A model of the neuropsychology of anxiety is proposed. The model is based in the first instance upon an analysis of the behavioural effects of the antianxiety drugs (benzodiazepines, barbiturates, and alcohol) in animals. From such psychopharmacologi-cal experiments the concept of a “behavioural inhibition system” (BIS) has been developed. This system responds to novel stimuli or to those associated with punishment or nonreward by inhibiting ongoing behaviour and increasing arousal and attention to the environment. It is activity in the BIS that constitutes anxiety and that is reduced by antianxiety drugs. The effects of the antianxiety drugs in the brain also suggest hypotheses concerning the neural substrate of anxiety. Although the benzodiazepines and barbiturates facilitate the effects of γ-aminobutyrate, this is insufficient to explain their highly specific behavioural effects. Because of similarities between the behavioural effects of certain lesions and those of the antianxiety drugs, it is proposed that these drugs reduce anxiety by impairing the functioning of a widespread neural system including the septo-hippocampal system (SHS), the Papez circuit, the prefrontal cortex, and ascending monoaminergic and cholinergic pathways which innervate these forebrain structures. Analysis of the functions of this system (based on anatomical, physiological, and behavioural data) suggests that it acts as a comparator: it compares predicted to actual sensory events and activates the outputs of the BIS when there is a mismatch or when the predicted event is aversive. Suggestions are made as to the functions of particular pathways within this overall brain system. The resulting theory is applied to the symptoms and treatment of anxiety in man, its relations to depression, and the personality of individuals who are susceptible to anxiety or depression.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0140525X00013066

Précis of The Neuropsychology of Anxiety: An Enquiry into the Functions of the Septo-Hippocampal System..

The current studies further investigated the effects, in animal models of anxiety, of novel putative anxiolytic and anxiogenic compounds believed to induce their effects by actions at the GABA-benzodiazepine receptor complex. It was expected that the results would also provide further validation for a novel test of anxiety based on the ratio of open to closed arm entries in an elevated plus maze in the rat. The novel putative anxiolytics CL 218,872 (10–20 mg/kg) and tracazolate (5 mg/kg) significantly elevated the percentage of time spent on the open arms of an elevated plus-maze, consistent with their anxiolytic activity in several other animal tests. Also consistent with results from other animal tests, no anxiolytic activity was observed for the phenylquinoline PK 8165 (10–25 mg/kg), the 3,4-benzodiazepine tofisopam (25–50 mg/kg), or buspirone (0.5–20 mg/kg). The benzodiazepine receptor inverse agonists FG 7142 (1–5 mg/kg) and CGS 8216 (3–10 mg/kg) had anxiogenic activity in this test, as did the atypical benzodiazepine Ro 5-4864 (1–5 mg/kg). Interestingly, however, the benzodiazepine receptor antagonists Ro 15-1788 (10–20 mg/kg) and ZK 93426 (5–10 mg/kg) had no anxiogenic activity in this test.

Anxiolytic and anxiogenic drug effects on exploratory activity in an elevated plus-maze: a novel test of anxiety in the rat

A simple system is described to analyze the possibility that increased exploratory behavior is an index for the anxiolytic effects of benzodiazepines in laboratory rodents. Mice were allowed free run in a two-chambered arena, where two-thirds of the area was illuminated and one-third was darkened. The two chambers were separated by a black partition equipped with photocells across the opening, and the entire cage rested on an Animex activity monitor. Transitions across the partition between the light and dark chambers, and total Animex locomotor activity, were increased by clonazepam and chlordiazepoxide, in dose-dependent ranges consistent with previously reported behavior models. The increased exploratory activity with benzodiazepines does not appear to be a non-specific increase in general motor activity, as locomotion in clonazepam and chlordiazepoxide treated mice placed in a bare, undifferentiated cage was not significantly different from vehicle treated mice.

Preliminary report of a simple animal behavior model for the anxiolytic effects of benzodiazepines

GABAA-receptors display an extensive structural heterogeneity based on the differential assembly of a family of at least 15 subunits (alpha 1-6, beta 1-3, gamma 1-3, delta, rho 1-2) into distinct heteromeric receptor complexes. The subunit composition of receptor subtypes is expected to determine their physiological properties and pharmacological profiles, thereby contributing to flexibility in signal transduction and allosteric modulation. In heterologous expression systems, functional receptors require a combination of alpha-, beta-, and gamma-subunit variants, the gamma 2-subunit being essential to convey a classical benzodiazepine site to the receptor. The subunit composition and stoichiometry of native GABAA-receptor subtypes remain unknown. The aim of this study was to identify immunohistochemically the main subunit combinations expressed in the adult rat brain and to allocate them to identified neurons. The regional and cellular distribution of seven major subunits (alpha 1, alpha 2, alpha 3, alpha 5, beta 2,3, gamma 2, delta) was visualized by immunoperoxidase staining with subunit-specific antibodies (the beta 2- and beta 3-subunits were covisualized with the monoclonal antibody bd-17). Putative receptor subtypes were identified on the basis of colocalization of subunits within individual neurons, as analyzed by confocal laser microscopy in double- and triple-immunofluorescence staining experiments. The results reveal an extraordinary heterogeneity in the distribution of GABAA-receptor subunits, as evidenced by abrupt changes in immunoreactivity along well-defined cytoarchitectonic boundaries and by pronounced differences in the cellular distribution of subunits among various types of neurons. Thus, functionally and morphologically diverse neurons were characterized by a distinct GABAA-receptor subunit repertoire. The multiple staining experiments identified 12 subunit combinations in defined neurons. The most prevalent combination was the triplet alpha 1/beta 2,3/gamma 2, detected in numerous cell types throughout the brain. An additional subunit (alpha 2, alpha 3, or delta) sometimes was associated with this triplet, pointing to the existence of receptors containing four subunits. The triplets alpha 2/beta 2,3/gamma 2, alpha 3/beta 2,3/gamma 2, and alpha 5/beta 2,3/gamma 2 were also identified in discrete cell populations. The prevalence of these seven combinations suggest that they represent major GABAA-receptor subtypes. Five combinations also apparently lacked the beta 2,3-subunits, including one devoid of gamma 2-subunit (alpha 1/alpha 2/gamma 2, alpha 2/gamma 2, alpha 3/gamma 2, alpha 2/alpha 3/gamma 2, alpha 2/alpha 5/delta).(ABSTRACT TRUNCATED AT 400 WORDS)

GABAA-receptor heterogeneity in the adult rat brain: differential regional and cellular distribution of seven major subunits.

Lysine acetylation is a key mechanism that regulates chromatin structure; aberrant acetylation levels have been linked to the development of several diseases. Acetyl-lysine modifications create docking sites for bromodomains, which are small interaction modules found on diverse proteins, some of which have a key role in the acetylation-dependent assembly of transcriptional regulator complexes. These complexes can then initiate transcriptional programmes that result in phenotypic changes. The recent discovery of potent and highly specific inhibitors for the BET (bromodomain and extra-terminal) family of bromodomains has stimulated intensive research activity in diverse therapeutic areas, particularly in oncology, where BET proteins regulate the expression of key oncogenes and anti-apoptotic proteins. In addition, targeting BET bromodomains could hold potential for the treatment of inflammation and viral infection. Here, we highlight recent progress in the development of bromodomain inhibitors, and their potential applications in drug discovery.

Targeting bromodomains: epigenetic readers of lysine acetylation

Several new lines of evidence suggest the existence of two or more distinct types of benzodiazepine receptors, in contrast to earlier results suggesting the presence of only one class of receptors. Appropriate thermoinactivation experiments indicate two receptors with different thermostabilities. Several triazolopyridazines, with some of the pharmacological properties of anxiolytics have recently been shown to displace 3H-diazepam and 3H-flunitrazepam with Ki values in the 6 to 100 nanomolar range. These new substances are active in conflict tests in rats and monkeys and prevent metrazol induced seizures in vivo, but strikingly lack the ataxia and sedative properties of the benzodiazepines. Hill analyses of dose-response curves for some of these substances yields Hill coefficients in the range of 0.4--0.6, suggesting that these compounds may be able to discriminate between several types of benzodiazepine receptors.

Some properties of brain specific benzodiazepine receptors: New evidence for multiple receptors

Brain-specific binding sites have been isolated on synaptosomal membrane fragments which recognize pharmacologically active benzodiazepine (BDZ's) and triazolopyridazines (TPZ's). While early evidence indicated the existence of a single homogeneous class of BDZ binding sites, more recent biological and pharmacological studies support the notion of BDZ receptor multiplicity. We now propose that two biochemically distinct BDZ receptors exist in brain which are responsible for the mediation of different pharmacological activities. Type I BDZ receptors display a high affinity for both BDZ's and TPZ's, are not coupled to GABA receptors or to chloride ionophores, and are the sites which mediate anxiolytic actions. Type II BDZ receptors display a high affinity for BDZ's display a low affinity for TPZ's, are coupled to GABA receptors and/or chloride ionophores, and are the sites which mediate pharmacological effects other than anxiolytic activity.

Resolution of two biochemically and pharmacologically distinct benzodiazepine receptors

CL 218,872 is the first non-benzodiazepine to selectively displace brain specific 3H-diazepam binding with a potency comparable to that of the benzodiazepines. Like the benzodiazepines, CL 218,872 increased punished responding in a conflict situation and protected against the convulsions induced by pentylenetetrazole. These three pharmacological properties are highly predictive of anxiolytic activity. Unlike the benzodiazepines, however, CL 218,872 was relatively inactive in tests designed to measure effects on neuronal systems which utilize GABA, glycine and serotonin as transmitters. Furthermore, CL 218,872 was relatively free of the ataxic and depressant side effects commonly associated with the benzodiazepines. Because of this high degree of selectivity, CL 218,872 may represent a new probe for investigating neuronal substrates of anxiety.

A synthetic non-benzodiazepine ligand for benzodiazepine receptors: a probe for investigating neuronal substrates of anxiety.

The in vitro and in vivo ability of benzodiazepines to inhibit specific 3H-diazepam binding correlated with their ability to increase punished responding in a conflict situation. Conflict and foot shock, the punishing stimulus used in most conflict procedures, also altered 3H-diazepam binding. These data implicate 3H-diazepam binding sites in mediating at least some of the anxiolytic properties of benzodiazepines and suggest the existence of some endogenous substance which might be involved in the etiology of anxiety.

Relationship between benzodiazepine receptors and experimental anxiety in rats

Brain specific benzodiazepine receptors appear to mediate the pharmacological properties of benzodiazepines. A neuronal localization for these receptors is suggested by the parallel decrease in the number of benzodiazepine receptors and cerebellar Purkinje cells in “nervous” mutant mice. Electrophysiological results are compatible with an action of benzodiazepines on neuronally localized, physiological receptors. Biochemical, electrophysiological and behavioral experiments highlight the possible importance of frontal cortex in mediating the anxiolytic properties of the benzodiazepines. Triazolopyridazines act upon benzodiazepine receptors, increase punished responding and protect against pentylenetetrazole-induced convulsions, but do not produce the side effects associated with benzodiazepines or affect classical neurotransmitter systems. The structural similarities between triazolopyridazines, purines and the indole portion of certain peptides may provide insights into the nature of the endogenous ligand.

Claire A. Klepner

Papers

Some properties of brain specific benzodiazepine receptors: New evidence for multiple receptors

Resolution of two biochemically and pharmacologically distinct benzodiazepine receptors

A synthetic non-benzodiazepine ligand for benzodiazepine receptors: a probe for investigating neuronal substrates of anxiety.

Relationship between benzodiazepine receptors and experimental anxiety in rats

Benzodiazepine receptors: cellular and behavioral characteristics.