Cannabis affects cognitive performance through the activation of the endocannabinoid system, and the molecular mechanisms involved in this process are poorly understood. Using the novel object-recognition memory test in mice, we found that the main psychoactive component of cannabis, delta9-tetrahydrocannabinol (THC), alters short-term object-recognition memory specifically involving protein kinase C (PKC)-dependent signaling. Indeed, the systemic or intra-hippocampal pre-treatment with the PKC inhibitors prevented the short-term, but not the long-term, memory impairment induced by THC. In contrast, systemic pre-treatment with mammalian target of rapamycin complex 1 inhibitors, known to block the amnesic-like effects of THC on long-term memory, did not modify such a short-term cognitive deficit. Immunoblot analysis revealed a transient increase in PKC signaling activity in the hippocampus after THC treatment. Thus, THC administration induced the phosphorylation of a specific Ser residue in the hydrophobic-motif at the C-terminal tail of several PKC isoforms. This significant immunoreactive band that paralleled cognitive performance did not match in size with the major PKC isoforms expressed in the hippocampus except for PKCθ. Moreover, THC transiently enhanced the phosphorylation of the postsynaptic calmodulin-binding protein neurogranin in a PKC dependent manner. These data demonstrate that THC alters short-term object-recognition memory through hippocampal PKC/neurogranin signaling.

The brain encodes, stores, and retrieves relevant information in the form of memories that are classified as short-term (STM) and long-term memories (LTM) depending on the interval between acquisition and retrieval. It is classically accepted that STM undergo a consolidation process to form LTM, but the molecular determinants involved are not well understood. Among the molecular components relevant for memory formation, we focused our attention on the protein kinase C (PKC) family of enzymes since they control key aspects of the synaptic plasticity and memory. Within the different PKC isoforms, PKC-gamma has been specifically associated with learning and memory since mice lacking this isoform (PKC-gamma KO mice) showed mild cognitive impairment and deficits in hippocampal synaptic plasticity. We now reveal that PKC-gamma KO mice present a severe impairment in hippocampal-dependent STM using different memory tests including the novel object-recognition and novel place-recognition, context fear conditioning and trace fear conditioning. In contrast, no differences between genotypes were observed in an amygdala-dependent test, the delay fear conditioning. Strikingly, all LTM tasks that could be assessed 24 h after acquisition were not perturbed in the KO mice.The analysis of c-Fos expression in several brain areas after trace fear conditioning acquisition showed a blunted response in the dentate gyrus of PKC-gamma KO mice compared to WT mice, but such differences between genotypes were absent when the amygdala or the prefrontal cortex were examined. In the hippocampus, PKC-gamma was found to translocate to the membrane after auditory trace, but not after delay fear conditioning. Together, these results indicate that PKC-gamma dysfunction affects specifically hippocampal-dependent STM performance and disclose PKC-gamma as a molecular player differentially involved in STM and LTM processes.

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Peripheral inputs to the brain continuously shape its function and adjust non-emotional memory, but the mechanisms involved are not fully understood. Cannabinoid type-1 receptors (CB1Rs), widely distributed in the organism, are well recognized players in memory performance and their systemic modulation significantly influence memory function. By assessing non-emotional memory in mice, we found a relevant role of peripheral CB1R in memory persistence. Indeed, peripherally restricted CB1R antagonist AM6545 showed a mnemonic effect occluded in adrenalectomized mice, after peripheral adrenergic blockade, or when vagus nerve was chemogenetically inhibited. Genetic CB1R deletion in dopamine β-hydroxylase-expressing cells enhanced memory persistence, supporting a role of peripheral CB1Rs modulating the adrenergic tone. Notably, while brain connectivity was slightly affected by peripheral CB1R inhibition, locus coeruleus activity and extracellular norepinephrine in the hippocampus, were increased, and intra-hippocampal β-adrenergic blockade prevented AM6545 mnemonic effects. Together, we disclose a novel peripheral mechanism relevant for non-emotional memory persistence modulation.

Williams–Beuren syndrome (WBS) is a rare genetic multisystemic disorder characterized by mild-to-moderate intellectual disability and hypersocial phenotype, while the most life-threatening features are cardiovascular abnormalities. Nowadays, there are no pharmacological treatments to directly ameliorate the main traits of WBS. The endocannabinoid system (ECS), given its relevance for both cognitive and cardiovascular function, could be a potential druggable target in this syndrome. We analyzed the components of the ECS in the complete deletion (CD) mouse model of WBS and assessed the impact of its pharmacological modulation in key phenotypes relevant for WBS. CD mice showed the characteristic hypersociable phenotype with no preference for social novelty and poor short-term object-recognition performance. Brain cannabinoid type-1 receptor (CB1R) in CD male mice showed alterations in density and coupling with no detectable change in main endocannabinoids. Endocannabinoid signaling modulation with subchronic (10 days) JZL184, a selective inhibitor of monoacylglycerol lipase, specifically normalized the social and cognitive phenotype of CD mice. Notably, JZL184 treatment improved cardiovascular function and restored gene expression patterns in cardiac tissue. These results reveal the modulation of the ECS as a promising novel therapeutic approach to improve key phenotypic alterations in WBS.

Alzheimer’s disease comprises amyloid-β and hyperphosphorylated Tau accumulation, imbalanced neuronal activity, aberrant oscillatory rhythms, and cognitive deficits. Non-Demented with Alzheimer’s disease Neuropathology (NDAN) defines a novel clinical entity with amyloid-β and Tau pathologies but preserved cognition. The mechanisms underlying such neuroprotection remain undetermined and animal models of NDAN are currently unavailable. We demonstrate that J20/VLW mice (accumulating amyloid-β and hyperphosphorylated Tau) exhibit preserved hippocampal rhythmic activity and cognition, as opposed to J20 and VLW animals, which show significant alterations. Furthermore, we show that the overexpression of mutant human Tau in coexistence with amyloid-β accumulation renders a particular hyperphosphorylated Tau signature in hippocampal interneurons. The GABAergic septohippocampal pathway, responsible for hippocampal rhythmic activity, is preserved in J20/VLW mice, in contrast to single mutants. Our data highlight J20/VLW mice as a suitable animal model in which to explore the mechanisms driving cognitive preservation in NDAN. Moreover, they suggest that a differential Tau phosphorylation pattern in hippocampal interneurons prevents the loss of GABAergic septohippocampal innervation and alterations in local field potentials, thereby avoiding cognitive deficits.

Alzheimer's disease comprises amyloid-β (Aβ) and hyperphosphorylated Tau (P-Tau) accumulation, imbalanced neuronal activity, aberrant oscillatory rhythms, and cognitive deficits. Non-Demented with Alzheimer's disease Neuropathology (NDAN) defines a novel clinical entity with Aβ and Tau pathologies, but preserved cognition. The mechanisms underlying such neuroprotection remain undetermined and animal models are currently unavailable for NDAN. We show that J20/VLW mice, accumulating Aβ and P-Tau, exhibit preserved hippocampal rhythmic activity and cognition, altered in J20 and VLW animals. Furthermore, we show that coexistence with Aβ renders a particular P-Tau signature in hippocampal interneurons. The GABAergic septohippocampal pathway, responsible for hippocampal rhythmic activity, is preserved in J20/VLW mice, in contrast to single mutants. Our data highlight J20/VLW mice as a suitable animal model to understand the mechanisms driving cognitive preservation in NDAN and suggest that a differential P-Tau pattern in hippocampal interneurons prevents GABAergic septohippocampal innervation loss and alterations in local field potentials, avoiding cognitive deficits.

Cannabis is the most widely used illicit drug worldwide. Its principal psychoactive component, ∆9-tetrahydrocannabinol (THC), acts as a partial agonist of the main cannabinoid receptor in the brain, the cannabinoid type-1 receptor (CB1R), being the main responsible for the central effects of THC including memory impairment. CB1Rs may form heterodimers with the serotonin 5-HT2A receptor (5-HT2AR) which were found responsible for the memory impairment produced by acute high dose of THC in mice. In this study we investigated whether a repeated low dose of THC (1 mg/kg), with no acute consequence on memory performance, could eventually have deleterious cognitive effects. We found that such a low dose of THC impairs novel object-recognition memory and fear conditioning memory after repeated treatment (7 days). This deficit was also detected 24 h after the last THC administration. At that time, a general enhancement of c-Fos expression was observed in several brain regions of THC-exposed animals. In addition, THC-treated mice showed a decreased spine density at CA1 pyramidal neurons and reduced long-term potentiation at Schaffer collateral-CA1 synapses. Interestingly, an up-regulation in the expression of CB1R/5-HT2AR heterodimers was observed in the hippocampus of THC-exposed mice and a pre-treatment with the 5-HT2AR antagonist MDL 100,907 (0.01 mg/kg) prevented enhanced heterodimerization and the THC-associated memory impairment. Together, these results reveal the significance of serotonergic signalling through 5-HT2ARs in the memory-impairing effects of repeated low doses of THC.