Higher Action Potential Amplitude Research Articles

Electrophysiological and Morphological Features of Rebound Depolarization Characterized Interneurons in Rat Superficial Spinal Dorsal Horn.

Substantia gelatinosa (SG) neurons, which are located in the spinal dorsal horn (lamina II), have been identified as the “central gate” for the transmission and modulation of nociceptive information. Rebound depolarization (RD), a biophysical property mediated by membrane hyperpolarization that is frequently recorded in the central nervous system, contributes to shaping neuronal intrinsic excitability and, in turn, contributes to neuronal output and network function. However, the electrophysiological and morphological properties of SG neurons exhibiting RD remain unclarified. In this study, whole-cell patch-clamp recordings were performed on SG neurons from parasagittal spinal cord slices. RD was detected in 44.44% (84 out of 189) of the SG neurons recorded. We found that RD-expressing neurons had more depolarized resting membrane potentials, more hyperpolarized action potential (AP) thresholds, higher AP amplitudes, shorter AP durations, and higher spike frequencies in response to depolarizing current injection than neurons without RD. Based on their firing patterns and morphological characteristics, we propose that most of the SG neurons with RD mainly displayed tonic firing (69.05%) and corresponded to islet cell morphology (58.82%). Meanwhile, subthreshold currents, including the hyperpolarization-activated cation current (Ih) and T-type calcium current (IT), were identified in SG neurons with RD. Blockage of Ih delayed the onset of the first spike in RD, while abolishment of IT significantly blunted the amplitude of RD. Regarding synaptic inputs, SG neurons with RD showed lower frequencies in both spontaneous and miniature excitatory synaptic currents. Furthermore, RD-expressing neurons received either Aδ- or C-afferent-mediated monosynaptic and polysynaptic inputs. However, RD-lacking neurons received afferents from monosynaptic and polysynaptic Aδ fibers and predominantly polysynaptic C-fibers. These findings demonstrate that SG neurons with RD have a specific cell-type distribution, and may differentially process somatosensory information compared to those without RD.

Development of Action Potential Waveform in Hippocampal CA1 Pyramidal Neurons

CA1 pyramidal neurons undergo intense morphological and electrophysiological changes from the second to third postnatal weeks in rats throughout a critical period associated with the emergence of exploratory behavior. Using whole cell current-clamp recordings in vitro and neurochemical methods, we studied the development of the somatic action potential (AP) waveform and some of the underlying channels in this critical period. At the third postnatal week, APs showed a more hyperpolarized threshold, higher duration and amplitude. Subthreshold depolarization broadened APs and depolarized their peak overshoots more pronouncedly in immature neurons (2 weeks old). These features were mimicked by pharmacologically blocking the fast-inactivating A-type potassium current (IA) and matched well with the higher concentrations of Kv4.2 and Kv4.3 and the lower concentrations of BK and Kv1.2 channels detected by Western blotting. Repetitive stimulation with high frequency trains (50 Hz) reproduced AP broadening associated to inactivation of the A-type current in immature cells. Moreover, repetitive firing showed changes in AP amplitude consistent with the inactivation of both sodium and potassium subthreshold currents, which resulted in higher AP amplitudes in the more immature neurons. We propose that maturation of AP waveform and excitability in this critical developmental period could be related to the onset of exploratory behaviors.

Ultrasound guidance for sural nerve conduction studies.

Ultrasound can potentially identify nerves and guide recording and stimulating electrode placement for nerve conduction studies (NCS). This prospective study was performed to determine whether ultrasound guidance of sural NCS results in higher action potential amplitude, fewer stimuli required, lower stimulus strength required, and less pain experienced. Fourteen healthy individuals underwent bilateral sural NCS, both with and without ultrasound guidance. Studies were separated by at least 48 h, and the order of testing was randomly assigned. Ultrasound guidance resulted in significantly fewer stimuli and lower stimuli strength required to obtain supramaximal responses (P < 0.01-0.03). Ultrasound guidance required significantly more time to perform than standard sural NCS (P < 0.01). There was no difference in sural nerve amplitude or pain rating between the 2 groups. Neuromuscular ultrasound can be used effectively to guide electrode placement during sural NCS. Muscle Nerve 59:705-707, 2019.

YIA3 Regional Action Potential Gradients in the Murine Left Atrium

Background Regional differences in action potential (AP) morphology in the adult left atrium (LA) may account for susceptibility to atrial fibrillation. The posterior LA wall close to the junction with the pulmonary veins (LA-PV) is an important area contributing to initiation and maintenance of atrial fibrillation. The posterior LA has a distinct embryologic origin: Its development is regulated by PITX2, a gene that has been inflicted in the genetic predisposition to AF. So far, it is not known whether the electrophysiology of the posterior LA differs from that of other parts of the LA. We therefore characterised the electrical phenotype of the LA-PV compared to other LA regions. Methods Transmembrane (TAPs) and optical (OAPs) action potentials were recorded from 20 superfused murine LA taken from 12 male and 8 female mice aged 12–20 W, bred on an MF1 background. Optical high-density AP mapping was performed and optical APs were recorded from 9 regions across the LA using a dedicated murine activation system (Hamamatsu ORCA flash 4, Di-4-Anepps, sampling rate 1–2 kHz). OAPs were analysed using custom made algorithms produced in MATLAB. At each cycle length, 25 action potentials were averaged to generate a mean waveform that was then used for analysis. TAPs were recorded from 3 LA regions: 1) the posterior LA towards the junction with the pulmonary vein (LA-PV), 2) the medial dome (LA-M) and 3) the LA lateral wall (LA-LW). All Preparations were paced at 100ms. Results OAP distribution maps (n = 8 LA) identified a LA-PV to LA-LW pattern of APD shortening and also demonstrated that there is relatively high local APD heterogeneity within the LA-PV region. TAP recordings identified a higher action potential amplitude (APA) in the LA-PV (84 ± 2 mV) than LA-M (78 ± 1 mV, p Conclusion Regional AP differences in the murine LA clearly suggest that the posterior left atrium has a distinct electrophysiological profile which may render this region susceptible to the genesis and maintenance of AF. Prolonged APD and higher AP amplitude suggest a role as a driver of electrical LA activity. Further studies are warranted to determine whether PITX2 is important for the maintenance of these electrophysiological differences.

Changes in motor unit properties in SOD1 (G93A) rats

In amyotrophic lateral sclerosis (ALS), progressive death of motor neurons results in denervation and reinnervation of muscles. It is not clear how ALS affects the properties of motor units (MUs). Properties of single MUs in the medial gastrocnemius (MG) muscle of rats bearing the human mutated superoxide dismutase gene type 1 (SOD1) were determined at 3 stages: asymptomatic (ALS I); early symptomatic (ALS II); and terminal (ALS III). In ALS II, higher proportions of FF (fast fatigable) and S (slow) MUs were observed, whereas in ALS III higher percentages of S and lower percentages of FF MUs were noted compared with controls. S motor neurons reinnervated fast muscle fibers, and those MUs gained some properties of fast MUs, including lower fatigue resistance, greater force generation, and higher action potential amplitudes. Changes in MU properties of SOD1 rats have progressive and multidirectional character and speed depending on the MU type.