idea that IL-1beta-produced memory deficits may be mediated via BDNF mRNA reductions in hippocampus.     

Formation of microglia-derived brain macrophages is blocked by adriamycin

Summary Injection of ricin, the toxic lectin fromRicinus communis, into the rat facial nerve leads to rapid degeneration of motor neurons and concomitant proliferation and transformation of endogenous microglia into brain macrophages. Using [³H]-thymidine autoradiography, immunocytochemistry for microglial markers and electron microscopy, we could show that when ricin was administered together with the cytostatic drug adriamycin, the retrogradely transported adriamycin inhibits the macrophage response induced by toxic ricin. It is concluded that under conditions of neuronal degeneration, e.g., following ricin intoxication, brain macrophages are predominantly, if not exclusively, derived from endogenous microglia.     

Fluid consumption in water-deprived rats after administration of naloxone or quaternary naloxone

1. 1. Water-deprived male rats were given access to water, or to a 0.005M sodium saccharin solution, or to a 0.9% sodium chloride solution, during a 30 min test period.

2. 2. Naloxone (0.01–10.0 mg/kg) produced dose-dependent reductions in the consumption of each fluid. Saccharin-drinking was significantly reduced by 0.01 mg/kg naloxone, and water- and saline-drinking by 0.1 mg/kg naloxone. Quaternary naloxone (0.01–10.0 mg/kg) had no effect on drinking under any condition.

3. 3. Access to the saline solution resulted in hyperdipsia, due to a prolongation of the initial bout of avid drinking in the thirsty rats. Naloxone, in small doses, completely abolished this hyperdipsia. Since the quaternary compound had no effect, it was concluded that opiate antagonist suppression of saline-induced hyperdipsia was probably mediated at central opiate receptors.

Extended enhancement of corticospinal connectivity with concurrent cortical and peripheral stimulation controlled by sensorimotor desynchronization

Background

Pairing cortical and peripheral input during motor imagery (MI)-related sensorimotor desynchronization (ERD) modulates corticospinal excitability at the cortical representation (hotspot) of the imagined movement.

Blockade of sensitisation-induced facilitation of appetitive conditioning by post-session intra-amygdala nafadotride

Prior D-amphetamine experience has been reported to enhance appetitive Pavlovian conditioning. The present study assessed the involvement of the mesoamygdaloid dopamine projection in this effect. Bilateral post-session intra-amygdala infusions of the D3 dopamine receptor antagonist, L-nafadotride, or vehicle were given during acquisition of a Pavlovian association in sensitised and unsensitised rats. During these sessions, subjects received presentations of a stimulus (CS(+)) paired with 10% sucrose availability. A second stimulus (CS(-)) was also presented but never paired with sucrose. Sensitised animals infused post-session with vehicle acquired a Pavlovian conditioned approach response during CS(+) presentations more rapidly than controls, as we have shown previously. However, post-session intra-amygdala L-nafadotride selectively retarded conditioned responding to the CS(+) in both groups of animals, abolishing the difference between sensitised and unsensitised rats. These results, therefore, extend the evidence for the involvement of the mesoamygdaloid dopamine projection in Pavlovian conditioning, and the facilitation of associative learning following sensitisation.     

Lipopolysaccharide-induced leptin release is not mediated by nitric oxide, but is blocked by dexamethasone

The adipocyte hormone, leptin, has homology with tumor necrosis factor-alpha (TNF-alpha) and the leptin receptor (OB-Rb) has homology with the interleukin(IL)-6 receptor. Lipopolysaccharide (LPS) from gram-negative bacteria stimulates the release of many pro-inflammatory cytokines, such as TNF-alpha, IL-1 and IL-6, among others. To test the hypothesis that LPS would also stimulate the release of leptin, LPS (0.6 mg/kg) was injected intravenously into conscious male rats bearing external jugular venous catheters. Vehicle (0.9% NaCl) was injected into control animals. Blood samples (0.3 ml) were drawn immediately before injection and every 10 min afterwards for 120 min. Plasma leptin concentrations increased gradually in the LPS-treated rats, reaching a peak at 120 min of nearly twice the starting level. To determine if this release was mediated by nitric oxide (NO), nitroarginine methyl ester (NAME), an inhibitor of NO synthase, was injected at doses of 11 or 23 mg/kg (i. v.). The lower dose decreased plasma leptin slightly, whereas the higher dose of NAME increased plasma leptin at 110 min but had no effect on LPS-induced leptin release. On the other hand, dexamethasone (DEX) (0.85 mg/kg), a synthetic glucocorticoid, injected 15 min before LPS, decreased LPS-induced leptin release by 80% (p < 0.001). The results indicate that LPS is a stimulant of leptin release, that NO has little control over basal or LPS-induced leptin release, but that glucocorticoids, epitomized by DEX, largely block LPS-induced leptin release. Increased release of leptin during infection may contribute to the decreased feeding, altered hormonal release and metabolic changes that occur during infection.     

Diagnosis of reversible versus irreversible cerebral ischemia by the intravenous administration of naloxone

Naloxone was given as an I.V. bolus of 0.8 mgs to four groups of patients with stroke: 1) 20 patients with C.T. proven cerebral infarcts of longer than 7 days duration; 2) 20 patients with acute cerebral ischemia of less than 24 hours; 3) 5 patients with C.T. proven intracerebral hemorrhage of less than 24 hours, and; 4) 3 patients with hyperacute cerebral ischemia which occurred during the performance of a cerebral angiogram. The patients with established cerebral infarctions of more than 7 days duration and the patients with intracerebral hematomas had no response to intravenous naloxone. Of 20 patients with acute cerebral ischemia of less than 24 hours duration, 7 had prompt, complete and long-lasting recovery. These patients had no subsequent evidence of cerebral infarct by C.T. scanner 48 hours after the onset of the cerebral ischemia and were asymptomatic when discharged. The 3 patients with hyperacute cerebral ischemia secondary to cerebral angiography had a dramatic response to the injection of naloxone. These findings suggest that intravenous naloxone may differentiate reversible versus irreversible cerebral ischemia.     

Memory enhancement induced by hypothalamic/fornix deep brain stimulation

Bilateral hypothalamic deep brain stimulation was performed to treat a patient with morbid obesity. We observed, quite unexpectedly, that stimulation evoked detailed autobiographical memories. Associative memory tasks conducted in a double-blinded "on" versus "off" manner demonstrated that stimulation increased recollection but not familiarity-based recognition, indicating a functional engagement of the hippocampus. Electroencephalographic source localization showed that hypothalamic deep brain stimulation drove activity in mesial temporal lobe structures. This shows that hypothalamic stimulation in this patient modulates limbic activity and improves certain memory functions.     

Anxiolytic-like effect induced by chronic stress is reversed by naloxone pretreatment

The present study assesses the influence of different restraint schedules on behavioral parameters determined by a conflict test, namely the light-dark transitions (LDT) as well as the opiate modulation on the behavioral consequences induced by chronic restraint. Finally, another group of animals that received naloxone (NAL) and/or chronic stress was either exposed to a single foot shock session or administered a single dose of the β-carboline FG 7142 (N′-methyl-β-carboline-3-carboxamide) immediately prior to the LDT test. We observed that a single restraint session (2 h) induced a decrease of LOT and time spent in the lit box, while chronic restraint (2 h per day for up to 7 days) induced a significant increase in both parameters. However, this increasing effect was blocked by a NAL administration (2 mg/kg IP) prior to each of the seven restraint events. A single foot shock or FG administration produced a clear anxiogenic response, an effect that was absent in animals previously submitted to chronic stress. In addition, NAL pretreatment abolished the chronic stress-induced attenuating effect on the behavioral suppression induced after either foot shock or FG administration. Therefore, these findings demonstrate that a previous history of chronic stress, leading to adaptation, induced an anxiolytic-like effect, and attenuated the behavioral supresslon produced by acute stressors. There seems to be an endogenous opiate mechanism involved in the behavioral influence induced by chronic stress.     

Morphological differentiation of cultured astrocytes is blocked by cadmium or cobalt

The morphological transformation of astrocytes in primary culture from flat to process bearing is induced by cyclic adenosine monophosphate (cAMP). Calcium currents in cultured astrocytes are also enhanced by cAMP. This correlation suggests the hypothesis that cAMP-induced calcium entry causes the morphological differentiation. The experiments reported here show that cadmium or cobalt, which block astrocyte calcium channels, also block the cAMP-induced morphological differentiation. These results support the hypothesized link between calcium entry and astrocyte differentiation.     

Effects of continuous naloxone administration on ventral tegmental self-stimulation

Continuous subcutaneous administration of naloxone (3 mg/kg/h), shifted ventral tegmental self-stimulation rate-frequency curves to the right, without suppressing behavioral performance. In addition this chronic blockade of opioid receptors altered μ binding parameters in the hippocampus and olfactory tubercle of naloxone-treated animals. These findings speak to the role opioid peptides play in the mediation of brain stimulation reward.     

Method of administration determines the effect of naloxone on pain

The opiate antagonist, naloxone, produces dose-dependent biphasic changes in clinical pain. The mechanism of the analgesia produced by low dose naloxone is unknown. To study the analgesic effect of naloxone, we have used a programmable infusion pump, which eliminates placebo-induced endorphin-mediated analgesia, to administer different doses of naloxone. We report that use of machine infusion of naloxone exclusively produces analgesia. The implications of this finding to the mechanism of naloxone-induced analgesia are discussed.     

Nasal administration of naloxone for detection of opiate dependence.

In clinical trials, nasally applied naloxone was used to identify opiate dependence in humans for the first time. Withdrawal distress was recorded, and pupillary response, pulse rate and blood pressure measured. A significant increase in withdrawal distress and pupillary dilation was observed after nasal administration of 1mg (1mg/400 microliters) naloxone in all subjects who also showed opiate-positive urine samples. In control subjects, no reaction to naloxone was observed. It may be concluded that the nasal route for naloxone administration is as effective as the parenteral route. This test is sensitive enough to identify the physically-dependent opiate user and might have a role in emergency medicine and withdrawal treatment.     

Heightened cortisol response to administration of naloxone in Tourette's syndrome

The release of corticotrophin-releasing factor (CRF) in the human has been shown to be under a direct inhibitory control derived from the locus coeruleus (LC). Opioids have been shown to inhibit CRF release. Based on our hypothesis of deranged opioid-noradrenergic activity in Tourette's syndrome (TS), we studied the effect of a naloxone challenge on plasma cortisol levels in 6 TS patients. In all patients naloxone produced a significant rise in cortisol secretion. These results support our hypothesis and suggest that in TS, noradrenergic LC receptors involved in CRF release are supersensitive as a result of chronic excessive endorphinergic activity.     

Olfactory discrimination learning is blocked by Leupeptin, a thiol protease inhibitor

Rats were trained on successive two-odor discriminations with the cues randomly located in an 8-arm radial maze. After several days of training using different odor pairs, the thiol protease inhibitor leupeptin was infused into the ventricles and testing continued. Leupeptin caused a pronounced, dose-dependent and reversible deficit in performance in this task. Previous studies have shown that these drug concentrations do not influence spontaneous activity, feeding and drinking, or the acquisition and retention of avoidance conditioning. The results are interpreted as supporting the hypothesis that a calcium-sensitive proteinase is involved in certain forms of memory that require modification of telencephalic circuitries.