Acute blockade of NR2C/D subunit-containing N-methyl-D-aspartate receptors modifies sleep and neural oscillations in mice.

N-methyl-d-aspartate receptors (NMDARs) play an important role in excitatory neurotransmission and have been associated with psychiatric conditions including schizophrenia and major depressive disorder. NMDARs are composed of two NR1 and two NR2 subunits. The type of NR2 subunit determines electrophysiological and pharmacological properties of the receptor. As the precise role of NR2C/D subunit-containing NMDARs is poorly understood in vivo, we have performed behavioural, quantitative electroencephalographic (qEEG) and polysomnographic analysis following acute pharmacological blockade of these receptor subtypes in adult male CD1 mice. We found that NR2C/D blockade impaired motor coordination and decreased the amount of gross movement. Moreover, EEG power in multiple frequency bands including theta and sigma were found to decrease significantly together with a decrease of theta oscillation frequency. Changes of these qEEG measures were accompanied by a decrease in time spent in slow-wave and rapid eye movement sleep, but an increase of time spent in quiet wakefulness. Furthermore, there was a significant decrease of sleep spindle oscillation density. These findings highlight the importance of NR2C/D-containing NMDARs and take a step towards establishing a link between electrophysiological correlates of psychiatric disorders and underlying synaptic dysfunctions.

Brain protein expression changes in WAG/Rij rats, a genetic rat model of absence epilepsy after peripheral lipopolysaccharide treatment.

Peripheral injection of bacterial lipopolysaccharide (LPS) facilitates 8-10Hz spike-wave discharges (SWD) characterizing absence epilepsy in WAG/Rij rats. It is unknown however, whether peripherally administered LPS is able to alter the generator areas of epileptic activity at the molecular level. We injected 1mg/kg dose of LPS intraperitoneally into WAG/Rij rats, recorded the body temperature and EEG, and examined the protein expression changes of the proteome 12h after injection in the fronto-parietal cortex and thalamus. We used fluorescent two-dimensional differential gel electrophoresis to investigate the expression profile. We found 16 differentially expressed proteins in the fronto-parietal cortex and 35 proteins in the thalamus. It is known that SWD genesis correlates with the transitional state of sleep-wake cycle thus we performed meta-analysis of the altered proteins in relation to inflammation, epilepsy as well as sleep. The analysis revealed that all categories are highly represented by the altered proteins and these protein-sets have considerable overlap. Protein network modeling suggested that the alterations in the proteome were largely induced by the immune response, which invokes the NFkB signaling pathway. The proteomics and computational analysis verified the known functional interplay between inflammation, epilepsy and sleep and highlighted proteins that are involved in their common synaptic mechanisms. Our physiological findings support the phenomenon that high dose of peripheral LPS injection increases SWD-number, modifies its duration as well as the sleep-wake stages and decreases body temperature.

Chronic Cerebral Hypoperfusion-Induced Disturbed Proteostasis of Mitochondria and MAM Is Reflected in the CSF of Rats by Proteomic Analysis.

Declining cerebral blood flow leads to chronic cerebral hypoperfusion which can induce neurodegenerative disorders, such as vascular dementia. The reduced energy supply of the brain impairs mitochondrial functions that could trigger further damaging cellular processes. We carried out stepwise bilateral common carotid occlusions on rats and investigated long-term mitochondrial, mitochondria-associated membrane (MAM), and cerebrospinal fluid (CSF) proteome changes. Samples were studied by gel-based and mass spectrometry-based proteomic analyses. We found 19, 35, and 12 significantly altered proteins in the mitochondria, MAM, and CSF, respectively. Most of the changed proteins were involved in protein turnover and import in all three sample types. We confirmed decreased levels of proteins involved in protein folding and amino acid catabolism, such as P4hb and Hibadh in the mitochondria by western blot. We detected reduced levels of several components of protein synthesis and degradation in the CSF as well as in the subcellular fractions, implying that hypoperfusion-induced altered protein turnover of brain tissue can be detected in the CSF by proteomic analysis.

Theta phase classification of interneurons in the hippocampal formation of freely moving rats.

Earlier work on freely moving rats classified neurons in Ammon's horn as pyramidal cells (including place cells) or interneurons (previously called "theta cells") based on temporal discharge correlates and waveform configurations, but the anatomical and biochemical diversity of interneurons suggests they may have other distinguishing characteristics. To explore this possibility, we made extracellular recordings as rats foraged for food in an open space, used accepted criteria to identify interneurons, and found two additional categorization methods. First, interneurons were separated into theta-modulated and theta-independent groups using spike autocorrelograms. Second, theta-modulated interneurons were further separated into four groups by the phase of the ∼8 Hz theta rhythm at which firing was most rapid. These phase groups resemble the four phase peak groups of five anatomically identified interneuron types (two with the same preferred phase) recorded during the slow (∼4 Hz) theta rhythm in urethane-anesthetized rats. We suggest that the similar number of peak phase groups in walking rats and urethane-anesthetized rats and the partial agreement between peak phase values reflect a similar organization of theta rhythm in both states, so that the discharge properties of anatomically identified interneurons can be described in freely moving rats. Interestingly, the average spatial firing precision of the interneuron classes does not differ significantly, suggesting that the strong location-specific firing of place cells may be due to segregated high- and low-precision interneuron ensembles rather than to one or more dedicated high-precision classes.

Convergent cross-species pro-cognitive effects of RGH-235, a new potent and selective histamine H3 receptor antagonist/inverse agonist.

The histamine H3 receptor is a favourable target for the treatment of cognitive deficits. Here we report the in vitro and in vivo profile of RGH-235, a new potent, selective, and orally active H3 receptor antagonist/inverse agonist developed by Gedeon Richter Plc. Radioligand binding and functional assays were used for in vitro profiling. Procognitive efficacy was investigated in rodent cognitive tests, in models of attention deficit hyperactive disorder (ADHD) and in cognitive tests of high translational value (rat touch screen visual discrimination test, primate fixed-foreperiod visual reaction time task). Results were supported by pharmacokinetic studies, neurotransmitter release, sleep EEG and dipsogenia. RGH-235 displayed high affinity to H3 receptors (Ki = 3.0-9.2 nM, depending on species), without affinity to H1, H2 or H4 receptors and >100 other targets. RGH-235 was an inverse agonist ([35S] GTPγS binding) and antagonist (pERK1/2 ELISA), showing favourable kinetics, inhibition of the imetit-induced dipsogenia and moderate effects on sleep-wake EEG. RGH-235 stimulated neurotransmitter release both in vitro and in vivo. RGH-235 was active in spontaneously hypertensive rats (SHR), generally considered as a model of ADHD, and revealed a robust pro-cognitive profile both in rodent and primate tests (in 0.3-1 mg/kg) and in models of high translational value (e.g. in a rodent touch screen test and in non-human primates). The multiple and convergent procognitive effects of RGH-235 support the view that beneficial cognitive effects can be linked to antagonism/inverse agonism of H3 receptors.

Cariprazine modulates sleep architecture in rats.

BACKGROUND: Cariprazine is a dopamine D3-preferring D3/D2 receptor partial agonist compound recently introduced to treat schizophrenia and bipolar disorder. Although cariprazine is clinically classified as a low-somnolence drug, to date no detailed polysomnographic study is available on its effect on sleep. AIMS: This study examined the acute systemic effects of cariprazine on the rat sleep architecture and electroencephalography spectral power. METHODS: Sprague Dawley rats were recorded during their normal sleep period for four hours, and their sleep stages were classified. RESULTS: Cariprazine (0.3 mg/kg i.p.) reduced the time spent in rapid eye movement (REM) sleep and increased REM latency. This dose of cariprazine decreased the gamma (40-80 Hz) band frequency oscillations and increased the theta (4-9 Hz) and alpha (9-15 Hz) frequencies during the wake periods but not during slow-wave sleep. The 0.03 mg/kg dose of cariprazine only increased the alpha power during the wake periods, while the 0.003 mg/kg dose was without any effect. CONCLUSION: Taken together, the present results suggest that the REM-suppressing effect of cariprazine may be related to its effectiveness in improving depressive symptoms, as various drugs with similar REM-reducing properties effectively treat the depressive state, whereas the gamma power-reducing effect of cariprazine may be indicative of its efficacy in schizophrenia or mania, as similar effects have been observed with other D2 and 5-HT2 receptor antagonist drugs. These data contribute to our understanding of the complex mechanism of action that may stand behind the clinical efficacy of cariprazine.

Deciphering the scopolamine challenge rat model by preclinical functional MRI.

During preclinical drug testing, the systemic administration of scopolamine (SCO), a cholinergic antagonist, is widely used. However, it suffers important limitations, like non-specific behavioural effects partly due to its peripheral side-effects. Therefore, neuroimaging measures would enhance its translational value. To this end, in Wistar rats, we measured whisker-stimulation induced functional MRI activation after SCO, peripherally acting butylscopolamine (BSCO), or saline administration in a cross-over design. Besides the commonly used gradient-echo echo-planar imaging (GE EPI), we also used an arterial spin labeling method in isoflurane anesthesia. With the GE EPI measurement, SCO decreased the evoked BOLD response in the barrel cortex (BC), while BSCO increased it in the anterior cingulate cortex. In a second experiment, we used GE EPI and spin-echo (SE) EPI sequences in a combined (isoflurane + i.p. dexmedetomidine) anesthesia to account for anesthesia-effects. Here, we also examined the effect of donepezil. In the combined anesthesia, with the GE EPI, SCO decreased the activation in the BC and the inferior colliculus (IC). BSCO reduced the response merely in the IC. Our results revealed that SCO attenuated the evoked BOLD activation in the BC as a probable central effect in both experiments. The likely peripheral vascular actions of SCO with the given fMRI sequences depended on the type of anesthesia or its dose.

Complementary spatial firing in place cell-interneuron pairs.

The hippocampal formation plays a pivotal role in representing the physical environment. While CA1 pyramidal cells display sharply tuned location-specific firing, the activity of many interneurons show weaker but significant spatial modulation. Although hippocampal interneurons were proposed to participate in the representation of space, their interplay with pyramidal cells in formation of spatial maps is not well understood. In this study, we investigated the spatial correlation between CA1 pyramidal cells and putative interneurons recorded concurrently in awake rats. Positively and negatively correlated pairs were found to be simultaneously present in the CA1 region. While pyramidal cell-interneuron pairs with positive spatial correlation showed similar firing maps, negative spatial correlation was often accompanied by complementary place maps, which could occur even in the presence of a monosynaptic excitation between the cells. Thus, location-specific firing increase of hippocampal interneurons is not necessarily a simple product of excitation by a pyramidal cell with a similarly positioned firing field. Based on our observation of pyramidal cells firing selectively in the low firing regions of interneurons, we speculate that the location-specific firing of place cells is partly determined by the location-specific decrease of interneuron activity that can release place cells from inhibition.

Chronic stepwise cerebral hypoperfusion differentially induces synaptic proteome changes in the frontal cortex, occipital cortex, and hippocampus in rats.

During chronic cerebral hypoperfusion (CCH), the cerebral blood flow gradually decreases, leading to cognitive impairments and neurodegenerative disorders, such as vascular dementia. The reduced oxygenation, energy supply induced metabolic changes, and insufficient neuroplasticity could be reflected in the synaptic proteome. We performed stepwise bilateral common carotid occlusions on rats and studied the synaptic proteome changes of the hippocampus, occipital and frontal cortices. Samples were prepared and separated by 2-D DIGE and significantly altered protein spots were identified by HPLC-MS/MS. We revealed an outstanding amount of protein changes in the occipital cortex compared to the frontal cortex and the hippocampus with 94, 33, and 17 proteins, respectively. The high alterations in the occipital cortex are probably due to the hypoxia-induced retrograde degeneration of the primary visual cortex, which was demonstrated by electrophysiological experiments. Altered proteins have functions related to cytoskeletal organization and energy metabolism. As CCH could also be an important risk factor for Alzheimer's disease (AD), we investigated whether our altered proteins overlap with AD protein databases. We revealed a significant amount of altered proteins associated with AD in the two neocortical areas, suggesting a prominent overlap with the AD pathomechanism.

Status epilepticus affects the gigantocellular network of the pontine reticular formation.

BACKGROUND: The impairment of the pontine reticular formation (PRF) has recently been revealed to be histopathologically connected with focal-cortical seizure induced generalized convulsive status epilepticus. To elucidate whether the impairment of the PRF is a general phenomenon during status epilepticus, the focal-cortical 4-aminopyridine (4-AP) application was compared with other epilepsy models. The presence of "dark" neurons in the PRF was investigated by the sensitive silver method of Gallyas in rats sacrificed at 3 h after focal 4-AP crystal or systemic 4-AP, pilocarpine, or kainic acid application. The behavioral signs of the developing epileptic seizures were scored in all rats. The EEG activity was recorded in eight rats. RESULTS: Regardless of the initiating drug or method of administration, "dark" neurons were consistently found in the PRF of animals entered the later phases of status epilepticus. EEG recordings demonstrated the presence of slow oscillations (1.5-2.5 Hz) simultaneously with the appearance of giant "dark" neurons in the PRF. CONCLUSION: We argue that the observed slow oscillation corresponds to the late periodic epileptiform discharge phase of status epilepticus, and that the PRF may be involved in the progression of status epilepticus.

Purkinje cell number-correlated cerebrocerebellar circuit anomaly in the valproate model of autism.

While cerebellar alterations may play a crucial role in the development of core autism spectrum disorder (ASD) symptoms, their pathophysiology on the function of cerebrocerebellar circuit loops is largely unknown. We combined multimodal MRI (9.4 T) brain assessment of the prenatal rat valproate (VPA) model and correlated immunohistological analysis of the cerebellar Purkinje cell number to address this question. We hypothesized that a suitable functional MRI (fMRI) paradigm might show some altered activity related to disrupted cerebrocerebellar information processing. Two doses of maternal VPA (400 and 600 mg/kg, s.c.) were used. The higher VPA dose induced 3% smaller whole brain volume, the lower dose induced 2% smaller whole brain volume and additionally a focal gray matter density decrease in the cerebellum and brainstem. Increased cortical BOLD responses to whisker stimulation were detected in both VPA groups, but it was more pronounced and extended to cerebellar regions in the 400 mg/kg VPA group. Immunohistological analysis revealed a decreased number of Purkinje cells in both VPA groups. In a detailed analysis, we revealed that the Purkinje cell number interacts with the cerebral BOLD response distinctively in the two VPA groups that highlights atypical function of the cerebrocerebellar circuit loops with potential translational value as an ASD biomarker.

Implementation of a galvanically isolated low-noise power supply board for multi-channel headstage preamplifiers.

Custom made multi-channel headstage preamplifiers are traditionally powered by battery. By the use of an isolated unregulated DC/DC converter integrated circuit (DCP010512B from Texas Instruments Inc., TX, USA), here we describe the implementation of a galvanically isolated low-noise power supply board for multi-channel headstage preamplifiers. The implemented galvanically isolated power supply board provides the same quality noise free recording as the battery power supply. The non-isolated part of the power supply board is powered by standard 230 V AC/6 V DC wall mount adapter or USB cable. The described galvanically isolated power supply board can replace the batteries in preamplifier power supplies without any deterioration of the quality of recordings.

Generalization of seizures parallels the formation of "dark" neurons in the hippocampus and pontine reticular formation after focal-cortical application of 4-aminopyridine (4-AP) in the rat.

Distribution and time course of the occurrence of "dark" neurons were compared with the EEG activity and behavior of rats during 4-aminopyridine (4-AP) induced epileptic seizures. A crystal of the K(+) channel blocker 4-AP (0.5 mg/kg) was placed onto the exposed parieto-occipital cortex of Halothane-anesthetized rats for 40 min. Thereafter, the anesthesia was discontinued and the behavioral signs of the epileptic seizure activity were observed. The presence of "dark" neurons was demonstrated by the sensitive silver method of Gallyas in rats sacrificed at 0, 3 and 6 h after the end of the 4-AP crystal application. The EEG activity was recorded in the rats with longer survival times. The EEG analysis revealed the generalization of the epileptic seizures. We found that the formation of "dark" neurons in the hippocampus and the pontine reticular formation paralleled the generalization of the seizures.

Stepwise occlusion of the carotid arteries of the rat: MRI assessment of the effect of donepezil and hypoperfusion-induced brain atrophy and white matter microstructural changes.

Bilateral common carotid artery occlusion (BCCAo) in the rat is a widely used animal model of vascular dementia and a valuable tool for preclinical pharmacological drug testing, although the varying degrees of acute focal ischemic lesions it induces could interfere with its translational value. Recently, a modification to the BCCAo model, the stepwise occlusion of the two carotid arteries, has been introduced. To acquire objective translatable measures, we used longitudinal multimodal magnetic resonance imaging (MRI) to assess the effects of semi-chronic (8 days) donepezil treatment in this model, with half of the Wistar rats receiving the treatment one week after the stepwise BCCAo. With an ultrahigh field MRI, we measured high-resolution anatomy, diffusion tensor imaging, cerebral blood flow measurements and functional MRI in response to whisker stimulation, to evaluate both the structural and functional effects of the donepezil treatment and stepwise BCCAo up to 5 weeks post-occlusion. While no large ischemic lesions were detected, atrophy in the striatum and in the neocortex, along with widespread white matter microstructural changes, were found. Donepezil ameliorated the transient drop in the somatosensory BOLD response in distant cortical areas, as detected 2 weeks after the occlusion but the drug had no effect on the long term structural changes. Our results demonstrate a measurable functional MRI effect of the donepezil treatment and the importance of diffusion MRI and voxel based morphometry (VBM) analysis in the translational evaluation of the rat BCCAo model.

Chronic Cerebral Hypoperfusion Induced Synaptic Proteome Changes in the rat Cerebral Cortex.

Chronic cerebral hypoperfusion (CCH) evokes mild cognitive impairment (MCI) and contributes to the progression of vascular dementia and Alzheimer's disease (AD). How CCH induces these neurodegenerative processes that may spread along the synaptic network and whether they are detectable at the synaptic proteome level of the cerebral cortex remains to be established. In the present study, we report the synaptic protein changes in the cerebral cortex after stepwise bilateral common carotid artery occlusion (BCCAO) induced CCH in the rat. The occlusions were confirmed with magnetic resonance angiography 5 weeks after the surgery. Synaptosome fractions were prepared using sucrose gradient centrifugation from cerebral cortex dissected 7 weeks after the occlusion. The synaptic protein differences between the sham operated and CCH groups were analyzed with label-free nanoUHPLC-MS/MS. We identified 46 proteins showing altered abundance due to CCH. In particular, synaptic protein and lipid metabolism, as well as GABA shunt-related proteins showed increased while neurotransmission and synaptic assembly-related proteins showed decreased protein level changes in CCH rats. Protein network analysis of CCH-induced protein alterations suggested the importance of increased synaptic apolipoprotein E (APOE) level as a consequence of CCH. Therefore, the change in APOE level was confirmed with Western blotting. The identified synaptic protein changes would precede the onset of dementia-like symptoms in the CCH model, suggesting their importance in the development of vascular dementia.

Implementation of a miniature sized, battery powered electrophysiological signal-generator for testing multi-channel recording equipments.

Testing electrophysiological recording equipments is an important task in multi-channel extracellular in vivo electrophysiology. In this paper, a miniature, battery powered multi-channel electrophysiological signal-generator (ESG) is described that was designed for this purpose. The device is based on a Xilinx CPLD (Complex Programmable Logic Device) and it is powered by a 3V lithium coin battery. It is a useful tool for calibration and testing the performance, quality and parameters of the recording equipments used for acquiring EEG, field potentials, ECG, EMG, and multiple unit activity. The device is ideally suited to identify instances when errors interfere with the proper recording, and repair of wiring or service of the equipment is needed. Two versions of the device are described; one is for 16 (ESG16), and another is for 32 channels (ESG32). Both versions provide amplitude and time calibration, as well as cross-talk and CMRR (common mode rejection ratio) testing for the recording equipment.

Improved version of the printed circuit board (PCB) modular multi-channel microdrive for extracellular electrophysiological recordings.

The modular multi-channel PCB microdrive was described some years ago, since then several improvements were introduced while using these drives. Utilizing several years of experience with the original PCB microdrive we redesigned it to improve its stability and usability. The application of the printed circuit board technology and the extensive use of flexible fused silica capillaries for fabrication of the microdrive are described in detail. The improved design led to a low cost and light-weight multi-channel microdrive with outstanding modularity for extracellular field, single unit or multiunit tetrode recording up to 64/128 channels.

Central sensitization-related changes of effective and functional connectivity in the rat inflammatory trigeminal pain model.

Central sensitization is a key mechanism in the pathology of several neuropathic pain disorders. We aimed to investigate the underlying brain connectivity changes in a rat model of chronic pain. Non-noxious whisker stimulation was used to evoke blood-oxygen-level-dependent (BOLD) responses in a block-design functional Magnetic Resonance Imaging (fMRI) experiment on 9.4T. Measurements were repeated two days and one week after injecting complete Freund's adjuvant into the rats' whisker pad. We found that acute pain reduced activation in the barrel cortex, most probably due to a plateau effect. After one week, increased activation of the anterior cingulate cortex was found. Analyses of effective connectivity driven by stimulus-related activation revealed that chronic pain-related central sensitization manifested as a widespread alteration in the activity of the somatosensory network. Changes were mainly mediated by the anterior cingulate cortex and the striatum and affected the somatosensory and motor cortices and the superior colliculus. Functional connectivity analysis of nested BOLD oscillations justified that the anterior cingular-somatosensory interplay is a key element of network changes. Additionally, a decreased cingulo-motor functional connectivity implies that alterations also involve the output tract of the network. Our results extend the knowledge about the role of the cingulate cortex in the chronification of pain and indicate that integration of multiple connectivity analysis could be fruitful in studying the central sensitization in the pain matrix.

Proteomic investigation of the prefrontal cortex in the rat clomipramine model of depression.

Neonatal rodents chronically treated with the tricyclic antidepressant clomipramine show depression-like behavior, which persists throughout adulthood. Therefore, this animal model is suitable to investigate the pathomechanism of depression, which is still largely unknown at the molecular level beyond monoaminergic dysfunctions. Here, we describe protein level changes in the prefrontal cortex of neonatally clomipramine-treated adult rats correlating with behavioral abnormalities. Clomipramine was administered to rat pups twice daily between postnatal days 8-21, while controls received saline injections. Behavioral tests were performed on 3months old rats. The proteomic study was conducted using two-dimensional differential gel electrophoresis. We have identified 32 proteins by mass spectrometry analysis of the significantly altered protein spots. The changed proteins are related to several biological functions, such as inflammation, transcription, cell metabolism and cytoskeleton organization. Among the altered proteins, the level of macrophage migration inhibitory factor showed the largest alteration, which was confirmed with Western blot. Macrophage migration inhibitory factor showed widespread distribution and was predominantly expressed in astrocytes in the forebrain of rats which were described using immunohistochemistry. We conclude that neonatal clomipramine exposure induces sustained modification in the proteome, which may form the molecular basis of the observed depression-like behavior in adult rats. BIOLOGICAL SIGNIFICANCE: It is known that some of the psychiatric disorders, such as autism, depression or schizophrenia may be at least in part, developmental disorders. We hypothesized that clomipramine treatment in early stage of brain development, which is known to induce depression-like behavior in adult rats, results in pathological distortion in neuronal and glial network development, which can be reflected by the cellular proteome in adulthood. Thus, we performed an unbiased proteomics experiment in adult rats, which were neonatally administered with clomipramine to reveal protein level changes three months after treatment. Many of the identified changed proteins are previously associated with depressive symptoms, e.g., the macrophage migration inhibitory factor (MIF), the level of which showed the largest alteration among the identified proteins. Based on our data, we suggest that neonatal clomipramine treatment is a reliable model to study the developmental effect of psychoactive drugs applied in the sensitive early phase of brain development. Furthermore, our findings support the idea that the alteration of early development of the brain induced by antidepressant treatment could result in sustained pathological changes in the cellular phenotype in the prefrontal cortex leading to depression-like behavioral symptoms.

The application of elastomeric connector for multi-channel electrophysiological recordings.

Interest in recording multi-channel electrophysiological data from behaving animals is rapidly growing, and many laboratories tend to record a large number of EEG and/or multi-unit channels, despite the limitation of the size of the headpiece that a small behaving animal can carry. A common drawback of these experiments, therefore, is the relatively large size of even the smallest, commercially available, high-density micro-connectors for the headset. To overcome this problem, we suggest the application of elastomeric or silicone inter-rubber connectors, that are widely used in electronics. The elastomeric or "zebra" connector consists of alternating thin strips of layered electrically conductive and non-conductive materials. The conductive strips provide electrical connections between uninsulated contact surfaces of printed circuit boards such as the connector plate of the micro-drive, that holds the brain electrode wires, and the preamplifier board of the recording system. In the present paper, we provide technical details of the design of this type of connector-sets and discuss common issues arising from their use. By comparing the applicability of two designs, we aim to demonstrate the simplicity, reliability and durability of the elastomeric inter-rubber connectors in electrophysiological experiments on freely moving laboratory animals.