Epilepsy is a neurological disorder characterized by recurrent epileptic seizures. Electrophysiological and neuroimaging studies in patients with epilepsy suggest that abnormal functional brain networks play a role in the development of epilepsy, i.e. epileptogenesis, resulting in the generation of spontaneous seizures and cognitive impairment. In this longitudinal study, we investigated changes in functional brain networks during epileptogenesis in the intraperitoneal kainic acid (IPKA) rat model of temporal lobe epilepsy (TLE) using resting state functional magnetic resonance imaging (rsfMRI) and graph theory. Additionally, we investigated whether these changes are related to the frequency of occurrence of spontaneous epileptic seizures in the chronic phase of epilepsy. Using a 7T MRI system, rsfMRI images were acquired under medetomidine anaesthesia before and 1, 3, 6, 10 and 16 weeks after status epilepticus (SE) induction in 20 IPKA animals and 7 healthy control animals. To obtain a functional network, correlation between fMRI time series of 38 regions of interest (ROIs) was calculated. Then, several graph theoretical network measures were calculated to describe and quantify the network changes. At least 17 weeks post-SE, IPKA animals were implanted with electrodes in the left and right dorsal hippocampus, EEG was measured for 7 consecutive days and spontaneous seizures were counted. Our results show that correlation coefficients of fMRI time series shift to lower values during epileptogenesis, indicating weaker whole brain network connections. Segregation and integration in the functional brain network also decrease, indicating a lower local interconnectivity and a lower overall communication efficiency. Secondly, this study demonstrates that the largest decrease in functional connectivity is observed for the retrosplenial cortex. Finally, post-SE changes in functional connectivity, segregation and integration are correlated with seizure frequency in the IPKA rat model.

Adenosine acts as an endogenous anticonvulsant and seizure terminator in the brain. Many of its anticonvulsive effects are mediated through the activation of the adenosine A₁ receptor, a G protein-coupled receptor with a wide array of targets. Activating A₁ receptors is an effective approach to suppress seizures. This review gives an overview of the neuronal targets of the adenosine A₁ receptor focusing in particular on signaling pathways resulting in neuronal inhibition. These include direct interactions of G protein subunits, the adenyl cyclase pathway and the phospholipase C pathway, which all mediate neuronal hyperpolarization and suppression of synaptic transmission. Additionally, the contribution of the guanyl cyclase and mitogen-activated protein kinase cascades to the seizure-suppressing effects of A₁ receptor activation are discussed. This review ends with the cautionary note that chronic activation of the A₁ receptor might have detrimental effects, which will need to be avoided when pursuing A₁ receptor-based epilepsy therapies.

The intrahippocampal kainic acid (IHKA) mouse model is an extensively used in vivo model to investigate the pathophysiology of mesial temporal lobe epilepsy (mTLE) and to develop novel therapies for drug-resistant epilepsy. It is characterized by profound hippocampal sclerosis and spontaneously occurring seizures with a major role for the injected damaged hippocampus, but little is known about the excitability of specific subregions. The purpose of this study was to electrophysiologically characterize the excitability of hippocampal subregions in the chronic phase of the induced epilepsy in the IHKA mouse model. We recorded field postsynaptic potentials (fPSPs) after electrical stimulation in the CA1 region and in the dentate gyrus (DG) of hippocampal slices of IHKA and healthy mice using a multielectrode array (MEA). In the DG, a significantly steeper fPSP slope was found, reflecting higher synaptic strength. Population spikes were more prevalent with a larger spatial distribution in the IHKA group, reflecting a higher degree of granule cell output. Only minor differences were found in the CA1 region. These results point to increased neuronal excitability in the DG but not in the CA1 region of the hippocampus of IHKA mice. This method, in which the excitability of hippocampal slices from IHKA mice is investigated using a MEA, can now be further explored as a potential new model to screen for new interventions that can restore DG function and potentially lead to novel therapies for mTLE.

We report the design, synthesis, and validation of the novel compound photocaged N⁶-cyclopentyladenosine (cCPA) to achieve precisely localized and timed release of the parent adenosine A1 receptor agonist CPA using 405 nm light. G_i protein-coupled A₁ receptors (A₁Rs) modulate neurotransmission via pre- and post-synaptic routes. The dynamics of the CPA-mediated effect on neurotransmission, characterized by fast activation and slow recovery, make it possible to implement a closed-loop control paradigm. The strength of neurotransmission is monitored as the amplitude of stimulus-evoked local field potentials. It is used for feedback control of light to release CPA. This system makes it possible to regulate neurotransmission to a pre-defined level in acute hippocampal brain slices incubated with 3 µM cCPA. This novel approach of closed-loop photopharmacology holds therapeutic potential for fine-tuned control of neurotransmission in diseases associated with neuronal hyperexcitability.

RATIONALE Major depression and spatial memory impairment are the most common comorbidities in patients with temporal lobe epilepsy (TLE). For these patients, treatment options are limited highlighting the need for innovative treatments such as Designer Receptors Exclusively Activated by Designer Drugs (DREADDs). Studies investigating the effect of DREADDs on these comorbidities are lacking. In the present study, we evaluated whether activation of hM4Di DREADDs with clozapine affects anhedonia (i.e. the inability to experience pleasure) and spatial memory in the intraperitoneal kainic acid (IPKA) rat model for TLE. METHOD Status epilepticus (SE) was elicited by i.p. kainic acid (KA) injections in male Sprague Dawley rats. A control group was injected with saline (SAL). Three months post-SE, animals received bilateral intrahippocampal adeno-associated viral vector injections (2x0.5µL) carrying the hM4Di DREADD or a SHAM construct, yielding four experimental groups: KA-DREADD (n=8), KA-SHAM (n=6), SAL-DREADD (n=5) and SAL-SHAM (n=5). Anhedonia was evaluated using the saccharin preference test (SPT) and the novel object test (NOL) to assess spatial memory impairment. Following hM4Di DREADDs activation by clozapine (0.1 mg/kg, s.c.), the SPT and NOL were repeated. RESULTS The KA group showed a significant reduction in preference towards saccharin compared to the SAL group (66.25% vs 96.96% respectively, p<0.001). In the NOL, a trend towards spatial memory impairment was observed in the KA group. DREADDs activation with clozapine increased preference towards saccharin in the KA-DREADD group, while spatial memory was not affected compared to SHAM groups. CONCLUSION The IPKA rat model displays anhedonic-like behavior whereas enlargement of sample size is required for characterization of spatial memory impairment. Although activation of hM4Di DREADDs did not alter spatial memory, an increased preference towards saccharin was present in the IPKA rat model containing hM4Di DREADDs, suggesting a potential antidepressant effect.