Introduction 

Neuroplasticity, the brain’s striking ability involving adaptive structural and functional changes, is vital in understanding and treating depression. A recent study has clarified the effectiveness of active cannabinoid compounds in cannabis in influencing neuroplasticity, while potentially facilitating depression treatment and recovery. By interacting with the brain’s endocannabinoid system, there are promising effects of cannabinoids upon mood regulation, stress response, and synaptic plasticity (foundation of neuroplasticity). While dynamic interplay between cannabinoids and neuroplasticity offers a novel prospective for depressive treatment, these compounds may facilitate neural circuits rewiring associated with mood disorders. Exploring the intricate cannabinoids mechanisms in modulating neuroplasticity opens up new pathways for therapeutic interventions, not just for depressive symptoms, but also the underlying neural processes for depression recovery. 

Neuroplasticity and its role in depression 

What is neuroplasticity? 

Neuroplasticity is the adaptive ability of the nervous system that adjusts in response to intrinsic or extrinsic stimuli.¹ This dynamic process is often post-disease or injury, either beneficial (restoring functions), neutral (no change), or negative (inducing pathological consequences) to the nervous system.

Two major mechanisms

Neuronal regeneration (collateral sprouting)

Neuronal regeneration is the repairing or replacing of damaged nerve cells, axons, synapses, and glial cells, by undamaged axonal growth at the neighbour in reinnervating targeted region(s).^2,3,4 It is further classified into synaptic plasticity (adaptive synaptic strengthening or weakening),⁵ and neurogenesis (new neuron formation from neural stem cells).⁶

Functional (cortical) reorganisation

It is the brain functions’ shifting from damaged to undamaged areas, manifesting as the preserved tissues in taking on a new functional role,^7,8 including equipotentiality (functional uptake by undamaged regions), vicariation (function take over by different regions in performing the same task as the injured region),¹ diaschisis (sudden, remote interconnected regional dysfunction). 

Neuroplasticity in depression 

Concerning depression, neuroplasticity is the brain’s adaptive and reorganisation capacity in response to its related mental health challenges. 

Major structural changes 

Major functional changes 

Neuroplasticity impairment 

Chronic stress and inflammation play a significant role in impairing neuroplasticity, resulting in depression. While persistent stress would raise cortisol levels, damaging the hippocampus and PFC, essential for memory and emotional regulation.¹⁹ Cytokines introduced by stress-induced inflammation could disrupt synaptic connectivity and neurogenesis, limiting the brain’s ability to form new neural connections.²⁰ These changes thus impede emotional resilience, cognitive flexibility, and the brain’s ability to recover from negative experiences. Hence, creating a common feeling of “stuck” among those with depression, as the brain struggles to regulate mood, adapt to new perspectives, and support positive thought patterns. 

Endocannabinoid system (ECS) and the brain 

What is the endocannabinoid system?

The endocannabinoid system (ECS) is a complex biological modulatory system in the central nervous system (CNS) and peripheral tissues. It plays a significant role in one’s mood, stress response, emotional response, and reward processing regulation among the circumstances of depression. 

Major components 

ECS consists of two main endocannabinoid receptors (ECRs): ECRs CB1 and CB2, their endogenous ligands (endocannabinoids), and a number of enzymes.

• Endocannabinoid receptors (ECRs), particularly CB1, centres upon mood and stress resilience regulation, plus neurotransmission modulation for neuroplasticity
• Endogenous ligands act as neurotransmitters, binding to ECRs to modulate neurotransmission, for emotional stability support
• Specialised enzymes, such as FAAH and MAGL, break down endocannabinoids for balanced level maintenance²¹

Cannabinoid receptors and neuroplasticity 

Cannabinoid receptors, primarily CB1, are crucial for neuroplasticity in depression management and recovery. While CB1 receptors activated by endocannabinoids modulate neurotransmitter release and support synaptic plasticity through lipid mediator anandamide, their role across brain regions is different in depression.²²

• Hippocampal CB1 activation supports neuroplasticity and neurogenesis, essential for memory and emotional resilience, where its reduced activity is related to stress adaptation impairments²³
• Prefrontal cortex CB1 influences decision-making, emotional control, and cognitive flexibility, which are commonly disrupted in depressive states²⁴
• Amygdala CB1 regulates fear and anxiety responses, and low levels can exacerbate emotional reactivity, worsening depressive symptoms²⁵

ECS dysregulation in depression

ECS dysregulation has been increasingly linked to depression because of the disrupted neurotransmitter balance critical for emotions and stress regulation, plus responses to reward stimuli. While decreased levels of endocannabinoids like anandamide and impaired CB1 receptor function lead to intensified sensitivity to stress and diminished mood stability²⁶. This limits the brain’s plasticity to recover from negative experiences and adapt to new perspectives. Meaning, targeting ECS function by enhancing endocannabinoid signalling would be promising to restore mood balance on depressive symptom reduction. 

Cannabinoids and neuroplasticity in depression 

Cannabinoid-induced neurogenesis and synaptogenesis 

Cannabinoids can stimulate neurogenesis (new neuron growth) and synaptogenesis (formation of new synapses) for enhancing brain function in depression. While its active forms like THC and CBD could activate CB1 receptors primarily in the hippocampus and PFC for the growth of new neurons and formation of new synaptic connections. While hippocampal neurogenesis facilitates memory and emotion resilience improvements, which are diminished under depression. Synaptogenesis in PFC could further enhance cognitive flexibility and emotional regulation, for better stress adaptation and decision-making.^27,28 By promoting these neuroplastic changes, cannabinoids could help rewire neural circuits responsible for mood, stress regulation, and cognitive enhancement, fostering the brain’s adaptivity against depressive symptoms. 

Cannabinoids and neuroinflammation reduction

Cannabinoids, particularly CBD and THC are significant in brain health and resilience maintenance through reducing neuroinflammation in depression.²⁹ While cannabinoids interact with the endocannabinoid system (ECS) to modulate immune cells in the CNS, activation of microglia (immune cells in the brain), which, when overactive, would release pro-inflammatory cytokines, contributing to neuroinflammation, is inhibited.

While CBD has been shown to downregulate these inflammatory responses, fostering a healthy neural environment, the reduced neuroinflammation could further support neurogenesis and synaptogenesis that are vital for neuroplasticity. By mitigating the harmful effects of chronic inflammation, cannabinoids are effective in neuron protection and repair promotion, ultimately enhancing cognitive function and emotional stability. Thereby highlighting the therapeutic potential of cannabinoids in addressing mood disorders and supporting mental health recovery.

Effects of specific cannabinoids on neuroplasticity

Tetrahydrocannabinol (THC)

The neuroplastic effects of tetrahydrocannabinol (THC),‌ the primary psychoactive compound in cannabis, are complex and multifaceted in depression. THC can promote neurogenesis and synaptic plasticity in certain brain regions, where their dysfunctions are common in depression. Chronic and high doses are also found to reduce neurogenesis and synaptic plasticity. Hence, its effect on mood regulation varies among individuals, ranging from temporary mood elevation, increased risks of mood disorders, to even depressive symptoms exacerbation.²¹

Cannabinol (CBD)

Cannabinol (CBD), as a non-psychoactive compound in cannabis, exhibits promising neuroplastic effects in depression. While potentially interacting‌with various neurotransmitters, CBD could help promote neurogenesis and synaptic plasticity modulation, strengthening neurons and synaptic connections crucial for brain health and mood regulation, to counteract the negative neuroplastic impact of depression and restore the disrupted brain function. The anti-inflammatory and antioxidant properties can protect neurons and support a conducive environment for neuroplasticity among depression.²¹

Endocannabinoids (e.g., anandamide)

Anandamide, an endocannabinoid neurotransmitter, is significant in depression neuroplastic modulation. While beneficial in promoting neurogenesis, which is crucial for brain repair and mood regulation, which is often impaired in depression, anandamide could further modulate synaptic connections, improve neural circuit changes and adaptations to stress, hence restoring emotional processing pathway balance alleviating depressive symptoms.²²

Challenges and considerations 

Several challenges are present when cannabinoids are used to promote neuroplasticity in depression cases:

Dosing complexity

Cannabinoids like THC and CBD can have dose-dependent effects on neuroplasticity, by which high doses or chronic use could result in adverse outcomes of worsening depressive symptoms. Therefore, determining the optimal dosing for neuroplasticity promotion while avoiding potential adverse effects requires careful measurement and monitoring.

Individual variability 

While individual differences in responses to cannabinoids exist, depending on genetic, physiological, and environmental factors. Prior exposure and testing are essential to predict their neuroplastic effect on depression. 

Regulatory hurdles 

Legal and regulatory restrictions on cannabinoids pose barriers to research and access, limiting standardised access to cannabinoids for depression treatment. 

Interaction with medications 

Cannabinoids may interact with other antidepressants, which could lead to adverse effects such as cognitive dependency, mood swings, or altered treatment outcomes. 

Long-term effects

Long-term effects of cannabinoids on neuroplasticity in depression are still under investigation, and safety concerns are raised about their sustained impact on brain function and mental health, with potential side effects having to be weighed against therapeutic benefits. 

Integration into traditional depression treatment 

A strategic implementation can facilitate the integration of cannabinoids into traditional depression treatment.

Collaborative care 

Collaboration between professionals, such as psychiatrists and cannabinoid specialists, is essential to ensure a comprehensive, complementary treatment plan to combine cannabinoids with other evidence-based treatments, such as psychotherapy or antidepressants, to enhance overall outcomes. 

Personalised therapy 

Ensure tailored cannabinoid therapy to each case's individual needs, taking their medical history, current medications, and responses to cannabinoids into consideration to optimise safety and treatment outcome. 

Dosage administration, monitoring, and adjustment 

Cannabinoid dosage, administration methods (e.g., oral, sublingual, inhalation), and dose frequency should be carefully considered to achieve optimal therapeutic effectiveness and safety. Regular monitoring and evaluation are also crucial for timely adjustments to minimise potential adverse effects. 

Education and support 

Educate patients on cannabinoid therapy, its potential benefits, side effects, and risks, to provide support throughout the entire treatment to enhance adherence and overall treatment success. 

Summary 

Cannabinoids, through their interactions with the endocannabinoid system, can have significant neuroplastic effects on depression recovery. While cannabinoids like THC, CBD, and anandamide can promote neurogenesis, synaptogenesis, and reduce neuroinflammation to facilitate healthy brain function restoration among depression. Challenges such as dosing complexity, individual diverse responses, and regulatory constraints must be navigated to allow cannabinoids integration into traditional depression treatment, to provide an innovative and collaborative approach to depression management. Overall, neuroplasticity facilitates recovery and improves outcomes for those battling depression.