Brain-Generated 17ß-Estradiol Modulates Long-Term Synaptic Plasticity in the Primary Auditory Cortex of Adult Male Rats.

Neuron-derived 17ß-estradiol (E2) alters synaptic transmission and plasticity in brain regions with endocrine and non-endocrine functions. Investigations into a modulatory role of E2 in synaptic activity and plasticity have mainly focused on the rodent hippocampal formation. In songbirds, E2 is synthesized by auditory forebrain neurons and promotes auditory signal processing and memory for salient acoustic stimuli; however, the modulatory effects of E2 on memory-related synaptic plasticity mechanisms have not been directly examined in the auditory forebrain. We investigated the effects of bidirectional E2 manipulations on synaptic transmission and long-term potentiation (LTP) in the rat primary auditory cortex (A1). Immunohistochemistry revealed widespread neuronal expression of the E2 biosynthetic enzyme aromatase in multiple regions of the rat sensory and association neocortex, including A1. In A1, E2 application reduced the threshold for in vivo LTP induction at layer IV synapses, whereas pharmacological suppression of E2 production by aromatase inhibition abolished LTP induction at layer II/III synapses. In acute A1 slices, glutamate and γ-aminobutyric acid (GABA) receptor-mediated currents were sensitive to E2 manipulations in a layer-specific manner. These findings demonstrate that locally synthesized E2 modulates synaptic transmission and plasticity in A1 and suggest potential mechanisms by which E2 contributes to auditory signal processing and memory.

Developmental age and biological sex influence muscarinic receptor function and neuron morphology within layer VI of the medial prefrontal cortex.

Acetylcholine (ACh) neurotransmission within the medial prefrontal cortex (mPFC) plays an important modulatory role to support mPFC-dependent cognitive functions. This role is mediated by ACh activation of its nicotinic (nAChR) and muscarinic (mAChR) classes of receptors, which are both present on mPFC layer VI pyramidal neurons. While the expression and function of nAChRs have been characterized thoroughly for rodent mPFC layer VI neurons during postnatal development, mAChRs have not been characterized in detail. We employed whole-cell electrophysiology with biocytin filling to demonstrate that mAChR function is greater during the juvenile period of development than in adulthood for both sexes. Pharmacological experiments suggest that each of the M1, M2, and M3 mAChR subtypes contributes to ACh responses in these neurons in a sex-dependent manner. Analysis of dendrite morphology identified effects of age more often in males, as the amount of dendrite matter was greatest during the juvenile period. Interestingly, a number of positive correlations were identified between the magnitude of ACh/mAChR responses and dendrite morphology in juvenile mice that were not present in adulthood. To our knowledge, this work describes the first detailed characterization of mAChR function and its correlation with neuron morphology within layer VI of the mPFC.

Axonal pathology in hPSC-based models of Parkinson's disease results from loss of Nrf2 transcriptional activity at the Map1b gene locus.

While mutations in the SNCA gene (α-synuclein [α-syn]) are causal in rare familial forms of Parkinson's disease (PD), the prevalence of α-syn aggregates in the cortices of sporadic disease cases emphasizes the need to understand the link between α-syn accumulation and disease pathogenesis. By employing a combination of human pluripotent stem cells (hPSCs) that harbor the SNCA-A53T mutation contrasted against isogenic controls, we evaluated the consequences of α-syn accumulation in human A9-type dopaminergic (DA) neurons (hNs). We show that the early accumulation of α-syn in SNCA-A53T hNs results in changes in gene expression consistent with the expression profile of the substantia nigra (SN) from PD patients, analyzed post mortem. Differentially expressed genes from both PD patient SN and SNCA-A53T hNs were associated with regulatory motifs transcriptionally activated by the antioxidant response pathway, particularly Nrf2 gene targets. Differentially expressed gene targets were also enriched for gene ontologies related to microtubule binding processes. We thus assessed the relationship between Nrf2-mediated gene expression and neuritic pathology in SNCA-A53T hNs. We show that SNCA-mutant hNs have deficits in neuritic length and complexity relative to isogenic controls as well as contorted axons with Tau-positive varicosities. Furthermore, we show that mutant α-syn fails to complex with protein kinase C (PKC), which, in turn, results in impaired activation of Nrf2. These neuritic defects result from impaired Nrf2 activity on antioxidant response elements (AREs) localized to a microtubule-associated protein (Map1b) gene enhancer and are rescued by forced expression of Map1b as well as by both Nrf2 overexpression and pharmaceutical activation in PD neurons.

Similar nicotinic excitability responses across the developing hippocampal formation are regulated by small-conductance calcium-activated potassium channels.

The hippocampal formation forms a cognitive circuit that is critical for learning and memory. Cholinergic input to nicotinic acetylcholine receptors plays an important role in the normal development of principal neurons within the hippocampal formation. However, the ability of nicotinic receptors to stimulate principal neurons across all regions of the developing hippocampal formation has not been determined. We show in this study that heteromeric nicotinic receptors mediate direct inward current and depolarization responses in principal neurons across the hippocampal formation of the young postnatal mouse. These responses were found in principal neurons of the CA1, CA3, dentate gyrus, subiculum, and entorhinal cortex layer VI, and they varied in magnitude across regions with the greatest responses occurring in the subiculum and entorhinal cortex. Despite this regional variation in the magnitude of passive responses, heteromeric nicotinic receptor stimulation increased the excitability of active principal neurons by a similar amount in all regions. Pharmacological experiments found this similar excitability response to be regulated by small-conductance calcium-activated potassium (SK) channels, which exhibited regional differences in their influence on neuron activity that offset the observed regional differences in passive nicotinic responses. These findings demonstrate that SK channels play a role to coordinate the magnitude of heteromeric nicotinic excitability responses across the hippocampal formation at a time when nicotinic signaling drives the development of this cognitive brain region. This coordinated input may contribute to the normal development, synchrony, and maturation of the hippocampal formation learning and memory network. NEW & NOTEWORTHY This study demonstrates that small-conductance calcium-activated potassium channels regulate similar-magnitude excitability responses to heteromeric nicotinic acetylcholine receptor stimulation in active principal neurons across multiple regions of the developing mouse hippocampal formation. Given the importance of nicotinic neurotransmission for the development of principal neurons within the hippocampal formation, this coordinated excitability response is positioned to influence the normal development, synchrony, and maturation of the hippocampal formation learning and memory network.

Rapid increases in immature synapses parallel estrogen-induced hippocampal learning enhancements.

Dramatic increases in hippocampal spine synapse density are known to occur within minutes of estrogen exposure. Until now, it has been assumed that enhanced spinogenesis increased excitatory input received by the CA1 pyramidal neurons, but how this facilitated learning and memory was unclear. Delivery of 17ß-estradiol or an estrogen receptor (ER)-α (but not ER-ß) agonist into the dorsal hippocampus rapidly improved general discrimination learning in female mice. The same treatments increased CA1 dendritic spines in hippocampal sections over a time course consistent with the learning acquisition phase. Surprisingly, estrogen-activated spinogenesis was associated with a decrease in CA1 hippocampal excitatory input, rapidly and transiently reducing CA1 AMPA activity via a mechanism likely reflecting AMPA receptor internalization and creation of silent or immature synapses. We propose that estrogens promote hippocampally mediated learning via a mechanism resembling some of the broad features of normal development, an initial overproduction of functionally immature connections being subsequently "pruned" by experience.

A Novel Multisensory Integration Task Reveals Robust Deficits in Rodent Models of Schizophrenia: Converging Evidence for Remediation via Nicotinic Receptor Stimulation of Inhibitory Transmission in the Prefrontal Cortex.

Atypical multisensory integration is an understudied cognitive symptom in schizophrenia. Procedures to evaluate multisensory integration in rodent models are lacking. We developed a novel multisensory object oddity (MSO) task to assess multisensory integration in ketamine-treated rats, a well established model of schizophrenia. Ketamine-treated rats displayed a selective MSO task impairment with tactile-visual and olfactory-visual sensory combinations, whereas basic unisensory perception was unaffected. Orbitofrontal cortex (OFC) administration of nicotine or ABT-418, an α4ß2 nicotinic acetylcholine receptor (nAChR) agonist, normalized MSO task performance in ketamine-treated rats and this effect was blocked by GABAA receptor antagonism. GABAergic currents were also decreased in OFC of ketamine-treated rats and were normalized by activation of α4ß2 nAChRs. Furthermore, parvalbumin (PV) immunoreactivity was decreased in the OFC of ketamine-treated rats. Accordingly, silencing of PV interneurons in OFC of PV-Cre mice using DREADDs (Designer Receptors Exclusively Activated by Designer Drugs) selectively impaired MSO task performance and this was reversed by ABT-418. Likewise, clozapine-N-oxide-induced inhibition of PV interneurons in brain slices was reversed by activation of α4ß2 nAChRs. These findings strongly imply a role for prefrontal GABAergic transmission in the integration of multisensory object features, a cognitive process with relevance to schizophrenia. Accordingly, nAChR agonism, which improves various facets of cognition in schizophrenia, reversed the severe MSO task impairment in this study and appears to do so via a GABAergic mechanism. Interactions between GABAergic and nAChR receptor systems warrant further investigation for potential therapeutic applications. The novel behavioral procedure introduced in the current study is acutely sensitive to schizophrenia-relevant cognitive impairment and should prove highly valuable for such research. SIGNIFICANCE STATEMENT: Adaptive behaviors are driven by integration of information from different sensory modalities. Multisensory integration is disrupted in patients with schizophrenia, but little is known about the neural basis of this cognitive symptom. Development and validation of multisensory integration tasks for animal models is essential given the strong link between functional outcome and cognitive impairment in schizophrenia. We present a novel multisensory object oddity procedure that detects selective multisensory integration deficits in a rat model of schizophrenia using various combinations of sensory modalities. Moreover, converging data are consistent with a nicotinic-GABAergic mechanism of multisensory integration in the prefrontal cortex, results with strong clinical relevance to the study of cognitive impairment and treatment in schizophrenia.

Postsynaptic nicotinic acetylcholine receptors facilitate excitation of developing CA1 pyramidal neurons.

The hippocampus plays a key role in learning and memory. The normal development and mature function of hippocampal networks supporting these cognitive functions depends on afferent cholinergic neurotransmission mediated by nicotinic acetylcholine receptors. Whereas it is well-established that nicotinic receptors are present on GABAergic interneurons and on glutamatergic presynaptic terminals within the hippocampus, the ability of these receptors to mediate postsynaptic signaling in pyramidal neurons is not well understood. We use whole cell electrophysiology to show that heteromeric nicotinic receptors mediate direct inward currents, depolarization from rest and enhanced excitability in hippocampus CA1 pyramidal neurons of male mice. Measurements made throughout postnatal development provide a thorough developmental profile for these heteromeric nicotinic responses, which are greatest during the first 2 wk of postnatal life and decrease to low adult levels shortly thereafter. Pharmacological experiments show that responses are blocked by a competitive antagonist of α4ß2* nicotinic receptors and augmented by a positive allosteric modulator of α5 subunit-containing receptors, which is consistent with expression studies suggesting the presence of α4ß2 and α4ß2α5 nicotinic receptors within the developing CA1 pyramidal cell layer. These findings demonstrate that functional heteromeric nicotinic receptors are present on CA1 pyramidal neurons during a period of major hippocampal development, placing these receptors in a prime position to play an important role in the establishment of hippocampal cognitive networks.

Nicotinic acetylcholine receptors in attention circuitry: the role of layer VI neurons of prefrontal cortex.

Cholinergic modulation of prefrontal cortex is essential for attention. In essence, it focuses the mind on relevant, transient stimuli in support of goal-directed behavior. The excitation of prefrontal layer VI neurons through nicotinic acetylcholine receptors optimizes local and top-down control of attention. Layer VI of prefrontal cortex is the origin of a dense feedback projection to the thalamus and is one of only a handful of brain regions that express the α5 nicotinic receptor subunit, encoded by the gene chrna5. This accessory nicotinic receptor subunit alters the properties of high-affinity nicotinic receptors in layer VI pyramidal neurons in both development and adulthood. Studies investigating the consequences of genetic deletion of α5, as well as other disruptions to nicotinic receptors, find attention deficits together with altered cholinergic excitation of layer VI neurons and aberrant neuronal morphology. Nicotinic receptors in prefrontal layer VI neurons play an essential role in focusing attention under challenging circumstances. In this regard, they do not act in isolation, but rather in concert with cholinergic receptors in other parts of prefrontal circuitry. This review urges an intensification of focus on the cellular mechanisms and plasticity of prefrontal attention circuitry. Disruptions in attention are one of the greatest contributing factors to disease burden in psychiatric and neurological disorders, and enhancing attention may require different approaches in the normal and disordered prefrontal cortex.

Cholinergic excitation in mouse primary vs. associative cortex: region-specific magnitude and receptor balance.

Cholinergic stimulation of the cerebral cortex is essential for tasks requiring attention; however, there is still some debate over which cortical regions are required for such tasks. There is extensive cholinergic innervation of both primary and associative cortices, and transient release of acetylcholine (ACh) is detected in deep layers of the relevant primary and/or associative cortex, depending on the nature of the attention task. Here, we investigated the electrophysiological effects of ACh in layer VI, the deepest layer, of the primary somatosensory cortex, the primary motor cortex, and the associative medial prefrontal cortex. Layer VI pyramidal neurons are a major source of top-down modulation of attention, and we found that the strength and homogeneity of their direct cholinergic excitation was region-specific. On average, neurons in the primary cortical regions showed weaker responses to ACh, mediated by a balance of contributions from both nicotinic and muscarinic ACh receptors. Conversely, neurons in the associative medial prefrontal cortex showed significantly stronger excitation by ACh, mediated predominantly by nicotinic receptors. The greatest diversity of responses to ACh was found in the primary somatosensory cortex, with only a subset of neurons showing nicotinic excitation. In a mouse model with attention deficits only under demanding conditions, cholinergic excitation was preserved in primary cortical regions but not in the associative medial prefrontal cortex. These findings demonstrate that the effect of ACh is not uniform throughout the cortex, and suggest that its ability to enhance attention performance may involve different cellular mechanisms across cortical regions.

The native serotonin 5-HT(5A) receptor: electrophysiological characterization in rodent cortex and 5-HT(1A)-mediated compensatory plasticity in the knock-out mouse.

The 5-HT(5A) receptor is the least understood serotonin (5-HT) receptor. Here, we electrophysiologically identify and characterize a native 5-HT(5A) receptor current in acute ex vivo brain slices of adult rodent prefrontal cortex. In the presence of antagonists for the previously characterized 5-HT(1A) and 5-HT2 receptors, a proportion of layer V pyramidal neurons continue to show 5-HT-elicited outward currents in both rats and mice. These 5-HT currents are suppressed by the selective 5-HT(5A) antagonist, SB-699551, and are not observed in 5-HT(5A) receptor knock-out mice. Further characterization reveals that the 5-HT(5A) current is activated by submicromolar concentrations of 5-HT, is inwardly rectifying with a reversal potential near the equilibrium potential for K+ ions, and is suppressed by blockers of Kir3 channels. Finally, we observe that genetic deletion of the inhibitory 5-HT(5A) receptor results in an unexpected, large increase in the inhibitory 5-HT(1A) receptor currents. The presence of functional prefrontal 5-HT(5A) receptors in normal rodents along with compensatory plasticity in 5-HT(5A) receptor knock-out mice testifies to the significance of this receptor in the healthy prefrontal cortex.

Cortical dopamine D5 receptors regulate neuronal circuit oscillatory activity and memory in rats.

INTRODUCTION: The dopamine D5 receptor (D5R) shows high expression in cortical regions, yet the role of the receptor in learning and memory remains poorly understood. This study evaluated the impact of prefrontal cortical (PFC) D5R knockdown in rats on learning and memory and assessed the role of the D5R in the regulation of neuronal oscillatory activity and glycogen synthase kinase-3 (GSK-3ß), processes integral to cognitive function. MATERIALS AND METHODS: Using an adeno-associated viral (AAV) vector, male rats were infused with shRNA to the D5R bilaterally into the PFC. Local field potential recordings were taken from freely moving animals and spectral power and coherence were evaluated in, and between, the PFC, orbitofrontal cortex (OFC), hippocampus (HIP), and thalamus. Animals were then assessed in object recognition, object location, and object in place tasks. The activity of PFC GSK-3ß, a downstream effector of the D5R, was evaluated. RESULTS: AAV-mediated knockdown of the D5R in the PFC induced learning and memory deficits. These changes were accompanied by elevations in PFC, OFC, and HIP theta spectral power and PFC-OFC coherence, reduced PFC-thalamus gamma coherence, and increased PFC GSK-3ß activity. CONCLUSION: This work demonstrates a role for PFC D5Rs in the regulation of neuronal oscillatory activity and learning and memory. As elevated GSK-3ß activity has been implicated in numerous disorders of cognitive dysfunction, this work also highlights the potential of the D5R as a novel therapeutic target via suppression of GSK-3ß.

Plasticity of prefrontal attention circuitry: upregulated muscarinic excitability in response to decreased nicotinic signaling following deletion of α5 or ß2 subunits.

Attention depends on cholinergic stimulation of nicotinic and muscarinic acetylcholine receptors in the medial prefrontal cortex. Pyramidal neurons in layer VI of this region express cholinergic receptors of both families and play an important role in attention through their feedback projections to the thalamus. Here, we investigate how nicotinic and muscarinic cholinergic receptors affect the excitability of these neurons using whole-cell recordings in acute brain slices of prefrontal cortex. Since attention deficits have been documented in both rodents and humans having genetic abnormalities in nicotinic receptors, we focus in particular on how the cholinergic excitation of layer VI neurons is altered by genetic deletion of either of two key nicotinic receptor subunits, the accessory α5 subunit or the ligand-binding ß2 subunit. We find that the cholinergic excitation of layer VI neurons is dominated by nicotinic receptors in wild-type mice and that the reduction or loss of this nicotinic stimulation is accompanied by a surprising degree of plasticity in excitatory muscarinic receptors. These findings suggest that disrupting nicotinic receptors fundamentally alters the mechanisms and timing of excitation in prefrontal attentional circuitry.

The nicotinic acetylcholine receptor alpha5 subunit plays a key role in attention circuitry and accuracy.

Stimulation of the prefrontal cortex by acetylcholine is critical for attention; however, the cellular mechanisms underlying its influence on attention pathways within the brain are not well understood. Pyramidal neurons in layer VI of the prefrontal cortex are believed to play an important role in this process because they are excited by acetylcholine and provide a major source of feedback projections to the thalamus. Here, we show using whole-cell electrophysiology that the relatively rare alpha5 subunit of the nicotinic acetylcholine receptor powerfully enhances nicotinic currents in layer VI pyramidal neurons in prefrontal cortical brain slices from adult mice. In addition, behavioral experiments using the five-choice serial reaction time test show that the presence of the nicotinic receptor alpha5 subunit also increases the accuracy of adult mice on this visual attention task under highly demanding conditions. Together, these findings demonstrate a novel and important role for the nicotinic receptor alpha5 subunit in adult brain circuitry required for attentional performance.

The Dendrite Arbor of Purkinje Cells Is Altered Following to Tail Regeneration in the Leopard Gecko.

Purkinje cells of the cerebellum have a complex arborized arrangement of dendrites and are among the most distinctive cell types of the nervous system. Although the neuromorphology of Purkinje cells has been well described for some mammals and teleost fish, for most vertebrates less is known. Here we used a modified Golgi-Cox method to investigate the neuromorphology of Purkinje cells from the lizard Eublepharis macularius, the leopard gecko. Using Sholl and Branch Structure Analyses, we sought to investigate whether the neuromorphology of gecko Purkinje cells was altered in response to tail loss and regeneration. Tail loss is an evolved mechanism commonly used by geckos to escape predation. Loss of the tail represents a significant and sudden change in body length and mass, which is only partially recovered as the tail is regenerated. We predicted that tail loss and regeneration would induce a quantifiable change in Purkinje cell dendrite arborization. Post hoc comparisons of Sholl analyses data showed that geckos with regenerated tails have significant changes in dendrite diameter and the number of dendrite intersections in regions corresponding to the position of parallel fiber synapses. We propose that the neuromorphological alterations observed in gecko Purkinje cells represent a compensatory response to tail regrowth, and perhaps a role in motor learning.

Preclinical methodological approaches investigating of the effects of alcohol on perinatal and adolescent neurodevelopment.

Despite much evidence of its economic and social costs, alcohol use continues to increase. Much remains to be known as to the effects of alcohol on neurodevelopment across the lifespan and in both sexes. We provide a comprehensive overview of the methodological approaches to ethanol administration when using animal models (primarily rodent models) and their translational relevance, as well as some of the advantages and disadvantages of each approach. Special consideration is given to early developmental periods (prenatal through adolescence), as well as to the types of research questions that are best addressed by specific methodologies. The zebrafish is used increasingly in alcohol research, and how to use this model effectively as a preclinical model is reviewed as well.

Transglutaminase 2 protects against ischemic insult, interacts with HIF1beta, and attenuates HIF1 signaling.

Transglutaminase 2 (TG2) is a multifunctional enzyme that has been implicated in the pathogenesis of neurodegenerative diseases, ischemia, and stroke. The mechanism by which TG2 modulates disease progression have not been elucidated. In this study we investigate the role of TG2 in the cellular response to ischemia and hypoxia. TG2 is up-regulated in neurons exposed to oxygen and glucose deprivation (OGD), and increased TG2 expression protects neurons against OGD-induced cell death independent of its transamidating activity. We identified hypoxia inducible factor 1beta (HIF1beta) as a TG2 binding partner. HIF1beta and HIF1alpha together form the heterodimeric transcription factor hypoxia inducible factor 1 (HIF1). TG2 and the transaminase-inactive mutant C277S-TG2 inhibited a HIF-dependent transcription reporter assay under hypoxic conditions without affecting nuclear protein levels for HIF1alpha or HIF1beta, their ability to form the HIF1 heterodimeric transcription factor, or HIF1 binding to its DNA response element. Interestingly, TG2 attenuates the up-regulation of the HIF-dependent proapoptotic gene Bnip3 in response to OGD but had no effect on the expression of VEGF, which has been linked to prosurvival processes. This study demonstrates for the first time that TG2 protects against OGD, interacts with HIF1beta, and attenuates the HIF1 hypoxic response pathway. These results indicate that TG2 may play an important role in protecting against the delayed neuronal cell death in ischemia and stroke.

Sex differences in the nicotinic excitation of principal neurons within the developing hippocampal formation.

The hippocampal formation (HF) plays an important role to facilitate higher order cognitive functions. Cholinergic activation of heteromeric nicotinic acetylcholine receptors (nAChRs) within the HF is critical for the normal development of principal neurons within this brain region. However, previous research investigating the expression and function of heteromeric nAChRs in principal neurons of the HF is limited to males or does not differentiate between the sexes. We used whole-cell electrophysiology to show that principal neurons in the CA1 region of the female mouse HF are excited by heteromeric nAChRs throughout postnatal development, with the greatest response occurring during the first two weeks of postnatal life. Excitability responses to heteromeric nAChR stimulation were also found in principal neurons in the CA3, dentate gyrus, subiculum, and entorhinal cortex layer VI (ECVI) of young postnatal female HF. A direct comparison between male and female mice found that principal neurons in ECVI display greater heteromeric nicotinic passive and active excitability responses in females. This sex difference is likely influenced by the generally more excitable nature of ECVI neurons from female mice, which display a higher resting membrane potential, greater input resistance, and smaller afterhyperpolarization potential of medium duration (mAHP). These findings demonstrate that heteromeric nicotinic excitation of ECVI neurons differs between male and female mice during a period of major circuitry development within the HF, which may have mechanistic implications for known sex differences in the development and function of this cognitive brain region.

Adolescent social instability stress alters markers of synaptic plasticity and dendritic structure in the medial amygdala and lateral septum in male rats.

Much evidence indicates that experiences in adolescence can alter the development of social behaviour. We previously demonstrated that male rats exposed to social instability stress in adolescence (SS; 1 h isolation and return to an unfamiliar cagemate daily from postnatal day [PND] 30-45) had reduced social interaction, impaired social recognition, reduced sexual performance, and increased aggression in competition for food reward compared with non-stressed control (CTL) rats. Here, we investigated whether SS affects stellate neuron morphology using the Golgi-Cox method and several markers of synaptic plasticity using western blotting in the medial amygdala (MeA) and lateral septum (LS), sites involved in social behaviour. On PND 46, 24 h after the last stress exposure, SS rats had increased dendritic arborisation, a greater number of dendrite terminals, and a higher average dendrite branch order in the anterodorsal MeA compared with CTL rats. SS rats had reduced dendritic arborization and a reduced total length of dendrite matter in the anteroventral MeA and a reduced number of dendrite terminals in the posterodorsal MeA compared with CTL rats. Moreover, SS rats had a reduced number of dendritic spines in the dorsal LS compared with CTL rats. SS rats had less synaptophysin in the MeA and more CaMKII in the LS than did CTL rats, and did not differ in spinophilin, PSD95, or glucocorticoid receptor protein expression in the MeA and LS. We discuss how changes in neural structure and in markers of synaptic plasticity the MeA and LS of adolescent SS rats compared with CTL rats may underlie their differences in social behaviour.

The Clock Mechanism Influences Neurobiology and Adaptations to Heart Failure in Clock∆19/∆19 Mice With Implications for Circadian Medicine.

In this study we investigated the role of the circadian mechanism on cognition-relevant brain regions and neurobiological impairments associated with heart failure (HF), using murine models. We found that the circadian mechanism is an important regulator of healthy cognitive system neurobiology. Normal Clock∆19/∆19 mice had neurons with smaller apical dendrite trees in the medial prefrontal cortex (mPFC), and hippocampus, showed impaired visual-spatial memory, and exhibited lower cerebrovascular myogenic tone, versus wild types (WT). We then used the left anterior descending coronary artery ligation model to investigate adaptations in response to HF. Intriguingly, adaptations to neuron morphology, memory, and cerebrovascular tone occurred in differing magnitude and direction between Clock∆19/∆19 and WT mice, ultimately converging in HF. To investigate this dichotomous response, we performed microarrays and found genes crucial for growth and stress pathways that were altered in Clock∆19/∆19 mPFC and hippocampus. Thus these data demonstrate for the first time that (i) the circadian mechanism plays a role in neuron morphology and function; (ii) there are changes in neuron morphology and function in HF; (iii) CLOCK influences neurobiological gene adaptations to HF at a cellular level. These findings have clinical relevance as patients with HF often present with concurrent neurocognitive impairments. There is no cure for HF, and new understanding is needed to reduce morbidity and improve the quality of life for HF patients.

Developmental ethanol exposure alters the morphology of mouse prefrontal neurons in a layer-specific manner.

Chronic developmental exposure to ethanol can lead to a wide variety of teratogenic effects, which in humans are known as fetal alcohol spectrum disorders (FASD). Individuals affected by FASD may exhibit persistent impairments to cognitive functions such as learning, memory, and attention, which are highly dependent on medial prefrontal cortex (mPFC) circuitry. The objective of this study was to determine long-term effects of chronic developmental ethanol exposure on mPFC neuron morphology, in order to better-understand potential neuronal mechanisms underlying cognitive impairments associated with FASD. C57BL/6-strain mice were exposed to ethanol or an isocaloric/isovolumetric amount of sucrose (control) via oral gavage, administered both to the dam from gestational day 10-18 and directly to pups from postnatal day 4-14. Brains from male mice were collected at postnatal day 90 and neurons were stained using a modified Golgi-Cox method. Pyramidal neurons within layers II/III, V and VI of the mPFC were imaged, traced in three dimensions, and assessed using Sholl and branch structure analyses. Developmental ethanol exposure differentially impacted adult pyramidal neuron morphology depending on mPFC cortical layer. Neurons in layer II/III exhibited increased size and diameter of dendrite trees, whereas neurons in layer V were not affected. Layer VI neurons with long apical dendrites had trees with decreased diameter that extended farther from the soma, and layer VI neurons with short apical dendrite trees exhibited decreased tree size overall. These layer-specific alterations to mPFC neuron morphology may form a novel morphological mechanism underlying long-term mPFC dysfunction and resulting cognitive impairments in FASD.