Optogenetic inhibition of the dorsal hippocampus CA3 region during early-stage cocaine-memory reconsolidation disrupts subsequent context-induced cocaine seeking in rats

The dorsal hippocampus (DH) is key to the long-term maintenance of cocaine memories following retrieval-induced memory destabilization; even though, it is not the site of protein synthesis-dependent memory reconsolidation. Here, we took advantage of the temporal and spatial specificity of an optogenetic manipulation to examine the role of the cornu ammonis 3 subregion of the DH (dCA3) in early-stage cocaine-memory reconsolidation. Male Sprague-Dawley rats expressing eNpHR3.0 in the DH were trained to self-administer cocaine in a distinct context and underwent extinction training in a different context. Rats then received a 15-min memory-reactivation session, to destabilize cocaine memories and trigger reconsolidation, or remained in their home cages (no-reactivation controls). Optogenetic inhibition of the dCA3 for 1 h immediately, but not 1 h, after memory reactivation resulted in cocaine-memory impairment as indicated by reduction in drug-seeking behavior selectively in the cocaine-paired context 3 d later, at test, relative to responding in no-inhibition, no-reactivation, and no-eNpHR3.0 controls. Cocaine-memory impairment was associated with reduced c-Fos expression, an index of neuronal activation, in the dCA3 stratum lucidum (SL) and stratum pyramidale (SP) at test. Based on these observations and extant literature, we postulate that recurrent circuits in the SP are activated during early-stage memory reconsolidation to maintain labile cocaine memories prior to protein synthesis-dependent restabilization in another brain region, such as the basolateral amygdala. Furthermore, SL and SP interneurons may enhance memory reconsolidation by limiting synaptic noise in the SP and also contribute to recall as elements of the updated cocaine engram or retrieval links.

The Role of Alcohol in Hippocampal Calcium Channel (Cav1.2) expression

Background and Hypothesis: Voltage-gated L-type calcium channels (Cav1.2 and Cav1.3) in the hippocampus play important roles in glutamatergic neurotransmission underlying memory and learning. Their overexpression has been implicated in neuroexcitatory cell death and disease states including chronic alcoholism. While increases in Cav1.2 gene expression have been reported in the hippocampus after chronic ethanol exposure in rats, the regional distribution of Cav1.2 protein after voluntary ethanol (EtOH) drinking has not been reported. We hypothesize that the expression of Cav1.2 channels within the hippocampus is increased by EtOH drinking in a region-specific manner. Methods: Male Sprague Dawley rats were allowed 28 days of intermittent access to a 10% EtOH solution. At 24 hours after the last exposure to EtOH, brains were collected and processed for immunohistochemistry. Cav1.2 associated immunofluorescent signal from subregions of the hippocampus was quantified using ImageJ analysis software. Results: Immunohistochemical results indicate that Cav1.2 immunoreactivity in the hippocampal stratum granulosum layer within the Dentate Gyrus and the stratum pyramidale layer within CA1 and CA3 regions was increased in response to EtOH treatment. There was no significant change in Cav1.2 immunoreactivity for the CA2 region. Conclusion: This study suggests that calcium signaling in subregions of the hippocampus is differentially affected by EtOH consumption that may contribute to eventual calcium-mediated apoptosis. Impact and Implications: Understanding the process of EtOH-induced hippocampal calcium signaling presents opportunities for understanding the consequences of chronic alcohol exposure related to hippocampal function including memory and learning, and possible interventional therapies for alcohol damage.

Neurodegeneration, Myelin Loss and Glial Response in the Three-Vessel Global Ischemia Model in Rat

(1) Background: Although myelin disruption is an integral part of ischemic brain injury, it is rarely the subject of research, particularly in animal models. This study assessed for the first time, myelin and oligodendrocyte loss in a three-vessel model of global cerebral ischemia (GCI), which causes hippocampal damage. In addition, we investigated the relationships between demyelination and changes in microglia and astrocytes, as well as oligodendrogenesis in the hippocampus; (2) Methods: Adult male Wistar rats (n = 15) underwent complete interruption of cerebral blood flow for 7 min by ligation of the major arteries supplying the brain or sham-operation. At 10 and 30 days after the surgery, brain slices were stained for neurodegeneration with Fluoro-Jade C and immunohistochemically to assess myelin content (MBP+ percentage of total area), oligodendrocyte (CNP+ cells) and neuronal (NeuN+ cells) loss, neuroinflammation (Iba1+ cells), astrogliosis (GFAP+ cells) and oligodendrogenesis (NG2+ cells); (3) Results: 10 days after GCI significant myelin and oligodendrocyte loss was found only in the stratum oriens and stratum pyramidale. By the 30th day, demyelination in these hippocampal layers intensified and affected the substratum radiatum. In addition to myelin damage, activation and an increase in the number of microglia and astrocytes in the corresponding layers, a loss of the CA1 pyramidal neurons, and neurodegeneration in the neocortex and thalamus was observed. At a 10-day time point, we observed rod-shaped microglia in the substratum radiatum. Parallel with ongoing myelin loss on the 30th day after ischemia, we found significant oligodendrogenesis in demyelinated hippocampal layers; (4) Conclusions: Our study showed that GCI-simulating cardiac arrest in humans—causes not only the loss of pyramidal neurons in the CA1 field, but also the myelin loss of adjacent layers of the hippocampus.

Improved identification and differentiation from epileptiform activity of human hippocampal sharpwave-ripples during NREM sleep

In rodents, pyramidal cell firing patterns from waking may be replayed in NREM sleep during hippocampal sharpwave-ripples (HC-SWR). In humans, HC-SWR have only been recorded with electrodes implanted to localize epileptogenesis. Here, we characterize human HC-SWR with rigorous rejection of epileptiform activity, requiring multiple oscillations and coordinated sharpwaves. We demonstrated typical SWR in those rare HC recordings which lack interictal epileptiform spikes (IIS), and with no or minimal seizure involvement. These HC-SWR have a similar rate (~12/min) and apparent intra-HC topography (ripple maximum in putative stratum pyramidale, slow wave in radiatum) as rodents, though with lower frequency (~85Hz compared to ~140Hz in rodents). Similar SWR are found in HC with IIS, but no significant seizure involvement. These SWR were modulated by behavior, being largely absent (<2/min) except during NREM sleep in both stage 2 (~9/min) and stage 3 (~15/min), distinguishing them from IIS. This study quantifies the basic characteristics of a strictly selected sample of SWR recorded in relatively healthy human hippocampi.

A Gradient of Hippocampal Inputs to the Medial Mesocortex

Memory-guided decisions depend on complex, finely tuned interactions between hippocampus and medial mesocortical regions anterior cingulate and retrosplenial cortices. The functional circuitry underlying these interactions is unclear. Using viral anatomical tracing,in vitroandin vivoelectrophysiology, and optogenetics, we show that such circuitry is characterized by a functional-anatomical gradient. While CG receives excitatory projections from dorsal-intermediate CA1 originated exclusively instratum pyramidale, retrosplenial cortex also receives inputs originating instratum radiatumandlacunosum-moleculare, including GAD+ neurons providing long-range GABAergic projections. Such hippocampal projections establishbona fidesynapses throughout cortical layers, with retrosplenial cortex densely targeted on its layer 3, around which it receives a combination of inhibitory and excitatory synapses. This gradient is reflected in the pattern of spontaneous oscillatory synchronicity found in the awake-behaving animal, compatible with the known functional similarity of hippocampus with retrosplenial cortex, which contrasts with the encoding of actions and “task-space” by cingulate cortex.HighlightsBoth MMC regions CG and RSC receive monosynaptic connections from the dorsal-intermediate CA1CG receives layer-sparse excitatory projections exclusively originated fromstratum piramidalewhereas RSC is targeted densely in superficial layers by a mixed excitatory and inhibitory input originating from all CA1strataCA1 monosynaptic projections correspond to active synapses onto distinct layers of the two MMC regionsDiverse synchrony between MMC and HIPP recordedin vivois consistent with the rostro-caudal diversity of direct HIPP-MMC connections

Metabolic and neuroprotective effects of dapagliflozin and liraglutide in diabetic mice

This study assessed the metabolic and neuroprotective actions of the sodium glucose cotransporter-2 inhibitor dapagliflozin in combination with the GLP-1 agonist liraglutide in dietary-induced diabetic mice. Mice administered low-dose streptozotocin (STZ) on a high-fat diet received dapagliflozin, liraglutide, dapagliflozin-plus-liraglutide (DAPA-Lira) or vehicle once-daily over 28 days. Energy intake, body weight, glucose and insulin concentrations were measured at regular intervals. Glucose tolerance, insulin sensitivity, hormone and biochemical analysis, dual-energy X-ray absorptiometry densitometry, novel object recognition, islet and brain histology were examined. Once-daily administration of DAPA-Lira resulted in significant decreases in body weight, fat mass, glucose and insulin concentrations, despite no change in energy intake. Similar beneficial metabolic improvements were observed regarding glucose tolerance, insulin sensitivity, HOMA-IR, HOMA-β, HbA1c and triglycerides. Plasma glucagon, GLP-1 and IL-6 levels were increased and corticosterone concentrations decreased. DAPA-Lira treatment decreased alpha cell area and increased insulin content compared to dapagliflozin monotherapy. Recognition memory was significantly improved in all treatment groups. Brain histology demonstrated increased staining for doublecortin (number of immature neurons) in dentate gyrus and synaptophysin (synaptic density) in stratum oriens and stratum pyramidale. These data demonstrate that combination therapy of dapagliflozin and liraglutide exerts beneficial metabolic and neuroprotective effects in diet-induced diabetic mice. Our results highlight important personalised approach in utilising liraglutide in combination with dapagliflozin, instead of either agent alone, for further clinical evaluation in treatment of diabetes and associated neurodegenerative disorders.

Critical role of trkB receptors in reactive axonal sprouting and hyperexcitability after axonal injury

Traumatic brain injury (TBI) causes many long-term neurological complications. Some of these conditions, such as posttraumatic epilepsy, are characterized by increased excitability that typically arises after a latent period lasting from months to years, suggesting that slow injury-induced processes are critical. We tested the hypothesis that trkB activation promotes delayed injury-induced hyperexcitability in part by promoting reactive axonal sprouting. We modeled penetrative TBI with transection of the Schaffer collateral pathway in knock-in mice having an introduced mutation in the trkB receptor (trkB F616A) that renders it susceptible to inhibition by the novel small molecule 1NMPP1. We observed that trkB activation was increased in area CA3 1 day after injury and that expression of a marker of axonal growth, GAP43, was increased 7 days after lesion. Extracellular field potentials in stratum pyramidale of area CA3 in acute slices from sham-operated and lesioned mice were normal in control saline. Abnormal bursts of population spikes were observed under conditions that were mildly proconvulsive but only in slices taken from mice lesioned 7–21 days earlier and not in slices from control mice. trkB activation, GAP43 upregulation, and hyperexcitability were diminished by systemic administration of 1NMPP1 for 7 days after the lesion. Synaptic transmission from area CA3 to area CA1 recovered 7 days after lesion in untreated mice but not in mice treated with 1NMPP1. We conclude that trkB receptor activation and reactive axonal sprouting are critical factors in injury-induced hyperexcitability and may contribute to the neurological complications of TBI.

Effects of μ-Opioid Receptor Modulation on GABAB Receptor Synaptic Function in Hippocampal CA1

Activation of μ-opioid receptors (MORs) alters information coding, synaptic plasticity, and spatial memory in hippocampal CA1. In CA1, MORs act by inhibiting GABA release onto both GABAA and GABAB receptors exclusively. MOR activation can facilitate excitatory inputs in CA1 dendritic layers by inhibiting synaptic activation of GABAA receptors. In this study, we use voltage-sensitive dye imaging to show that MOR activation by the MOR agonist DAMGO suppressed GABAB inhibitory postsynaptic potentials in all layers of CA1. When stimulating excitatory input in stratum oriens (SO), stratum radiatum (SR), or stratum lacunosum-moleculare (SLM) with five pulses at 20 Hz in the presence of bicuculline (50 μM), DAMGO (1 μM) was most effective at increasing the amplitude of the last excitatory event. This effect was reversed by the MOR antagonist CTOP (1 μM) and occluded by the GABAB receptor agonist CGP 55845 (10 μM). DAMGO was less effective at increasing the amplitude of later excitatory events compared with the effect of CGP 55845. DAMGO was relatively ineffective at increasing the amplitude of excitatory inputs in SLM but had significantly greater effects on excitatory events as they propagated to stratum pyramidale (SP). When stimulating in SR, DAMGO was least effective at increasing excitatory amplitudes in SLM and most effective in SP and SO. Finally, DAMGO was equally effective at increasing excitatory activity amplitudes in all layers of CA1 after stimulating in SO. Therefore MOR suppresses GABAB synaptic hyperpolarizations in all layers of CA1 and most effectively facilitates excitatory activity in CA1 output layers.

Receptor Protein Tyrosine Phosphatase γ Is a Marker for Pyramidal Cells and Sensory Neurons in the Nervous System and Is Not Necessary for Normal Development

ABSTRACT In order to gain insight into the biological role of receptor protein tyrosine phosphatase γ (RPTPγ), we have generated RPTPγ-null mice. RPTPγ was disrupted by insertion of the β-galactosidase gene under the control of the RPTPγ promoter. As the RPTPγ-null mice did not exhibit any obvious phenotype, we made use of these mice to study RPTPγ expression and thus shed light on potential biological functions of this phosphatase. Inspection of mouse embryos shows that RPTPγ is expressed in a variety of tissues during embryogenesis. RPTPγ is expressed in both embryonic and adult brains. Specifically, we detected RPTPγ expression in cortical layers II and V and in the stratum pyramidale of the hippocampus, indicating that RPTPγ is a marker for pyramidal neurons. Mixed primary culture of glial cells showed a lack of expression of RPTPγ in astrocytes and a low expression of RPTPγ in oligodendrocytes and in microglia. Interestingly, RPTPγ expression was detected in all sensory organs, including the ear, nose, tongue, eye, and vibrissa follicles, suggesting a potential role of RPTPγ in sensory neurons. An initial behavioral analysis showed minor changes in the RPTPγ-null mice.