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LaFrancois, J. J.

Publications and source records attributed to LaFrancois, J. J..

7 recordsLinked to original sources
bioRxiv2025

Chemogenetic activation of hippocampal area CA2 promotes acute and chronic seizures in a mouse model of epilepsy

Pyramidal cells (PCs) of hippocampal area CA2 exhibit increased excitability in temporal lobe epilepsy (TLE) and in mouse models of TLE. In epileptic mice, selective inhibition of CA2 PCs reduces chronic seizures. Here we asked if activating CA2 PCs increases seizures. Mice expressing Cre recombinase in CA2 PCs (Amigo2-Cre mice) were injected with the convulsant pilocarpine to induce a period of severe seizures (status epilepticus, SE), which leads to chronic seizures after 3-4 weeks (epilepsy). Epileptic mice were injected with a Cre-dependent adeno-associated virus (AAV) to express an excitatory designer receptor exclusively activated by designer drug (eDREADD; hM3Dq) in dorsal CA2 bilaterally and implanted with subdural EEG electrodes. After recovery, mice were recorded continuously using video and EEG for 6 weeks, 3 weeks with drinking water containing the eDREADD activator clozapine-N-oxide (CNO) and 3 weeks without CNO. CA2 activation with CNO caused a significant increase in seizure frequency and duration. Seizures occurred in clusters (many seizures per day over several consecutive days) and mice given water with CNO had a greater maximum number of seizures per day during a cluster compared to water without CNO. CNO had no significant effect in control mice. In naive Amigo2-Cre mice expressing hM3Dq, pre-treatment with CNO before pilocarpine administration shortened the latency to SE and increased EEG power at the start of SE. Taken together with prior findings, the results suggest that CA2 is a control point for regulating seizures in the pilocarpine mouse model of TLE. HIGHLIGHTSO_LIChemogenetic excitation of CA2 increased chronic seizure frequency and duration in epileptic mice. C_LIO_LIWhen seizures occurred in clusters, CA2 excitation increased the peak of the cluster. C_LIO_LIWhen sexes were separated, males showed effects on seizure frequency but both sexes showed effects on seizure duration and clusters. C_LIO_LIChemogenetic excitation of CA2 promoted pilocarpine-induced status epilepticus in normal mice. C_LI GRAPHICAL ABSTRACTLegend: In adult mice, injecting the convulsant pilocarpine induces severe seizures (status epilepticus, SE) and ultimately leads to chronic intermittent seizures (epilepsy). Selective activation of hippocampal area CA2 during the period of chronic seizures led to greater seizure frequency and duration, as well as a greater number of seizures/day at the peak of a seizure cluster. Effects were greatest in males. In naive mice, activation of CA2 prior to pilocarpine administration facilitated SE. Therefore, CA2 influences acute and chronic seizures in this mouse model. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=73 SRC="FIGDIR/small/696896v1_ufig1.gif" ALT="Figure 1"> View larger version (16K): org.highwire.dtl.DTLVardef@174f63dorg.highwire.dtl.DTLVardef@1d2478corg.highwire.dtl.DTLVardef@573c56org.highwire.dtl.DTLVardef@13a72e7_HPS_FORMAT_FIGEXP M_FIG C_FIG

neuroscience↗
bioRxiv2024

Field EPSPs of dentate gyrus granule cells studied by selective optogenetic activation of hilar mossy cells in hippocampal slices.

Glutamatergic dentate gyrus (DG) mossy cells (MCs) innervate the primary DG cell type, granule cells (GCs). Numerous MC synapses are on GC proximal dendrites in the inner molecular layer (IML). However, field recordings of the GC excitatory postsynaptic potential (fEPSPs) have not been used to study this pathway selectively. Here we describe methods to selectively activate MC axons in the IML using mice with Cre recombinase expressed in MCs. Slices were made after injecting adeno-associated virus (AAV) encoding channelrhodopsin (ChR2) in the DG. In these slices, we show that fEPSPs could be recorded reliably in the IML in response to optogenetic stimulation of MC axons. Furthermore, fEPSPs were widespread across the septotemporal axis. However, fEPSPs were relatively weak because they were small in amplitude and did not elicit a significant population spike in GCs. They also showed little paired pulse facilitation. We confirmed the extracellular findings with patch clamp recordings of GCs despite different recording chambers and other differences in methods. Together the results provide a simple method for studying MC activation of GCs and add to the evidence that this input is normally weak but widespread across the GC population. KEY POINTSO_LIWe describe a method to activate the MC input to GCs selectively using optogenetics in hippocampal slices C_LIO_LIMC excitation is weakly excitatory but so common among GCs that a field EPSP is generated at the site of MC synapses on GCs C_LIO_LIMC excitation of GCs is consistent across the septotemporal axis and contralaterally C_LIO_LIUsing the characteristics of optogenetically-evoked fEPSPs, electrical stimulation of the MC input to GCs can be optimized. C_LI

neuroscience↗
bioRxiv2023

Increasing adult neurogenesis protects mice from epilepsy.

ABSTRACTNeurogenesis occurs in the adult brain in the hippocampal dentate gyrus, an area that contains neurons which are vulnerable to insults and injury, such as severe seizures. Previous studies showed that increasing adult neurogenesis reduced neuronal damage after these seizures. Because the damage typically is followed by chronic life-long seizures (epilepsy), we asked if increasing adult-born neurons would prevent epilepsy. Adult-born neurons were selectively increased by deleting the pro-apoptotic gene Bax from Nestin-expressing progenitors. Tamoxifen was administered at 6 weeks of age to conditionally delete Bax in Nestin-CreERT2Baxfl/fl mice. Six weeks after tamoxifen administration, severe seizures (status epilepticus; SE) were induced by injection of the convulsant pilocarpine. After mice developed epilepsy, seizure frequency was quantified for 3 weeks. Mice with increased adult-born neurons exhibited fewer chronic seizures. Postictal depression was reduced also. These results were primarily in female mice, possibly because they were the more affected by Bax deletion than males, consistent with sex differences in Bax. The female mice with enhanced adult-born neurons also showed less neuronal loss of hilar mossy cells and hilar somatostatin-expressing neurons than wild type females or males, which is notable because these two hilar cell types are implicated in epileptogenesis. The results suggest that selective Bax deletion to increase adult-born neurons can reduce experimental epilepsy, and the effect shows a striking sex difference. The results are surprising in light of past studies showing that suppressing adult-born neurons can also reduce chronic seizures.

neuroscience↗
bioRxiv2023

Choline supplementation in early life improves and low levels of choline can impair outcomes in a mouse model of Alzheimer's disease.

Maternal choline supplementation (MCS) improves cognition in Alzheimers disease (AD) models. However, effects of MCS on neuronal hyperexcitability in AD are unknown. We investigated effects of MCS in a well-established mouse model of AD with hyperexcitability, the Tg2576 mouse. The most common type of hyperexcitability in Tg2576 mice are generalized EEG spikes (interictal spikes; IIS). IIS also are common in other mouse models and occur in AD patients. Im mouse models, hyperexcitability is also reflected by elevated expression of the transcription factor {Delta}FosB in the granule cells (GCs) of the dentate gyrus (DG), which are the principal cell type. Therefore we studied {Delta}FosB expression in GCs. We also studied the the neuronal marker NeuN within hilar neurons of the DG because other studies have reduced NeuN protein expression is a sign of oxidative stress or other pathology. This is potentially important because hilar neurons regulate GC excitability. Tg2576 breeding pairs received a diet with a relatively low, intermediate or high concentration of choline. After weaning, all mice received the intermediate diet. In offspring of mice fed the high choline diet, IIS frequency declined, GC {Delta}FosB expression was reduced, and NeuN expression was restored. Using the novel object location task, spatial memory improved. In contrast, offspring exposed to the relatively low choline diet had several adverse effects, such as increased mortality. They had the weakest hilar NeuN immunoreactivity and greatest GC {Delta}FosB protein expression. However, their IIS frequency was low, which was surprising. The results provide new evidence that a diet high in choline in early life can improve outcomes in a mouse model of AD, and relatively low choline can have mixed effects. This is the first study showing that dietary choline can regulate hyperexcitability, hilar neurons, {Delta}FosB and spatial memory in an animal model of AD.

neuroscience↗
bioRxiv2022

Enhanced excitability of the hippocampal CA2 region and its contribution to seizure generation in a mouse model of temporal lobe epilepsy

The hippocampal CA2 region, an area important for social memory, has been suspected to play a role in temporal lobe epilepsy (TLE) because of its resistance to the degeneration observed in neighboring CA1 and CA3 regions in both human and rodent models of TLE. However, little is known about whether alterations in CA2 properties serve to promote seizure generation or propagation. Here we have used the pilocarpine-induced status epilepticus (PILO-SE) model of TLE to explore the role of CA2. Ex vivo electrophysiological recordings from acute hippocampal slices revealed a set of coordinated changes that enhance CA2 intrinsic excitability, reduce CA2 local inhibitory input, and increase CA2 excitatory output to its major CA1 synaptic target. Moreover, selective silencing of CA2 pyramidal cells using a chemogenetic approach caused a significant decrease in the frequency of spontaneous seizures. These findings provide the first evidence that CA2 actively contributes to TLE seizure activity and may thus be a promising therapeutic target.

neuroscience↗
bioRxiv2020

Bidirectional regulation of cognitive and anxiety-like behaviors by dentate gyrus mossy cells in male and female mice

The dentate gyrus (DG) of the hippocampus is important for cognitive and affective behaviors. However, the circuits underlying these behaviors are unclear. DG mossy cells (MCs) have been a focus of attention because of their excitatory synapses on the primary DG cell type, granule cells (GCs). However, MCs also activate DG GABAergic neurons which inhibit GCs. We took advantage of specific methods and a gain- and loss-of function strategy with Designer Receptors Exclusively Activated by Designer Drugs (DREADDs) to study MCs in diverse behaviors. Using this approach, manipulations of MCs could bidirectionally regulate behavior. The results suggest that inhibiting MCs can reduce anxiety-like behavior and improve cognitive performance. However, not all cognitive or anxiety-related behaviors were influenced, suggesting specific roles of MCs in some but not all types of cognition and anxiety. Notably, several behaviors showed sex-specific effects, with females often showing more pronounced effects than the males. We also used the immediate early gene c-Fos to address whether DREADDs bidirectionally regulated MC or GC activity. We confirmed excitatory DREADDs increased MC c-Fos. However, there was no change in GC c-Fos, consistent with MC activation leading to GABAergic inhibition of GCs. In contrast, inhibitory DREADDs led to a large increase in GC c-Fos, consistent with a reduction in MC excitation of GABAergic neurons, and reduced inhibition of GCs. Taken together, these results suggest that MCs regulate anxiety and cognition in specific ways. We also raise the possibility that cognitive performance may be improved by reducing anxiety. SIGNIFICANCE STATEMENTThe dentate gyrus (DG) has many important cognitive roles as well as being associated with affective behavior. This study addressed how a glutamatergic DG cell type called mossy cells (MCs) contributes to diverse behaviors, which is timely because it is known that MCs regulate the activity of the primary DG cell type, granule cells (GCs), but how MC activity influences behavior is unclear. We show, surprisingly, that activating MCs can lead to adverse behavioral outcomes, and inhibiting MCs have an opposite effect. Importantly, the results appeared to be task-dependent and showed that testing both sexes was important. Additional experiments indicated what MC and GC circuitry was involved. Taken together, the results suggest how MCs influence behaviors that involve the DG.

neuroscience↗