Gender differences in the effects of haloperidol on avoidance conditioning in mice

Gender-Specific Differences in Low-Dose Haloperidol Response for Prevention of Postoperative Nausea and Vomiting: A Register-Based Cohort Study

Background

Postoperative nausea and vomiting (PONV) is one of the most common and distressing complications after general anesthesia and surgery, with young non-smoking females receiving postoperative opioids being high-risk patients. This register-based study aims to evaluate the effect of low-dose haloperidol (0.5 mg intravenously) directly after induction of general anesthesia to reduce the incidence of PONV in the postoperative anesthesiological care unit (PACU).

Methods

Multivariable regression models were used to investigate the association between low-dose haloperidol and the occurrence of PONV using a patient registry containing 2,617 surgical procedures carried out at an university hospital.

Results

Haloperidol 0.5 mg is associated with a reduced risk of PONV in the total collective (adjusted odds ratio = 0.75, 95% confidence interval: [0.56, 0.99], p = 0.05). The results indicate that there is a reduced risk in male patients (adjusted odds ratio = 0.45, 95% confidence interval: [0.28, 0.73], p = 0.001) if a dose of 0.5 mg haloperidol was administered while there seems to be no effect in females (adjusted odds ratio = 1.02, 95% confidence interval: [0.71, 1.46], p = 0.93). Currently known risk factors for PONV such as female gender, duration of anesthesia and the use of opioids were confirmed in our analysis.

Conclusion

This study suggests that low-dose haloperidol has an antiemetic effect in male patients but has no effect in female patients. A confirmation of the gender-specific effects we have observed in this register-based cohort study might have major implications on clinical daily routine.

Effects of co-administration of amitriptyline and fluoxetine on inhibitory avoidance in mice

We have previously observed that, while the impairing effects of amitriptyline on inhibitory avoidance in mice are consistently observed, those of acute fluoxetine are negligible. Two experiments were designed to investigate whether a regular dose of fluoxetine potentiates the effect of a low dose of amitriptyline that is ineffective when administered alone. Male and female CD1 mice were administered i.p. 30 min before training, as follows. In the first experiment, they were injected with saline, one of three doses of amitriptyline (2.5, 5, 10mg/kg), one dose of fluoxetine (15 mg/kg), or a combination of amitriptyline (2.5mg/kg) and fluoxetine (15 mg/kg). In the second experiment, the mice were injected with saline, amitriptyline (2.5mg/kg), one of three doses of fluoxetine (10, 15, 20mg/kg), or a combination of 2.5mg/kg of amitriptyline and one of the three mentioned doses of fluoxetine. Drug doses were selected based on previous experiments in our laboratory reported in other publications. The behavioural procedure used to test the effects of these treatments was step-through inhibitory avoidance. The joint administration of amitriptyline 2.5mg/kg and fluoxetine 15 mg/kg had a clear impairing effect on inhibitory avoidance as observed in the two experiments. The dose of 2.5mg/kg of amitriptyline, given alone, was ineffective. Doses of 5mg/kg, or higher, of amitriptyline impaired inhibitory avoidance. The only effect detected when fluoxetine was administered separately was in the males of the experiment 1, which exhibited less avoidance than controls. Our preclinical research throws light on the benefits of the combined administration of antidepressants.

Long-term consequences of early experience on adult avoidance learning in female rats: role of the dopaminergic system

Following our hypothesis that juvenile emotional and/or cognitive experience should affect learning performance at preweaning age as well as adulthood, the present study in female Wistar rats aimed to examine the impact of (i) avoidance training at preweaning age, (ii) exposure to repeated maternal separation, (iii) the combination of both, and (iv) the blockade of dopaminergic neurotransmission on adult two-way active avoidance learning in rats. We found that preweaning, i.e. three week old, rats were less capable of avoidance learning compared to adults. Our main findings revealed that preweaning avoidance training alone improved avoidance learning in adulthood. Furthermore, maternal separation alone also improved avoidance learning in preweaning and in adult rats, but this effect of maternal separation did not add up to the beneficial effect of preweaning avoidance training on adult learning. In addition, the pharmacological blockade of dopamine receptors during preweaning avoidance training via systemic application of haloperidol impaired preweaning avoidance performance in a dose-dependent manner. Testing the haloperidol-treated preweaning presumed "non-learners" as adults revealed that they still showed improved learning as adults. Taken together, our results strongly support the hypothesis that emotional as well as cognitive experience at preweaning age leaves an enduring "memory trace," which can facilitate learning in adulthood. Our pharmaco-behavioral studies suggest that unlike the adult brain, preweaning learning and memory formation is less dependent on dopaminergic mechanisms, which raises the intriguing question of possible alternative pathways.

A common role for psychotropic medications: memory impairment

The psychopathologic profile of mental disorders is very diverse and psychotropic medications used to treat them differ in their chemical structure. Nevertheless, these drugs share these four characteristics: delayed onset of clinical response, not one of them can be said to cure, there is a high number of non-responders, and the mechanism responsible for their therapeutic action is not known. It is hypothesized that the action of psychotropic medications is memory impairment, understanding memory as the trace left in the nervous system not only by individual experiences but also by genetic and epigenetic phenomena. It is suggested that it would be beneficial to translate some research strategies from the neurobiology of learning and memory to the study of the effects of psychotropic medications. The hypothesis is briefly assessed according to the following three criteria: (a). the comparison between the molecular effects of psychotropic medications and the so-called molecular biology of learning and memory, (b). the effects of these drugs, preferentially after chronic use, on memory tests, and (c). the effects of drugs that impair memory on tests used for screening psychotropic medications. Finally, some general suggestions for future research are pointed out.

Predicting how equipotent doses of chlorpromazine, haloperidol, sulpiride, raclopride and clozapine reduce locomotor activity in mice

Distinguishing the specific effects of neuroleptics on one particular behaviour from its non-specific effects on motility is not easy. In this study, the effects of five neuroleptics on spontaneous motor activity were compared and the ED(50) values of these drugs to impair activity were calculated. Male and female mice were evaluated in an actimeter or in a shuttle-box used as an open field after the administration of chlorpromazine (0.4, 1.2, 3.6 mg/kg), haloperidol (0.1, 0.3, 0.9 mg/kg), raclopride (0.1, 0.3, 0.9 mg/kg), sulpiride (10, 30, 90 mg/kg) and clozapine (0.4, 1.2, 3.6 mg/kg), and two automatic and two observational activity measures were obtained. A very high correlation between automatic and observational measures, absence of sex differences, and a dose-dependent decrease of activity were observed with every compound. The results allow us to make accurate comparisons between these drugs in their potency in reducing spontaneous motor activity.

Dose dependency of sex differences in the effects of repeated haloperidol administration in avoidance conditioning in mice

Sex differences in the effects of haloperidol in active avoidance conditioning in mice have previously been found in various studies carried out in our laboratory. Males were more affected than females by the disruptive effects of this neuroleptic. The work described here broadens the study of these sex differences to higher doses of haloperidol (0.1 and 0.2 mg/kg) using a repeated administration schedule (5 days). The results did not show sex differences in the deteriorating effects of this dopamine antagonist in the escape-avoidance response, but a tendency in the number of nonresponses was observed in the same direction as former results: male animals were more sensitive than females to the inhibitory effect of the low dose of haloperidol. It is concluded that the appearance of sex differences in the effects of haloperidol on active avoidance conditioning is a dose-dependent phenomenon.

The higher the dose, the greater the sex differences in escape-avoidance response in mice after acute administration of haloperidol

Sex differences in the effects of haloperidol in the escape-avoidance response have previously been found in various studies carried out in our laboratory in which mice were used as experimental subjects. Males were more affected than females by the disruptive effects of this neuroleptic of frequent clinical use. In the present work these sex differences were evaluated in a unique training session using several doses of the drug (0.075, 0.25, and 0.75 mg/kg i.p.). The number of avoidances, escapes, nonresponses, crossings during the adaptation period, crossings during intertrial intervals, and response latencies were analyzed. Statistically significant sex differences were found in the number of escapes and nonresponses: males showed fewer escape responses and more nonresponses than females. These sex differences were dose dependent: a positive correlation was obtained between doses of haloperidol and sex differences observed in the number of escapes and nonresponses. The higher the dose, the greater the sex differences. These are related not only to the impairment of motor activity, because no sex differences were found in the number of crossings during the adaptation period and intertrial intervals.