Effects of PSA Removal from NCAM on the Critical Period Plasticity Triggered by the Antidepressant Fluoxetine in the Visual Cortex

Sertraline for Functional Recovery After Acute Ischemic Stroke: A Prospective Observational Study

Background: Neuroprotective and neurorestorative effects have been postulated for selective serotonin-reuptake inhibitors (SSRI). We hypothesized that sertraline, which is characterized by less severe adverse effects and more stable pharmacokinetics than classic SSRI, is associated with improved functional recovery in acute ischemic stroke patients with motor deficits.

Methods: Prospective observational study of consecutive acute ischemic stroke patients who received sertraline for clinically suspected post-stroke depression (PSD) or at high risk for PSD. Eligibility comprised acute motor deficit caused by ischemic stroke (≥2 points on NIHSS motor items) and functional independence pre-stroke (mRS ≤1). Decision to initiate treatment with SSRI during hospital stay was at the discretion of the treating stroke physician. Patients not receiving sertraline served as control group. Favorable functional recovery defined as mRS ≤2 was prospectively assessed at 3 months. Multivariable logistic regression analysis was used to explore the effects of sertraline on 3-months functional recovery. Secondary outcomes were frequency of any and incident PSD (defined by BDI ≥10) at 3 months.

Results: During the study period (03/2017–12/2018), 114 patients were assigned to sertraline (n = 72, 62.6%) or control group (n = 42, 37.4%). At study entry, patients in sertraline group were more severely neurologically affected than patients in the control group (NIHSS: 8 [IQR, 5–11] vs. 5 [IQR, 4–7]; p = 0.002). Also, motor NIHSS scores were more pronounced in sertraline than in control group (4 [IQR 2–7] vs. 2 [IQR 2–4], p = 0.001). After adjusting for age and baseline NIHSS, multivariable regression analysis revealed a significant association between sertraline intake and favorable functional outcome at 3 months (OR 3.10, 95% CI 1.02–9.41; p = 0.045). There was no difference between both groups regarding the frequency of any depression at 3 months (26/53 [49.1%] vs. 14/28 [50.0%] patients, p = 0.643, BDI ≥10). However, fewer incident depressions were observed in sertraline group patients compared to patients in control group (0/53 [0%] vs. 5/28 [17.9%] patients, p = 0.004).

Conclusions: In this non-randomized comparison, early treatment with sertraline tended to favor functional recovery in patients with acute ischemic stroke. While exploratory in nature, this hypothesis needs further investigation in a clinical trial.

PSA Depletion Induces the Differentiation of Immature Neurons in the Piriform Cortex of Adult Mice

Immature neurons are maintained in cortical regions of the adult mammalian brain. In rodents, many of these immature neurons can be identified in the piriform cortex based on their high expression of early neuronal markers, such as doublecortin (DCX) and the polysialylated form of the neural cell adhesion molecule (PSA-NCAM). This molecule plays critical roles in different neurodevelopmental events. Taking advantage of a DCX-CreERT2/Flox-EGFP reporter mice, we investigated the impact of targeted PSA enzymatic depletion in the piriform cortex on the fate of immature neurons. We report here that the removal of PSA accelerated the final development of immature neurons. This was revealed by a higher frequency of NeuN expression, an increase in the number of cells carrying an axon initial segment (AIS), and an increase in the number of dendrites and dendritic spines on the immature neurons. Taken together, our results demonstrated the crucial role of the PSA moiety in the protracted development of immature neurons residing outside of the neurogenic niches. More studies will be required to understand the intrinsic and extrinsic factors affecting PSA-NCAM expression to understand how the brain regulates the incorporation of these immature neurons to the established neuronal circuits of the adult brain.

Selective serotonin reuptake inhibitors for functional recovery after stroke: similarities with the critical period and the role of experience-dependent plasticity

There has been a growing interest in the potential for plasticity-inducing pharmacological interventions to enhance post-stroke recovery. One group of drugs that continues to garner a great deal of attention in this regard is a class of antidepressants called the selective serotonin reuptake inhibitors. Here we propose a model for the mechanism by which these drugs may enhance plasticity after ischemic brain injury. First, we review the research in animal models demonstrating how selective serotonin reuptake inhibitors reopen the critical period for ocular dominance plasticity in adulthood. We then compare this period of heightened plasticity to the cellular and biochemical milieu of perilesional tissue after an ischemic event in the adult brain. We argue that selective serotonin reuptake inhibitors administered acutely after an ischemic stroke alter excitatory-inhibitory balance in perilesional tissue and reinstate a type of plasticity reminiscent of the critical period in development. Finally, we discuss opportunities for future research in this area in both the preclinical and clinical realms.

Potential mechanisms for phencyclidine/ketamine-induced brain structural alterations and behavioral consequences

Evidence of structural abnormalities in the nervous system of recreational drug [e.g., phencyclidine (PCP) or ketamine] users and/or preclinical animal research models suggests interference with the activity of multiple neurotransmitters, particularly glutamate neurotransmission. The damage to the central nervous system (CNS) may include neuronal loss, synaptic changes, disturbed neural network formation and reduced projections to subcortical fields. Notably, the reduced projections may considerably compromise the establishment of the subcortical areas, such as the nucleus accumbens located in the basal forebrain. With its abundant dopaminergic innervation, the nucleus accumbens is believed to be directly associated with addictive behaviors and mental disorders. This review seeks to delineate the relationship between PCP/ketamine-induced loss of cortical neurons and the reduced level of polysialic acid neural cell adhesion molecule (PSA-NCAM) in the striatum, and the likely changes in striatal synaptogenesis during development. The basic mechanism of how PSA-NCAM cell surface expression may be regulated will also be discussed, as well as the hypothesis that PSA-NCAM activity is critical to the regulation of synaptic protein expression. Overall, the present review will address the general hypothesis that damage/interruption of cortico-striatal communication and subcortical synaptogenesis could underlie the erratic/sensitization or addictive states produced by chronic or prolonged PCP/ketamine usage.

Emerging Roles of Synapse Organizers in the Regulation of Critical Periods

Experience remodels cortical connectivity during developmental windows called critical periods. Experience-dependent regulation of synaptic strength during these periods establishes circuit functions that are stabilized as critical period plasticity wanes. These processes have been extensively studied in the developing visual cortex, where critical period opening and closure are orchestrated by the assembly, maturation, and strengthening of distinct synapse types. The synaptic specificity of these processes points towards the involvement of distinct molecular pathways. Attractive candidates are pre- and postsynaptic transmembrane proteins that form adhesive complexes across the synaptic cleft. These synapse-organizing proteins control synapse development and maintenance and modulate structural and functional properties of synapses. Recent evidence suggests that they have pivotal roles in the onset and closure of the critical period for vision. In this review, we describe roles of synapse-organizing adhesion molecules in the regulation of visual critical period plasticity and we discuss the potential they offer to restore circuit functions in amblyopia and other neurodevelopmental disorders.

Synaptic and circuit development of the primary sensory cortex

Animals, including humans, optimize their primary sensory cortex through the use of input signals, which allow them to adapt to the external environment and survive. The time window at the beginning of life in which external input signals are connected sensitively and strongly to neural circuit optimization is called the critical period. The critical period has attracted the attention of many neuroscientists due to the rapid activity-/experience-dependent circuit development that occurs, which is clearly differentiated from other developmental time periods and brain areas. This process involves various types of GABAergic inhibitory neurons, the extracellular matrix, neuromodulators, transcription factors, and neurodevelopmental factors. In this review, I discuss recent progress regarding the biological nature of the critical period that contribute to a better understanding of brain development.