Chlordiazepoxide reduces discriminability but not rate of forgetting in delayed conditional discrimination

Effects of Lorazepam and citalopram on human defensive reactions: ethopharmacological differentiation of fear and anxiety

Drugs that are clinically effective against generalized anxiety disorder preferentially alter rodent risk assessment behavior, whereas drugs that are clinically effective against panic disorder preferentially alter rodent flight behavior. The theoretical principle of "defensive direction" explains the pattern of associations between emotion and defensive behavior in terms of the differing functional demands arising from cautious approach to threat (anxiety) versus departure from threat (fear), offering the prospect that clinically important emotions may be explained using a single rubric of defense. We used a within-subjects, placebo-controlled, design to test this theory, measuring the effects of citalopram and lorazepam on the defensive behavior of 30 healthy adult male humans. We indexed human defensive behavior with a translation of an active avoidance task used to measure rodent defense and found that lorazepam significantly reduced the intensity of defensive behavior during approach to threat (hypothetically anxiety-related) but not departure from threat (hypothetically fear-related). Contrary to prediction, citalopram did not affect either form of defensive reaction. Since lorazepam is a drug with well established anxiety reducing properties, these data support the hypothesis that anxiety is an emotion elicited by threat stimuli that require approach. These data also contribute to the validation of a novel human analog of an established experimental model of rodent fear and anxiety.

A two-dimensional neuropsychology of defense: fear/anxiety and defensive distance

We present in this paper a picture of the neural systems controlling defense that updates and simplifies Gray's "Neuropsychology of Anxiety". It is based on two behavioural dimensions: 'defensive distance' as defined by the Blanchards and 'defensive direction'. Defensive direction is a categorical dimension with avoidance of threat corresponding to fear and approach to threat corresponding to anxiety. These two psychological dimensions are mapped to underlying neural dimensions. Defensive distance is mapped to neural level, with the shortest defensive distances involving the lowest neural level (periaqueductal grey) and the largest defensive distances the highest neural level (prefrontal cortex). Defensive direction is mapped to separate parallel streams that run across these levels. A significant departure from prior models is the proposal that both fear and anxiety are represented at all levels. The theory is presented in a simplified form that does not incorporate the interactions that must occur between non-adjacent levels of the system. It also requires expansion to include the dimension of escapability of threat. Our current development and these proposed future extensions do not change the core concepts originally proposed by Gray and, we argue, demonstrate their enduring value.

Effects of procedural parameters on response accuracy: lessons from delayed (non-)matching procedures in animals

The experimental analysis of behaviour in operant paradigms has identified numerous variables which affect performance. We will focus on the delayed (non-)matching tasks in order to illustrate the influence of procedural variables on acquisition and performance in operant tasks of cognitive function. Systematic variation of these parameters can help dissociate different cognitive processes which may be differentially affected by drug treatment or brain lesions. Use of different parameters, however, could equally account for controversial drug or lesion effects reported in the literature. Consideration of these factors will increase our understanding of the relative contribution of these and other features and parameters of the procedural arrangements to the final behavioural outcome.

Quantitative reanalysis of lesion effects on rate of forgetting in macaques

In Ringo's reanalysis (Behav. Brain Res., 42 (1991) 123-124), differences between d' discriminability measures of memory performance by macaque monkeys in normal and lesioned groups did not change systematically with retention-interval duration. There was therefore no evidence of an effect of brain lesion on rate of forgetting. Our quantitative analysis in which power and negative exponential functions were fitted to the d' measures yielded a different conclusion. The rate parameter of the best-fitting functions provided a measure of rate of forgetting. Parameter values for rate of forgetting were significantly greater for lesioned groups than for normal groups, whereas the parameter describing performance in the absence of a delay did not differ between normal and lesion conditions.

Effects of stimulation or blockade of central nicotinic-cholinergic receptors on performance of a novel version of the rat stimulus discrimination task

This study evaluated the effects of two central nicotinic-cholinergic receptor agonists and an antagonist on performance accuracy of a rat, delayed stimulus discrimination task (DSDT). Rats were trained to discriminate between an auditory and visual stimulus by pressing a right or left lever. To diminish the rat's ability to use mediating spatial strategies to solve the task, computer automated, retractable doors separated the animal from the levers during delay intervals, thus reducing positioning at the lever. After stable baselines were achieved, rats were grouped and administered placebo (saline) and nicotine, lobeline or mecamylamine in a randomized dose series. Each group received two complete series of the selected compound on different occasions. Mecamylamine impaired DSDT accuracy in a dose-dependent manner while optimal doses of nicotine and lobeline significantly improved accuracy. Nicotine differed from lobeline in regard to its interaction with a dose of mecamylamine (1.0 mg/kg) that had not impaired DSDT accuracy. Combined administration of lobeline and mecamylamine was followed by a significantly increased level of DSDT accuracy that was similar to the improvement following administration of lobeline alone. In contrast, combined administration of nicotine and mecamylamine did not result in increased DSDT accuracy. Furthermore, lobeline administration similarly improved accuracy of trials associated with both the light and the tone, while nicotine improved accuracy of trials associated with the light to a much greater degree. These data suggest that the increases in DSDT accuracy associated with lobeline may be expressed through non-nicotinic mechanisms or a nicotinic receptor which is not blocked by mecamylamine.

Dissociation between cognitive and motor/motivational deficits in the delayed matching to position test: effects of scopolamine, 8-OH-DPAT and EAA antagonists

The effects of the muscarinic antagonists scopolamine HBr and MeBr, the 5-HT1A agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT), and the N-methyl-d-aspartate (NMDA) antagonists MK-801 and CGS-19755 on performance of rats in a delayed matching-to-position task were examined. Pretreatment with scopolamine HBr (0.05 and 0.1 mg/kg), resulted in a delay-dependent decrease in the percentage of correct responses and discriminability (log d), but had no effect on either the latency to complete trials, or the rate of trial completion during the fixed duration session. Scopolamine MeBr (0.1 mg/kg) did not impair percent correct or increase the response latency but did decrease the rate of trial completion. 8-OH-DPAT (up to 0.3 mg/kg), had no effect on percent correct, but did induce a small decrease in discriminability. The impairment in discriminability occurred only at a dose that substantially reduced the rate of trial completion. Both MK-801 (0.05 mg/kg) and CGS 19755 (10 mg/kg) induced a delay-independent impairment in percent correct, discriminability and a reduction in the rate of trial completion without affecting latency. A lower dose of CGS 19755 (5.0 mg/kg) induced a slight impairment in discriminability without significantly affecting the other measures. Taken together, these results demonstrate some dissociation between drug-induced cognitive and motor/motivational deficits in the DMTP test. However, the data question the specificity of putative cognitive impairments reported in many previous studies with the 5-HT1A agonist 8-OH-DPAT.

The effects of AMPA-induced lesions of the medial septum and vertical limb nucleus of the diagonal band of Broca on spatial delayed non-matching to sample and spatial learning in the water maze

These experiments investigated in the rat the impact on spatial delayed non-matching to sample and on acquisition of the Morris water maze of (i) AMPA-induced lesions of the medial septal nucleus, which produced a marked reduction of hippocampal choline acetyltransferase activity and acetylcholine levels (measured using in vivo dialysis) together with lesser reductions in cholinergic markers in the cingulate cortex and (ii) similar AMPA-induced lesions of the vertical limb nucleus of the diagonal band of Broca (vDB), which produced more marked reductions in cholinergic markers in the cingulate cortex than in the hippocampus. Medial septal lesions produced a delay-dependent deficit in spatial working memory, while lesions of the vDB resulted in a delay-independent performance deficit. In addition, rats with vDB lesions adopted biased response strategies during the imposition of long delays. Neither lesion significantly affected the acquisition of a spatial reference memory task, the Morris water maze. The results are discussed in terms of cholinergic- and GABAergic-dependent functions of the hippocampal formation and cingulate cortex in spatial short-term and reference memory.

Effects of benzodiazepine receptor ligands on the performance of an operant delayed matching to position task in rats: opposite effects of FG 7142 and lorazepam

The effects of a series of benzodiazepine (BZ) receptor ligands, ranging from a full agonist through to partial inverse agonists, were examined on short term working memory in the rat. The behavioural paradigm used was a discrete trial, operant delayed matching to position task, as originally described by Dunnett (1985), with delays of 0, 5, 15 and 30 s. The benzodiazepine receptor (BZR) full agonist lorazepam (0.25, 0.375 and 0.5 mg/kg) dose and delay dependently impaired matching accuracy. Lorazepam also increased the latency to respond and decreased the number of nose pokes made into the food tray during the delays. In contrast, the BZR partial agonist ZK 95,962 (1, 3, 10 mg/kg) did not affect matching accuracy, but did increase the speed of responding. The BZR antagonist ZK 93,426 (1.25, 5, 25 mg/kg) had no effects in this paradigm. The BZR weak partial inverse agonists Ro 15-4513 (0.1, 1 and 10 mg/kg) and ZK 90,886 (1, 3 and 10 mg/kg) did not affect accuracy of performance. However, both of these drugs increased the latency to respond and decreased nose poke responses. These motoric effects were particularly strong following 10 mg/kg Ro 15-4513. This shows that the effects of drugs on the accuracy of responding and on the speed of responding can be dissociated. The BZR partial inverse agonist FG 7142 had effects on matching accuracy that were dependent upon dose. The lowest dose of FG 7142 (1 mg/kg) significantly improved accuracy, whereas the highest dose (10 mg/kg) impaired accuracy.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of benzodiazepine receptor ligands on simultaneous visual discriminations of variable difficulty

Benzodiazepine receptor (BZR) ligands have been demonstrated to affect the performance in tasks measuring attentional abilities. In such tasks, subjects typically are required to discriminate visual and/or auditory stimuli. The possibility that the effects of BZR ligands on the performance in tasks measuring attention are primarily due to effects on discriminative processes has not been tested systematically. Rats were trained to discriminate between simultaneously presented pairs of visual stimuli flashing either at 5 Hz versus 4.17, 3.75, 2.5, 1.67 or 1.25 Hz (group 1; FAST), or at 1.25, 1.46, 1.67, 2.5 or 3.33 Hz versus 5 Hz (group 2; SLOW) for 4.8 s (20 trials per discrimination type; sequence of pairs was randomized). In both groups, response accuracy depended significantly on the discriminability of the stimuli, with near perfect accuracy in response to most different pairs of stimuli and near chance-level accuracy in response to least different pairs of stimuli. Administration of the BZR full agonist chlordiazepoxide (1.56, 6.25, 9.38 mg/kg; i.p.) potently increased the number of errors of omission which, following the higher doses, confounded the effects on absolute numbers of correct and incorrect responses. However, the available data do not suggest that the agonist affected the animals' abilities to discriminate between the stimuli. Similarly, administration of the BZR ligands ZK 93 426 and MDL 26,479 (which negatively modulate GABAergic transmission) produced no systematic effects. These data suggest that the effects of BZR ligands on the performance in tasks measuring attentional abilities are not primarily due to effects on the animals' ability to discriminate sensory stimuli.

Effect of a new anxiolytic, DN-2327, on learning and memory in rats

The effects of a new anxiolytic, (2-(7-chloro-1,8-naphthyridin-2-yl)-3- [(1,4-dioxa-8-azaspiro[4.5]dec-8-yl)-carbonylmethyl] isoindolin-1-one (DN-2327), on the execution of step-through passive avoidance and delayed spontaneous alternation tasks were assessed and compared with those of diazepam (DZP) and buspirone. DN-2327 and buspirone (both 10 and 20 mg/kg, PO) impaired performance in the 48-h passive avoidance recall test when given prior to the test session, but not when given before the training trial. DZP impaired the performance at doses of more than 5 and more than 10 mg/kg PO when given prior to the test session and when given before the training trial, respectively. The action of DZP (10 mg/kg PO) when given before the training trial was antagonized by flumazenil (20 mg/kg, IP) and tended to be antagonized by DN-2327 (10 and 30 mg/kg, PO), but was not affected by buspirone. No evidence for possible amnesic effects of DN-2327 or buspirone on working memory was found in the delayed spontaneous alternation task, but DZP (3 and 10 mg/kg, PO) caused significant impairment of working memory. Electroshock sensitivities detected by flinch, jump, and vocalization thresholds were not influenced significantly by DN-2327 (30 and 100 mg/kg, PO), DZP (10 and 30 mg/kg, PO) or buspirone (30 and 100 mg/kg, PO).(ABSTRACT TRUNCATED AT 250 WORDS)

Behavioral microanalysis of spatial delayed alternation performance: rehearsal through overt behavior, and effects of scopolamine and chlordiazepoxide

Rats were trained in an operant spatial delayed alternation task utilizing retention intervals from 2 to 32 s. In addition to response accuracy, operations of the levers during the retention intervals were recorded and analyzed. Animals were tested following the administration of the muscarinic antagonists scopolamine hydrobromide and methylbromide, and the benzodiazepine receptor agonist chlordiazepoxide. In vehicle-treated animals, the relative number of correct responses and correct rehearsal operations (operation of the forthcoming correct lever during retention intervals) varied with the length of the retention intervals, and these measures were correlated. The response rate for rehearsal operations increased with the length of the retention intervals. It is speculated that the delay-dependent increase in response rate reflects an effect of delayed reward that was also associated with a delay-dependent increase in the tendency to alternate between levers. The effects of delay on the accuracy of rehearsal operations may have contributed to the delay-dependent correct responding. Scopolamine hydrobromide (0.01, 0.03, 0.1, 0.3 mg/kg) and methylbromide (0.1, 0.3 mg/kg) impaired correct responding, but did not seem to interfere with the relative number of correct rehearsal operations. As only the presentation of the panel light indicated trial onset, it is speculated that the cholinergic receptor blockade resulted in an increase in the probability of a repositioning response that was triggered by light onset. Chlordiazepoxide (1, 3, 5, 10 mg/kg) did not affect behavioral performance. These results suggest that in tasks that allow the development of rehearsal operations, delay-dependent response accuracy does not represent a sufficient condition for conclusions on task demands on memory.(ABSTRACT TRUNCATED AT 250 WORDS)

Behavioral analysis of diazepam-induced memory deficits: evidence for sedation-like effects

Rats were trained on a nonmatching-to-sample task with delays of 2, 5, and 10 min. Subsequently, performance was assessed in three groups of rats following treatment with saline or diazepam (2.0 mg/kg) administered acutely or tested chronically in six administrations. Relative to treatment with saline, diazepam produced a deficit in discrimination performance, which was greater in the acutely treated rats than in those treated chronically. The deficit was not dependent on the length of the delays. Diazepam-treated animals differed from controls in erring on trials in which they failed to investigate both test objects, failed to investigate the test object for a long enough period of time, and displaced the test object on the preferred side of the apparatus. The hypothesis that these effects represented a sedation-like reduction in behavioral variability was also supported by evidence of a diazepam-induced decrease in gross bodily activity, increase in inactivity, and increase in latencies to respond to objects. No support was found for the involvement of diazepam-induced changes in habituation, extinction, or reward effects.

Effects of cholinergic and non-cholinergic drugs on visual discrimination and delayed visual discrimination performance in rats

The effects of several centrally active drugs were investigated using two visual discrimination tasks: a two-lever food-rewarded conditional brightness discrimination, and a similar conditional brightness discrimination where a delay was introduced between the disappearance of the stimulus and the opportunity to respond on the levers for food. The substances tested (amphetamine, scopolamine, methylscopolamine, physostigmine, diazepam and beta-carboline benzodiazepine receptor antagonist, ZK 93426), all produced differing profiles of action on the performance parameters recorded. In the simple conditional visual discrimination, amphetamine increased omissions without significant effects on accuracy or response latency. Physostigmine enhanced response latencies and failures to respond without significant effects on accuracy. ZK 93426 had no consistent effects on accuracy although at higher doses, some increase in response latency was seen in the delayed responding version of the visual discrimination task. Diazepam had negative effects on all parameters in both discrimination procedures. Scopolamine disrupted responding, but not accuracy in the simple discrimination, whereas accuracy was reduced in a dose, but not delay dependent manner in the delayed discrimination. A similar effect to that observed with scopolamine was observed following methylscopolamine in the delayed discrimination procedure. In the simple visual discrimination small increases in accuracy were recorded, accompanied by increased response latencies.