Persistent sexually dimorphic effects of adolescent THC exposure on hippocampal synaptic plasticity and episodic memory in rodents

Cannabinol (CBN) alleviates age-related cognitive decline by improving synaptic and mitochondrial health

Age-related cognitive decline and neurodegenerative diseases, such as Alzheimer's disease, represent major global health challenges, particularly with an aging population. Mitochondrial dysfunction appears to play a central role in the pathophysiology of these conditions by driving redox dysregulation and impairing cellular energy metabolism. Despite extensive research, effective therapeutic options remain limited. Cannabinol (CBN), a cannabinoid previously identified as a potent inhibitor of oxytosis/ferroptosis through mitochondrial modulation, has demonstrated promising neuroprotective effects. In cell culture, CBN targets mitochondria, preserving mitochondrial membrane potential, enhancing antioxidant defenses and regulating bioenergetic processes. However, the in vivo therapeutic potential of CBN, particularly in aging models, has not been thoroughly explored. To address this gap, this study investigated the effects of CBN on age-associated cognitive decline and metabolic dysfunction using the SAMP8 mouse model of accelerated aging. Our results show that CBN significantly improves spatial learning and memory, with more pronounced cognitive benefits observed in female mice. These cognitive improvements are accompanied by sex-specific changes in metabolic parameters, such as enhanced oxygen consumption and energy expenditure. Mechanistically, CBN modulates key regulators of mitochondrial dynamics, including mitofusin 2 (MFN2) and dynamin-related protein 1 (DRP1), while upregulating markers of mitochondrial biogenesis including mitochondrial transcription factor A (TFAM) and translocase of outer mitochondrial membrane 20 (TOM20). Additionally, CBN upregulates key synaptic proteins involved in vesicle trafficking and postsynaptic signaling suggesting that it enhances synaptic function and neurotransmission, further reinforcing its neuroprotective effects. This study provides in vivo evidence supporting CBN's potential to mitigate age-related cognitive and metabolic dysfunction, with notable sex-specific effects, highlighting its promise for neurodegenerative diseases and cognitive decline.

Neural basis of adolescent THC-induced potentiation of opioid responses later in life

Use of one addictive drug typically influences the behavioral response to other drugs, either administered at the same time or a subsequent time point. The nature of the drugs being used, as well as the timing and dosing, also influence how these drugs interact. Here, we tested the effects of adolescent THC exposure on the development of morphine-induced behavioral adaptations following repeated morphine exposure during adulthood. We found that adolescent THC administration paradoxically prevented the development of anxiety-related behaviors that emerge during a forced abstinence period following morphine administration but facilitated reinstatement of morphine CPP. Following forced abstinence, we then mapped the whole-brain response to a moderate dose of morphine and found that adolescent THC administration led to an overall increase in brain-wide neuronal activity and increased the functional connectivity between frontal cortical regions and the ventral tegmental area. Last, we show using rabies virus-based circuit mapping that adolescent THC exposure triggers a long-lasting elevation in connectivity from the frontal cortex regions onto ventral tegmental dopamine cells. Our study adds to the rich literature on the interaction between drugs, including THC and opioids, and provides potential neural substates by which adolescent THC exposure influences responses to morphine later in life.

The effect of traumatic brain injury on learning and memory: A synaptic focus

Deficits in learning and memory are some of the most commonly reported symptoms following a traumatic brain injury (TBI). We will examine whether the neural basis of these deficits stems from alterations to bidirectional synaptic plasticity within the hippocampus. Although the CA1 subregion of the hippocampus has been a focus of TBI research, the dentate gyrus should also be given attention as it exhibits a unique ability for adult neurogenesis, a process highly susceptible to TBI-induced damage. This review examines our current understanding of how TBI results in deficits in synaptic plasticity, as well as how TBI-induced changes in endocannabinoid (eCB) systems may drive these changes. Through the synthesis and amalgamation of existing data, we propose a possible mechanism for eCB-mediated recovery in synaptic plasticity deficits. This hypothesis is based on the plausible roles of CB1 receptors in regulating inhibitory tone, influencing astrocytes and microglia, and modulating glutamate release. Dysregulation of the eCBs may be responsible for deficits in synaptic plasticity and learning following TBI. Taken together, the existing evidence indicates eCBs may contribute to TBI manifestation, pathogenesis, and recovery, but it also suggests there may be a therapeutic role for the eCB system in TBI.

Adolescent THC impacts on mPFC dopamine-mediated cognitive processes in male and female rats

RATIONALE

Adolescent cannabis use is linked to later-life changes in cognition, learning, and memory. Rodent experimental studies suggest Δ9-tetrahydrocannabinol (THC) influences development of circuits underlying these processes, especially in the prefrontal cortex, which matures during adolescence.

OBJECTIVE

We determined how 14 daily THC injections (5 mg/kg) during adolescence persistently impacts medial prefrontal cortex (mPFC) dopamine-dependent cognition.

METHODS

In adult Long Evans rats treated as adolescents with THC (AdoTHC), we quantify performance on two mPFC dopamine-dependent reward-based tasks-strategy set shifting and probabilistic discounting. We also determined how acute dopamine augmentation with amphetamine (0, 0.25, 0.5 mg/kg), or specific chemogenetic stimulation of ventral tegmental area (VTA) dopamine neurons and their projections to mPFC impact probabilistic discounting.

RESULTS

AdoTHC sex-dependently impacts acquisition of cue-guided instrumental reward seeking, but has minimal effects on set-shifting or probabilistic discounting in either sex. When we challenged dopamine circuits acutely with amphetamine during probabilistic discounting, we found reduced discounting of improbable reward options, with AdoTHC rats being more sensitive to these effects than controls. In contrast, neither acute chemogenetic stimulation of VTA dopamine neurons nor pathway-specific chemogenetic stimulation of their projection to mPFC impacted probabilistic discounting in control rats, although stimulation of this cortical dopamine projection slightly disrupted choices in AdoTHC rats.

CONCLUSIONS

These studies confirm a marked specificity in the cognitive processes impacted by AdoTHC exposure. They also suggest that some persistent AdoTHC effects may alter amphetamine-induced cognitive changes in a manner independent of VTA dopamine neurons or their projections to mPFC.

Metabotropic NMDAR Signaling Contributes to Sex Differences in Synaptic Plasticity and Episodic Memory

NMDA receptor (NMDAR)-mediated calcium influx triggers the induction and initial expression of long-term potentiation (LTP). Here we report that in male rodents, ion flux-independent (metabotropic) NMDAR signaling is critical for a third step in the production of enduring LTP, i.e., cytoskeletal changes that stabilize the activity-induced synaptic modifications. Surprisingly, females rely upon estrogen receptor alpha (ERα) for the metabotropic NMDAR operations used by males. Blocking NMDAR channels with MK-801 eliminated LTP expression in hippocampal field CA1 of both sexes but left intact theta burst stimulation (TBS)-induced actin polymerization within dendritic spines. A selective antagonist (Ro25-6981) of the NMDAR GluN2B subunit had minimal effects on synaptic responses but blocked actin polymerization and LTP consolidation in males only. Conversely, an ERα antagonist thoroughly disrupted TBS-induced actin polymerization and LTP in females while having no evident effect in males. In an episodic memory paradigm, Ro25-6981 prevented acquisition of spatial locations by males but not females, whereas an ERα antagonist blocked acquisition in females but not males. Sex differences in LTP consolidation were accompanied by pronounced differences in episodic memory in tasks involving minimal (for learning) cue sampling. Males did better on acquisition of spatial information whereas females had much higher scores than males on tests for acquisition of the identity of cues (episodic "what") and the order in which the cues were sampled (episodic "when"). We propose that sex differences in synaptic processes used to stabilize LTP result in differential encoding of the basic elements of episodic memory.

Adolescent THC impacts on mPFC dopamine-mediated cognitive processes in male and female rats

Rationale

Adolescent cannabis use is linked to later-life changes in cognition, learning, and memory. Rodent experimental studies suggest Δ9-tetrahydrocannabinol (THC) influences development of circuits underlying these processes, especially in the prefrontal cortex, which matures during adolescence.

Objective

We determined how 14 daily THC injections (5mg/kg) during adolescence persistently impacts medial prefrontal cortex (mPFC) dopamine-dependent cognition.

Methods

In adult Long Evans rats treated as adolescents with THC (AdoTHC), we quantify performance on two mPFC dopamine-dependent reward-based tasks-strategy set shifting and probabilistic discounting. We also determined how acute dopamine augmentation with amphetamine (0, 0.25, 0.5 mg/kg), or specific chemogenetic stimulation of ventral tegmental area (VTA) dopamine neurons and their projections to mPFC impacts probabilistic discounting.

Results

AdoTHC sex-dependently impacts acquisition of cue-guided instrumental reward seeking, but has minimal effects on set-shifting or probabilistic discounting in either sex. When we challenged dopamine circuits acutely with amphetamine during probabilistic discounting, we found reduced discounting of improbable reward options, with AdoTHC rats being more sensitive to these effects than controls. In contrast, neither acute chemogenetic stimulation of VTA dopamine neurons nor pathway-specific chemogenetic stimulation of their projection to mPFC impacted probabilistic discounting in control rats, although stimulation of this cortical dopamine projection slightly disrupted choices in AdoTHC rats.

Conclusions

These studies confirm a marked specificity in the cognitive processes impacted by AdoTHC exposure. They also suggest that some persistent AdoTHC effects may alter amphetamine-induced cognitive changes in a manner independent of VTA dopamine neurons or their projections to mPFC.

Pre- versus Post-synaptic Forms of LTP in Two Branches of the Same Hippocampal Afferent

There has been considerable controversy about pre- versus postsynaptic expression of memory-related long-term potentiation (LTP), with corresponding disputes about underlying mechanisms. We report here an instance in male mice, in which both types of potentiation are expressed but in separate branches of the same hippocampal afferent. Induction of LTP in the dentate gyrus (DG) branch of the lateral perforant path (LPP) reduces paired-pulse facilitation, is blocked by antagonism of cannabinoid receptor type 1, and is not affected by suppression of postsynaptic actin polymerization. These observations are consistent with presynaptic expression. The opposite pattern of results was obtained in the LPP branch that innervates the distal dendrites of CA3: LTP did not reduce paired-pulse facilitation, was unaffected by the cannabinoid receptor blocker, and required postsynaptic actin filament assembly. Differences in the two LPP termination sites were also noted for frequency facilitation of synaptic responses, an effect that was reproduced in a two-step simulation by small adjustments to vesicle release dynamics. These results indicate that different types of glutamatergic neurons impose different forms of filtering and synaptic plasticity on their afferents. They also suggest that inputs are routed to, and encoded by, different sites within the hippocampus depending upon the pattern of activity arriving over the parent axon.

Sex differences in the context dependency of episodic memory

Context contributes to multiple aspects of human episodic memory including segmentation and retrieval. The present studies tested if, in adult male and female mice, context influences the encoding of odors encountered in a single unsupervised sampling session of the type used for the routine acquisition of episodic memories. The three paradigms used differed in complexity (single vs. multiple odor cues) and period from sampling to testing. Results show that males consistently encode odors in a context-dependent manner: the mice discriminated novel from previously sampled cues when tested in the chamber of initial cue sampling but not in a distinct yet familiar chamber. This was independent of the interval between cue encounters or the latency from initial sampling to testing. In contrast, female mice acquired both single cues and the elements of multi-cue episodes, but recall of that information was dependent upon the surrounding context only when the cues were presented serially. These results extend the list of episodic memory features expressed by rodents and also introduce a striking and unexpected sex difference in context effects.

Metabotropic NMDA Receptor Signaling Contributes to Sex Differences in Synaptic Plasticity and Episodic Memory

Men generally outperform women on encoding spatial components of episodic memory whereas the reverse holds for semantic elements. Here we show that female mice outperform males on tests for non-spatial aspects of episodic memory ("what", "when"), suggesting that the human findings are influenced by neurobiological factors common to mammals. Analysis of hippocampal synaptic plasticity mechanisms and encoding revealed unprecedented, sex-specific contributions of non-classical metabotropic NMDA receptor (NMDAR) functions. While both sexes used non-ionic NMDAR signaling to trigger actin polymerization needed to consolidate long-term potentiation (LTP), NMDAR GluN2B subunit antagonism blocked these effects in males only and had the corresponding sex-specific effect on episodic memory. Conversely, blocking estrogen receptor alpha eliminated metabotropic stabilization of LTP and episodic memory in females only. The results show that sex differences in metabotropic signaling critical for enduring synaptic plasticity in hippocampus have significant consequences for encoding episodic memories.

Consequences of adolescent drug use

Substance use in adolescence is a known risk factor for the development of neuropsychiatric and substance use disorders in adulthood. This is in part due to the fact that critical aspects of brain development occur during adolescence, which can be altered by drug use. Despite concerted efforts to educate youth about the potential negative consequences of substance use, initiation remains common amongst adolescents world-wide. Additionally, though there has been substantial research on the topic, many questions remain about the predictors and the consequences of adolescent drug use. In the following review, we will highlight some of the most recent literature on the neurobiological and behavioral effects of adolescent drug use in rodents, non-human primates, and humans, with a specific focus on alcohol, cannabis, nicotine, and the interactions between these substances. Overall, consumption of these substances during adolescence can produce long-lasting changes across a variety of structures and networks which can have enduring effects on behavior, emotion, and cognition.

Cognitive Alterations in Addictive Disorders: A Translational Approach

The cognitive decline in people with substance use disorders is well known and can be found during both the dependence and drug abstinence phases. At the clinical level, cognitive decline impairs the response to addiction treatment and increases dropout rates. It can be irreversible, even after the end of drug abuse consumption. Improving our understanding of the molecular and cellular alterations associated with cognitive decline could be essential to developing specific therapeutic strategies for its treatment. Developing animal models to simulate drug abuse-induced learning and memory alterations is critical to continue exploring this clinical situation. The main aim of this review is to summarize the most recent evidence on cognitive impairment and the associated biological markers in patients addicted to some of the most consumed drugs of abuse and in animal models simulating this clinical situation. The available information suggests the need to develop more studies to further explore the molecular alterations associated with cognitive impairment, with the ultimate goal of developing new potential therapeutic strategies.

Women are Taking the Hit: Examining the Unique Consequences of Cannabis Use Across the Female Lifespan

Cannabis use has risen dramatically in recent years due to global decriminalization and a resurgence in the interest of potential therapeutic benefits. While emerging research is shaping our understanding of the benefits and harms of cannabis, there remains a paucity of data specifically focused on how cannabis affects the female population. The female experience of cannabis use is unique, both in the societal context and because of the biological ramifications. This is increasingly important given the rise in cannabis potency, as well as the implications this has for the prevalence of Cannabis Use Disorder (CUD). Therefore, this scoping review aims to discuss the prevalence of cannabis use and CUD in women throughout their lifespan and provide a balanced prospective on the positive and negative consequences of cannabis use. In doing so, this review will highlight the necessity for continued research that goes beyond sex differences.