Neuroprotective effects of levothyroxine on cognition deficits and memory in an experimental model of Huntington's disease in rats: An electrophysiological study

Huntington's disease (HD) is a neurodegenerative disorder characterized by cognitive deficits and motor function. Levothyroxine (L-T4) is a synthetic form of Thyroxine (T4), which can improve cognitive ability. The aim of the present study was to determine the neuroprotective effect of L-T4 administration in rats with 3-nitropropionic acid (3-NP)-induced Huntington's disease. Forty-eight Wistar male rats were divided into six groups (n = 8): Group 1 control group that received physiological saline, Group 2 and 3: which received L-T4 (30 and 100 μg/kg), Group 4: HD group that received 3-NP and Groups 5 and 6: The treatment of the HD rats with L-T4 (30 and 100 μg/kg). Spatial memory, locomotor activity, and frequency of neuronal firing were assessed. After decapitation, the Brain-Derived Neurotrophic Factor (BDNF) and Total antioxidant capacity (TAC) levels in the striatum was measured. The results showed that the indices of spatial memory (mean path length and latency time) and motor dysfunction (immobility time) significantly increased, while time spent in the goal quadrant, swimming speed, spike rate, and striatum levels of BDNF significantly decreased in the HD group compared to the control group. L-T4 treatment significantly enhanced time spent in the goal quadrant, swimming speed, motor activity (number of line crossing and rearing), spike rate and striatal BDNF level. This research showed that L-T4 prevented the disruption of motor activity and cognitive deficiencies induced by 3-NP. The beneficial effects of L-T4 may be due to an increase in the concentration of BDNF and enhancement of the spike rate in the striatum.

Exendin-4 increases the firing activity of hippocampal CA1 neurons through TRPC4/5 channels

The central neuropeptide GLP-1 is synthesized by preproglucagon (PPG) neurons in the brain. GLP-1 receptors are widely distributed in central nervous system. Hippocampus is a key component of the limbic system which is involved in learning, memory, and cognition. Previous studies have shown that overexpression of GLP-1 receptors in the hippocampus could improve the process of learning and memory. However, up to now, the direct electrophysiological effects and possible molecular mechanisms of GLP-1 in hippocampal CAl neurons remain unexplored. The present study aims to evaluate the effects and mechanisms of GLP-1 on the spontaneous firing activity of hippocampal CAl neurons. Employing multibarrel single-unit extracellular recordings, the present study showed that micro-pressure administration of GLP-1 receptor agonist, exendin-4, significantly increased the spontaneous firing rate of hippocampal CA1 neurons in rats. Furthermore, application of the specific GLP-1 receptor antagonist, exendin(9-39), alone significantly decreased the firing rate of CA1 neurons, suggesting that endogenous GLP-1 modulates the firing activity of CA1 neurons. Co-application of exendin(9-39) completely blocked exendin-4-induced excitation of hippocampal CA1 neurons. Finally, the present study demonstrated for the first time that the transient receptor potential canonical 4 (TRPC4)/TRPC5 channels may be involved in exendin-4-induced excitation. The present studies may provide a rationale for further investigation of the modulation of GLP-1 on learning and memory as well as its possible involvement in Alzheimer's disease.

Configuration-sensitive face-body interactions in primate visual cortex

Traditionally, the neural processing of faces and bodies is studied separately, although they are encountered together, as parts of an agent. Despite its social importance, it is poorly understood how faces and bodies interact, particularly at the single-neuron level. Here, we examined the interaction between faces and bodies in the macaque inferior temporal (IT) cortex, targeting an fMRI-defined patch. We recorded responses of neurons to monkey images in which the face was in its natural location (natural face-body configuration), or in which the face was mislocated with respect to the upper body (unnatural face-body configuration). On average, the neurons did not respond stronger to the natural face-body configurations compared to the summed responses to their faces and bodies, presented in isolation. However, the neurons responded stronger to the natural compared to the unnatural face-body configurations. This configuration effect was present for face- and monkey-centered images, did not depend on local feature differences between configurations, and was present when the face was replaced by a small object. The face-body interaction rules differed between natural and unnatural configurations. In sum, we show for the first time that single IT neurons process faces and bodies in a configuration-specific manner, preferring natural face-body configurations.

Effects of Memantine on the Spontaneous Firing Frequency of Hippocampal CA1 Pyramidal Neurons in Intact and Alzheimer Rat Model: An Electrophysiological Study

Introduction

Memantine (MEM) is a noncompetitive N-methyl-D-aspartate receptor (NMDAR) antagonist clinically used for the treatment of Alzheimer disease (AD) in mild to severe conditions. The present study was conducted to investigate the effects of memantine on the spontaneous firing frequency of CA1 pyramidal neurons in rats caused by an electrical lesion of Nucleus Basalis Magnocellularis (NBM). Then, this model of AD rats was compared with the intact adult male rats.

Methods

In this study, adult male rats were divided into two groups. Group I (lesion of NBM, n=53) includes the following subgroups: lesion+saline, sham+saline, lesion+MEM 5 mg/kg, lesion+MEM 10 mg/kg, and lesion+MEM 20mg/kg. Group II (intact, n=48) includes the following subgroups: intact+saline, intact+MEM 3mg/kg, intact+MEM 5mg/kg, and intact+MEM 10mg/kg. Extracellular single-unit recording (15 min baseline+105 min after MEM or saline) was performed under urethane-anesthetized rats.

Results

The results showed that the mean frequency of CA1 pyramidal neurons after saline in the lesion+saline (P<0.001) group significantly decreases compared with the intact+saline and sham+saline groups. In addition, after saline and memantine, the mean frequency of CA1 pyramidal neurons in the lesion+MEM 10 mg/kg (P<0.01) and lesion+MEM 20 mg/kg (P<0.001) groups significantly increased compared with the lesion+saline group. Also, the mean frequencies of CA1 pyramidal neurons in the intact+MEM 10 mg/kg (P<0.001) group significantly decreased compared with the intact+saline group.

Conclusion

Results showed that memantine increases the electrical activity of CA1 pyramidal neurons in a rat model of AD. Furthermore, in the intact adult male rats, the low-dose memantine, contrary to high dose, does not decrease the electrical activity of CA1 pyramidal neurons.

Dopaminergic and nitric oxide systems interact to regulate the electrical activity of neurons in the medial septal nucleus in rats

Research characterizing the neuronal substrate of anxiety has implicated different brain areas, including the medial septal nucleus (m-SEPT). Previous reports indicated a role of dopamine and nitric oxide (NO) in anxiety-related behaviors. In this study, the extracellular single-unit recording was performed from the m-SEPT in adult male albino Wistar rats. Baseline activity was recorded for 5 min, and the post-injection recording was performed for another 5 min after the microinjection of each drug. The results showed that (1) both D1- and D2-like receptor agonists (SKF-38393 and quinpirole) enhanced the firing rate of m-SEPT neurons; (2) both D1- and D2-like antagonists (SCH-23390 and sulpiride) attenuated the firing rate of m-SEPT neurons; (3) L-arginine (NO precursor) increased the firing rate of m-SEPT neurons, but a non-specific NOS inhibitor, L-NAME, elicited no significant alterations; (4) the non-specific NOS inhibitor reversed the enhanced firing rate produced by SKF-38393 and quinpirole; (5) neither of the dopaminergic antagonists changed the enhanced activity resulted from the application of the NO precursor. These results contribute to our understanding of the complex neurotransmitter interactions in the m-SEPT and showed that both dopaminergic and NO neurotransmission are involved in the modulation of the firing rate of neurons in the m-SEPT.

Prolonged morphine exposure during adolescence alters the responses of lateral paragigantocellularis neurons to naloxone in adult morphine dependent rats

INTRODUCTION

Adolescence is a critical period in brain development, and it is characterized by persistent maturational alterations in the function of central nervous system. In this respect, many studies show the non-medical use of opioid drugs by adolescents. Although this issue has rather widely been addressed during the last decade, cellular mechanisms through which adolescent opioid exposure may induce long-lasting effects are not duly understood. The present study examined the effect of adolescent morphine exposure on neuronal responses of lateral paragigantocellularis nucleus to naloxone in adult morphine-dependent rats.

METHODS

Adolescent male Wistar rats (31 days old) received increasing doses of morphine (from 2.5 to 25 mg/kg, twice daily, s.c.) for 10 days. Control subjects were injected saline with the same protocol. After a drug-free interval (20 days), animals were rendered dependent on morphine during 10 days (10 mg/kg, s.c., twice daily). Then, extracellular single-unit recording was performed to investigate neural response of LPGi to naloxone in adult morphine-dependent rats.

RESULTS

Results indicated that adolescent morphine treatment increases the number of excitatory responses to naloxone, enhances the baseline activity and alters the pattern of firing in neurons with excitatory responses in adult morphine-dependent rats. Moreover, the intensity of excitatory responses is reduced following the early life drug intake.

CONCLUSION

It seems that prolonged opioid exposure during adolescence induces long-lasting neurobiological changes in LPGi responsiveness to future opioid withdrawal challenges.

Deep Brain Stimulation Using Animal Models of Parkinson's Disease

The use of deep brain stimulation (DBS) as a therapy for neurological disorders, especially Parkinson's disease (PD), is widely applied in the field of functional neurosurgery. Both the subthalamic nucleus and the globus pallidus interna are major targets for PD. Experimental DBS is performed using animal models to evaluate new indications and promote advancements in technology. In this chapter, we reviewed our experience with the concept of experimental DBS, including its development and validation. The following work aimed to establish that experimental DBS in animals is an adequate tool for exploring new indications for DBS and to further refine DBS technology.

Mutual assistance of nucleus accumbens cannabinoid receptor-1 and orexin receptor-2 in response to nicotine: a single-unit study

Background and purpose:

The nucleus accumbens (NAc) express both orexin-2 receptor (OX2R) and cannabinoid receptor type 1 (CB1R). Orexin and cannabinoid regulate the addictive properties of nicotine. In this study, the effect of the CB1R blockade on the electrical activity of NAc neurons in response to nicotine, and its probable interaction with the OX2R in this event, within this area, were examined via the single-unit recording.

Experimental approach:

The spontaneous firing rate of NAc was initially recorded for 15 min, and then 5 min before subcutaneous injection of nicotine (0.5 mg/kg)/saline, AM251 and TCS-OX2-29 were injected into the NAc. Neuronal responses were recorded for 70 min, after nicotine administration.

Findings/Results:

Nicotine excited the NAc neurons significantly and intra-NAc microinjection of AM251 (25 and 125 ng/rat), as a selective CB1R antagonist, prevented the nicotine-induced increases of NAc neuronal responses. Moreover, microinjection of AM251 (125 ng/rat), before saline injection, could not affect the percentage of change of the neuronal response. Finally, simultaneous intra-NAc administration of the effective or ineffective doses of AM251 and TCS-OX2-29 (a selective antagonist of OX2R) prevented the nicotine- induced increases of NAc neuronal responses, so that there was a significant difference between the group received ineffective doses of both antagonists and the AM251 ineffective dose.

Conclusion and implications:

The results suggest that the CB1R can modulate the NAc reaction to the nicotine, and it can be concluded that there is a potential interplay between the OX2R and CB1R in the NAc, in relation to nicotine.

Single-unit Recording in Awake Behaving Non-human Primates

Non-human primates (NHPs) have been widely used as a species model in studies to understand higher brain functions in health and disease. These studies employ specifically designed behavioral tasks in which animal behavior is well-controlled, and record neuronal activity at high spatial and temporal resolutions while animals are performing the tasks. Here, we present a detailed procedure to conduct single-unit recording, which fulfils high spatial and temporal resolutions while macaque monkeys (i.e., widely used NHPs) perform behavioral tasks in a well-controlled manner. This procedure was used in our previous study to investigate the dynamics of neuronal activity during economic decision-making by the monkeys. Monkeys' behavior was quantitated by eye position tracking and button press/release detection. By inserting a microelectrode into the brain, with a grid system in reference to magnetic resonance imaging, we precisely recorded the brain regions. Our experimental system permits rigorous investigation of the link between neuronal activity and behavior.

Recording and quantifying sympathetic outflow to muscle and skin in humans: methods, caveats and challenges

The development of microneurography, in which the electrical activity of axons can be recorded via an intrafascicular microelectrode inserted through the skin into a peripheral nerve in awake human participants, has contributed a great deal to our understanding of sensorimotor control and the control of sympathetic outflow to muscle and skin. This review summarises the different approaches to recording muscle sympathetic nerve activity (MSNA) and skin sympathetic nerve activity (SSNA), together with discussion on the issues that determine the quality of a recording. Various analytical approaches are also described, with a primary emphasis on those developed by the author, aimed at maximizing the information content from recordings of postganglionic sympathetic nerve activity in awake humans.

KCC2 antagonism and gabaergic synchronization in the entorhinal cortex in the absence of ionotropic glutamatergic receptor signalling

γ-Aminobutyric acid (GABA), which is released by interneurons, plays an active role in generating interictal epileptiform spikes during blockade of ionotropic glutamatergic signalling, but it remains unclear whether and how the K+-Cl- cotransporter 2 (KCC2) influences these paroxysmal events. Therefore, we employed tetrode recordings in the in vitro rat entorhinal cortex (EC) to analyze the effects of the KCC2 antagonist VU0463271 on 4-aminopyridine (4AP)-induced interictal spikes that were pharmacologically isolated by applying ionotropic glutamatergic receptor antagonists. After the addition of VU0463271, these interictal spikes continued to occur at similar rates as in control (i.e., during application of 4AP with ionotropic glutamatergic receptor antagonists) but were smaller and shorter. Despite the absence of ionotropic glutamatergic receptor signalling, both interneurons and principal cells increased their firing during interictal spikes. Moreover, we found that KCC2 antagonism increased interneuron firing but decreased principal cell firing during the interictal spike rising phase; in contrast, during the falling phase, interneuron firing decreased in the presence of VU0463271 while no change was observed in principal cell firing. Overall, our results show that KCC2 antagonism enhances interneuron excitability at the onset of interictal spikes generated by the EC neuronal networks during blockade of ionotropic glutamatergic transmission but disrupts later neuronal recruitment.

Cortical processing of configurally perceived odor mixtures

Most odors are not composed of a single volatile chemical species, but rather are mixtures of many different volatile molecules, the perception of which is dependent on the identity and relative concentrations of the components. Changing either the identity or ratio of components can lead to shifts between configural and elemental perception of the mixture. For example, a 30/70 ratio of ethyl isobutyrate (odorant A, a strawberry scent) and ethyl maltol (odorant B, a caramel scent) is perceived as pineapple by humans - a configural percept distinct from the components. In contrast, a 68/32 ratio of the same odorants is perceived elementally, and is identified as the component odors. Here, we examined single-unit responses in the anterior and posterior piriform cortex (aPCX and pPCX) of mice to these A and B mixtures. We first demonstrate that mouse behavior is consistent with a configural/elemental perceptual shift as concentration ratio varies. We then compared responses to the configural mixture to those evoked by the elemental mixture, as well as to the individual components. Hierarchical cluster analyses suggest that in the mouse aPCX, the configural mixture was coded as distinct from both components, while the elemental mixture was coded as similar to the components. In contrast, mixture perception did not predict pPCX ensemble coding. Similar electrophysiological results were also observed in rats. The results suggest similar perceptual characteristics of the AB mixture across species, and a division in the roles of aPCX and pPCX in the coding of configural and elemental odor mixtures.

Carbon monofilament electrodes for unit recording and functional MRI in same subjects

Extracellular electrophysiology and functional MRI are complementary techniques that provide information about cellular and network-level neural activity, respectively. However, electrodes for electrophysiology are typically made from metals, which cause significant susceptibility artifacts on MR images. Previous work has demonstrated that insulated carbon fiber bundle electrodes reduce the volume of magnetic susceptibility artifacts and can be used to record local field potentials (LFP), but the relatively large diameter of the probes make them unsuitable for multi- and single-unit recordings. Although single carbon fiber electrodes have recently been used to record single-unit activity, these probes require modifications in order to aid insertion and the use of these probes in fMRI has yet to be validated. Therefore, there is a need for a single-carbon fiber electrode design that (1) minimizes the volume of the susceptibility artifact, (2) can record from a wide frequency band that includes LFP and multi- and single-unit recording, and (3) is practical to insert without additional modifications. Here, we demonstrate that carbon-fiber electrodes made from single carbon monofilaments (35 μm in diameter) meet all of these criteria. Carbon monofilament electrodes modified with the conductive polymer poly(3,4-ethylenedioxythiophene) (PEDOT) have lower impedances and higher signal-to-noise ratio recordings than platinum-iridium electrodes, a current gold standard for chronic single-unit recording. Furthermore, these probes distort a significantly smaller volume of voxels compared to tungsten and platinum-iridium electrodes in agarose phantom and in vivo MR images, leading to higher contrast-to-noise ratio in regions proximal to the electrode implantation site during fMRI. Collectively, this work establishes that carbon monofilaments are a practical choice for combined electrophysiology-fMRI experiments.

Melatonin improves quality and longevity of chronic neural recording

The chronic performance of implantable neural electrodes is hindered by inflammatory brain tissue responses, including microglia activation, glial scarring, and neuronal loss. Melatonin (MT) has shown remarkable neuroprotective and neurorestorative effects in treating central nervous system (CNS) injuries and degeneration by inhibiting caspase-1, -3, and -9 activation and mitochondrial cytochrome c release, as well as reducing oxidative stress and neuroinflammation. This study examined the effect of MT administration on the quality and longevity of neural recording from an implanted microelectrode in the visual cortex of mice for 16 weeks. MT (30 mg/kg) was administered via daily intraperitoneal injection for acute (3 days before and 14 days post-implantation) and chronic (3 days before and 16 weeks post-implantation) exposures. During the first 4 weeks, both MT groups showed significantly higher single-unit (SU) yield, signal-to-noise ratio (SNR), and amplitude compared to the vehicle control group. However, after 4 weeks of implantation, the SU yield of the acute treatment group dropped to the same level as the control group, while the chronic treatment group maintained significantly higher SU yield compared to both acute (week 5-16) and control (week 0-16) mice. Histological studies revealed a significant increase in neuronal viability and decrease in neuronal apoptosis around the implanted electrode at week 16 in the chronic group in comparison to control and acute subjects, which is correlated with reduced oxidative stress and increased number of pro-regeneration arginase-1 positive microglia cells. These results demonstrate the potent effect of MT treatment in maintaining a high-quality electrode-tissue interface and suggest that MT promotes neuroprotection possibly through its anti-apoptotic, anti-inflammatory, and anti-oxidative properties.

Peripheral and central administration of T3 improved the histological changes, memory and the dentate gyrus electrophysiological activity in an animal model of Alzheimer's disease

The amyloid beta (Aβ) induced Alzheimer's disease (AD) is associated with formation the amyloid plaques, cognitive impairments and decline in spontaneous discharge of neurons. In the current study, we evaluated the effect of subcutaneous (S. C) and intrahippocampal (I. H) administrations of triiodothyronine (T3) on the histological changes, memory and the dentate gyrus (DG) electrophysiological activity in an animal model of AD. Eighty adult male Wistar rats (250-300 g) were divided randomly into five groups: Sham-Operated (Sh-O), AD + Vehicle (S. C), AD + Vehicle (I. H), AD+ T3 (S. C) and AD + T3 (I. H). In order to induce animal model of AD, Aβ (10 ng/μl, bilaterally) were injected intrahippocampally. Rats were treated with T3 and/or normal saline for 10 days. Passive avoidance and spatial memory were evaluated in shuttle box apparatus and Morris water maze, respectively. Neuronal single unit recording was assessed from hippocampal DG. The percent of total time that animals spent in target quarter, the mean latency time (sec), the step through latency and the average number of spikes/bin were decreased significantly in AD rats compared with the Sh-O group (p < 0.001) and were increased significantly in AD groups that have received T3 (S. C and I. H) in compared with AD group (p < 0.01, p < 0.001). Also, formation of amyloid plaques was decreased in AD rats treated with T3.The results showed that T3 injection (S. C and I. H), by reduction of neural damage and increment of neuronal spontaneous activity improved the memory deficits in Aβ-induced AD rats.

Central and peripheral administrations of levothyroxine improved memory performance and amplified brain electrical activity in the rat model of Alzheimer's disease

Alzheimer's disease (AD) is associated with cognitive impairments and a decline in the spontaneous neuronal discharge. In the current study, we evaluated the effect of subcutaneous (S.C.) and intrahippocampal (I.H.) administrations of levothyroxine (LT-4) on the passive avoidance and spatial memory, as well as electrophysiological activity in an animal model of AD. One hundred-sixty male Wistar rats were divided into two main groups. The S.C. group included two Sham and four AD (vehicle or L-T4 25, 50 & 100μg/kg); and the I.H. had consisted of two Sham and two AD (vehicle or L-T4 10μg/kg) subgroups. To make an animal model of AD, amyloid beta (Aβ) plus ibotenic acid (Ibo) were injected I.H. Rats were treated with L-T4 and/or normal saline for ten days. Passive avoidance and spatial memory were evaluated in shuttle box and Morris water maze, respectively. Neuronal single unit recording was assessed from hippocampal dentate gyrus (DG). Results showed that the mean latency time (s) increased significantly (p<0.001) in AD animals and decreased significantly in both S.C. and I.H. L-T4 injected AD animals, compared with the AD group (p<0.001). The percentage of total time that animals spent in goal quarter and the step through latency decreased significantly in AD rats (p<0.001) and increased significantly in both S.C. and I.H. L-T4 injected AD animals in comparison with the AD group (p<0.01, p<0.001). Data showed that the average number of spikes/bin significantly decreased in the AD group (p<0.001). The S.C. and I.H. L-T4 injections in AD rats significantly increased the spike rate in comparison to the AD group (p<0.001). In conclusion, both S.C. and I.H. injections of L-T4 alleviated memory deficits and spontaneous neuronal activity in Aβ-induced AD rats. Also, I.H. microinjection of L-T4 had more beneficial effects on memory and neuronal electrophysiological activity in comparison to S.C. administration.

Long-lasting single-neuron labeling by in vivo electroporation without microscopic guidance

In order to make a direct link between the morphological and functional study of the nervous system, we established an experimental protocol for labeling individual neurons persistently without microscopic guidance by injecting a plasmid encoding fluorescent protein electroporatively after recording their activity extracellularly. Using a glass pipette filled with electrolyte solution containing a plasmid encoding green fluorescent protein (GFP), single-neuron recording and electroporation were performed on anesthetized rats. When performing the electroporation at the completion of recording, the degree of contact between the target neuron and the electrode tip was adjusted by monitoring the change of the trace of recorded action potentials and the increase of electrode resistance. The expression of GFP and its immunostaining with a polyclonal antibody enabled us to clearly see the basic structural components such as cell bodies, axons, dendrites, and even smaller components such as spines. Identification of the morphological subtypes of neurons was possible with every labeled neuron. The optimum condition for labeling was a 30% increase of the electrode resistance, and the labeling success rate evaluated 3 days after labeling was 40%. The rate evaluated one month after labeling was only slightly lower (33%). We also confirmed experimentally that this recording and labeling procedure can be similarly successful in head-fixed behaving rats. This new experimental protocol will be a breakthrough in systems neuroscience because it makes a direct link between the morphology and behavior-related activity of single neurons.