Comparative studies with thieno- and benzodiazepines: spatial delayed alternation behaviour in the monkey (Macaca mulatta)

Is the behavioural effect of diazepam in rats unique to negative secondary stimuli?

Studies of the behavioural effects of benzodiazepines have focused in particular on situations with negative secondary stimuli, i.e., stimuli signalling negative primary events such as punishment or non-reward. The general result is that benzodiazepines attenuate behavioural reactions to this type of stimuli. The aim of the present study was to investigate if there are any differences between positive and negative secondary stimuli in this respect. Rats were treated with diazepam in a modified Skinner box with two levers. One of the levers always gave a small reward. A lamp being ON or OFF was used as a secondary stimulus indicating if the other lever would give a large or no reward. Pretreatment with diazepam (1.0 mg/kg) did not act differently on the response to the positive or negative secondary stimulus. The main effect was a general attenuation of optimal responding with a concomitant decrease in water intake. An alternative hypothesis stating that benzodiazepines alter the reactivity to secondary stimuli more in general is supported.

Differential, postnatal ontogeny of opiate and benzodiazepine receptor subtypes in rat cerebral cortex: binding characteristics of tifluadom and brotizolam

The postnatal development of 3[H] ethylketocyclazocine (EKC) binding characteristics was examined using membranes from the cerebral cortex of rats at various ages. Binding site affinity did not vary significantly between postnatal days 1 and 90. However, the apparent density of cortical binding sites increased fivefold between birth and adulthood. These results were similar to another ontogenic study of brain opiate receptor binding. Whereas EKC was equally potent as a competitor for 3[H] EKC binding in cortex from neonatal and adult rats, tifluadom was three times more potent in neonatal cortex than in adult cortex as a displacer of specific EKC binding. Brotizolam, a new thienodiazepine and a potent sedative hypnotic, also was distinctly more potent as an inhibitor of 3H-diazepam binding in neonatal rat brain cortex than in adult rat brain cortex. These results suggest that subtypes of benzodiazepine receptors, as well as some opiate receptor subtypes, exhibit different rates of postnatal development.

Activity of the chloro- and triazolo-benzodiazepines. Behavioural studies in the monkey (Macaca mulatta)

The effects of 1,4-benzodiazepines with various heterocyclic ring structures (triazolo, triazino and imidazo), and of 1,4-benzodiazepines with chlorine substitution in the phenyl ring (4'- chlorodiazepam , 2'- chlorodiazepam and 2'- chloronordiazepam ) were studied on spatial-delayed alternation and delayed matching-to-sample tasks in the monkey. Within the dose range 0.25-0.75 mg kg-1, the triazolo compounds had marked activity, decreasing the number of correct responses and increasing total response time. The triazino was less potent and the imidazo compounds were the least likely to disrupt performance. Smaller doses (0.005, 0.01 and 0.05 mg kg-1) of triazolam did not impair performance on the tasks, and larger doses of imidazo (1.0, 3.0 and 7.5 mg kg-1) were without effect on delayed alternation. Within the dose range 1.0-10.0 mg kg-1, 4'- chlorodiazepam was without effect and only the largest dose of diazepam and 2'- chlorodiazepam impaired performance. 2'- Chloronordiazepam decreased the number of correct responses at all doses (1.0, 3.0 and 10.0 mg kg-1) and with the largest dose, the total response time was increased. The studies suggest that the effects of a drug on higher nervous function in the monkey cannot easily be predicted from standard pharmacological tests in other animals or other species of monkey.

Inhibitory effects of brotizolam, a new thienodiazepine, on limbic forebrain and neostriatal dopaminergic systems in vivo and in vitro

Studies were performed to elucidate the effects of brotizolam, a newly synthesized thienodiazepine, chemically related to the benzodiazepines, on dopamine turnover in the limbic forebrain and neostriatum. Intraperitoneally administered brotizolam retarded the rate of alpha-methyl-p-tyrosine-induced depletion of dopamine in the olfactory tubercle (OT), nucleus accumbens (NA) and caudate nucleus (CN). Significant retardation was observed with brotizolam in doses ranging from 0.1-10 mg/kg in the olfactory tubercle, and from 1-10 mg/kg in the nucleus accumbens and caudate nucleus. These inhibitory effects of brotizolam were antagonized by bicuculline, a GABA antagonist, in all of the regions examined. Using slices of the olfactory tubercle, nucleus accumbens and caudate nucleus, the effects of brotizolam on dopaminergic nerve terminals were examined in vitro. Basal release of dopamine was not affected by brotizolam in concentrations up to 10(-6) M; however, K+-stimulated release of dopamine was significantly reduced by brotizolam at 10(-7) M or above. The reduction of K+-stimulated release of dopamine was antagonized by bicuculline, added in the superfusion medium. These data suggest that brotizolam inhibits the release of dopamine in the limbic forebrain and neostriatal systems probably through mechanisms including a facilitation of GABAergic action on dopaminergic nerve terminals.