Activation of histaminergic H3 receptors in the rat basolateral amygdala improves expression of fear memory and enhances acetylcholine release

The basolateral amygdala (BLA) is involved in learning that certain environmental cues predict threatening events. Several studies have shown that manipulation of neurotransmission within the BLA affects the expression of memory after fear conditioning. We previously demonstrated that blockade of histaminergic H3 receptors decreased spontaneous release of acetylcholine (ACh) from the BLA of freely moving rats, and impaired retention of fear memory. In the present study, we examined the effect of activating H3 receptors within the BLA on both ACh release and expression of fear memory. Using the microdialysis technique in freely moving rats, we found that the histaminergic H3 agonists R-alpha-methylhistamine (RAMH) and immepip, directly administered into the BLA, augmented spontaneous release of ACh in a similar manner. Levels of ACh returned to baseline on perfusion with control medium. Rats receiving intra-BLA, bilateral injections of the H3 agonists at doses similar to those enhancing ACh spontaneous release, immediately after contextual fear conditioning, showed stronger memory for the context-footshock association, as demonstrated by longer freezing assessed at retention testing performed 72 h later. Post-training, bilateral injections of 15 ng oxotremorine also had a similar effect on memory retention, supporting the involvement of the cholinergic system. Thus, our results further support a physiological role for synaptically released histamine, that in addition to affecting cholinergic transmission in the amygdala, modulates consolidation of fear memories     

Footshock stress but not contextual fear conditioning induces long‐term enhancement of auditory‐evoked potentials in the basolateral amygdala of the freely behaving rat

In this study, rats were bilaterally implanted with electrodes in the amygdala for chronic recording. Auditory click stimulation evoked in the basolateral nucleus a field potential characterized by three positive components: P1, P2 and P3 (peak latencies around: 10, 20 and 30 ms, respectively) which were each followed by three negative components: N1, N2 and N3 (peak latencies around: 13, 30 and 50 ms, respectively). Animals were divided into three groups (context-same, context-different and control). Following footshock administration, animals were either re-exposed to the same conditioning chamber (context-same group) or placed in a different context (context-different group) for electrophysiological and behavioural (evaluation of freezing response) recordings. The two early positive-negative complexes (P1-N1 and P2-N2) increased in amplitude from 2 min to 24 h following footshock in both context-same and context-different groups. No significant difference was observed between these two groups. The demonstration of significantly larger freezing responses in context-same subjects on exposure to the aversive conditioned environment indicated that this similarity of effects was not due to lack of conditioning of context under the experimental conditions chosen. We conclude that footshock stress produces general long-lasting changes in amygdala auditory field potentials that are not significantly affected by contextual fear conditioning.     

Differential expression of EGR-1 mRNA in the amygdala following diazepam in contextual fear conditioning

The amygdaloid complex is thought to be a major site of action of anxiolytic benzodiazepine agonists. To investigate whether activity in the amygdaloid complex is altered with anxiolytic effects of diazepam, mRNA expression of the immediate-early gene EGR-1 was examined in the amygdala following blockade of fear conditioning by diazepam. It was previously shown that mRNA expression of EGR-1 (also called, NGFI-A, Zif 268, Krox 24) increases in the lateral nucleus of the amygdala (LA) shortly following contextual fear conditioning. It was therefore hypothesized that diazepam would block both contextual fear and the concomitant increase in EGR-1 mRNA expression in the LA induced by fear conditioning. Rats administered systemic diazepam before fear conditioning displayed both anxiolytic effects during the post-shock period and amnesic effects during a retention test 24 h later. Diazepam blocked the fear-conditioning-induced increase in EGR-1 expression in the LA. In addition, diazepam significantly increased EGR-1 mRNA expression in the central nucleus of the amygdala (CeA) in a dose-dependent manner. The results reveal differential regulation of EGR-1 by diazepam in the central and lateral nuclei of the amygdala suggesting that these two amygdala nuclei act in a reciprocal manner during the anxiolytic and amnesic action of the benzodiazepine agonist.     

Extinction of auditory fear conditioning requires MAPK/ERK activation in the basolateral amygdala

Whereas the neuronal substrates underlying the acquisition of auditory fear conditioning have been widely studied, the substrates and mechanisms mediating the acquisition of fear extinction remain largely elusive. Previous reports indicate that consolidation of fear extinction depends on the mitogen-activated protein kinase/extracellular-signal regulated kinase (MAPK/ERK) signalling pathway and on protein synthesis in the medial prefrontal cortex (mPFC). Based on experiments using the fear-potentiated startle paradigm suggesting a role for neuronal plasticity in the basolateral amygdala (BLA) during fear extinction, we directly addressed whether MAPK/ERK signalling in the basolateral amygdala is necessary for the acquisition of fear extinction using conditioned freezing as a read-out. First, we investigated the regional and temporal pattern of MAPK/ERK activation in the BLA following extinction learning in C57Bl/6J mice. Our results indicate that acquisition of extinction is associated with an increase of phosphorylated MAPK/ERK in the BLA. Moreover, we found that inhibition of the MAPK/ERK signalling pathway by intrabasolateral amygdala infusion of the MEK inhibitor, U0126, completely blocks acquisition of extinction. Thus, our results indicate that the MAPK/ERK signalling pathway is required for extinction of auditory fear conditioning in the BLA, and support a role for neuronal plasticity in the BLA during the acquisition of fear extinction.     

Serotonin depresses excitatory synaptic transmission and depolarization‐evoked Ca2+ influx in rat basolateral amygdala via 5‐HT1A receptors

The actions of serotonin on rat basolateral amygdala neurons were studied with conventional intracellular recording techniques and fura-2 fluorimetric recordings. Bath application of 5-hydroxytryptamine (5-HT or serotonin) reversibly suppressed the excitatory postsynaptic potential in a concentration-dependent manner without affecting the resting membrane potential and neuronal input resistance. Extracellular Ba₂₊ or pertussis toxin pretreatment did not affect the depressing effect of 5-HT suggesting that it is not mediated through activation of G_i/o protein-coupled K₊ conductance. The sensitivity of postsynaptic neurons to glutamate receptor agonist was unaltered by the 5-HT pretreatment. In addition, the magnitude of paired-pulse facilitation was increased in the presence of 5-HT indicating a presynaptic mode of action. The effect of 5-HT was mimicked by the selective 5-HT_1A agonist 8-hydroxy-dipropylaminotetralin (8-OH-DPAT) and was blocked by the selective 5-HT_1A antagonist 1-(2-methoxyphenyl)-4[4-(2-phthalimido)butyl]piperazine oxadiazol-3-yl]methyl]phenyl]methanesulphonamide. In contrast, the selective 5-HT₂ receptor antagonist ketanserin failed to affect the action of 5-HT. The effects of 5-HT and 8-OH-DPAT on the high K₊-induced increase in [Ca₂₊]_i were studied in acutely dissociated basolateral amygdala neurons. High K₊-induced increase in [Ca₂₊]_i was blocked by Ca₂₊-free solution and Cd₂₊ suggesting that Ca₂₊ entry responsible for the depolarizaton-evoked increase in [Ca₂₊]_i occurred through voltage-dependent Ca₂₊ channels. Application of 5-HT and 8-OH-DPAT reduced the K₊-induced Ca₂₊ influx in a concentration-dependent manner. The effect of 5-HT was completely abolished in slices pretreated with Rp-cyclic adenosine 3′,5′-monophosphothioate (Rp-cAMP), a regulatory site antagonist of protein kinase A, suggesting that 5-HT may act through a cAMP-dependent mechanism. Taken together, these results suggest that functional 5-HT_1A receptors are present in the excitatory terminals and mediate the 5-HT inhibition of synaptic transmission in the amygdala. Introduction     

Beta1- and beta2-adrenoceptors in basolateral nucleus of amygdala and their roles in consolidation of fear memory in rats

It is known that beta-adrenoceptor (AR) in the basolateral nucleus of amygdala (BLA) plays an essential role in fear memory formation. However, the cellular and subcellular distributions of beta1- and beta2-ARs in the BLA and their roles in fear memory formation are poorly understood. Here, we report that both beta1- and beta2-ARs are predominantly expressed in BLA neurons but not in astrocytes. beta1-AR is distributed in the cell membrane and cytoplasm of neurons, whereas beta2-AR is localized not only in the cell membrane and cytoplasm but also in the nucleus. Intra-BLA infusion of the beta1-AR antagonist metoprolol and atenolol or the beta2-AR antagonist ICI118551 and butoxamine produces a severe deficit in 24-h auditory fear memory, leaving 1-h memory intact. Western-blot analysis reveals that the protein level of cytoplasmic beta1-AR significantly increases 2- and 4-h postconditioning, whereas that of cytoplasmic or nuclear beta2-AR is unchanged. The present results indicate that beta1- and beta2-ARs in the BLA have differential subcellular localizations and both are required for the consolidation of auditory fear memory.     

Circadian and Estral Changes in the Hypothalamic Prostaglandin E2 Content and [3H]Prostaglandin E2 Binding in Female Rats

Prostaglandin E₂, (PGE₂) is involved in the luteinizing hormone-releasing hormone-stimulated luteinizing hormone surge in female rats and may act via specific membrane receptors. The following studies were performed to determine whether there were any changes in the hypothalamic PGE₂ binding and/or PGE₂ content which were specific to proestrus and not to the rest of the estrous cycle. Groups of female Wistar rats were sacrificed at 3-h intervals throughout the estrous cycle to determine both the circadian and circaestral changes in the hypothalamic PGE₂ content and [³H]PGE₂ binding. The hypothalamic PGE₂ content was maximal at 1700 h on each of the 4 consecutive days of the estrous cycle but was independent of the stage of the cycle. [³H]PGE₂ binding also displayed a circadian rhythm; the lowest binding occurred near the circadian peak of PGE₂, suggesting that the PGE₂ binding sites were occupied by endogenous PGE₂. Since such circadian rhythms were not observed in the hypothalamus of male rats, they may be under the control of ovarian steroids. Also, since PGE₂ binding and the PGE₂ content both exhibit a diurnal pattern independent of the day of the cycle, there may be changes in the PGE₂ receptor-mediated process coupled to an adenylyl cyclase which could explain the luteinizing hormone surge in proestrus.     

Protein synthesis in the amygdala, but not the auditory thalamus, is required for consolidation of Pavlovian fear conditioning in rats

The amygdala is an essential neural substrate for Pavlovian fear conditioning. Nevertheless, long-term synaptic plasticity in amygdaloid afferents, such as the auditory thalamus, may contribute to the formation of fear memories. We therefore compared the influence of protein synthesis inhibition in the amygdala and the auditory thalamus on the consolidation of Pavlovian fear conditioning in Long-Evans rats. Rats received three tone-footshock trials in a novel conditioning chamber. Immediately after fear conditioning, rats were infused intra-cranially with the protein synthesis inhibitor, anisomycin. Conditional fear to the tone and conditioning context was assessed by measuring freezing behaviour in separate retention tests conducted at least 24 h following conditioning. Post-training infusion of anisomycin into the amygdala impaired conditional freezing to both the auditory and contextual stimuli associated with footshock. In contrast, intra-thalamic infusions of anisomycin or a broad-spectrum protein kinase inhibitor [1-(5'-isoquinolinesulphonyl)-2-methylpiperazine, H7] did not affect conditional freezing during the retention tests. Pre-training intra-thalamic infusion of the NMDA receptor antagonist 2-amino-5-phosphonopentanoic acid (APV), which blocks synaptic transmission in the auditory thalamus, produced a selective deficit in the acquisition of auditory fear conditioning. Autoradiographic assays of cerebral [14C]-leucine incorporation revealed similar levels of protein synthesis inhibition in the amygdala and thalamus following intra-cranial anisomycin infusions. These results reveal that the establishment of long-term fear memories requires protein synthesis in the amygdala, but not the thalamus, after auditory fear conditioning. Forms of synaptic plasticity that depend on protein synthesis, such as long-term potentiation, are likely candidates for the encoding and long-term storage of fear memories in the amygdala.     

Calcium Signalling in Mouse Bergmann Glial Cells Mediated by α1-adrenoreceptors and H1 Histamine - Receptors

The presence of adrenergic and histaminergic receptors in Bergmann glial cells from cerebellar slices from mice aged 20–25 days was determined using fura-2 Ca²⁺ microfluorimetry. To measure the cytoplasmic concentration of Ca²⁺ ([Ca²⁺]_i), either individual cells were loaded with the Ca²⁺-sensitive probe fura-2 using the whole-cell patch-clamp technique or slices were incubated with a membrane-permeable form of the dye (fura-2/AM) and the microfluorimetric system was focused on individual cells. The monoamines adrenalin and noradrenalin (0.1-10 μM) and histamine (10-100 μM) triggered a transient increase in [Ca²⁺]_i. The involvement of the α₁-adrenoreceptor was inferred from the observations that monoamine-triggered [Ca²⁺]_i responses were blocked by the selective α¹-adreno-antagonist prazosin and were mimicked by the α¹-adreno-agonist phenylephrine. The monoamine-induced [Ca²⁺]_i signals were not affected by β- and α₂-adrenoreceptor antagonists (propranolol and yohimbine), and were not mimicked by β- and α₂-adrenoreceptor agonists (isoproterenol and clonidine). Histamine-induced [Ca²⁺]_i responses demonstrated specific sensitivity to only H₁ histamine receptor modulators. [Ca²⁺]_i responses to monoamines and histamine did not require the presence of extracellular Ca²⁺ and they were blocked by preincubation of slices with thapsigargin (500 nM), indicating that the [Ca²⁺]_i increase is due to release from intracellular pools. No [Ca²⁺]_i responses were recorded after application of aspartate, bradykinin, dopamine, GABA, glycine, oxytocin, serotonin, somatostatin, substance P, taurine or vasopressin. We conclude that cerebellar Bergmann glial cells are endowed with α₁ -adrenoreceptors and H₁ histamine receptors which induce the generation of intracellular [Ca²⁺]_i signals via activation of Ca²⁺ release from inositol-l,4,5-trisphosphate-sensitive intracellular stores.     

Critical Role for M3 Muscarinic Receptors in Paradoxical Sleep Generation in the Cat

In the cat, microdialysis application of 200 μM carbachol to the peri-locus coeruleus a (peri-LCα) of the mediodorsal pontine tegmentum produced a marked (≤5–fold) increase in paradoxical sleep. This effect was blocked by 5–50 μM 4–diphenylacetoxy-N-methylpiperidine methiodide (4–DAMP), an M₁/M₃-selective muscarinic receptor antagonist. In contrast, the effect was not reversed by methoctramine, an M₂-selective antagonist, or pirenzepine, an M₁-selective antagonist, even at concentrations as high as 500 μM. In addition, unilateral application of 5 μM 4–DAMP alone to the peri-LCa induced both a >60% decrease in paradoxical sleep and a state of paradoxical sleep without atonia, whereas 50 μM pirenzepine and 500 μM methoctramine had no effect. Our findings are further evidence for the important role played by the peri-LCα and demonstrate a critical role for M₃ muscarinic cholinergic receptors in the generation of paradoxical sleep.     

Anticholinesterase Activity of Histamine H2-Receptor Antagonists in the Dog: Their Possible Role in Gastric Motor Activity

We studied the anticholinesterase activity of three H₂-receptor antagonists (cimetidine, ranitidine, and famotidine) in vitro and in conscious dogs with chronically implanted strain-gauge force transducers. In vivo, acetylcholine (ACh) was infused intravenously at a dose of 0.05 mg/(kg · min) for 5 minutes with or without a background continuous intravenous infusion of H₂-receptor antagonists or neostigmine during the quiescent period of the interdigestive state. Cimetidine and ranitidine enhanced the ACh-induced contractions in a dose-dependent manner in the gastric antrum, whereas famotidine did not. In vitro, the median inhibitory concentration (IC₅₀) of the acetyl-cholinesterase activity of ranitidine was 3.5 × 10⁻⁶ M, and that of cimetidine 2.5 × 10⁻⁴ M, whereas famotidine had no effect on cholinesterase activity even at concentrations up to 10⁻³ M. The effects of a bolus intravenous injection of the three H₂-receptor antagonists on gastric motor activity also were examined in the digestive state. Cimetidine at 10.0 mg/kg and ranitidine at 3.0 mg/kg significantly increased gastric motor activity. This dose of ranitidine, however, sometimes caused the dogs to collapse and significantly decreased blood pressure in the anesthetized dogs. In conclusion, the H₂-receptor antagonists cimetidine and ranitidine enhanced gastric motor activity through the mechanism of their anticholinesterase activity, but further studies on gastric emptying and the circulatory system are needed.     

Hydroxylamine blocks adenosine A1 receptor-mediated inhibition of synaptic transmission in rat hippocampus

The nitric oxide donor hydroxylamine (NH₂OH) induced a transient depression of the evoked synaptic potential recorded in the rat hippocampal CA1 region. This depression was abolished with an adenosine A₁ antagonist, 8-cyclopentyltheophylline. In addition, hydroxylamine reversed adenosine A₁ receptor-mediated inhibition of the evoked population spike, the fEPSP and the intracellularly recorded EPSP. The inhibitory modulation of adenosine A₁ receptor activation by hydroxylamine suggests the presence of a potent endogenous regulatory site.     

Metabolism of vitamin D2 and vitamin D3 in patients on anticonvulsant therapy

We examined the effect of short-term treatment with pharmacological doses of vitamin D2 or vitamin D3 on the serum concentration of 1,25(OH)2D metabolites in epileptic patients on chronic anticonvulsant drug therapy. Nine patients were studied before and after treatment with vitamin D2 4000 IU daily for 24 weeks and 10 before and after treatment with vitamin D3 in the same dose. Before treatment the serum concentrations of 1,25(OH)2D and 25(OH)D were significantly lower in epileptics than in normal subjects (P less than 0.01). Vitamin D2 treatment increased the serum concentration of 1,25(OH)2D2, but a corresponding decrease in 1,25(OH)2D3 resulted in an unchanged serum concentration of total 1,25(OH)2D. The serum concentration of 25(OH)D2 and 25(OH)D increased significantly, whereas there was a small decrease in 25(OH)D3. Vitamin D3 treatment did not change the serum concentration of 1,25(OH)2D3 whereas serum 25(OH)D3 increased significantly. The correlation between the serum ratio of 1,25(OH)2D2/1,25(OH)2D3 and 25(OH)D2/25(OH)D3 estimated on vitamin D2-treated epileptic patients and normal subjects was highly significant (P less than 0.01). The data indicate that the serum concentration of 1,25(OH)2D2 and 1,25(OH)2D3 are directly proportional to the amount of their precursors 25(OH)D2 and 25(OH)D3 and that the concentration of total 1,25(OH)2D is tightly regulated.     

Neuronal Ca2+ Channels and Nicotinic ACh Receptors as Functional Targets of the Nootropic Nefiracetam

Abstract: Piracetam-like nootropics (or cognitive enhancers) have been used for the treatment of various forms of dementia, including Alzheimer's disease. The underlying mechanisms of their actions, however, are largely unknown. Our recent studies have demonstrated that nefiracetam, a nootropic agent, can markedly enhance activities of neuronal L-and N-type (α_1B) Ca²⁺ channels as well as those of presynaptic nicotinic acetylcholine (ACh) receptors, thereby increasing neurotransmitter release. Aniracetam exerted a slight facilitatory effect on Ca²⁺ channels, but no effect on nicotinic ACh receptors. Piracetam and oxiracetam have no such actions on Ca²⁺ channels and nicotinic ACh receptors. It is suggested that inhibitory G-proteins (Go/Gi) and protein kinase A (PKA) mediate the nefiracetam action on Ca²⁺ channels, whereas protein kinase C (PKC) mediates the drug action on nicotinic ACh receptors. In the hippocampus of the rodent, nefiracetam induces a long-lasting (>4 h) facilitation of synaptic transmission. The 'LTP-like' facilitation appears to result from activation of presynaptic nicotinic ACh receptors (and Ca²⁺ channels as well) by nefiracetam. In conclusion, nefiracetam is distinguished from other nootropic agents for its preferential actions on both presynaptic Ca²⁺ channels and nicotinic ACh receptors, and could therefore be of great therapeutic importance to the neurotransmission failure that contributes to the symptoms of Alzheimer's disease and associated disorders.     

Effect of vitamin D2 and D3 on bone-mineral content in carbamazepine-treated epileptic patients

ABSTRACT In order to clarify whether carbamazepine causes disturbances in calcium and bone metabolism we examined the effect of vitamin D₂ or D₃ in 30 epileptic outpatients. They had been treated for at least 1 year with carbamazepine given as monotherapy. The local bone mineral in the forearms and the total bone mineral was measured before and during treatment with the vitamins (4000 IU/day) for 24 weeks. The bone mineral was not significantly different from controls before the study and it remained unchanged in both treatment groups during the study periods. Similarly, the biochemical indices of bone metabolism were virtually unchanged during the treatment period. We, thus, conclude that epileptic patients on carbamazepine monotherapy have normal bone metabolism.     

Different metabolism of vitamin D2 and vitamin D3 in epileptic patients on carbamazepine

Serum concentrations of vitamin D metabolites were measured in 30 epileptic outpatients on monotherapy with carbamazepine before and during treatment with either vitamin D2 or vitamin D3, 4000 IU per day for 24 weeks. Vitamin D2 treatment increased the serum concentration of 25OHD2, but a corresponding decrease in 25OHD3 resulted in an unchanged serum value of total 25OHD. Vitamin D3 treatment increased the serum concentration of 25OHD3. The resulting serum level of 25OHD was consequently twice the level of that in the D2-treated group. The serum concentrations of the dihydroxy metabolites showed a similar difference between the 2 treatment groups. We conclude that treatment with vitamins D2 and D3 in the same doses produces considerably different serum concentrations of vitamin D metabolites. If the present findings can be extrapolated to normal subjects, it is important to consider more carefully which D-vitamin should be used, both with regard to therapy and supplementation.     

Differential effects of 5-HT3 receptor antagonism on working memory failure due to deficiency of hippocampal cholinergic and glutamatergic transmission in rats

The muscarinic acetylcholine receptor antagonist scopolamine significantly increased the number of errors (attempts to pass through two incorrect panels of the three panel-gates at four choice points) in the working memory task with a three-panel runway setup, when injected bilaterally at 3.2 μg/side into the dorsal hippocampus. Concurrent infusion of the selective and potent 5-hydroxytryptamine₃ (5-HT₃) receptor antagonist Y-25130 (0.32 and 1.0 μg/side) significantly attenuated the increase in working memory errors induced by intrahippocampal 3.2 μg/side scopolamine. Intrahippocampal Y-25130 (1.0 μg/side) by itself did not affect working memory errors. On the other hand, intrahippocampal administration of the competitive NMDA receptor antagonist (±)-3-(2-carboxypiperazin-4-yl)propyl-1-phosphonic acid (CPP) at 32 ng/side caused a significant increase in the number of working memory errors. However, Y-25130 at 1.0 μg/side did not affect the increase in working memory errors when infused intrahippocampally together with 32 ng/side CPP. These results suggest that antagonism of hippocampal 5-HT₃ receptors is ineffective against working memory failure resulting from blockade of NMDA receptor-mediated neurotransmission, but that it can compensate deficiency of septohippocampal cholinergic activity involved in working memory function of rats.     

Changes in protein kinase C (PKC) activity,isozyme translocation,and GAP-43 phosphorylation in the rat hippocampal formation after a single-trial contextual fear conditioning paradigm

The hippocampus plays an important role in spatial learning and memory. However, the biochemical alterations that subserve this function remain to be fully elucidated. In this study, rats were subjected to a single-trial contextual fear conditioning (CFC) paradigm; the activation of different protein kinase C (PKC) subtypes and the levels and phosphorylation of the plasticity-associated protein GAP-43 were assayed in the hippocampus at varying times after training. We observed a rapid activation of hippocampal PKC (15 min through 24 h), with differential translocation of the PKC isotypes studied. At early times after CFC (15-90 min), PKCalpha and PKCgamma translocated to the membrane, while PKCbetaII and PKCepsilon moved more transiently (15 to 30 min) to the cytosol. These PKC isotypes returned to the membrane at later time points after CFC. Correlating with these changes in PKC translocation and activity, there was an early decrease in GAP-43 phosphorylation followed by a more sustained increase from 1.5-72 h. GAP-43 protein levels were also increased after 3 h, and these levels remained elevated for at least 72 h. These changes in PKC and GAP-43 were specific to the CFC trained animals and no changes were seen in animals exposed to the same stimuli in a non-associative fashion. Comparison of translocation of different PKC isotypes with the changes in GAP-43 phosphorylation suggested that PKCbetaII and PKCepsilon may mediate both the early changes in the phosphorylation of this protein and the increases in GAP-43 expression at later times after CFC.     

Oesophageal motor function and outcome of treatment with H2-blockers in erosive oesophagitis

Abstract We studied the oesophageal motor function in 19 patients with reflux oesophagitis before and after 3–6 months of treatment with high-dose H₂-receptor antagonists to compare the results in healed vs unhealed patients. At the end of treatment, the frequency of transient lower oesophageal sphincter (LES) relaxations unassociated with a peristaltic sequence was significantly lower (P < 0.05) in the healed group in fed conditions compared both with its baseline and with the unhealed one. The frequency of primary peristalsis was significantly increased (P < 0.01) particularly in the healed group (P < 0.05). On the other hand, failed peristalsis decreased significantly (P < 0.05) after treatment in the healed patients in fasting conditions. Our data suggest that oesophageal dysmotility observed in those patients who do not heal with high-dose H₂-receptor antagonists, may be due to either the persistence of the mucosal lesions or to the presence of a primary motor disorder, whereas in those who heal, these abnormalities may represent a consequence of the oesophageal mucosal lesions.     

Evidence that D2 receptor-mediated activation of hypothalamic tuberoinfundibular dopaminergic neurons in the male rat occurs via inhibition of tonically active afferent dynorphinergic neurons

The purpose of the present study was to determine if D₂ receptor-mediated activation of hypothalamic tuberoinfundibular dopaminergic (TIDA) neurons occurs via afferent neuronal inhibition of tonically active inhibitory dynorphinergic neurons in the male rat. To this end, the effects of either surgical deafferentation of the mediobasal hypothalamus or administration of a κ opioid receptor agonist (U-50,488) or antagonist (nor-binaltorphimine (NOR-BNI)) on D₂ receptor-mediated activation of TIDA neurons were assessed. For comparison, the activity of mesolimbic DA neurons was also determined in these studies. TIDA and mesolimbic DA neuronal activities were estimated by measuring dopamine synthesis (accumulation of 3,4-dihydroxyphenylalanine (DOPA) following decarboxylase inhibition) and metabolism (concentrations of 3,4-dihydroxyphenylacetic acid (DOPAC)) in terminals of these neurons in the median eminence and nucleus accumbens, respectively. Intraperitoneal administration of the D₂ receptor agonist quinelorane caused a dose-dependent increase in DOPAC in the median eminence and a decrease in DOPAC in the nucleus accumbens; surgical deafferentation of the mediobasal hypothalamus prevented the effect of quinelorane in the median eminence, but not the nucleus accumbens. Activation of κ opioid receptors with U-50,488 had no effect per se, but blocked quinelorane-induced increases in median eminence DOPA. In contrast, U-50,488 had no effect on DOPA in the nucleus accumbens of either vehicle- or quinelorane-treated rats. Blockade of κ opioid receptors with NOR-BNI increased median eminence DOPA, and prevented the stimulatory effects of quinelorane on dopamine synthesis. Administration of prolactin also increased median eminence DOPA, but did not alter the ability of quinelorane to stimulate dopamine synthesis. Neither NOR-BNI nor prolactin had any effect on DOPA in the nucleus accumbens of vehicle- or quinelorane-treated rats. These results suggest that D₂ receptor-mediated activation of TIDA neurons occurs via an afferent neuronal mechanism involving, at least in part, inhibition of tonically active inhibitory dynorphinergic neurons in the male rat.