A comparison of the effects of corticotropin releasing factor and sauvagine on food intake

Corticotropin releasing factor (CRF) and sauvagine (SVG) when administered ICV both reduced spontaneous feeding as well as feeding induced by deprivation or the administration of ethylketocyclazocine (EKC). For spontaneous- and EKC-induced feeding, SVG produced a larger and longer-lasting suppressive effect than did CRF. Both peptides produced a conditioned taste aversion when paired with a novel saccharin taste. As with the feeding effects, SVG produced a stronger aversion than CRF. These studies further establish the similarity between CRF and SVG and suggest that they may have a disruptive effect on feeding.     

Alphaxalone,a steroid anesthetic,inhibits the startle-enhancing effects of corticotropin releasing factor,but not strychnine

Corticotropin releasing factor (CRF) is a 41 amino acid peptide implicated in the expression of stress-and fear-enhanced behaviors. CRF potentiates the amplitude of the startle reflex, and this effect is reversed by benzodiazepines (BDZ), suggesting that the startle-enhancing effects of CRF are modulated by changes in the GABA/BDZ receptor complex. In the present study, CRF-potentiated startle is inhibited by alphaxalone, a pregnane steroid anesthetic that is thought to act via the GABA/BDZ receptor complex. Alphaxalone (ALX) does not reduce CRF-potentiated startle by producing a generalized reduction in reactivity, since blockade of CRF-stimulated startle was not accompanied by an ALX-induced reduction in baseline startle amplitude, and ALX does not reduce strychnine-potentiated startle. The effects of alphaxalone on CRF-potentiated startle may not be generalized to all CRF-stimulated behaviors, since alphaxalone failed to disrupt CRF-stimulated locomotor activity. CRF-potentiated startle is a useful assay for studying the effects of novel anxiolytic agents, and alphaxalone appears to be a steroid anesthetic with anxiolytic properties in this assay.     

Separate neural substrates of the locomotor-activating properties of amphetamine, heroin, caffeine and corticotropin releasing factor (CRF) in the rat

Destruction of dopamine terminals within the nucleus accumbens (N.Acc.) with 6-hydroxydopamine blocked the locomotor activating properties of d-amphetamine, but not caffeine or corticotropin-releasing factor (CRF). Infusion of muscimol into the region of nucleus accumbens efferent terminals in the substantia innominata and lateral preoptic region (SI/LPO) blocked amphetamine-, but not caffeine- or CRF-stimulated locomotion. These muscimol infusions also blocked heroin-stimulated locomotion. These results suggest that amphetamine, acting through a process dependent on N.Acc. dopamine transmission, stimulates locomotion by decreasing GABAergic activity within this N.Acc.-SI/LPO projection; heroin, known to act through a process dependent on N.Acc. opiate receptor activation, also stimulates locomotion by decreasing GABAergic activity within the SI/LPO; caffeine and CRF produce their activation through different neural substrates.     

Role of corticotropin releasing factor (CRF) receptors 1 and 2 in CRF-potentiated acoustic startle in mice

Rationale Hypersecretion of corticotropin releasing factor (CRF) has been implicated in both severe anxiety disorders and major depression. Although the role of the CRF₁ receptor in the anxiogenic effects of CRF is well supported, the role of CRF₂ receptors in anxiety-like behaviors is less clear. In rats, CRF increases the acoustic startle reflex (ASR) via its action in the extended amygdala, providing a putative measure of CRF-mediated anxiogenic activity.Objective To characterize the effect of CRF on ASR in mice and determine the respective roles of CRF₁ and CRF₂ receptors in CRF-potentiated ASR.Methods The present study examined: (1) the time course and dose response functions for the effects of human/rat (h/r)-CRF (0.02–0.6 nmol, ICV (intracerebroventricular)) on ASR in two inbred strains of mice; (2) the effects of the CRF₁ receptor antagonist NBI-30775 (20 mg/kg, intraperitoneal) and the CRF₂ receptor antagonist Antisauvagine-30 (1–10 nmol, ICV) on CRF-potentiated ASR and (3) the effects of the CRF₂ receptor agonist urocortin 2 (0.2–6 nmol, ICV) on ASR in mice.Results h/r-CRF significantly increased ASR in mice in a time-dependent manner with maximal efficacy at the 0.2 and 0.6 nmol doses. 129S6/SvEvTac mice exhibited a slightly increased duration of action and lower minimal effective dose threshold for CRF effects on ASR compared to C57BL/6J mice. Both selective CRF₁ and CRF₂ antagonists attenuated h/r-CRF-potentiated ASR without affecting acoustic startle when given alone. The selective CRF₂ receptor agonist urocortin 2 increased ASR (1 and 2 nmol), albeit with less efficacy than the non-selective CRF receptor agonist h/r-CRF.Conclusions Both CRF₁ and CRF₂ receptors appear to contribute to the h/r-CRF-induced increases in ASR in mice. These data support the hypothesis that both receptors contribute to the anxiogenic effects of CRF.     

Corticotropin releasing factor (CRF): studies in alcohol preferring and non-preferring rats

Electroencephalographic (EEG) responses to corticotropin releasing factor (CRF) as well as CRF concentrations in several brain regions were measured in two lines of rats which have been genetically selected for alcohol preferring (P) or non-preferring (NP) behaviors. Fifteen rats were implanted with chronic electrodes and EEG spectra were evaluated following intracerebroventricular (ICV) administration of CRF (0.15 nmol) or saline. P rats demonstrated a significantly increased EEG response to CRF in the theta frequency range (ANOVA: PREF × DRUG 4–6 Hz,P<0.03; 6–8 Hz,P<0.05) in frontal cortex. A significantly lower concentration of CRF was found in the P rats in hypothalamus (P<0.02), amygdala (P<0.003), prefrontal cortex (P<0.01), and cingulate cortex (P<0.02). The finding that P rats had an increased response to exogenously administered CRF, taken together with decreased CRF concentrations, suggests that CRF receptors may be up-regulated in these animals. Differences in the regulation of CRF neurons may contribute to the expression of behavioral preference for ethanol consumption in these rat lines.Presented in part at the 1990 RSA meeting, Toronto, Canada     

Swim stress enhances nociceptin/orphanin FQ-induced inhibition of rat dorsal raphe nucleus activity in vivo and in vitro: Role of corticotropin releasing factor

The effects of nociceptin/orphanin FQ on putative serotonin (5HT) neurons of the dorsal raphe nucleus (DRN), known to modulate the behavioral responses to stress, were investigated in vivo and in vitro. In DRN slices from unstressed rats, nociceptin/orphanin FQ concentration-dependently inhibited the firing rate of putative 5HT neurons (EC₅₀ = 21.6 ± 1.21 nM) and the selective NOP receptor antagonist UFP-101 shifted the concentration-response curve to the right (estimated pA₂ 6.86). Nociceptin/orphanin FQ potency was enhanced in slices prepared from rats previously subjected to a 15 min swim stress (EC₅₀ = 1.98 ± 0.11 nM). Swim stress did not change the number or affinity of NOP receptors in DRN. Stress-elicited potentiation involved corticotropin-releasing factor (CRF)₁ receptors, GABA signaling and protein synthesis, being attenuated by pre-treatment with antalarmin (20 mg/kg, i.p.), diazepam (2.4 mg/kg, i.p.) and cycloheximide (2.5 mg/kg, i.p.), respectively. In anesthetized unstressed rats, locally applied nociceptin/orphanin FQ (0.03 and 0.1 ng/30 nl) inhibited the firing rate of DRN neurons (to 80 ± 7 and 54 ± 10% of baseline, respectively). Nociceptin/orphanin FQ inhibition was potentiated both 24 h after swim stress and 1 h after CRF (30 ng/30 nl intra-DRN). Stress-induced potentiation was prevented by the selective CRF₁ receptor antagonist, NBI 30755 (20 mg/kg, i.p.). In contrast, the inhibitory response of DRN neurons to the 5HT_1A agonist, 8OH-DPAT (1μg/1 μl, intra-DRN) was not potentiated by swim stress, ruling out a non-specific enhanced permeability of GIRK channel. Together, these findings suggest that CRF and the nociceptin/orphanin FQ/NOP system interact in the DRN during stress to control 5HT transmission; this may play a role in stress-related neuropsychopathologies.     

黄蜀葵总黄酮对脑卒中后抑郁大鼠下丘脑CRF表达的影响

目的研究黄蜀葵总黄酮（TFA）对脑卒中后抑郁（PSD）大鼠下丘脑CRF表达的影响。方法线栓法制备局灶性脑缺血大鼠模型,复合孤养和应激制备PSD大鼠模型。观察PSD大鼠糖水消耗量的变化,应用免疫组化法检测PSD大鼠下丘脑CRF阳性神经元的平均光密度,应用逆转录聚合酶链反应检测下丘脑CRFmRNA的表达。结果TFA（50、100mg·kg-1,ig,qdx24d）可明显增加PSD大鼠糖水消耗量,降低PSD大鼠CRF阳性神经元的平均光密度值,并抑制下丘脑CRFmRNA的过度表达。结论TFA可显著降低PSD大鼠下丘脑CRF和CRFmRNA的过度表达,其机制可能与TFA抑制HPA轴的过度亢进有关。     

A stimulatory effect of intraaccumbens injections of noradrenaline on the behavior of rats in the forced swim test

Intraaccumbens injections of catecholamines noradrenaline and dopamine, though not of serotonin, stimulated locomotion by rats in an open field, 10–15 min later. Similar effects were observed 5 min after microinjection of apomorphine whereas clonidine only attenuated locomotor activity. On the other hand, intraaccumbens administration of phenylephrine, isoproterenol and quipazine, in doses similar to an effective dose of noradrenaline, did not alter rat open field behavior. The escape-directed activity of rats in the forced swim test (FST) was stimulated 5 min after local administration of noradrenaline, phenylephrine, isoproterenol or apomorphine only. No effects in the FST were observed 15 min after noradrenaline injection or after intracaudate noradrenaline administration. The stimulatory effects of intraaccumbens noradrenaline injection in the FST were antagonized by the local pretreatment of rats with phentolamine, though not with propranolol. Accordingly, it is possible to conclude that both catecholamines, but not serotonin, play complex and probably distinct roles within the nucleus accumbens in the stimulation of activity by rats in the FST and the open field test.     

Vasopressin analogs: sedative properties and passive avoidance behavior in rats.

The effects of several types of vasopressin analogs that are considered to be resistant to some of the physiologically significant enzymatic systems were investigated utilizing rats trained in a passive avoidance task. Enhancement of avoidance latencies was observed 2, 7 and 13 days after the single learning trial when deamino-carbavasopressins, triglycyl-8-lysine-vasopressin or its des-glycinamide derivative, and deamino-D-arginine-vasopressin were given shortly after the learning trial in the dose of 1 microgram s.c. (8-L-Arginine)deamino-6-carba-vasopressin and (8-L-ornithine)deamino-6-carba-vasopressin were also active in the dose of 0.1 microgram. Lysine vasopressin and its des-glycinamide derivative failed to enhance avoidance latencies in part of the experiments if doses of 0.3--3 micrograms were administered and 7 or 13 day intervals were used between the learning and the test trials. Enhancement of avoidance latencies was also observed, if some of the peptides were injected 20 min but not 120 or 180 min before the test trial. Marked depression of exploratory behavior of rats in an open field was found after s.c. injections of low doses (1--3 micrograms kg-1) of deamino-carba-vasopressins. Higher doses (10--30 micrograms kg-1) induced sleep-like immobility not accompanied by ataxia or catalepsy.     

Cholinergic drugs reverse AF64A-induced impairment of passive avoidance learning in rats

The cholinergic neurotoxin AF64A was administered to rats in order to produce learning impairment to test the effect of cholinergic drugs. Seven days after receiving an intracerebroventricular injection of AF64A (2.5–7.5 nmol), rats were subjected to one-trial passive avoidance acquisition and tested 24 h later. Learning was significantly impaired at 3.75 nmol AF64A, a dose at which significant reduction in acetylcholine level and choline acetyltransferase and acetylcholinesterase activity in the hippocampus was observed but changes in monoamine levels in the hippocampus, general behavior, or sensory sensitivity were not observed. Arecoline (4 mg/kg, IP) and physostigmine (0.1 mg/kg, IP) significantly decreased the learning impairment produced by AF64A (3.75 nmol) when given before the acquisition of passive avoidance learning but not when given after the acquisition or before the 24 h retention test. These drugs and oxotremorine (0.1 mg/kg, IP) given immediately after the acquisition, however, improved passive avoidance retention when the interval between the acquisition and the test was shortened to 1 h. These results indicate that the impairment of learning in AF64A-treated rats is caused by a memory retention deficit and suggest that such impairment can be effectively ameliorated by cholinergic drugs.     

Exploration and latent learning: Differential effects of dexamphetamine on components of exploratory behaviour in rats

Summary Exploratory behaviour of undrugged rats in a modified Y-maze was recorded during repeated daily trials. Two types of exploration entries into the arms of the maze and a non-locomotor measure, investigation of troughs at the ends of the arms were scored. Latent learning about the location of food-mash in particular troughs was found to be a function of the number of training trials; also there was evidence that learning was greatest in rats which had the highest scores on entries and trough investigation, which validated these as measures of exploration.Dexamphetamine 0.25, 0.50, 1.0 mg/kg had differential effects on activity. Entries were increased while trough investigation was reduced. It is suggested that dexamphetamine reduces true exploration while increasing locomotor activity in a non-specific manner.I thank Mr. J. R. H. Bryant for technical assistance and Mr. B. Hutchings for acting as the co-observer in Experiment II. I am extremely grateful to Dr. I. P. Stolerman and Dr. H. Steinberg for help and discussion and to Smith Kline & French for gifts of rats. This work was supported by research grant No. MH-03313 from the National Institute of Mental Health, U. S. Public Health Service.Beit Memorial Research Fellow     

Hyperalgesia, low-anxiety, and impairment of avoidance learning in neonatal caffeine-treated rats

Rationale The nonselective adenosine receptor antagonist caffeine is used clinically to treat apnea in preterm infants. The brain developmental stage of preterm infants is usually at a period of rapid brain growth, referred as brain growth spurt, which occurs during early postnatal life in rats and is highly sensitive to central nervous system (CNS) acting drugs. Objectives The aim of this work was to study whether caffeine treatment during brain growth spurt produces long-term effects on the adenosine receptor-regulated behaviors including nociception, anxiety, learning, and memory. Methods Neonatal male and female Sprague–Dawley rats were administered either deionized water or caffeine (15–20 mg kg⁻¹ day⁻¹) through gavage (0.05 ml/10 g) over postnatal days (PN) 2–6. The hot-plate test, elevated plus-maze, dark-light transition test, and step-through inhibitory avoidance learning task were examined in juvenile rats. Furthermore, the responses to adenosine A₁ receptor agonist N(6)-cyclopentyladenosine (CPA)-induced hypothermia and A_2A receptor agonist CGS21680-induced locomotor depression were also compared. Results Caffeine-treated rats showed hyperalgesia in hot-plate test, less anxiety than controls in the elevated plus-maze and dark–light transition, and impairment in step-through avoidance learning test. Moreover, the responses to CPA-induced hypothermia and CGS21680-induced locomotor depression were enhanced in caffeine-treated rats. Conclusion These results indicate that caffeine exposure during brain growth spurt alters the adenosine receptor-regulated behaviors and the responsiveness to adenosine agonists, suggesting the risk of adenosine receptor-related behavioral dysfunction may exist in preterm newborns treated for apnea with caffeine.     

Effects of antimuscarinic cholinergic drugs injected systemically or into the hippocampo-entorhinal area upon passive avoidance learning in young rats

Passive avoidance learning was significantly impaired by atropine (5 mg/kg, IP) or scopolamine (0.5 mg/kg), but not by methyl-atropine (5 mg/kg) or methyl-scopolamine (0.5 mg/kg), from postnatal day 15 on. In contrast, an improvement was observed, not significant at 11 days and significant at 13 days, probably due to nonspecific effects. Retention of the response increased from 6 h at 13 days, to 24 h at 17 days. In treated rats, retention was abolished at 13 and 15 days, and impaired at 17 and 20 days. Acquisition of the response was also significantly impaired by bilateral injections of atropine (1, 5, and 20 g) into the posteroventral hippocampo-entorhinal (VHE) area, from day 15 on. Concomitantly, extinction was accelerated. At 14 days, atropine had no influence. At 13 days, a facilitatory action was observed, with better acquisition and greater resistance to extinction, possibly linked to affective changes. The results conform that central muscarinic cholinergic mechanisms are involved in passive avoidance learning from postnatal day 15 on, and demonstrate that some pathways of this system are located in the VHE area, become efficient at 15 days, and improve markedly between 17 and 18 days.     

The effect of 1-δ1-trans-tetrahydrocannabinol on learning and retention of avoidance performance in rats

Forty-eight rats were trained for 1 h and tested the next day for 1 h on a discriminated Sidman avoidance task in a 2×2 crossover design using tetrahydrocannabinol (THC) and placebo. A dose of 4 mg/kg impaired performance on Day 2, but improved Day 1 learning. It is shown that this method can elucidate some of the mechanisms through which a drug works.     

Effects of developmental lead exposure on inhibitory avoidance learning and glutamate receptors in rats

Chronic lead (Pb) exposure during development is known to produce learning deficits. AMPA and NMDA receptors have been shown to participate in the synaptic mechanisms involved in certain forms of learning and memory. We investigated whether the effects of Pb on AMPA and NMDA receptors are associated with Pb-induced impairment in learning and memory. Rats were exposed to 0.2% lead acetate at different developmental stages including a maternally exposed group (including gestation and lactation period), a postweaning exposed group, and a continuously exposed group. Lead treatment impaired learning acquisition, but not memory retention in step-down avoidance learning task in all treatment groups. In parallel with the behavioral data, autoradiographic analyses of brain sections indicated that the [³H]AMPA binding was decreased in the CA1 and dentate gyrus of the hippocampus and entorhinal cortex in all three Pb-exposed groups. However, an increase in [³H]MK801 binding was only observed in CA1 of the hippocampus in the continuously Pb-exposed rats. The findings suggest that alterations in AMPA receptor may contribute to the Pb-induced deficits in learning acquisition of inhibitory avoidance.     

Effects of histamine and opioid systems on memory retention of passive avoidance learning in rats

The present study investigated the effect of interactions between histamine receptor agents and the opioid peptidergic system on memory retention of passive avoidance learning in rats. Post-training intracerebroventricular (i.c.v.) injections were carried out in all the experiments. Administration of histamine (20 micro g/rat) reduced, but the histamine H(1) receptor antagonist, pyrilamine (20 and 50 micro g/rat), and the histamine H(2) receptor antagonist, cimetidine (10 and 50 micro g/rat), increased memory retention in rats. The histamine receptor antagonists decreased the response induced by histamine. Morphine (1-10 micro g/rat) reduced, while pentazocine (5 and 10 micro g/rat) or the opioid receptor antagonist, naloxone (5 and 15 micro g/rat), increased memory retention. The combination of histamine with morphine showed potentiation. Effects of pyrilamine and cimetidine were attenuated by morphine. The responses to pentazocine and naloxone also were decreased by histamine. It is concluded that the histaminergic system has an interaction with opioidergic system that is involved in the memory retention process.     

Prior,repeated exposure to cocaine potentiates locomotor responsivity to central injections of corticotropin-releasing factor (CRF) in rats

Rationale There is considerable evidence that the stress-related neuropeptide, corticotropin-releasing factor (CRF), plays an important role in mediating behavioural changes induced by prior experience with cocaine. From this perspective, it is conceivable that repeated exposure to cocaine induces a form of sensitization in CRF systems that makes animals more responsive to CRF following prolonged drug-free periods.Objectives To study the effects of repeated cocaine exposure on locomotor activity induced by different doses of CRF after drug-free periods ranging from 24 h to 28 days.Methods Male Wistar rats were injected once daily for 7 days with cocaine (15 mg/kg, IP on days 1 and 7 in locomotor chambers; 30 mg/kg, IP, on days 2–6 in home cages) or saline. In experiment 1, starting 10 days after the last injection, animals were tested for their locomotor response to intracerebroventricular (ICV) injections of vehicle and three doses of CRF (0.25, 0.5, and 5 µg). In experiment 2, animals were tested for their locomotor response to ICV injections of 0.5 µg CRF after drug-free periods of 1–2, 10–11 and 28–29 days.Results Compared to saline pre-exposed animals, cocaine pre-exposed animals showed a significantly greater locomotor response to CRF, relative to vehicle, at all doses tested (experiment 1) and after drug-free periods of up to 28 days (experiment 2). The effects were clear and extremely consistent in magnitude between experiments and conditions.Conclusions These results suggest that cocaine pre-exposure induces long-term changes in the responsivity of the central nervous system to CRF.     

Facilitation of copulatory performance in male rats by naloxone: Effects of hypophysectomy, 17 α-estradiol,and luteinizing hormone releasing hormone

Three experiments were performed to explore the mechanism whereby systemic administration of the opiate receptor antagonist, naloxone hydrochloride (20 mg/kg) causes reductions in the frequency of intromissions preceding ejaculation and latency to ejaculation in sexually experienced male rats. Administration of naloxone to male rats which were hypophysectomized in addition to being castrated and implanted SC with 30 mm silastic capsules containing testosterone caused such behavioral changes, suggesting that these behavioral effects of naloxone do not result from interference with the binding of endorphin of pituitary origin. Surprisingly, a significant facilitatory effect of naloxone on sexual performance was absent in castrated controls bearing 30 mm testosterone implants. Recent evidence suggests that 17α-hydroxylated estrogens, which may be produced in gonadally intact males, possess appreciable affinity for opioid receptors. However, daily administration of 17α-estradiol (50 μg) to castrated, testosterone-implanted males failed to make them as behaviorally responsive to naloxone as gonadally intact animals. Administration of LHRH (1 μg given SC 1.5 hr prior to testing) caused a significant reduction in ejaculation latency in gonadally intact males but not in castrated males bearing 30 mm testosterone implants. It is suggested that the facilitatory effect of naloxone on masculine sexual performance results, in part, from a drug-induced release of LHRH.     

Effects of third intracerebroventricular injections of corticotropin- releasing factor (CRF) on ethanol drinking and food intake

 Corticotropin releasing factor (CRF), a neuropeptide secreted by hypothalamic and extrahypothalamic neurons, is thought to mediate stress-related behaviors. The tension reduction hypothesis suggests that ethanol drinking reduces stress; that drinking is reinforced by this reduced stress; and that the probability of drinking therefore subsequently increases. CRF also decrease food intake, and might decrease ethanol drinking similarly. We addressed these hypotheses directly by assessing the effects of intracerebroventricular (ICV) CRF upon ethanol drinking (1 h/day). Rats were provided drinking tubes containing ethanol solutions that were gradually incremented in concentration (from 2% to 8% w/v, over 38 days). Ethanol intakes remained stable, ranging from 0.4 to 0.5 g/kg per hour on average, and a two-bottle choice test revealed that ethanol was preferred reliably to water. Third-ICV cannulae were surgically implanted and CRF or vehicle was acutely injected immediately prior to the sessions. CRF dose-dependently reduced ethanol intake by 31% (0.5 μg) and 64% (5.0 μg), and reduced 24-h food by 9% and 21%, respectively, but did not alter body weights. ICV CRF reduced ethanol drinking despite any acute stress-like effects that may have been present. Hence, these data are inconsistent with the tension reduction hypothesis. On the other hand, our results support the concept that food intake and ethanol drinking may be mediated by similar mechanisms. Received: 26 November 1997 / Final version: 11 April 1998     

Antagonism of the stimulant and depressant effects of ethanol in rats by naloxone

The action of naloxone (0.5 and 2 mg/kg IP) on the behavioural effects of a low (2 g/kg PO) and a high dose (4 g/kg PO) of ethanol was studied in rats. Ethanol at the low dose increased spontaneous motility, enhancing open-field external ambulations and reducing shuttle-box latency. All these effects were antagonized by naloxone. Ethanol at the high dose produced hypomotility, decreasing open-field external ambulations and impairing shuttle-box performance. In this case, naloxone also reduced the ethanol effect, but its action was less consistent. Therefore, although mechanisms other than a specific opioid receptor blockade by naloxone must be considered, an involvement of opioid peptides in the effects of ethanol cannot be discounted.