Putting the brakes on the "drive to eat": Pilot effects of naltrexone and reward-based eating on food cravings among obese women

Appropriate use of the fixed-dose, extended-release combination of naltrexone and bupropion as treatment for obesity in primary care

Background

Obesity is considered a chronic disease and is influenced by biological, environmental, and behavioral factors that can contribute to its progression. Although lifestyle changes are integral to treating obesity and maintaining a healthful weight, weight reduction from behavioral intervention alone is often insufficient because neurophysiologic factors may work against such changes in lifestyle and behavior. Research suggests that the mechanisms underlying food cravings and obesity overlap with dopaminergic signaling in the brain and pathways involved in addiction. As a result, patients who are differentially impacted by food cravings may have better outcomes with treatments targeting neural systems implicated in both homeostatic and hedonic food consumption or addictive behaviors.

Methods

In this clinical review, we describe the safety and efficacy data for the fixed-dose, extended-release combination of naltrexone and bupropion (NB-ER) compared with its monotherapy constituents (naltrexone and bupropion), as well as discuss the appropriate use of NB-ER to treat patients with obesity.

Results

NB-ER is approved for the treatment of patients with obesity, with studies showing that patients can achieve significant weight reduction compared with placebo when treatment is combined with a reduced-calorie diet and increased physical activity. Across NB-ER phase 3 trials, responders to treatment had a mean body weight reduction of 11.7 % at 56 weeks. Of note, the unique combination of naltrexone, an opioid receptor antagonist, and bupropion, a norepinephrine-dopamine reuptake inhibitor associated with stimulating pro-opiomelanocortin cells (POMC), in NB-ER may work together to target POMC cells to prevent endogenous negative feedback, thereby decreasing appetite and improving weight-related outcomes.

Conclusions

Unlike monotherapy with its component drugs, NB-ER is optimized for the treatment of obesity. The appropriate use of NB-ER should consider the specific characteristics and adiposity-related complications of an individual.

Orgasms, sexual pleasure, and opioid reward mechanisms

INTRODUCTION

Sexual activity produces pleasure related to sexual arousal, desire, and genitosensory and erogenous stimulation. Orgasms produce a whole brain and body rush of ecstatic pleasure followed by relaxation and refractoriness. This pleasure results from the activation of neurochemical reward pathways in the brain. This is differentiated by spinal pathways that control climax, the particular motor movements of the pelvic floor and the experience of tension release.

OBJECTIVES

To relate the activation of key neurochemical reward and bonding systems, notably dopamine, oxytocin, and opioids, to the pleasure of sexual activity in general and orgasms in particular.

METHODS

A narrative review of the neurochemical and neuroanatomical mechanisms activated during sexual stimulation and orgasm in rats and humans, and how they are related overall to the generation of sexual pleasure and reward.

RESULTS

Appetitive sexual pleasure involves the activation of dopamine and oxytocin release in hypothalamic and mesolimbic regions that regulate sexual arousal and desire, and are reinforced by localized opioid activity. Orgasms are thought to result in part from a massive release of opioids into these regions that inhibits dopamine and oxytocin transmission, but that initiates molecular changes to sensitize both systems and induce sexually conditioned place and partner preferences. Serotonin is also activated at orgasm and contributes to feelings of satiety and refractoriness. Orgasm disorders are distressing, cause resentment and conflict in a relationship, and diminish overall sexual health and well-being.

CONCLUSIONS

Orgasms are an important component of sexual pleasure for humans and perhaps all vertebrates. Endogenous opioids like β-endorphin that bind to mu opioid receptors are likely responsible for sexual pleasure and reward.

The Turkish validity and reliability of the Reward-Based Eating Drive (RED-13) Scale

TRIAL REGISTRATION

The study was registered on ClinicalTrials.gov (number: NCT05017506).

Mindfulness-Based Mobile Health to Address Unhealthy Eating Among Middle-Aged Sexual Minority Women With Early Life Adversity: Mixed Methods Feasibility Trial

BACKGROUND

Sexual minority women (lesbian, gay, bisexual, pansexual, queer, and other nonheterosexual women) remain considerably underrepresented in health research despite being at a higher risk for diabetes and obesity as well as stigma and psychological distress than their heterosexual peers. In addition, early life adversity (ELA) is prevalent among sexual minority women, which further increases risks for obesity, psychological distress, and poor cardiovascular health. App-based mindfulness interventions are potentially promising for this group in mitigating the adverse health effects of ELA, reducing food craving and unhealthy eating, addressing the risks associated with obesity.

OBJECTIVE

This mixed methods feasibility trial aimed to test a mindfulness-based mobile health approach for middle-aged sexual minority women (aged 30-55 years) with ELA and overweight or obesity (BMI ≥25 kg/m2) to improve health outcomes.

METHODS

The single-arm trial was advertised on social media and various lesbian, gay, bisexual, transgender, and queer web-based groups. At baseline, after the intervention (2 months), and at the 4-month follow-up, participants completed assessments of primary outcomes (food craving, emotional eating, and weight via a mailed scale) and secondary outcomes (depression, anxiety, mindfulness, and emotion dysregulation). A standardized weight measure was mailed to participants for weight reporting. Feasibility and acceptability were assessed after the intervention via surveys and semistructured exit interviews.

RESULTS

We screened 442 individuals, among which 30 eligible sexual minority women (mean age 40.20, SD 7.15 years) from various US regions were enrolled in the study. At baseline, 86% (26/30) and 80% (24/30) of participants had elevated depressive and anxiety symptoms, respectively. Among the 30 enrolled participants, 20 (66%) completed all intervention modules, 25 (83%) were retained at the 2-month follow-up, and 20 (66%) were retained at the 4-month follow-up. None reported adverse effects. From baseline to the 4-month follow-up, large effects were found in food craving (Cohen d=1.64) and reward-based eating (Cohen d=1.56), whereas small effects were found with weight (Cohen d=0.20; 4.21 kg on average). Significant improvements were also found in the secondary outcomes (depression, Cohen d=0.98; anxiety, Cohen d=0.50; mindfulness, Cohen d=0.49; and emotion dysregulation, Cohen d=0.44; all P<.05). Participants with higher levels of parental verbal and emotional abuse were particularly responsive to the intervention. Participants reported that the program aligned with their goals and expectations, was easy to use, and facilitated changes in eating behavior and mental health. Barriers to engagement included the need for diverse teachers, individualized support, and body positive language.

CONCLUSIONS

This early phase feasibility trial provides proof-of-concept support for a mindfulness mobile health approach to improve obesity-related outcomes among sexual minority women and warrants a larger randomized controlled trial in the future. The findings also suggest the need to address trauma and psychological health when addressing weight-related outcomes among sexual minority women.

Food Addiction: A Comprehensive Review

Food addiction is associated with dysfunctions in the reward circuit, such as hyperresponsiveness during the exposure to high-calorie flavors in overweight and obese individuals. Similar to drug addiction, there is also impaired self-regulatory control supported by deregulation of the frontostriatal circuit. The inclusion of validated measures of food addiction in clinical research, such as the Yale Food Addiction Scale, has increased the understanding of the clinical utility of this concept. Furthermore, food addiction, eating disorders, and obesity are interrelated. Thus, it is important to recognize food addiction among individuals affected by obesity and candidates for bariatric surgery (ie, preoperative and postoperative assessment). In this context, it has been reported that food addiction may impede weight loss and increase the likelihood of regaining weight when associated with personality traits such as neuroticism and impulsiveness, which are also related to mood disorders, anxiety, and addictive behaviors.

Effects of internet-delivered eating disorder prevention on reward-based eating drive: A randomized controlled trial

OBJECTIVE

This study is a secondary analysis testing the effects of an internet eating disorder prevention program on reward-based eating drive in a high-risk sample of college-aged women.

METHOD

We analyzed data from 278 women who were randomized to internet dissonance-based intervention (DBI-I), internet cognitive-behavioral treatment (CBTI), or no intervention (NI). Both active conditions consisted of self-guided activities completed over the course of four weeks. Linear mixed effects modeling was used to test the effect of internet intervention on reward-based eating drive.

RESULTS

DBI-I was associated with greater reductions in reward-based eating over time than NI. No other Condition × Time effects were found.

DISCUSSION

The results provide preliminary support for DBI-I as a strategy for reducing reward-based eating drive in a high-risk population relative to no intervention.

Disordered Eating among People with Schizophrenia Spectrum Disorders: A Systematic Review

Disordered eating, or abnormal eating behaviours that do not meet the criteria for an independent eating disorder, have been reported among people with schizophrenia. We aimed to systemati-cally review literature on disordered eating among people with schizophrenia spectrum disorder (SSD). Seven databases were systematically searched for studies that described the prevalence and correlates of disordered eating among patients with SSD from January 1984 to 15 February 2021. Qualitative analysis was performed using the National Institutes of Health scales. Of 5504 records identified, 31 studies involving 471,159 subjects were included in the systematic review. The ma-jority of studies (17) rated fair on qualitative analysis and included more men, and participants in their 30s and 40s, on antipsychotics. The commonest limitations include lack of sample size or power calculations, poor sample description, not using valid tools, or not adjusting for con-founders. The reported rates were 4.4% to 45% for binge eating, 16.1% to 64%, for food craving, 27% to 60.6% for food addiction, and 4% to 30% for night eating. Positive associations were re-ported for binge eating with antipsychotic use and female gender, between food craving and weight gain, between food addiction and increased dietary intake, and between disordered eating and female gender, mood and psychotic symptoms. Reported rates for disordered eating among people with SSD are higher than those in the general population. We will discuss the clinical, treatment and research implications of our findings.

Tobacco withdrawal increases junk food intake: The role of the endogenous opioid system

BACKGROUND

The aims of this study were to 1) determine whether acute nicotine withdrawal increases the intake of junk food (high in salt, fat, and sugar) and 2) assess whether the endogenous opioid system is involved in junk food intake during nicotine withdrawal using naltrexone as a pharmacological probe.

METHODS

Smokers were randomly assigned to 24-hr withdrawal from tobacco products (n = 42) or smoking ad libitum (n = 34). A non-smoking group (n = 29) was included. Participants completed two laboratory sessions where a placebo or 50 mg of naltrexone was administered. At the end of each session, participants were given a tray of snack items that differed in high to low energy density and dimensions of salty, sweet, and fat. Self-reported mood and withdrawal measures were collected immediately before the snacks were offered. Generalized linear and logistic models were used to assess the effects of acute smoking withdrawal, drug, and sex on the intake of snack items and self-reported measures.

RESULTS

Choice and consumption of food items were impacted by smoking condition (withdrawal > ad lib smoking and non-smokers; p < .05), the opioid blockade (naltrexone < placebo; p < .05), and sex (male > female; p < .05). The effects were evidenced in high sweet and high fat foods. No differences were found in low sweet and fat foods.

CONCLUSIONS

These findings extend earlier studies indicating impact of tobacco use on appetite, and identify the regulatory influence of the endogenous opioid system on appetite during nicotine withdrawal.

Blockade of Opiodergic System During Early Weaning Reverts Feeding Behavior Altered Patterns

Adverse experiences that occur during the early stages of life can have permanent repercussions in adulthood. Among these experiences, early weaning is one that can alter the molecular, cellular, and behavior patterns in later life. Centered on this fact, the objective of the current study was to evaluate the effect of early weaning at 15 days of life of Wistar rats on their feeding behavior and if the opioidergic system blockade would cause a reversal of these outcomes. Experimental groups were formed based on the weaning period of each litter. On postnatal day 15, the group D15 was weaned and, on postnatal day 30 (natural weaning), the group D30 was weaned. The rats weaned on postnatal day 15, and administered subcutaneous Naltrexone (3 mg/kg) were from group D15 + NTX. Those weaned at 15 days of age exhibited higher depressive-like behavior, lesser reactivity time to sucrose, and higher intake of palatable food than the control group. The Naltrexone administration was observed to reverse some outcomes, such as increasing the reactivity time to sucrose and decreasing the quantity of palatable food consumed, to levels similar to those of the control group. Together, the findings of the present study are indicative of the vital role played by the opioidergic system in inducing the changes noted in the eating behavior patterns during adulthood, post early weaning.

Safety and efficacy of naltrexone for weight loss in adult patients - a systematic review

INTRODUCTION

This is a report of a systematic review of the safety and efficacy of naltrexone or naltrexone/bupropion on weight loss.

MATERIAL AND METHODS

The databases Medline, PubMed, and Embase as well as the Cochrane Controlled Trials Register for randomized controlled trials were searched for studies published from January 1966 to January 2018. A meta-analysis, randomised controlled trials, controlled trials, uncontrolled trials, cohort studies and open-label studies were analysed.

RESULTS

Of 191 articles, 14 fulfilled the inclusion criteria: 1 meta-analysis, 10 randomized controlled trials, and 3 studies without randomization were found. In these studies, the efficacy and safety of naltrexone/bupropion in obesity were analysed. In the majority of these studies, patients with at least 5% or 10% weight loss, as a primary outcome, were investigated. Generally, naltrexone/bupropion treatment can be a promising therapy for obese patients, including when combined with mental health treatment.

CONCLUSIONS

Based on these studies, it can be said that naltrexone/bupropion treatment is effective in the weight loss of overweight subjects. The naltrexone/bupropion treatment was well tolerated by the patients, and side effects were rarely reported.

Ultraprocessed Food: Addictive, Toxic, and Ready for Regulation

Past public health crises (e.g., tobacco, alcohol, opioids, cholera, human immunodeficiency virus (HIV), lead, pollution, venereal disease, even coronavirus (COVID-19) have been met with interventions targeted both at the individual and all of society. While the healthcare community is very aware that the global pandemic of non-communicable diseases (NCDs) has its origins in our Western ultraprocessed food diet, society has been slow to initiate any interventions other than public education, which has been ineffective, in part due to food industry interference. This article provides the rationale for such public health interventions, by compiling the evidence that added sugar, and by proxy the ultraprocessed food category, meets the four criteria set by the public health community as necessary and sufficient for regulation—abuse, toxicity, ubiquity, and externalities (How does your consumption affect me?). To their credit, some countries have recently heeded this science and have instituted sugar taxation policies to help ameliorate NCDs within their borders. This article also supplies scientific counters to food industry talking points, and sample intervention strategies, in order to guide both scientists and policy makers in instituting further appropriate public health measures to quell this pandemic.

The Opioid System and Food Intake: Use of Opiate Antagonists in Treatment of Binge Eating Disorder and Abnormal Eating Behavior

Eating disorders (EDs) and substance use disorders (SUDs) commonly co-occur, especially in conjunction with affective syndromes, yet little is known about opiate abuse and ED symptoms in patients on naltrexone-bupropion therapy. Moreover, evidence suggests that the opioid system can also be regarded as one of the major systems regulating the anticipatory processes preceding binge eating episodes. The lack of evidence in the effectiveness of psychotherapy treatment in addition to psychotropic mediations compounds the difficulties in stabilizing individuals with EDs. This article aims to exhaustively review literature relating to the use of opioid antagonists in the management of binge eating disorder (BED) and other abnormal eating habits and how this can be augmented by the use of psychological approaches to come up with the most effective therapy or combination of therapies to manage these conditions. Although this approach is promising, it has not been evaluated. A review of the literature pertaining to the use of naltrexone in patients with EDs was performed through PubMed, PsycINFO and MEDLINE. We selected 63 relevant articles published between 1981 and 2018 and those written in English. Search terms included “Opioid antagonists”, “naltrexone”, “bupropion” and “Psychotherapy” each combined with “Binge Eating Disorder”, “Bulimia Nervosa”, “Anorexia Nervosa”, “Eating Disorder”, “EDNOS” and “Obesity”. While working with these articles, we also identified several problems related to use of these methods in real clinical practice. Seventy-seven articles were reviewed, and 63 were selected for inclusion. Data obtained from these sources confirmed that the blockade of opioid receptors diminishes food intake. More recent findings also indicate that the combination of bupropion and naltrexone can induce weight loss. Augmentation of this by introducing psychotherapy may lead to better outcomes. Cognitive behavioral therapy (CBT) was the most frequently recommended psychotherapy intervention, showing efficacy for EDs and chemical addictions as documented by most of the studies, but with uncertain efficacy when utilized as augmentation strategy. There are limited data supporting the use of psychotherapy in augmentation of standard therapy in ED; however, there is evidence to support that psychotherapy is safe in this population and has been effective in cases of patients with opiate addiction with and without psychiatric comorbidities as well as BED. More research is needed to establish treatment guidelines. Combining pharmacotherapeutic and psychotherapeutic interventions leads to the achievement of a better outcome in managing patients with EDs. Involving families or the use of support groups increases chances of adherence to the prescribed interventions resulting in higher rates of remission. However, it is clear that all of these interventions must occur in the context of a comprehensive treatment program. We believe that patient-specific psychotherapy may not only facilitate the treatment process, but also cause significant alterations in eating pattern. This approach for BED may lead to more significant treatment outcomes, but this possibility must be tested in larger samples.

Does the Neuroimmune Modulator Ibudilast Alter Food Craving? Results in a Sample With Alcohol Use Disorder

OBJECTIVE

Ibudilast (IBUD) is a neuroimmune modulator that inhibits phosphodiesterase-4 and -10 and macrophage migration inhibitory factor. A randomized, placebo-control, crossover human laboratory trial advanced IBUD development for alcohol use disorder and found that IBUD reduced tonic levels of alcohol craving. Given the importance of considering medication effects on other appetitive behavior, the present study tested the effect of IBUD (50 mg bid) on food craving.

METHOD

The present study was a secondary data analysis of the trial of IBUD in non-treatment seekers with alcohol use disorder (N = 19). High-fat/high-sugar food craving was measured daily. Moreover, because substantial literatures show that small alcohol doses and psychological stress increase eating of high-fat/high-sugar food, craving for high-fat/high-sugar food was measured after alcohol infusion and stress reactivity.

RESULTS

Results indicated that IBUD did not alter tonic high-fat/high-sugar food craving. Alcohol infusion did not generally increase high-fat/high-sugar food craving but psychological stress did. Likewise, IBUD did not affect high-fat/high-sugar food craving after alcohol infusion but IBUD did increase high-fat/high-sugar food craving after psychological stress. Follow-up analyses revealed that, among individuals with lower depressive symptomatology, IBUD compared to placebo heightened the effect of psychological stress on high-fat/high-sugar food craving.

CONCLUSIONS

These results advance the development of IBUD for addiction indications by demonstrating that IBUD compared to placebo does not suppress other appetitive responses, namely craving for high-fat/high-sugar food among individuals with alcohol use disorder.

Rapid Assessment of Reward-Related Eating: The RED-X5

OBJECTIVE

The prevalence of obesity has created a plethora of questionnaires characterizing psychological aspects of eating behavior, such as reward-related eating (RRE). The Reward-based Eating Drive questionnaires (RED-9, RED-13) broadly and deeply assess the RRE construct. However, large-sample research designs require shorter questionnaires that capture RRE quickly and precisely. This study sought to develop a brief, reliable, and valid version of the RED questionnaire.

METHODS

All-subset correlation was used to find a subset that maximally associated with the full RED-13 in two separate samples. Results were validated in a third independent sample. Internal consistency, test-retest reliability, and ability to explain variance in external outcomes were also assessed.

RESULTS

A five-item questionnaire (RED-X5) correlated strongly with RED-13 in the independent sample (r = 0.95). RED-X5 demonstrated high internal consistency (omega total ≥ 0.80) and 6-month test-retest reliability (r = 0.72). RED-X5 accurately reproduced known associations between RED-13 and BMI, diabetes status, and craving for sweet and savory foods. As a novel finding, RED questionnaires predicted laboratory intake of chips.

CONCLUSIONS

RED-X5 is a short, reliable, and valid measure of the RRE construct and can be readily implemented in large-sample research designs in which questionnaire space is limited.

Testing a mobile mindful eating intervention targeting craving-related eating: feasibility and proof of concept

Theoretically driven smartphone-delivered behavioral interventions that target mechanisms underlying eating behavior are lacking. In this study, we administered a 28-day self-paced smartphone-delivered intervention rooted in an operant conditioning theoretical framework that targets craving-related eating using mindful eating practices. At pre-intervention and 1-month post-intervention, we assessed food cravings among adult overweight or obese women (N = 104; M age = 46.2 ± 14.1 years; M BMI = 31.5 ± 4.5) using ecological momentary assessment via text message (SMS), self-reported eating behavior (e.g., trait food craving), and in-person weight. Seventy-eight participants (75.0%) completed the intervention within 7 months ('all completers'), and of these, 64 completed the intervention within 3 months ('timely completers'). Participants experienced significant reductions in craving-related eating (40.21% reduction; p < .001) and self-reported overeating behavior (trait food craving, p < .001; other measures ps < .01). Reductions in trait food craving were significantly correlated with weight loss for timely completers (r = .30, p = .020), this pattern of results was also evident in all completers (r = .22, p = .065). Taken together, results suggest that smartphone-delivered mindful eating training targeting craving-related eating may (1) target behavior that impacts a relative metabolic pathway, and (2) represent a low-burden and highly disseminable method to reduce problematic overeating among overweight individuals. ClinicalTrials.gov registration: NCT02694731.

A narrative review of potential treatment strategies for food addiction

The concept of food addiction (FA) remains controversial with research being in the nascent stages; FA like any addiction can have a devastating impact on the lives of those afflicted. There exists a clinical need for treatment strategies for those affected. This article reviews potential treatment strategies for FA. The treatment strategies target four core behaviours of the addiction phenotype specifically craving through the opioid system, impulsivity as a personality trait, compulsivity through the serotonergic system and lastly motivation through the dopaminergic system. A range of pharmacological and psychological interventions are reviewed. Future research should seek to test and validate the proposed clinical treatment strategies.

The effectiveness of naltrexone combined with current smoking cessation medication to attenuate post smoking cessation weight gain: a literature review

Background

Smoking is the number one cause of preventable morbidity and mortality globally and although many countries have invested heavily in smoking cessation programs, 21% of the global population still smoke. Post cessation weight gain has been identified as a barrier to attempting cessation and is implicated in the high rates of relapse. Naltrexone has been touted as a possible solution to address post smoking cessation weight gain.

Results

The results from seven original studies assessing the effectiveness of naltrexone in combination with existing smoking cessation medications to attenuate post smoking cessation weight gain were obtained and critically reviewed. Five returned positive results and two returned results that were statistically insignificant. The positive results were seen more often in those identified as more likely to exhibit hedonic eating behaviour for example women and participants who were categorised as overweight or obese.

Conclusion

The evidence suggests further investigation in to a combination of naltrexone and approved smoking cessation medications is warranted and could provide a solution to attenuate post smoking cessation weight gain especially in women and those classified as overweight or obese. This may provide the tool required to remove a perceived barrier to smoking cessation and improve global statistics.

Improving Assessment of the Spectrum of Reward-Related Eating: The RED-13

A diversity of scales capture facets of reward-related eating (RRE). These scales assess food cravings, uncontrolled eating, addictive behavior, restrained eating, binge eating, and other eating behaviors. However, these scales differ in terms of the severity of RRE they capture. We sought to incorporate the items from existing scales to broaden the 9-item Reward-based Eating Drive scale (RED-9; Epel et al., 2014), which assesses three dimensions of RRE (lack of satiety, preoccupation with food, and lack of control over eating), in order to more comprehensively assess the entire spectrum of RRE. In a series of 4 studies, we used Item Response Theory models to consider candidate items to broaden the RED-9. Studies 1 and 2 evaluated the abilities of additional items from existing scales to increase the RED-9's coverage across the spectrum of RRE. Study 3 evaluated candidate items identified in Studies 1 and 2 in a new sample to assess the extent to which they accounted for more variance in areas less well-covered by the RED-9. Study 4 tested the ability of the RED-13 to provide consistent coverage across the range of the RRE spectrum. The resultant RED-13 accounted for greater variability than the RED-9 by reducing gaps in coverage of RRE in middle-to-low ranges. Like the RED-9, the RED-13 was positively correlated with BMI. The RED-13 was also positively related to a diagnosis of type 2 diabetes as well as cravings for sweet and savory foods. In summary, the RED-13 is a brief self-report measure that broadly captures the spectrum of RRE and may be a useful tool for identifying individuals at risk for overweight or obesity.

Endogenous Opiates and Behavior: 2015

This paper is the thirty-eighth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2015 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior, and the roles of these opioid peptides and receptors in pain and analgesia, stress and social status, tolerance and dependence, learning and memory, eating and drinking, drug abuse and alcohol, sexual activity and hormones, pregnancy, development and endocrinology, mental illness and mood, seizures and neurologic disorders, electrical-related activity and neurophysiology, general activity and locomotion, gastrointestinal, renal and hepatic functions, cardiovascular responses, respiration and thermoregulation, and immunological responses.