Adinazolam affects biogenic amine release in hippocampal CA1 neuronal circuitry

Recent findings and advancements in the detection of designer benzodiazepines: a brief review

This review article takes a closer look at a new class of psychoactive substances called designer benzodiazepines (DBZs) and the challenges of their detection. These are adinazolam, clonazolam, deschloroetizolam, diclazepam, etizolam, flualprazolam, flubromazepam, flubromazolam, phenazepam, and pyrazolam. They are central nervous system depressants and sedatives that can cause psychomotor impairment and increase the overdose risk when combined with other sedatives. DBZs undergo phase I and II metabolism similar to traditional benzodiazepines, but their specific metabolic pathways and the influence of genetic polymorphisms are yet to be clarified. Advances in liquid chromatography-tandem mass spectrometry (LC-MS/MS) have enhanced the method's sensitivity for DBZs and their metabolites in biological samples and coupled with improved blood sampling methods require less blood for drug monitoring. Further research should focus on elucidating their pharmacokinetic properties and metabolism in humans, especially in view of genetic polymorphisms and drug interactions that could inform clinical treatment choices. Even though we have witnessed important advances in DBZ detection and measurement, further refinements are needed to expand the scope of detectable DBZs and their metabolites. All this should help toxicological research to better identify and characterise the risks of chronic and polydrug abuse and facilitate clinical, forensic, and regulatory responses to this growing issue.

Is hippocampal atrophy a future drug target?

Hippocampus is the brain structure, vital for episodic and declarative memory. Atrophy of the human hippocampus is seen in a variety of psychiatric and neurological disorders e.g. recurrent depression, schizophrenia, bipolar disorder, post-traumatic stress disorder, epilepsy, head injury, and Alzheimer's disease (AD). Importantly, aging hippocampus also undergoes atrophy. In many instances, for example, AD, the atrophy precedes the development of symptoms while in others, there is a temporal relationship between atrophy and symptomatology. The presence of atrophied hippocampus is one of the most consistent features of many common psychiatric disorders. Several factors contribute to this atrophy. Stress is one of the most profound factors implicated and the mechanisms involve glucocorticoids, serotonin, excitatory amino acids etc. Hippocampal formation as a whole can undergo atrophy or its individual structural components e.g. apical dendrities can exhibit atrophy. Several drugs of unrelated classes have been shown to prevent atrophy indicating heterogenous manner in which hippocampal atrophy is produced. These include, tianeptine (affects structural plasticity in hippocampus and is an effective antidepressant); phenytoin (antiseizure and neuroprotective); fluoxetine (downregulates neurodegenerative enzyme and increases neuroprotective hippocampal S100 beta); lithium (neuroprotective and antiapoptotic); tricyclic antidepressants (increase hippocampal neurogenesis); antipsychotics (reduce hippocampal neuronal suppression); sodium valproate (increases neurogenesis) and mifepristone (antioxidant, neuroprotective and anti-glucocorticoid). Now the most important question is: to what extent does the hippocampal atrophy play a role in the genesis of symptoms of diseases or their progression? And if it does, can we achieve the same degree of prevention or reversal seen in experimental animals, in humans also. An even more important question is: whether the prevention of atrophy would be clinically useful in affecting disease, viz slowing its progression, reducing morbidity, complications or positively affecting the outcome of one or more of its clinically important aspects. If the answer to this is yes, we would have to know at what stage of the disease we use the drugs, dose, duration, follow-up and efficacy. The use of these drugs in the above mentioned conditions can not only test the potential of atrophy as a future drug target, but could also help in learning more about the hippocampus in both health and diseases.

Reduced basal release of serotonin from the ventrobasal thalamus of the rat in a model of neuropathic pain

Drugs that inhibit reuptake of monoamines are frequently used to treat pain syndromes, e.g. neuropathy or fibromyalgia, where mechanical allodynia is present. Several lines of evidence suggest the involvement of supraspinal sites of action of these drugs. However, a direct study of supraspinal serotonin (5-HT) or norepinephrine (NE) release in an animal model in which allodynia is expressed, e.g. neuropathy, has not been done. The ventrobasal (VB) thalamus and the hypothalamus are major supraspinal projection regions for spinal neurons that transmit nociceptive information and are innervated by monoaminergic fibers. This study determined if peripheral neuropathy would induce changes in extracellular monoamines in VB thalamus and hypothalamus. Male Sprague-Dawley rats had spinal nerve roots L5 and L6 tightly ligated (neuropathic rats; NP) or sham (SHAM) surgery; contralateral and ipsilateral VB thalamus and contralateral hypothalamus were dialyzed with modified artificial cerebral spinal fluid (aCSF), with and without fluoxetine. NP rats had significantly decreased 5-HT content in dialysates of the contralateral VB thalamus compared with SHAM rats with (82% decrease) or without (63% decrease) fluoxetine in the perfusion medium over the 180 min of the study. There were no differences in the ipsilateral VB thalamus. In contrast, release of 5-HT was unchanged in the hypothalamic dialysates of SHAM vs. NP rats. NE release was not different in dialysates of either the VB thalamus or hypothalamus of SHAM vs. NP rats. Synthesis of 5-HT, as assessed by accumulation of 5-hydroxytrytophan after treatment with an L-amino acid decarboxylase inhibitor, was not different between NP and SHAM rats in VB thalamic and hypothalamic brain tissue. This study is the first to demonstrate changes in monoamine release supraspinally in NP rats. The differential effect between VB thalamus and hypothalamus suggests that a terminal field change may be involved. Putative mechanisms for mediating this change include alterations of GABA-ergic systems and/or plasticity related to alterations in N-methyl-D-aspartate receptor activation and nitric oxide release related to afferent hyperactivity induced by neuropathic pain.

Mechanism of triazolo-benzodiazepine and benzodiazepine action in anxiety and depression: behavioral studies with concomitant in vivo CA1 hippocampal norepinephrine and serotonin release detection in the behaving animal

1. Real time, in vivo microvoltammetric studies were performed, using miniature carbon-based sensors, to concurrently detect norepinephrine (NE) release and serotonin (5-HT) release, in 2 separate electrochemical signals, within CA1 region of hippocampus in the freely moving and behaving, male, Sprague Dawley laboratory rat. 2. Concurrently, four parameters of open-field behavior, i.e. Ambulations, Rearing, Fine Movements and Central Ambulatory behavior (a measure of anxiety reduction behavior), were assayed by infrared photobeam detection. 3. Time course studies showed that the mechanism of action of the triazolobenzodiazepine (TBZD), adinazolam, (Deracyn) is dramatically different from that of the classical benzodiazepine (BZD), diazepam (Valium, i.e., adinazolam increased, whereas diazepam decreased, 5-HT release within CA1 region of hippocampus in the freely moving and behaving rat. 4. Adinazolam initially increased NE release and then decreased NE release in CA1 region of hippocampus in the freely moving and behaving rat whereas diazepam only decreased the electrochemical signal for NE; the decrease in NE produced by adinazolam was greater than the decrease in NE release produced by diazepam. 5. The Behavioral Activity Patterns, derived from same animal controls, simultaneously with detection of in vivo microvoltammetric signals for NE release and 5-HT release, showed that the BZD, diazepam, exhibited more potent sedative properties than did the TBZD adinazolam. 6. Hippocampal 5-HT and NE release effects of the TBZD, adinazolam, concomitant with behavioral effects lends explanation to the dual anxiolytic/antidepressant properties of the TBZDs.

Alprazolam, diazepam, yohimbine, clonidine: in vivo CA1 hippocampal norepinephrine and serotonin release profiles under chloral hydrate anesthesia

1. Although the GABA-A receptor complex has been the main focus of anti-anxiety therapy, the neural interaction in the septohippocampal circuit between GABA-A and the neurotransmitter, 5-HT, compels a study of the monoamine, 5-HT, in anxiety as well. 2. Neurochemistry for anxiety is also intimately involved with the neurotransmitter, NE. Indeed, 5-HT is a component of the dorsal ascending noradrenergic bundle and both neurotransmitters, NE and 5-HT, have been implicated in clinical depression. 3. In vivo microvoltammetric studies were performed using miniature carbon based sensors to detect NE release and concurrent 5-HT release, with 2 separate neural electrochemical signals, within CA1 region of hippocampus, in the chloral hydrate anesthetized rat. 4. Time course studies showed that both the triazolobenzodiazepine (TBZD), alprazolam, and the benzodiazepine (BZD), diazepam, decreased hippocampal NE release. 5. The in vivo and on line neurochemical profile of hippocampal 5-HT release for alprazolam differed from that of diazepam, i.e. alprazolam increased hippocampal 5-HT release, whereas diazepam decreased hippocampal 5-HT release. 6. Time course studies showed that the alpha 2-adrenergic antagonist, yohimbine, an anxiogenic agent, increased both NE and 5-HT release in CA1 region of hippocampus; the alpha 2-adrenergic agonist, clonidine, decreased NE release and increased 5-HT release in the same region. 7. Neither the profile for the TBZD, alprazolam, nor that of the BZD, diazepam, mimicked the neurochemical profile for the anxiogenic agent, yohimbine; the neurochemical profile for the TBZD, alprazolam, was similar to that of the alpha 2-adrenergic agonist, clonidine. 8. Interestingly, alprazolam's hippocampal 5-HT/NE interaction is similar to clonidine's 5-HT/NE action at alpha 2-adrenergic autoreceptors, resulting in enhanced 5-HT release. 9. Enhanced 5-HT release in hippocampus, exhibited by the atypical TBZD, alprazolam, and not by the typical BZD, diazepam, may be an underlying mechanism for the antidepressant activity exhibited by alprazolam.

I. Serotonin (5-HT) within dopamine reward circuits signals open-field behavior. II. Basis for 5-HT--DA interaction in cocaine dysfunctional behavior

Light microscopic immunocytochemical studies, using a sensitive silver intensification procedure, show that dopamine (DA) and serotonin (5-HT) axons terminate on neurons in the nucleus accumbens (NAcc) (A10) terminals and also in dorsal striatum (DSTr) (A9) terminals. The data demonstrate a prominent endogenous anatomic interaction at these distal presynaptic sites between the neurotransmitters 5-HT and DA; the pattern of the 5-HT-DA interaction differs between A10 and A9 terminals. Moreover, in distinction to the variance shown anatomically between 5-HT--DA interactions at distal A9 and A10 sites, the 5-HT--DA interactions at the level of DA somatodendrites, the proximal site, are similar, i.e. 5-HT terminals in the midbrain tegmentum are profuse and have a massive overlap with DA neurons in both ventral tegmental area (VTA) and substantia nigra pars compacta (SNpc). We suggest with reference to the DA neurons of A10 and A9 pathways, inclusive of somatodendrites (sites of proximal presynaptic interactions in the midbrain) and axons (sites of distal presynaptic interactions), that 5-HT--DA interactions in A10 terminals are more likely to exceed those in the DStr arrangement. Furthermore, our neuroanatomic data show that axonally released DA at A10 terminals may originate from proximal 5-HT somatodendrites, i.e. dorsal raphe (DR) or the proximal DA somatodendrites, VTA. In vivo microvoltammetric studies were done with highly sensitive temporal and spatial resolution; the studies demonstrate basal (endogenous) real time 5-HT release at distal A10 and distal A9 terminal fields and real time 5-HT release at proximal A10 VTA somatodendrites. In vivo microvoltammetric studies were performed concurrently and on line with studies of DA release, also at distal A10 and distal A9 terminal fields and at proximal A10 somatodendrites. Serotonin release was detected in a separate voltammetric peak from the DA voltammetric peak. The electrochemical signal for 5-HT release was detected within 10-12 s and that for DA release within 12-15 s, after each biogenic amine diffused through the synaptic environment onto the microelectrode surface. The electrochemical signal for 5-HT and a separate electrochemical signal for DA are detected on the same voltammogram within 22-27 s; each electrochemical signal represents current changes in picoamperes, within seconds of detection time. The amplitude of each electrochemical signal reflects the changes in diffusion of each biogenic amine to the microelectrode surface. Each neurotransmitter has a distinct potential at which oxidation occurs; this results in a recording which has a distinct peak for a specific neurotransmitter. The concentration of each neurotransmitter within the synaptic environment is directly related to the electrochemical signal detected via the Cottrell equation. Voltammograms were recorded every 5 min. At the time that basal 5-HT release and basal DA release were recorded within same animal control, open-field behavioral studies were performed, also concurrently, by infrared photocell beams. The frequency of each behavioral parameter was monitored every 100 ms; the number of behavioral events, were summated every 5 min during the time course of study. Thus, the detection of neurotransmitters occurs in real time, while simultaneously monitoring the animal's behavior by infrared photocell beams. The results from the in vivo microvoltammetric and behavioral data from this study show that basal 5-HT release at distal A10 and A9 terminals dramatically increased with DA release. Moreover, each increase in basal 5-HT release, at both A10 and at A9 terminal fields occurred consistently and at the same time as each increase in open-field locomotion and stereotypy occurred naturally during the animal's exploration in a novel chamber. Thus, the terminology 'synchronous and simultaneous' describes aptly the correlation between 5-HT release at distal A10 and A9 terminal fields and open-field locomo

Serotonin turnover rate, [3H]paroxetine binding sites, and 5-HT1A receptors in the hippocampus of rats subchronically treated with clonazepam

Selective central benzodiazepine agonists, such as clonazepam, are known to modify serotonin and 5-hydroxyindoleacetic content in the brain. In order to further study the effect of this benzodiazepine on serotonin turnover rate, rats received clonazepam, 10 mg/kg for 10 days, and the concentrations of serotonin and 5-hydroxyindoleacetic acid were determined in the hippocampus after inhibition of monoamineoxidase with pargyline. The results indicate a reduction in the turnover rate of the monoamine. In addition, the systemic administration of clonazepam produced a decrease in the Bmax of [3H]DPAT binding to 5-HT1A sites in the hippocampus. By contrast, this effect was not observed if clonazepam was delivered into the dorsal raphe nucleus by osmotic minipumps. The binding of [3H]paroxetine to 5-HT reuptake sites was increased by the treatment with clonazepam. The present observations indicate that clonazepam produces a reduction of serotonin turnover rate in the hippocampus of the rat concomitant with a down-regulation of 5-HT1A binding sites, probably by an effect at the forebrain projections. There is also an up-regulation of the serotonin transporter, which might contribute to a reduction in the synaptic availability of serotonin during clonazepam treatment.

Learned helplessness and in vivo hippocampal norepinephrine release

Hippocampal norepinephrine release was measured using in vivo microdialysis in rats before and after exposure to inescapable tail shock stress and after testing for learned helplessness. Rats that did not develop learned helplessness after stress had higher basal norepinephrine release after stress than rats developing learned helplessness or than control rats. After the shuttlebox test for learned helplessness, K(+)-stimulated norepinephrine release was lower in learned helpless than in nonhelpless or control rats. These results confirm an important role for the hippocampal noradrenergic system in differential behavioral responses to stress.

Extraneuronal noradrenaline in the prefrontal cortex of morphine-dependent rats: tolerance and withdrawal mechanisms

The changes in extracellular concentrations of noradrenaline (NA) in the prefrontal cortex of morphine-dependent rats were studied by microdialysis following an acute morphine challenge and during naloxone-precipitated withdrawal. Animals were implanted with morphine- or placebo-containing pellets for 5 days. In control rats a challenge dose of morphine (5 mg/kg s.c.) induced a maximum decrease in NA output of about 45% of pre-drug levels. In contrast, morphine challenge had no effect on extraneuronal NA concentrations in morphine-implanted animals. In control animals, naloxone (2 mg/kg i.p.) produced no behavioral effect nor changed NA levels. However, in morphine-dependent animals naloxone suddenly increased extraneuronal NA by 175% of baseline dialysate levels in the first sample after the injection and precipitated a morphine-withdrawal symptomatology that paralleled the changes in NA output. Thus, chronic morphine treatment in rats results in the development of tolerance to the acute inhibitory effect of morphine on extraneuronal NA and is associated with a stimulation of prefrontocortical NA output during naloxone-precipitated withdrawal.

5-HT1A agonists uncouple noradrenergic somatodendritic impulse flow and terminal release

Both noradrenergic (NE) and serotonergic (5-HT) systems have been implicated in anxiety and depression, as well as in the therapeutic actions of drugs treating these conditions. We have used microelectrode recordings of nerve cell impulse frequencies and in vivo voltammetric recordings of monoamine release to evaluate effects of the arylpiperazine 5-HT1A anxiolytics, buspirone and ipsapirone. Both buspirone and ipsapirone significantly depressed 5-HT neuronal firing rates in dorsal raphe (DR), but significantly increased NE neuronal firing rates in locus coeruleus (LC). In CA1 region of hippocampus, both buspirone and ipsapirone significantly depressed NE release with potencies greater than those required for the significant depression of 5-HT release. It is concluded that, contrary to the belief that the 5-HT1A arylpiperazines act primarily through 5-HT mechanisms, alterations in NE function may be critically important for their therapeutic effects, just as is the case for the benzodiazepine anxiolytics and the tricyclic antidepressants.