Effects of acute and chronic treatment with fluoxetine on stress-induced hyperthermia in telemetered rats and mice

Abuse potential assessment of the dual orexin receptor antagonist daridorexant in rats

BACKGROUND

Drugs that act on the central nervous system (CNS) and have sedative effects can lead to abuse in humans. New CNS-active drugs often require evaluation of their abuse potential in dedicated animal models before marketing approval. Daridorexant is a new dual orexin receptor antagonist (DORA) with sleep-promoting properties in animals and humans. It was approved in 2022 in the United States and Europe for the treatment of insomnia disorder.

AIMS

Nonclinical evaluation of abuse potential of daridorexant using three specific rat models assessing reinforcement, interoception, and withdrawal.

METHODS

Reinforcing effects of daridorexant were assessed in an operant rat model of intravenous drug self-administration. Similarity of interoceptive effects to those of the commonly used sleep medication zolpidem was tested in an operant drug discrimination task. Withdrawal signs indicative of physical dependence were evaluated upon sudden termination of chronic daridorexant treatment. Rat experiments were conducted at a dose range resulting in daridorexant plasma concentrations equaling or exceeding those achieved at the clinically recommended dose of 50 mg in humans.

RESULTS

Daridorexant had no reinforcing effects, was dissimilar to zolpidem in the drug discrimination task, and did not induce any withdrawal-related signs upon treatment discontinuation that would be indicative of physical dependence.

OUTCOMES

Daridorexant showed no signs of abuse or dependence potential in rats. Our data indicate that daridorexant, like other DORAs, has a low potential for abuse in humans.

The hole-board apparatus in the study of anxiety

Anxiety disorders pose a significant challenge in contemporary society, and their impact in terms of social and economic burden is overwhelming. Behavioral research conducted on animal subjects is crucial for comprehending these disorders and, from a translational standpoint, for introducing innovative therapeutic approaches. In this context, the Hole-Board apparatus has emerged as a widely utilized test for studying anxiety-related behaviors in rodents. Although a substantial body of literature underscores the utility and reliability of the Hole-Board in anxiety research, recent decades have witnessed a range of studies that have led to uncertainties and misinterpretations regarding the validity of this behavioral assay. The objective of this review is twofold: firstly, to underscore the utility and reliability of the Hole-Board assay, and concurrently, to examine the underlying factors contributing to potential misconceptions surrounding its utilization in the study of anxiety and anxiety-related behaviors. We will present results from both conventional quantitative analyses and multivariate approaches, while referencing a comprehensive collection of studies conducted using the Hole-Board.

Antidepressant effects of novel positive allosteric modulators of Trk-receptor mediated signaling - a potential therapeutic concept?

BACKGROUND

Major depressive disorder (MDD) is defined as a complex mental disorder which is characterized by a pervasive low mood and aversion to activity. Several types of neurotransmitter systems e.g. serotonergic, glutamatergic and noradrenergic systems have been suggested to play an important role in the origination of depression, but neurotrophins such as brain derived neurotrophic factor (BDNF) have also been implicated in the disease process.

OBJECTIVES

The purpose of this study was to examine the effects of a newly developed class of molecules, characterized as positive allosteric modulators of neurotrophin/Trk receptor mediated signaling (Trk-PAM), on neurotransmitter release and depression-like behavior in vivo.

METHODS

The effect of and possible interaction of neurotrophin/Trk signaling pathways with serotonergic and glutamatergic systems in the modulation of depression-related responses was studied using newly developed Trk-PAM compounds (ACD855, ACD856 and AC26845), as well as ketamine and fluoxetine in the forced swim test (FST) in rodents. Moreover, in vivo microdialysis in freely moving rats was used to assess changes in neurotransmitter levels in the rat.

RESULTS

The results from the study show that several different compounds, which all potentiate Trk-receptor mediated signaling, display antidepressant-like activity in the FST. Moreover, the data also indicate that the effects of both fluoxetine and ketamine in the FST, both used in clinical practice, are mediated via BDNF/TrkB signaling, which could have implications for novel therapies in MDD.

CONCLUSIONS

Trk-PAMs could provide an interesting avenue for the development of novel therapeutics in this area.

Infrared thermography for non-invasive measurement of social inequality aversion in rodents and potential usefulness for future animal-friendly studies

Infrared thermography is a method that detects thermal radiation energy and can measure the body surface temperature of animals from a distance. While rectal temperature has traditionally been used to measure animals' core temperature, thermal imaging can avoid the stress and potential rise of body temperature deriving from handling of the animals. Additionally, being non-invasive and contactless, thermal imaging allows free movement of the animals. The validity of this technique as a psychophysiological method has been proven in a series of stress-induced hyperthermia (SIH) studies of mice under social inequality conditions. Restraint in a holder elicits SIH in mice. A restrained mouse surrounded by freely moving cage mates displays increased SIH suggesting that social inequality enhances the stress. Social inequality can be examined also in unrestrained mice, in particular through unequal distribution of food. In this protocol, a food-deprived mouse is given a small piece of cheese, while its cage mate is given a large piece of cheese. This inequity causes SIH, suggesting social inequality aversion in mice. Thus, social inequality in different situations similarly increased SIH. Importantly, in future studies infrared thermography could also be used to evaluate emotional arousal states different from stress (for example to assess reactivity to rewards or in social and sexual preference tests). Moreover, the technique could be used to investigate also cognitive arousal induced by novelty. Indeed, infrared thermography could be a particularly useful tool for animal-friendly studies of cognition and emotion in rodents.

Endogenous and exogenous serotonin, but not sumatriptan, ameliorate seizures and neuroinflammation in the pentylenetetrazole-induced seizure model in rats

ABSTRACT Background: Epilepsy has neuropsychiatric comorbidities such as depression, bipolar disorder, and anxiety. Drugs that target epilepsy may also be useful for its neuropsychiatric comorbidities. Objective: To investigate the effects of serotonergic modulation on pro-inflammatory cytokines and the seizures in pentylenetetrazole (PTZ)-induced seizure model in rats. Methods: Male Wistar rats were injected intraperitoneally with serotonin, selective serotonin reuptake inhibitor fluoxetine, 5-HT1B/D receptor agonist sumatriptan, or saline 30 min prior to PTZ treatment. Behavioral seizures were assessed by the Racine's scale. Concentrations of IL-1β, IL-6, and TNF-α in serum and brain tissue were determined by ELISA. Results: Serotonin and fluoxetine, but not sumatriptan, alleviated PTZ-induced seizures by prolonging onset times of myoclonic-jerk and generalized tonic-clonic seizures. The anti-seizure effect of fluoxetine was greater than that of serotonin. Likewise, serotonin and fluoxetine, but not sumatriptan, reduced PTZ-induced increases in the levels of IL-1β and IL-6 in both serum and brain tissue. None of the administered drugs including PTZ affected TNF-α concentrations. Conclusions: Our findings suggest that endogenous and exogenous serotonin exhibits anticonvulsant effects by suppressing the neuroinflammation. It seems that 5-HT1B/D receptors do not mediate anticonvulsant and anti-neuroinflammatory effects of serotonin.

Stress-induced hyperthermia and hypothermia

Stress affects core body temperature (T_c). Many kinds of stress induce transient, monophasic hyperthermia, which diminishes gradually if the stressor is terminated. Stronger stressors produce a longer-lasting effect. Repeated/chronic stress induces anticipatory hyperthermia, reduces diurnal changes in T_c, or slightly increases T_c throughout the day. Animals that are exposed to chronic stress or a cold environment exhibit an enhanced hyperthermic response to a novel stress. These changes persist for several days after cessation of stress exposure. In contrast, long-lasting inescapable stress sometimes induces hypothermia. In healthy humans, psychologic stress induces slight increases in T_c, which are within the normal range of T_c or just above it. Some individuals, however, develop extremely high T_c (up to 41°C) when they are exposed to emotional events or show persistent low-grade high T_c (37-38°C) during or after chronic stress situations. In addition to the nature of the stressor itself, such stress-induced thermal responses are modulated by sex, age, ambient temperature, cage mates, past stressful experiences and cold exposure, and coping. Stress-induced hyperthermia is driven by mechanisms distinct from infectious fever, which requires inflammatory mediators. However, both stress and infection activate the dorsomedial hypothalamus-rostral medullary raphe region-sympathetic nerve axis to increase T_c.

Acute Exposure to Fluoxetine Alters Aggressive Behavior of Zebrafish and Expression of Genes Involved in Serotonergic System Regulation

Zebrafish, Danio rerio, is an emerging model organism in stress and neurobehavioral studies. In nature, the species forms shoals, yet when kept in pairs it exhibits an agonistic and anxiety-like behavior that leads to the establishment of dominant-subordinate relationships. Fluoxetine, a selective serotonin reuptake inhibitor, is used as an anxiolytic tool to alter aggressive behavior in several vertebrates and as an antidepressant drug in humans. Pairs of male zebrafish were held overnight to develop dominant-subordinate behavior, either treated or non-treated for 2 h with fluoxetine (5 mg L^-1), and allowed to interact once more for 1 h. Behavior was recorded both prior and after fluoxetine administration. At the end of the experiment, trunk and brain samples were also taken for cortisol determination and mRNA expression studies, respectively. Fluoxetine treatment significantly affected zebrafish behavior and the expression levels of several genes, by decreasing offensive aggression in dominants and by eliminating freezing in the subordinates. There was no statistically significant difference in whole-trunk cortisol concentrations between dominant and subordinate fish, while fluoxetine treatment resulted in higher (P = 0.004) cortisol concentrations in both groups. There were statistically significant differences between dominant and subordinate fish in brain mRNA expression levels of genes involved in stress axis (gr, mr), neural activity (bdnf, c-fos), and the serotonergic system (htr2b, slc6a4b). The significant decrease in the offensive and defensive aggression following fluoxetine treatment was concomitant with a reversed pattern in c-fos expression levels. Overall, an acute administration of a selective serotonin reuptake inhibitor alters aggressive behavior in male zebrafish in association with changes in the neuroendocrine mediators of coping styles.

Transcriptome composition of the preoptic area in mid-age and escitalopram treatment in male mice

The decrease in serotonergic neurotransmission during aging can increase the risk of neuropsychiatric diseases such as depression in elderly population and decline the reproductive system. Therefore, it is important to understand the age-associated molecular mechanisms of brain aging. In this study, the effect of aging and chronic escitalopram (antidepressant) treatment to admit mice was investigated by comparing transcriptomes in the preoptic area (POA) which is a key nucleus for reproduction. In the mid-aged brain, the immune system-related genes were increased and hormone response-related genes were decreased. In the escitalopram treated brains, transcription-, granule cell proliferation- and vasoconstriction-related genes were increased and olfactory receptors were decreased. Since homeostasis and neuroprotection-related genes were altered in both of mid-age and escitalopram treatment, these genes could be important for serotonin related physiologies in the POA.

Endpoints of drug discovery for menopausal vasomotor symptoms: interpretation of data from a proxy of disease

OBJECTIVE

Estrogen supplementation is considered a reliable therapeutic approach to symptoms of vasomotor dysregulation (hot flashes) associated with the menopausal transition and sex hormone deprivation. Implication of changes in central neurotransmission in the pathogenesis of hot flashes has prompted the off-label use of serotonergic and γ-aminobutyric acid-ergic drugs as a therapeutic alternative, claiming similarity of outcomes to those of estrogen treatment.

METHODS

Using telemetric recordings in a rat model of estrogen deficit-induced vasomotor dysregulation, we compared the long- and short-term effects of estrogen supplementation and treatment with neuropharmaceuticals (venlafaxine, desvenlafaxine, fluoxetine, agomelatine, gabapentin) on endpoints of thermoregulation.

RESULTS

Among the tested drugs, only fluoxetine was capable to emulate the restorative action of estradiol on the diurnal oscillations in skin temperature and control of heat dissipation. Unlike estradiol, several of the tested compounds produced marked transient decreases in skin temperature within the first 2 hours of application while being unable to restore physiological diurnal patterns of thermoregulation.

CONCLUSIONS

Our findings suggest that in this animal model of impaired thermoregulation, neuropharmaceuticals may simulate therapeutic effects by eliciting immediate but transient hypothermia, which is not associated with the recovery of physiological control of heat dissipation. Therefore, short-term monitoring of drug actions in this disease model may considerably bias readouts of drug discovery for menopausal vasomotor symptoms.

Models of anxiety: stress-induced hyperthermia (SIH) in singly housed mice

Described in this unit is the stress-induced hyperthermia (SIH) test in mice in a single-housed format. This protocol has proven reliable in detecting the anxiolytic properties of test compounds. In this test, SIH is quantified in singly housed mice using a rectal temperature measurement as the stressor. Rectal temperature is measured twice at a 10-min interval. Due to the stress experienced during the first temperature measurement, the temperature of the second measurement (T(2)) is ∼0.8° to 1.5°C higher than that of the first (T(1)). This difference in temperature (ΔT = T(2) - T(1)) is defined as the SIH response. The SIH response is reduced by different classes of anxiolytics. The SIH test is simple and robust, it does not require training of animals, and test compound effects on motor behavior, feeding, and nociception do not affect test outcome. Furthermore, it is one of few anxiety tests that focuses on the physiological component of anxiety.

Fluoxetine counteracts the cognitive and cellular effects of 5-fluorouracil in the rat hippocampus by a mechanism of prevention rather than recovery

5-Fluorouracil (5-FU) is a cytostatic drug associated with chemotherapy-induced cognitive impairments that many cancer patients experience after treatment. Previous work in rodents has shown that 5-FU reduces hippocampal cell proliferation, a possible mechanism for the observed cognitive impairment, and that both effects can be reversed by co-administration of the antidepressant, fluoxetine. In the present study we investigate the optimum time for administration of fluoxetine to reverse or prevent the cognitive and cellular effects of 5-FU.

Male Lister-hooded rats received 5 injections of 5-FU (25 mg/kg, i.p.) over 2 weeks. Some rats were co-administered with fluoxetine (10 mg/kg/day, in drinking water) for 3 weeks before and during (preventative) or after (recovery) 5-FU treatment or both time periods (throughout). Spatial memory was tested using the novel location recognition (NLR) test and proliferation and survival of hippocampal cells was quantified using immunohistochemistry. 5-FU-treated rats showed cognitive impairment in the NLR task and a reduction in cell proliferation and survival in the subgranular zone of the dentate gyrus, compared to saline treated controls. These impairments were still seen for rats administered fluoxetine after 5-FU treatment, but were not present when fluoxetine was administered both before and during 5-FU treatment. The results demonstrate that fluoxetine is able to prevent but not reverse the cognitive and cellular effects of 5-FU. This provides information on the mechanism by which fluoxetine acts to protect against 5-FU and indicates when it would be beneficial to administer the antidepressant to cancer patients.

The age of anxiety: role of animal models of anxiolytic action in drug discovery

Anxiety disorders are common, serious and a growing health problem worldwide. However, the causative factors, aetiology and underlying mechanisms of anxiety disorders, as for most psychiatric disorders, remain relatively poorly understood. Animal models are an important aid in giving insight into the aetiology, neurobiology and, ultimately, the therapy of human anxiety disorders. The approach, however, is challenged with a number of complexities. In particular, the heterogeneous nature of anxiety disorders in humans coupled with the associated multifaceted and descriptive diagnostic criteria, creates challenges in both animal modelling and in clinical research. In this paper, we describe some of the more widely used approaches for assessing the anxiolytic activity of known and potential therapeutic agents. These include ethological, conflict-based, hyponeophagia, vocalization-based, physiological and cognitive-based paradigms. Developments in the characterization of translational models are also summarized, as are the challenges facing researchers in their drug discovery efforts in developing new anxiolytic drugs, not least the ever-shifting clinical conceptualization of anxiety disorders. In conclusion, to date, although animal models of anxiety have relatively good validity, anxiolytic drugs with novel mechanisms have been slow to emerge. It is clear that a better alignment of the interactions between basic and clinical scientists is needed if this is to change.

Acetylsalicylic acid as an augmentation agent in fluoxetine treatment resistant depressive rats

Clinical studies have reported that adjunctive acetylsalicylic acid (aspirin) therapy is beneficial for patients with treatment resistant depression (TRD). However, there still exist negative epidemiological data on the link between aspirin and depression. Therefore, this study aimed to further investigate whether aspirin can be used as an augmentation agent in fluoxetine treatment resistant depressive rats induced by chronic unpredictable mild stress (CUMS). In this study, the effects of CUMS regimen and antidepressant treatment were assessed by behavioral testing, hippocampal expression of cyclooxygenase-2 (COX-2) and prostaglandin E(2) (PGE(2)). 4-week fluoxetine treatment reversed the behavioral changes in approximately 70-80% depressive rats. That is, 20-30% depressive rats were resistant to fluoxetine. In the hippocampus of fluoxetine treatment resistant depressive rats, a significant upregulation of COX-2 level and PGE(2) concentration was observed. However, in these rats adjunctive aspirin treatment significantly improved the depressive behaviors and downregulated the COX-2 level and PGE(2) concentration in the hippocampus. Thus, our results suggest that aspirin can be served as an effective adjunctive agent in the treatment resistant depression mediated by inhibition of the COX-2 level and PGE(2) concentration.

Fluoxetine reverses the memory impairment and reduction in proliferation and survival of hippocampal cells caused by methotrexate chemotherapy

RATIONALE

Adjuvant cancer chemotherapy can cause long-lasting, cognitive deficits. It is postulated that these impairments are due to these drugs targeting neural precursors within the adult hippocampus, the loss of which has been associated with memory impairment.

OBJECTIVES

The present study investigates the effects of the chemotherapy, methotrexate (MTX) on spatial working memory and the proliferation and survival of the neural precursors involved in hippocampal neurogenesis, and the possible neuroprotective properties of the antidepressant fluoxetine.

METHODS

Male Lister hooded rats were administered MTX (75 mg/kg, two i.v. doses a week apart) followed by leucovorin rescue (i.p. 18 h after MTX at 6 mg/kg and at 26, 42 and 50 h at 3 mg/kg) and/or fluoxetine (10 mg/kg/day in drinking water for 40 days). Memory was tested using the novel location recognition (NLR) test. Using markers, cell proliferation (Ki67) and survival (bromodeoxyuridine/BrdU), in the dentate gyrus were quantified.

RESULTS

MTX-treated rats showed a cognitive deficit in the NLR task compared with the vehicle and fluoxetine-treated groups. Cognitive ability was restored in the group receiving both MTX and fluoxetine. MTX reduced both the number of proliferating cells in the SGZ and their survival. This was prevented by the co-administration of fluoxetine, which alone increased cell numbers.

CONCLUSIONS

These results demonstrate that MTX induces an impairment in spatial working memory and has a negative long-term effect on hippocampal neurogenesis, which is counteracted by the co-administration of fluoxetine. If translatable to patients, this finding has the potential to prevent the chemotherapy-induced cognitive deficits experienced by many cancer survivors.

Metyrapone blunts stress-induced hyperthermia and increased locomotor activity independently of glucocorticoids and neurosteroids

Metyrapone, a cytochrome P(450) inhibitor used to inhibit corticosterone synthesis, triggers biological markers of stress and also reduces stress-induced anxiety-like behaviors. To address these controversial effects, 6 separate investigations were carried out. In a first set of investigations, abdominal temperature (T(abd)), spontaneous locomotor activity (A(S)) and electroencephalogram (EEG) were recorded in freely moving rats treated with either saline or 150 mg kg(-1) metyrapone. An increase in T(abd) and A(S) occurred in saline rats, while, metyrapone rats exhibited an immediate decrease, both variables returning to basal values 5h later. Concomitantly, the EEG spectral power increased in the gamma and beta 2 bands and decreased in the alpha frequency band, and the EMG spectral power increased. This finding suggests that metyrapone depressed stress-induced physiological response while arousing the animal. In a second step, restraint stress was applied 5h after injection. Metyrapone significantly blunted the stress-induced T(abd) and A(S) rise, without affecting the brain c-fos mRNA increase. Corticosterone (5 and 40 mg kg(-1)) injected concomitantly to metyrapone failed to reverse the observed metyrapone-induced effects in T(abd) and A(S). Finasteride (50 mg kg(-1)), which blocks neurosteroid production, was also unable to block these effects. In conclusion, metyrapone acutely reduced stress-induced physiological response in freely behaving rats independently from glucocorticoids and neurosteroids.

Blockade of dopamine, but not noradrenaline, transporters produces hyperthermia in rats that lack serotonin transporters

To investigate whether life-long disturbed serotonin neurotransmission may result in adaptive changes of dopaminergic and noradrenergic systems, effects of drugs on stress-induced hyperthermia were studied in serotonin transporter knockout rats. The noradrenalin transporter blocker atomoxetine was more effective in reducing stress-induced hyperthermia, induced by an injection, in serotonin transporter (SERT) knockout (SERT(-/-)) rats compared to SERT(+/+) rats. The dopamine transporter blocker GBR12909 increased the core body temperature in SERT(-/-) rats, and had no effect on the SERT(+/+) rats. Finally, the noradrenalin transporter together with dopamine transporter blocker bupropion was more effective in decreasing the stress of an injection in SERT(-/-) rats than in SERT(+/+) rats. These data suggest that the sensitivity of dopamine and noradrenalin receptors is changed in serotonin transporter knockout rats. The lack of the serotonin transporter in SERT(-/-) rats might reflect humans with a life-long disturbed serotonin system, making this rat a good model to study possible changes in dopaminergic and noradrenergic systems in psychiatric disorders.

[Effect of social interaction on skin temperature in mice]

We investigated physiological and behavioral characteristics of socially stressed animals in a resident-intruder paradigm. ICR male mice (resident, n = 14) were exposed individually to a novel male conspecific (intruder, n = 14) in their homecage for 30 min. Along with behavioral analyses, the skin temperatures of both the resident and the intruder were measured simultaneously using a multipoint radiation thermometer. There were no significant differences between the resident and intruder in the amount of locomotion, flight and aggressive behaviors. The mean skin temperature of the residents during the interaction was higher than before the interaction. In addition, the skin temperatures of the intruders were consistently higher than the residents. The results suggest that social stress causes elevation in skin temperature as well as stress-induced hyperthermia in core temperature. Moreover, infrared radiation thermometers may provide an alternative means of measuring physiological parameters of two (or more) subjects simultaneously in the study of animal social behavior.

Translational aspects of pharmacological research into anxiety disorders: the stress-induced hyperthermia (SIH) paradigm

In anxiety research, the search for models with sufficient clinical predictive validity to support the translation of animal studies on anxiolytic drugs to clinical research is often challenging. This review describes the stress-induced hyperthermia (SIH) paradigm, a model that studies the activation of the autonomic nervous system in response to stress by measuring body temperature. The reproducible and robust SIH response, combined with ease of testing, make the SIH paradigm very suitable for drug screening. We will review the current knowledge on the neurobiology of the SIH response, discuss the role of GABA(A) and serotonin (5-HT) pharmacology, as well as how the SIH response relates to infectious fever. Furthermore, we will present novel data on the SIH response variance across different mice and their sensitivity to anxiolytic drugs. The SIH response is an autonomic stress response that can be successfully studied at the level of its physiology, pharmacology, neurobiology and genetics and possesses excellent animal-to-human translational properties.

Development of a home cage locomotor tracking system capable of detecting the stimulant and sedative properties of drugs in rats

The advent of automated locomotor activity methodologies has been extremely useful in removing the subjectivity and bias out of measuring this parameter in rodents. However, many of these behavioural studies are still conducted in novel environments, rather than in ones that the animals are familiar with, such as their home cage. The purpose of the present series of experiments was to develop an automated home cage tracking (HCT) profile using EthoVision software and assessing the acute effects of stimulant (amphetamine and methamphetamine, 0-5 mg/kg, sc) and sedative (diazepam, 0-20 mg/kg, sc and chlordiazepoxide, 0-50 mg/kg sc) drugs in this apparatus. Young adult male Sprague-Dawley rats were used, and the home cage locomotor activity was recorded for 11-60 min following administration (n=4 per group). For amphetamine and methamphetamine, a dose-dependent increase in home cage activity was evident for both drugs, with a plateau, followed by reduction at higher doses. Methamphetamine was more potent, whereas amphetamine produced greater maximal responses. Both diazepam and chlordiazepoxide dose-dependently reduced locomotor activity, with diazepam exhibiting a greater potency and having stronger sedative effects than chlordiazepoxide. Three doses of each drug were selected at the 31-40 min time period following administration, and compared to open field responses. Diazepam, chlordiazepoxide and amphetamine did not produce significant changes in the open field, whilst methamphetamine produced a significant increase in the 2.5 mg/kg group. In conclusion, these studies have successfully developed a sensitive HCT methodology that has been validated using drugs with stimulant and sedative properties in the same test conditions, with relatively small numbers of animals required to produce statistically significant results. It has proven superior to the open field investigations in allowing dose-response effects to be observed over a relatively short observation period (i.e. 10 min) for both stimulants and sedatives. In addition, the HCT system can determine differences in potency and efficacy between drugs of a similar chemical class.