Main Research Findings

1) PEA-P reduces depression-like phenotypes induced by corticosterone use by activating the BDNF/TrkB/CREB signaling pathways.

2) PEA-P was found to have reinforcing and rewarding effects, as well as psychoactive properties that induced positive effects on psychomotor behavior

Selected Data
1) The study conducted by the research team of Lee et al employed both in vitro and in vivo experimental models to investigate the antidepressant effects of 2-phenylethylamine (PEA) and to determine whether its therapeutic actions were mediated through the brain-derived neurotrophic factor (BDNF)/tropomyosin receptor kinase B (TrkB)/cAMP response element-binding protein (CREB) signaling pathway. The investigators combined cellular, molecular, and behavioral techniques to evaluate the effects of PEA on hippocampal neuronal morphology, synaptic protein expression, neurotrophic signaling, and depression-like behaviors induced by chronic corticosterone (CORT) exposure. Male C57BL/6N mice were housed under controlled environmental conditions with unrestricted access to food and water and maintained on a standard 12-hour light/dark cycle throughout the experiments [1].
To examine the cellular effects of PEA, primary hippocampal neurons were isolated from embryonic day 18 (E18) mouse embryos and cultured under standard conditions. Neurons were plated on poly-D-lysine- and laminin-coated coverslips and maintained in neurobasal medium supplemented with serum, B27, and N2. At ten days in vitro, neurons were transfected with a green fluorescent protein (GFP) plasmid using Lipofectamine to enable visualization of dendritic spines. Four days after transfection, cultured neurons were exposed to corticosterone at a concentration of 50 μM for 24 hours to induce cellular changes associated with depression, followed by treatment with PEA at a concentration of 100 μM for an additional 24 hours. Confocal microscopy was subsequently used to examine dendritic spine density and morphology. An investigator blinded to treatment groups quantified dendritic spines located on secondary dendrites, and individual spines were classified into filopodia, thin, mushroom, and stubby subtypes according to established morphological criteria [1].
To determine whether PEA influenced synaptic integrity and neurotrophic signaling, cultured hippocampal neurons underwent biochemical analysis following treatment. Total cellular protein was isolated using radioimmunoprecipitation assay (RIPA) buffer, and protein concentrations were measured before separation by SDS-polyacrylamide gel electrophoresis and transfer to polyvinylidene fluoride membranes for Western blot analysis. Primary antibodies against synaptophysin (SYP), postsynaptic density protein 95 (PSD95), BDNF, TrkB, CREB, phosphorylated CREB (p-CREB), and β-actin were used to evaluate changes in excitatory synaptic proteins and intracellular signaling molecules. Protein bands were visualized using chemiluminescence and quantified with ImageJ software after normalization to β-actin. Reverse transcription polymerase chain reaction (RT-PCR) was also performed to quantify mRNA expression of BDNF and TrkB using RNA extracted from cultured neurons, with glyceraldehyde-3-phosphate dehydrogenase (GAPDH) serving as the internal reference gene.
The in vivo component of the study utilized a chronic corticosterone-induced mouse model of depression. Mice received daily intraperitoneal injections of corticosterone at a dose of 20 mg/kg or saline for 21 consecutive days. Beginning on day 17, subsets of corticosterone-treated animals additionally received either 50 mg/kg of PEA or the 10 mg/kg of tricyclic antidepressant imipramine, which served as a positive control, during the final four days of corticosterone exposure. Following treatment, hippocampal tissue was collected for molecular analyses, including RT-PCR and Western blotting, to measure mRNA and protein expression of BDNF, TrkB, synaptophysin, and PSD95. These analyses were performed to determine whether the neuroprotective effects observed in cultured neurons also occurred within the hippocampus of animals exhibiting depression-like behaviors [1].
Behavioral testing was conducted after completion of the treatment protocol to evaluate depression- and anxiety-related behaviors. Anhedonia was assessed using the sucrose preference test, in which mice were acclimated to sucrose solution before undergoing food and water deprivation and subsequent measurement of sucrose versus water consumption. Behavioral despair was evaluated using both the tail suspension test and the forced swimming test. During the tail suspension test, mice were suspended by the tail for five minutes while immobility time was recorded. In the forced swimming test, mice were placed in a water-filled cylinder for five minutes, and durations of immobility, swimming, and climbing behaviors were quantified.
Anxiety-like behavior was examined using the elevated plus maze, which consisted of two open and two enclosed arms elevated above the floor. Time spent in the open and closed arms was recorded using automated video tracking software. All behavioral assessments were performed using standardized protocols commonly employed in preclinical models of depression and anxiety.By integrating neuronal culture experiments, chronic animal models, behavioral assessments, gene expression analyses, protein quantification, and morphometric evaluation of dendritic spines, the investigators comprehensively examined the mechanisms through which PEA influences depression-related neuroplasticity and behavioral outcomes [1].
2) The study performed by the research team of Ryu et al investigated the psychomotor, rewarding, reinforcing, and affective effects of β-phenylethylamine (β-PEA) while examining the contribution of dopamine D1 receptor signaling to these behavioral responses. Male C57BL/6 mice were used for the open-field, conditioned place preference (CPP), dopamine enzyme-linked immunosorbent assay (ELISA), and Western blot experiments, whereas male Sprague-Dawley rats were used for ultrasonic vocalization (USV) and intravenous self-administration studies. Animals were housed under controlled temperature, humidity, and 12-hour light/dark cycle conditions with free access to food and water, except during food training for the self-administration experiments, during which rats underwent controlled food restriction to facilitate operant responding. β-PEA and the selective dopamine D1 receptor antagonist SCH23390 were administered intraperitoneally or intravenously depending on the experimental protocol [2].
To evaluate the acute psychomotor effects of β-PEA, mice were first acclimated and habituated to the testing environment before receiving intraperitoneal injections of saline or β-PEA at doses of 3, 10, 30, or 50 mg/kg. Immediately following administration, animals were placed in an automated open-field chamber for 30 minutes. Behavioral software quantified total locomotor activity while trained observers measured stereotypic behaviors including circling and head-twitching responses. Temporal analyses were also performed by dividing the recording period into five-minute intervals, allowing the investigators to determine both the magnitude and duration of behavioral changes following β-PEA administration. To determine whether dopamine D1 receptor activation mediated these effects, an additional cohort of mice received SCH23390 before β-PEA administration, after which the same open-field behavioral assessments were conducted [2].
The rewarding properties of β-PEA were assessed using a conditioned place preference paradigm. Mice first completed a pre-conditioning session to determine baseline chamber preference. During the conditioning phase, animals received alternating injections of saline or β-PEA before being confined to either the drug-paired or saline-paired compartment over several days. A post-conditioning preference test was then conducted without drug administration, during which mice were allowed unrestricted access to both compartments. The primary outcome measures included time spent in the drug-paired chamber and the conditioned place preference score, calculated by comparing post-conditioning preference with baseline values. This paradigm allowed the researchers to determine whether repeated β-PEA exposure produced rewarding contextual associations indicative of abuse liability.
Positive affective responses to β-PEA were examined using ultrasonic vocalization recordings in rats. Following acclimation and habituation, baseline 50-kHz ultrasonic vocalizations were recorded before administration of either saline or 50 mg/kg β-PEA. Vocalizations were then continuously monitored for an additional 30 minutes using specialized ultrasonic microphones and analysis software. Because 50-kHz calls are widely recognized as indicators of positive emotional states in rodents, both the total number of vocalizations and their temporal distribution across five-minute intervals were analyzed to determine whether β-PEA induced positive affective behavior.
To evaluate reinforcing effects, rats underwent food training followed by surgical implantation of chronic jugular vein catheters for intravenous self-administration. After recovery, animals self-administered saline or β-PEA at doses of 0.1, 0.3, or 1.0 mg/kg per infusion during daily two-hour sessions under fixed-ratio schedules of reinforcement, progressing from FR1 to FR3 across eleven consecutive days. Responses on the active lever delivered an intravenous drug infusion followed by a timeout period, whereas inactive lever presses had no programmed consequence. After completion of fixed-ratio training, rats underwent a six-hour progressive-ratio session in which the response requirement increased after each infusion to determine the reinforcing strength of β-PEA by measuring total infusions, active and inactive lever responses, and breakpoint. Additional self-administration experiments incorporated SCH23390 pretreatment to determine whether dopamine D1 receptor blockade altered β-PEA-taking behavior [2].
To investigate the neurobiological mechanisms underlying these behavioral effects, separate groups of mice received acute saline or β-PEA before rapid dissection of the dorsal striatum. Dopamine concentrations were quantified using enzyme-linked immunosorbent assays, while Western immunoblotting measured expression of tyrosine hydroxylase (TH), dopamine transporter (DAT), phosphorylated DAT (p-DAT), and vesicular monoamine transporter-2 (VMAT-2). Protein extracts were separated by gel electrophoresis, transferred to PVDF membranes, incubated with specific primary and secondary antibodies, and quantified by densitometric analysis. Together, these complementary behavioral, biochemical, and pharmacological approaches enabled the investigators to comprehensively evaluate both the behavioral actions of β-PEA and the dopaminergic mechanisms responsible for its psychoactive and reinforcing properties [2].

Discussion
1) The study by Lee et al demonstrated that PEA effectively reversed both the cellular and behavioral abnormalities produced by chronic CORT exposure, supporting its potential antidepressant activity through modulation of the BDNF/TrkB/CREB signaling pathway. In cultured hippocampal neurons, CORT treatment significantly impaired dendritic spine architecture, producing an overall reduction in dendritic spine density and substantial alterations in spine morphology. Specifically, CORT exposure decreased the total number of dendritic spines by approximately 37% relative to untreated controls. Morphological analysis further revealed marked reductions in mature thin and mushroom spines, accompanied by increases in immature filopodia and stubby spines, indicating impaired synaptic maturation and neuronal plasticity. Treatment with PEA largely reversed these structural abnormalities by restoring dendritic spine density and normalizing the distribution of spine subtypes, demonstrating that PEA protects hippocampal neurons from CORT-induced synaptic damage. These findings suggest that PEA promotes structural plasticity within hippocampal neurons, an effect that is considered essential for normal learning, memory, and emotional regulation [1].
PEA also restored excitatory synaptic function by reversing the reductions in synaptic proteins produced by chronic corticosterone exposure. Western blot analysis demonstrated that CORT significantly decreased expression of the presynaptic protein SYP and the postsynaptic scaffold protein PSD95, indicating substantial impairment of excitatory synapses. Following PEA treatment, expression of both proteins increased toward control levels, suggesting recovery of synaptic integrity. Additional molecular analyses showed that CORT markedly suppressed both BDNF and TrkB protein expression in cultured hippocampal neurons, while significantly reducing phosphorylation of CREB without altering total CREB expression. Administration of PEA restored BDNF and TrkB protein levels and substantially increased CREB phosphorylation, indicating reactivation of the BDNF/TrkB/CREB signaling pathway. Because this signaling cascade regulates neuronal survival, synaptic plasticity, and activity-dependent gene transcription, restoration of these molecular markers provides mechanistic evidence explaining the neuroprotective effects of PEA observed at the structural level [1].
The molecular findings obtained in cultured neurons were reproduced in the chronic CORT-treated mouse model. Long-term corticosterone administration significantly reduced hippocampal mRNA and protein expression of BDNF and TrkB, confirming disruption of neurotrophic signaling associated with depression-like pathology. Likewise, expression of the synaptic proteins SYP and PSD95 was markedly decreased at both the transcriptional and protein levels. Treatment with either PEA or the reference antidepressant imipramine significantly restored BDNF and TrkB gene expression as well as protein abundance within the hippocampus. Similar improvements were observed for SYP and PSD95, indicating recovery of excitatory synaptic function following PEA administration. The comparable effects produced by PEA and imipramine suggest that PEA possesses antidepressant-like properties capable of reversing corticosterone-induced molecular deficits that are characteristic of chronic stress and depressive disorders.
Behavioral testing demonstrated that the molecular improvements induced by PEA translated into meaningful functional recovery. In the sucrose preference test, chronic corticosterone exposure reduced sucrose consumption by approximately 44%, reflecting the development of anhedonia, a core symptom of major depressive disorder. PEA administration restored sucrose preference to levels comparable with untreated control animals, indicating recovery of normal reward-related behavior. Similarly, corticosterone significantly increased immobility during the tail suspension test, demonstrating behavioral despair. Treatment with PEA markedly reduced immobility time, producing improvements comparable to those observed with imipramine. Comparable antidepressant-like effects were observed during the forced swimming test, where corticosterone substantially increased immobility while reducing active swimming behavior. Administration of PEA significantly decreased immobility and increased swimming time, indicating improved behavioral coping responses and reduced depression-like behavior. These findings consistently demonstrated that PEA alleviated multiple behavioral manifestations of chronic stress-induced depression [1].

Figure 1: Changes in behavioral testing outcomes following treatment with experimental compounds following exposure to corticosterone.
PEA also improved anxiety-related behaviors produced by chronic corticosterone administration. During the elevated plus maze, CORT-treated mice spent significantly less time exploring the open arms and correspondingly more time in the enclosed arms, reflecting increased anxiety-like behavior. Treatment with PEA reversed these behavioral abnormalities by increasing time spent in the open arms while reducing time spent in the closed arms, indicating reduced anxiety. The magnitude of these behavioral improvements closely paralleled those observed following treatment with imipramine, further supporting the therapeutic potential of PEA. Collectively, the cellular, molecular, and behavioral findings demonstrated that PEA effectively counteracted corticosterone-induced depression-like pathology by restoring dendritic spine architecture, increasing excitatory synaptic protein expression, reactivating the BDNF/TrkB/CREB signaling pathway, and improving both depressive- and anxiety-like behaviors. These results provide strong evidence that enhancement of hippocampal neuroplasticity represents a primary mechanism through which PEA exerts its antidepressant effects and support further investigation of PEA as a potential therapeutic agent for stress-related mood disorders [1].
2) The results of the study by Ryu et al demonstrated that acute administration of β-PEA produced significant psychomotor, rewarding, reinforcing, and positive affective effects in rodents, with these behavioral changes closely associated with enhanced dopaminergic neurotransmission and activation of dopamine D1 receptors. In the open-field test, β-PEA produced dose-dependent stereotypic behaviors, with the highest dose of 50 mg/kg significantly increasing circling behavior compared with saline-treated controls. Temporal analysis revealed that this increase was most pronounced approximately 10 minutes after administration, indicating a rapid onset of psychomotor stimulation [2].
Similarly, β-PEA significantly increased head-twitching responses, another stereotypic behavior associated with enhanced monoaminergic signaling, with the greatest responses occurring during the first 15 minutes following administration. Interestingly, despite these marked stereotypic behaviors, β-PEA did not significantly alter overall locomotor activity, suggesting that the compound selectively induced repetitive psychomotor behaviors rather than generalized hyperactivity. These findings indicate that acute β-PEA administration produces distinct behavioral changes that resemble those observed with psychostimulant compounds while demonstrating a unique behavioral profile characterized by stereotypy rather than increased locomotion.
Behavioral measures of reward further demonstrated that β-PEA possesses rewarding properties. During the CPP experiment, no differences in chamber preference were observed among treatment groups before conditioning, confirming that the animals had no inherent preference for either compartment. Following repeated conditioning sessions, however, mice receiving 50 mg/kg β-PEA spent significantly more time in the drug-paired compartment than saline-treated controls, resulting in a significant increase in CPP scores. These findings demonstrate that β-PEA successfully established positive contextual associations, indicating that the compound possesses rewarding effects capable of reinforcing environmental cues associated with drug exposure. Complementing these findings, ultrasonic vocalization recordings showed that acute β-PEA administration significantly increased the number of 50-kHz ultrasonic vocalizations, particularly during the first 10 minutes after injection. Because 50-kHz vocalizations are widely recognized as indicators of positive emotional and motivational states in rodents, these results suggest that β-PEA induces an acute positive affective state in addition to its rewarding behavioral effects [2].
The intravenous self-administration experiments provided strong evidence that β-PEA functions as a reinforcing stimulus. Under both FR1 and FR3 schedules of reinforcement, rats receiving the highest dose of β-PEA of 1.0 mg/kg per infusion exhibited significantly greater numbers of drug infusions and active lever presses than saline-treated animals, while inactive lever responding remained unchanged. This selective increase in active responding demonstrated that the animals were intentionally working to obtain β-PEA rather than displaying nonspecific increases in activity. Temporal analyses further showed that animals consistently self-administered β-PEA throughout the testing sessions, confirming stable reinforcing behavior. Reinforcing efficacy was examined more rigorously using a progressive-ratio schedule, where the response requirement increased after each infusion. Under these demanding conditions, rats self-administering the highest β-PEA dose achieved significantly higher breakpoints, earned more total infusions, and generated substantially more active lever responses than control animals. The increased breakpoint indicated that the animals were willing to perform progressively greater amounts of work to obtain β-PEA, demonstrating robust reinforcing properties comparable to those observed with other psychostimulant drugs in preclinical models [2].
Biochemical analyses revealed that these behavioral effects were accompanied by significant alterations in dopaminergic signaling within the dorsal striatum. Acute β-PEA administration significantly increased dopamine concentrations in this brain region compared with saline controls. Western blot analysis further demonstrated elevated expression of tyrosine hydroxylase, the rate-limiting enzyme responsible for dopamine synthesis, and increased phosphorylation of the dopamine transporter (p-DAT), suggesting enhanced dopamine production and altered dopamine transporter activity. In contrast, total dopamine transporter (DAT) and vesicular monoamine transporter-2 (VMAT-2) expression remained unchanged, indicating that β-PEA primarily influenced dopamine neurotransmission through functional modulation rather than changes in overall protein abundance. These neurochemical findings strongly support the conclusion that β-PEA enhances dopaminergic neurotransmission within the dorsal striatum, providing a mechanistic explanation for its rewarding and reinforcing behavioral effects.
Pharmacological inhibition of dopamine D1 receptors further established the importance of dopaminergic signaling in mediating β-PEA’s behavioral actions. Pretreatment with the selective D1 receptor antagonist SCH23390 significantly reduced β-PEA-induced circling behavior without affecting overall locomotion or head-twitching responses, suggesting that D1 receptor activation specifically contributes to certain stereotypic behaviors. More importantly, SCH23390 markedly decreased β-PEA self-administration by significantly reducing both active lever responses and the number of drug infusions throughout the testing session. These findings demonstrate that dopamine D1 receptor activation is critical for the reinforcing properties of β-PEA and substantially contributes to its abuse-related behavioral profile. Collectively, the results indicate that β-PEA possesses rewarding, reinforcing, psychomotor, and positive affective properties that are mediated through enhanced dopaminergic neurotransmission and dopamine D1 receptor activation within the dorsal striatum, highlighting mechanisms that may underlie both its psychoactive effects and its potential for abuse [2].

Disclaimer

**LAB USE ONLY**
*This information is for educational purposes only and does not constitute medical advice. THE PRODUCTS DESCRIBED HEREIN ARE FOR RESEARCH USE ONLY. All clinical research must be conducted with oversight from the appropriate Institutional Review Board (IRB). All preclinical research must be conducted with oversight from the appropriate Institutional Animal Care and Use Committee (IACUC) following the guidelines of the Animal Welfare Act (AWA).

Citations

[1] Lee YJ, Kim HR, Lee CY, et al. 2-Phenylethylamine (PEA) Ameliorates Corticosterone-Induced Depression-Like Phenotype via the BDNF/TrkB/CREB Signaling Pathway. Int J Mol Sci. 2020;21(23):9103. Published 2020 Nov 30. doi:10.3390/ijms21239103

[3] Ryu IS, Kim OH, Kim JS, et al. Effects of β-Phenylethylamine on Psychomotor, Rewarding, and Reinforcing Behaviors and Affective State: The Role of Dopamine D1 Receptors. Int J Mol Sci. 2021;22(17):9485. Published 2021 Aug 31. doi:10.3390/ijms22179485

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