Behavioral and neurochemical mechanisms of the action of mild stress in the enhancement of feeding.

Rats were trained to respond under a cyclic-ratio schedule of reinforcement composed of an ascending, followed by a descending, sequence of ratio values. Subjects were trained while exposed to 70 dB white noise, then tested while exposed to 70 or 90 dB white noise. Exposure to 90 dB white noise elevated the response function (p<.02). Naloxone was then administered intraperitoneally at 0.3. 1.0. and 3.0 mg/kg under 70 dB and 90 dB white noise. Naloxone administration (1.0 and 3.0 mg/kg) significantly depressed the response function obtained under 90 dB white noise (ps<.01) but did not affect the function obtained under 70 dB white noise. These findings suggest that mild stress increases food intake through a mechanism affecting palatability enhanced by the release of endogenous opioids.

Behavioural and histopathological analyses of ibuprofen treatment on the effect of aggregated Abeta(1-42) injections in the rat.

It has been suggested that inflammatory processes may play a role in the development of Alzheimer's disease (AD), and that nonsteroidal anti-inflammatory drug treatments may provide protection against the onset of AD. In the current study male Wistar rats were trained in two-lever operant chambers under an alternating lever cyclic-ratio ratio (ALCR) schedule. When responding showed no trends, subjects were divided into groups. One group was bilaterally injected into the CA3 area of the hippocampus with 5 microl of aggregated beta-amyloid (Abeta) suspension, and one group was bilaterally injected into the CA3 area of the hippocampus with 5 microl of sterile saline. Subgroups were treated twice daily with 0.1 ml (40 mg/kg) ibuprofen administered orally. The results indicated that chronic administration of ibuprofen protected against detrimental behavioural effects following aggregated Abeta injections. Withdrawal of ibuprofen treatment from aggregated Abeta-injected subjects produced a decline in behavioural performance to the level of the non-treated aggregated Abeta-injected group. Ibuprofen treatment reduced the numbers of reactive astrocytes following aggregated Abeta injection, and withdrawal of ibuprofen resulted in an increase of reactive astrocytes. These results suggest that induced inflammatory processes may play a role in AD, and that ibuprofen treatment may protect against some of the symptoms seen in AD.

Delayed behavioral effects following intrahippocampal injection of aggregated A beta (1-42).

Beta amyloid protein (A beta) is the major extracellular component of Alzheimer's disease (AD) plaques. In the current study, A beta (1-42) was aggregated in vitro using a method which produces A beta aggregates similar to those found in the AD brain. Twelve male Sprague-Dawley rats were trained in two-lever operant chambers under an alternating lever cyclic-ratio (ALCR) schedule. When performance was stable on the ALCR schedule, six subjects were injected (bilaterally into the CA3 area of the dorsal hippocampus) with 5.0 microliters aggregated A beta in suspension, and the remaining six subjects were injected with 5.0 microliters sterile water. Behavioral testing resumed 5 days after surgery and continued for 90 days post-injection. Aggregated A beta injection did not affect the number of lever switching errors made in a daily session but did affect the number of incorrect lever response perseverations. After approximately 30 days post-injection, aggregated A beta injection detrimentally affected ability to track the changing parameters of the schedule, and decreased the efficiency by which subjects obtained reinforcers. From approximately day 50 post-injection onward, A beta-injected subjects demonstrated significantly higher numbers of incorrect lever response perseverations than did sterile water-injected subjects. These effects appeared to be central rather than peripheral, as A beta injection did not decrease running response rates under the ALCR schedule. The delayed onset of behavioral effects seen in this and other behavioral studies may be a result of a cascade of potentially harmful responses induced through glial activation following aggregated A beta injection.

Effects of propranolol, buspirone, pCPA, reserpine, and chlordiazepoxide on open-field behavior.

The study examined the possibility that propranolol, buspirone, pCPA, and reserpine have antianxiety effects by comparing their effects with those of chlordiazepoxide on an open-field test of emotionality in rats. The effects of intraperitoneal injections of d,l, propranolol (5, 10, 20 mg/kg), buspirone (1.25, 2.5, 5 mg/kg), reserpine (0.5 mg/kg), parachlorophenylalanine (pCPA) (100 mg/kg), and chlordiazepoxide (CDP) (2.5, 5, 10 mg/kg) were compared with performance of rats under saline or water using an open-field test on 5 successive days. Significant effects were found on peripheral movements, rearing, grooming, immobility, and defecation. The patterns of effects of high doses of propranolol and buspirone resembled those of CDP, while pCPA had some of the effects of CDP, and reserpine produced few effects. With propranolol, buspirone, and CDP, there was evidence of dose sensitivity. The effects of repeated testing across 5 days were different from these of CDP or other drugs. The results are consistent with the hypothesis that the effects of propranolol and buspirone on open-field behavior are anxiolytic, and may be mediated by action on the same brain systems.

Utilization of a novel model of food reinforced behavior involving neuropeptide Y, insulin, 2-deoxy-d-glucose and naloxone.

The cyclic-ratio schedule methodology exposes animals to an ascending followed by a descending sequence of ratio values over six consecutive cycles. The response functions, obtained by plotting response rates against reinforcement rates at each schedule value, are argued to provide features useful in the evaluation of drug effects on feeding behavior. In the present study the effects of s.c. insulin (5.0IU/kg), i.c.v. neuropeptide Y (NPY) (5.0µg/5.0µl), i.c.v. insulin (0.5mU/5.0µl), i.c.v. 2-deoxyglucose (2-DG) (10.0µg/5.0µl), i.c.v. naloxone (NLX) (50.0µg/5.0µl) in conjunction with i.c.v. NPY (5.0µg/5.0µl), and i.c.v. NLX alone (50.0µg/5.0µl) were assessed, i.c.v. NPY, insulin and 2-DG caused an elevation of the response function obtained by plotting response rates against reinforcement rates but did not affect the slope of the function. This elevation was similar to that observed after increasing the incentive value of the reinforcer (i.e., similar to increasing a 5.0% sucrose concentration reinforcer to 10.0%, and to substituting 45mg sweet food pellets for 45mg grain pellets). S.c. insulin produced no shift in the function from baseline, and i.c.v. NLX blocked the effect of i.c.v. NPY. I.c.v. NLX given alone reduced the slope of the response function, by selectively reducing response rates at the higher schedule values, a shift in the function similar to that observed following an increase in body weight. Since the literature on NPY and insulin would suggest that their effects are mediated through mechanisms associated with internal regulation, these findings were not predicted.

Cranial irradiation with Gaalas laser leads to naloxone reversible analgesia in rats.

Laser irradiation of the rat cranium can produce analgesia. The present experiment investigated the mechanism of such action. 27 rats received all possible combinations of laser (0, 6.4, and 12J/cm2) and naloxone (0, 5, and 10 mg/kg) prior to a hot plate test. Laser (820 nm, KHz pulsing, Omega Laser Systems, London) was applied to the rats' skulls and hind paw lick latencies (in seconds) were recorded immediately, 30 min., and 24 hr. after the administration of treatment. When animals were tested immediately following laser irradiation at 12J/cm2 significant analgesia resulted. Treatment with naloxone at either dose antagonised this effect, but naloxone produced no significant hyperalgesia when given alone. This suggests that opioid peptide mechanisms mediate the analgesic action of low-intensity laser irradiation of the cranium.

Analgesic effects of cranial laser treatment in two rat nociception models.

The present experiments sought to establish dose dependency and time course for effects of cranial laser irradiation in two rodent models of pain. These were the hot plate and tail flick tests, which are both widely used to quantify analgesic drug effects. The laser used was an Omega Biotherapy 3ML (wavelength 820 nM, average power output 100 mW, pulse frequency 5 kHz) and irradiation was applied to rats' shaved heads above the midbrain. In the first experiment, four groups of 10 rats received doses of 0, 6, 12, 18, and 24 J/cm2 in random orders prior to hot plate testing either immediately, 30 min, 1 h or 24 h postlaser. The second study employed three groups of 10 rats receiving 0, 12, and 18 J/cm2 in random orders prior to tail flick testing at the three shorter times above. Latency to lick hind paws on the hot plate was highly significantly prolonged by laser treatment across all doses and time periods, F(4, 126) = 4.51, p < 0.01. There was good dose dependency for immediate observations, but at 24 h 18 J/cm2 was the most effective dose. Laser treatment also delayed tail flick responses at both doses and all time periods, F(2, 54) = 10.60, p < 0.001, but 12 and 18 J/cm2 doses were similar in efficacy.

A pharmacological evaluation of the pull-up test for muscle relaxation in rats.

The pull-up test for muscle relaxation is described and validated. At testing, rats were evaluated for their ability to recover ('pull-up') from a fully inverted head-down position. Control animals rapidly regained position (median: 1 s). Known muscle relaxants increased latency to pull-up compared to controls. The test proved sensitive to the effects of barbiturates and benzodiazepines which produced graded dose-response functions. In general, results in the pull-up test corresponded with known potencies, with weaker muscle relaxants such as clobazam and oxazepam being less active. The test was relatively insensitive to non-benzodiazepine compounds (e.g., haloperidol, etomidate, morphine, fentanyl and risperidone) producing cataleptic, catatonic, neuroleptic, analgesic, sedative or hypnotic effects. In terms of ED50 values for barbiturates and benzodiazepines, the pull-up test correlated significantly with ED50s from the rotarod test, the antipentylenetetrazol test, ataxia in rats and muscle relaxation in cats. It was concluded that the pull-up test was relatively specific for muscle relaxation and provided a simple alternative to more time-consuming or equipment-intensive tests.

Direct evidence for mediation of an anticonflict effect of baclofen by GABAb receptors.

The present article reports an experiment on the effects of baclofen (0, 0.5, 1.0, and 2.0 mg/kg) on punished drinking in rats and the modification of these by delta-amino-n-valeric acid (DANVA) (0 and 10.0 mg/kg). Baclofen significantly enhanced punished drinking and this increase was abolished by DANVA, which had no intrinsic anxiogenic activity. It is concluded that GABAb receptors probably mediate this effect of baclofen and that such receptors may be a potential site of anxiolytic drug action.

Effects of chlordiazepoxide and putative anxiogenics on conditioned suppression in rats.

This paper reports two experiments. In Experiment 1, the effects of chlordiazepoxide alone and in combination with a series of putative antagonists at various sites on the GABA/benzodiazepine receptor complex on conditioned suppression of operant behavior in rats were assessed. Response rates during presentation of a stimulus associated with shock (CS responding) and when only positive reinforcement is effective (pre-CS responding) were analysed. Chlordiazepoxide (10 mg/kg) significantly increased CS responding. This effect was significantly antagonised by Ro15-1788 (10 mg/kg) and by picrotoxin (1.5 mg/kg), but not by bicuculline (1.5 mg/kg) or by delta-amino-n-valeric acid (10 or 20 mg/kg). Chlordiazepoxide also significantly, albeit more slightly, increased pre-CS responding and none of the other drugs tested significantly antagonised this action, though Ro15-1788 plus chlordiazepoxide resulted in pre-CS response rates not significantly different from either chlordiazepoxide alone or control. These interactions are discussed in the context of the proposed GABA/benzodiazepine receptor complex with the conclusion that drug effects at the benzodiazepine- and picrotoxin-sensitive channel sites have an important role in mediating anxiolytic action. However, behavioral evidence of an important role for GABAa or GABAb receptors remains very limited. The second experiment studied the intrinsic actions of bicuculline, picrotoxin, and Ro15-1788 on conditioned suppression. Responding during a conditioned stimulus associated with a mild (0.125 to 0.15 mA) electric shock (CS responding) and a control rate of responding (pre-CS responding) were recorded. Bicuculline (1.5 mg/kg) and Ro15-1788 (10 mg/kg) did not significantly affect either response rate.(ABSTRACT TRUNCATED AT 250 WORDS)

Cyclic-ratio schedule analysis of a serotonin agonist and depletor on consummatory behaviour.

Four male Wistar rats, 180 days old at the start of the experiment, at 85% of their free-feeding body weight were trained to respond on a geometric cyclic-ratio schedule comprised of the following ratio values: 2, 4, 8, 16, 32 and 64, for 0.1 ml of 5% sucrose reinforcement. The response functions (response rates plotted against reinforcement rates) were linear and of negative slope over the range of ratio values from 2 to 16. IP administration of 1.0 mg/kg 5-MeODMT reduced the x- and y-intercepts of the linear portion of the response function without altering the slope relative to 2.0 ml/kg 0.85% saline IP. This was interpreted as a perceived palatability effect. IP administration of 100 mg/kg pCPA elevated the reinforcement rate intercept but also decreased the slope of the response function. This finding was interpreted as an increase in the perceived palatability of the reinforcer, coupled with a decrease in motivation at higher schedule conditions, possibly due to peripheral effects of pCPA.

Effects of agonists and antagonists at the GABA/benzodiazepine receptor on conditioned suppression in rats.

Certain drugs generally regarded as GABA agonists, such as valproate and combinations of muscimol and baclofen, have been reported to produce apparent anxiolytic effects in various animal behavioral tests. The present paper reports two experiments on the effects of these agents on conditioned suppression in rats. In the first study, muscimol (0, 1.25 micrograms/kg or 1 mg/kg), baclofen (0, 1 mg/kg) and combinations of these treatments failed to alleviate conditioned suppression. Experiment Two showed that valproate (200 mg/kg) did attenuate conditioned suppression, and that its effects were antagonised by picrotoxin (1.5 mg/kg), but not by bicuculline (1.5 mg/kg), Ro 15-1788 (10 mg/kg) or by delta-amino-n-valeric acid (10 mg/kg). The findings are discussed in the context of the proposed GABA/benzodiazepine receptor complex, with the conclusion that there is little evidence for a mediating role of GABAa or GABAb receptors in such drug actions, and that the site of valproate action is probably the chloride ion channel associated with the receptor complex.

Chlordiazepoxide and valproate enhancement of saline drinking by nondeprived rats: effects of bicuculline, picrotoxin and Ro15-1788.

Drinking of 0.85% saline by nondeprived rats was significantly enhanced by chlordiazepoxide (5 or 10 mg/kg) and by valproate (100 or 300 mg/kg), drug effects being strongest in the earlier parts of a 30-minute test. When given alone, both bicuculline and picrotoxin significantly reduced saline drinking at 2.5 mg/kg, but not 1.5 mg/kg. Administration of valproate at either dose or of chlordiazepoxide (10 mg/kg) completely prevented bicuculline action and 5 mg/kg chlordiazepoxide reduced it. Picrotoxin, however, largely prevented the actions of both chlordiazepoxide and valproate. The increase in saline drinking induced by valproate (300 mg/kg) was also blocked by RO15-1788 (10 or 25 mg/kg). These findings are discussed in the context of the three-site model of the GABA/benzodiazepine receptor complex. It is concluded that drugs acting at the benzodiazepine site or the chloride ion channel affect saline drinking, but that there is little evidence of an important functional role for the GABAa site at present.

Chlordiazepoxide and the drinking of water by rats: effects of shock and other suppressive measures.

The effects of chlordiazepoxide (5 and 10 mg/kg) on fluid consumption in water deprived rats were assessed. Drinking was inhibited to approximately equal extents by a water preload, by d-amphetamine (1.5 mg/kg), by neophobia and by shock at mild (0.3 mA) or moderate (0.5 mA) intensities, the latter condition having an enhanced level of deprivation also. At both doses chlordiazepoxide significantly enhanced drinking in the neophobia, mild shock and, especially, the moderate shock condition but failed to increase drinking suppressed by preload or d-amphetamine. It is concluded that the increases in drinking suppressed by neophobia or shock which chlordiazepoxide induces may be due to anxiolytic actions of the drug or to enhanced palatability since they cannot be explained in terms of nonspecific enhancement of fluid consumption.

Valproate enhances fluid consumption suppressed by shock or neophobia, but not by partial satiation or d-amphetamine, in rats.

The effects of sodium valproate (100 and 300 mg/kg) on fluid consumption in water deprived rats were assessed. Drinking was inhibited to approximately equal extents by a water pre-load, by d-amphetamine (1.5 mg/kg), by neophobia and by shock at mild (0.3mA) or moderate (0.5mA) intensities, the latter condition having an enhanced level of deprivation also. At both doses valproate significantly enhanced drinking in the neophobia, mild shock and moderate shock conditions but failed to increase drinking suppressed by pre-load or d-amphetamine. It is concluded that the increases in drinking suppressed by neophobia or shock which valproate induces are due to anxiolytic actions of the drug and not non-specific enhancement of fluid consumption. The present results also constitute a further parallel between the actions of valproate and those of benzodiazepines.

Behavioral effects of GABA agonists in relation to anxiety and benzodiazepine action.

A considerable body of biochemical and neurophysiological evidence implicates GABA in anxiety and in benzodiazepine action. The present article surveys the behavioral effects of GABA agonists and their interactions with drugs acting at the benzodiazepine receptor in animal anxiety paradigms. Certain GABA agonists, notably valproate, simulate many behavioral actions of benzodiazepines. Moreover, several behavioral studies of the interaction of GABA agonists with benzodiazepines support the hypothesis of a benzodiazepine receptor complex with one or more GABA, benzodiazepine and probably other binding sites. However, there are also a number of anomalous findings of GABA agonist action alone and in combination with benzodiazepines. It is argued that these paradoxical results can better be accounted for in terms of the receptor complex and the distribution of the drugs, rather than by suggesting that the anxiolytic actions of benzodiazepines are not mediated by GABA systems. The potential clinical usefulness of GABA agonists in anxiety is commented upon.

Neurotransmitters, anxiety and benzodiazepines: a behavioral review.

The possible involvement of serotonin, GABA and opioid peptides in anxiety and in the mechanism of action of benzodiazepine tranquilizers have recently been the subjects of intensive biochemical, neurophysiological and behavioral research. The present review examines the behavioral evidence, viewing anxiety and benzodiazepine action as far as possible separately. Four behavioral paradigms of experimental anxiety or "conflict behaviors" are described and assessed for soundness with some practical considerations. The functional significance and pharmacology of benzodiazepine receptors are discussed, and the cases for a number of putative endogenous ligands are examined. Conflict behavior is attenuated by drugs which reduce functional serotonin activity and enhanced by serotonin agonists, but there is little evidence to implicate serotonin in benzodiazepine action. GABA antagonists both intensify conflict and reduce benzodiazepine effects, but evidence of the reverse effects with GABA agonists is more equivocal. The interpretation of behavioral effects of opiate agonists and antagonists and their interactions with benzodiazepines is hindered by their actions on motivational systems other than anxiety, and evidence for an important role of opioid peptides is only suggestive. Some promising lines for future research are indicated.

Effects of valproate on hyponeophagia in rats: competitive antagonism with picrotoxin and non-competitive antagonism with RO 15-1788.

The effects of valproate (30-500 mg/kg), alone and in combination with picrotoxin (1.5 mg/kg) or RO 15-1788 (10 mg/kg) were studied in two experiments on hyponeophagia in rats. Valproate reduced eating latency and increased eating time and amount eaten of novel food, except at 500 mg/kg which reduced feeding. Picrotoxin induced generally opposite actions alone and shifted valproate dose/response curves to the right. RO 15-1788 had no detectable intrinsic action, but prevented both the behavioural facilitation and inhibition produced by valproate. These findings are discussed in the context of the GABA hypothesis of benzodiazepine action, with the conclusions that they provide behavioural support for the hypothesis of a receptor complex with GABA and benzodiazepine binding sites, and that an optimal and submaximal level of activity at the benzodiazepine site is a necessary condition for anxiolytic actions of valproate.

Effects of chlordiazepoxide and of valproate on hyponeophagia in rats. Evidence for a mutual antagonism between their anxiolytic properties.

The effects of chlordiazepoxide (0,2.5 and 7.5 mg/kg), of valproate (0,100 and 300 mg/kg), and of combinations of these drugs, on hyponeophagia in rats, were studied using a food preference test. Chlordiazepoxide alone reduced the latency for eating, and also enhanced the time of eating and the amount of familiar food eaten at the smaller dose, and of novel food eaten at the larger dose. Valproate alone reduced the latency of eating and enhanced time of eating and the amount of novel food eaten, especially at 300 mg/kg. However, valproate antagonised the effects of chlordiazepoxide on all behavioural measures. These findings are discussed in the context of the GABA hypothesis of the actions of benzodiazepines, with the conclusion that valproate has an atypical pharmacological profile amongst putative GABA agonists, and may have partial agonist activity at the proposed benzodiazepine/GABA receptor complex.