A mixture of eight fatty acids (linoleic, palmitic, stearic, myristic, elaidic, lauric, oleic, and palmitoleic acids) at similar concentrations identified in human amniotic fluid produces anxiolytic-like effects comparable to diazepam in Wistar rats. However, individual effects of each fatty acid remain unexplored. In Wistar rats, we evaluated the separate action of each fatty acid at the corresponding concentrations previously found in human amniotic fluid on anxiety-like behaviour. Individual effects were compared with vehicle, an artificial mixture of the same eight fatty acids, and a reference anxiolytic drug (diazepam, 2 mg/kg). Myristic acid, the fatty acid mixture, and diazepam increased the time spent in the open arms of the elevated plus maze and reduced the anxiety index compared with vehicle, without altering general locomotor activity. The other fatty acids had no effect on anxiety-like behaviour, but oleic acid reduced locomotor activity. Additionally, myristic acid produced anxiolytic-like effects only when the concentration corresponded to the one identified in human amniotic fluid (30 𝜇g/mL) but did not alter locomotor activity. We conclude that of the eight fatty acids contained in the fatty acid mixture, only myristic acid produces anxiolytic-like effects when administered individually at a similar concentration detected in human amniotic fluid.

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Zebrafish (Danio rerio) is a popular and valuable species used in many different biomedical research areas. The complex behavior that fish exhibit in response to different stimuli allows researchers to explore the biological and pharmacological basis of affective and mood disorders. In this sense, anxiety is commonly studied in preclinical research with animal models in rodents. During the last decade, those models have been successfully adapted to zebrafish. Stressful stimuli, such as novel environments, chemical substances, light conditions, and predator images, can trigger defensive behaviors considered indicators of an anxiety-like state. In the first stage, models were adapted and validated with different stressors and anxiolytic drugs with promising results and are now successfully used to generate scientific knowledge. In that sense, zebrafish allows several routes of administration and other methodological advantages to explore the anxiolytic effects of natural products in behavioral tests as novel tank, light-dark chamber, and black/white maze, among others. The present work will review the main findings on preclinical research using adult zebrafish to explore anxiolytics effects of natural products as plant secondary metabolites such as flavonoids, alkaloids and terpenes or standardized extracts of plants, among others. Scientific literature confirms the utility of zebrafish tests to explore anxiety-like states and anxiolytic-like effects of plant secondary metabolites, which represent a useful and ethical tool in the first stages of behavioral.

Fatty acids (C6–C18) found in human amniotic fluid, colostrum, and maternal milk reduce behavioral indicators of experimental anxiety in adult Wistar rats. Unknown, however, is whether the anxiolytic-like effects of fatty acids provide a natural mechanism against anxiety in young offspring. The present study assessed the anxiolytic-like effect of a mixture of lauric acid, myristic acid, palmitic acid, palmitoleic acid, stearic acid, oleic acid, elaidic acid, and linoleic acid in Wistar rats on postnatal day 28. Infant rats were subjected to the elevated plus maze, defensive burying test, and locomotor activity test. Diazepam was used as a reference anxiolytic drug. A group that was pretreated with picrotoxin was used to explore the participation of γ-aminobutyric acid-A (GABAA) receptors in the anxiolytic-like effects. Similar to diazepam, the fatty acid mixture significantly increased the frequency of entries into and time spent on the open arms of the elevated plus maze and decreased burying behavior in the defensive burying test, without producing significant changes in spontaneous locomotor activity. These anxiolytic-like effects were blocked by picrotoxin. Results suggest that these fatty acids that are contained in maternal fluid may reduce anxiety-like behavior by modulating GABAergic neurotransmission in infant 28-day-old rats.

A mixture of eight fatty acids (linoleic, oleic, palmitic, stearic, myristic, elaidic, lauric, and palmitoleic acids) at similar concentrations that have been identified in human amniotic fluid exerts anxiolytic-like effects similar to diazepam in adult Wistar rats through actions at γ-aminobutyric acid-A (GABA A) receptors, but unknown is whether any of these fatty acids exerts a predominant action over the others in infant rats. Of these fatty acids, some actions of oleic acid have already been identified, and it is one of the most abundant in amniotic fluid. Therefore, the aim of this study was to explore the effect of oleic acid on anxiety-like behavior and motoric activity in infant rats. To explore sedative actions, 28-day-old Wistar rats received 80-320 µg oleic acid or a sedative dose of diazepam (5 mg/kg). In a dose-response study, other groups of rats were injected with 10-80 µg oleic acid or 1 mg/kg diazepam. In an interaction study, rats that received oleic acid were pretreated with the GABA A receptor antagonists picrotoxin or flumazenil to explore the participation of this receptor in the effects of oleic acid on behavior in the elevated plus maze, rotarod test, and open field test. Oleic acid produced sedative effects but did not exert any anxiolytic-like actions. Hypoactivity and motor incoordination that were induced by oleic acid were blocked by flumazenil and picrotoxin. In conclusion, oleic acid reduced locomotor activity and motor incoordination through actions at the GABA A receptor.

The present study investigated the sensitivity to stress and diazepam in weaning (21-day old) Wistar rats. A single 15-min session of forced swimming was used to induce anxiety-like behavior. The group that was forced to swim exhibited an increase in anxiety-like behavior in the elevated plus maze (EPM) and open field test (OFT) compared to the non-stressed group. Diazepam (1 h before the tests) reduced anxiety-like behavior in rats forced to swim compared to the vehicle stressed group. The dose-response curve for diazepam indicated that the 0.5 mg kg−1 dose (1 h before the EPM and OFT) was the minimum effective dose in reducing anxiety-like behavior without altering locomotor activity in weaning rats. These results indicate that weaning rats can develop anxiety-like behavior after a brief, single session of stress, and that rats at this age are seemingly more sensitive to diazepam than adult rats, which may be taken into account for clinical applications.

The defensive burying test is an experimental model that is used to explore anxiety-like behavior in adult rats. Because the expression of anxiety-like behavior may differ between infant and adult rats, we tested the impact of chambers with different sizes and shapes on defensive burying in 28-day-old Wistar rats. The first two chambers had base areas of 560 cm, but one was rectangular and the other round. The base areas of the other two chambers were 282 cm, also with one rectangular and one round. We examined the effects of vehicle and 1 mg/kg diazepam on defensive burying in the various chambers. Locomotor activity was also measured to identify or exclude any sedative effects. Independent of the treatments used, the infant rats showed a shorter burying latency in the three modified chambers and a longer cumulative burying time compared with the original apparatus. The effects of diazepam (i.e. increased latency and decreased burying time) were only significant in the small round chamber, without significant effects on general motor activity. These results suggest that a small round chamber that is used to test burying behavior is sensitive to the anxiolytic actions of diazepam when the experimental subjects are very young rats.