Recording Temperature Affects the Excitability of Mouse Superficial Dorsal Horn Neurons, In Vitro

2008 ◽  
Vol 99 (5) ◽  
pp. 2048-2059 ◽  
Author(s):  
B. A. Graham ◽  
A. M. Brichta ◽  
R. J. Callister
Keyword(s):  
Spinal Cord ◽  
Elevated Temperature ◽  
Dorsal Horn ◽  
Current Injection ◽  
Resting Membrane Potential ◽  
Temperature Sensitive ◽  
Superficial Dorsal Horn ◽  
Pain Mechanisms

Superficial dorsal horn (SDH) neurons in laminae I–II of the spinal cord play an important role in processing noxious stimuli. These neurons represent a heterogeneous population and are divided into various categories according to their action potential (AP) discharge during depolarizing current injection. We recently developed an in vivo mouse preparation to examine functional aspects of nociceptive processing and AP discharge in SDH neurons and to extend investigation of pain mechanisms to the genetic level of analysis. Not surprisingly, some in vivo data obtained at body temperature (37°C) differed from those generated at room temperature (22°C) in spinal cord slices. In the current study we examine how temperature influences SDH neuron properties by making recordings at 22 and 32°C in transverse spinal cord slices prepared from L3–L5 segments of adult mice (C57Bl/6). Patch-clamp recordings (KCH3SO4 internal) were made from visualized SDH neurons. At elevated temperature all SDH neurons had reduced input resistance and smaller, briefer APs. Resting membrane potential and AP afterhyperpolarization amplitude were temperature sensitive only in subsets of the SDH population. Notably, elevated temperature increased the prevalence of neurons that did not discharge APs during current injection. These reluctant firing neurons expressed a rapid A-type potassium current, which is enhanced at higher temperatures and thus restrains AP discharge. When compared with previously published whole cell recordings obtained in vivo (37°C) our results suggest that, on balance, in vitro data collected at elevated temperature more closely resemble data collected under in vivo conditions.

Developmental Changes in the Fidelity and Short-Term Plasticity of GABAergic Synapses in the Neonatal Rat Dorsal Horn

2008 ◽  
Vol 99 (6) ◽  
pp. 3144-3150 ◽  
Author(s):  
Rachel A. Ingram ◽  
Maria Fitzgerald ◽  
Mark L. Baccei
Keyword(s):  
Spinal Cord ◽  
Dorsal Horn ◽  
Receptive Fields ◽  
Neuronal Firing ◽  
Neonatal Rat ◽  
Superficial Dorsal Horn ◽  
Short Term ◽  
Dorsal Horn Neurons ◽  
Gabaergic Synapses

The lower thresholds and increased excitability of dorsal horn neurons in the neonatal rat suggest that inhibitory processing is less efficient in the immature spinal cord. This is unlikely to be explained by an absence of functional GABAergic inhibition because antagonism of γ-aminobutyric acid (GABA) type A receptors augments neuronal firing in vivo from the first days of life. However, it is possible that more subtle deficits in GABAergic signaling exist in the neonate, such as decreased reliability of transmission or greater depression during repetitive stimulation, both of which could influence the relative excitability of the immature spinal cord. To address this issue we examined monosynaptic GABAergic inputs onto superficial dorsal horn neurons using whole cell patch-clamp recordings made in spinal cord slices at a range of postnatal ages (P3, P10, and P21). The amplitudes of evoked inhibitory postsynaptic currents (IPSCs) were significantly lower and showed greater variability in younger animals, suggesting a lower fidelity of GABAergic signaling at early postnatal ages. Paired-pulse ratios were similar throughout the postnatal period, whereas trains of stimuli (1, 5, 10, and 20 Hz) revealed frequency-dependent short-term depression (STD) of IPSCs at all ages. Although the magnitude of STD did not differ between ages, the recovery from depression was significantly slower at immature GABAergic synapses. These properties may affect the integration of synaptic inputs within developing superficial dorsal horn neurons and thus contribute to their larger receptive fields and enhanced afterdischarge.

scholarly journals Low-Affinity Kainate Receptors and Long-Lasting Depression of NMDA-Receptor–Mediated Currents in Rat Superficial Dorsal Horn

1998 ◽  
Vol 80 (2) ◽  
pp. 895-902 ◽  
Author(s):  
Sandra Sequeira ◽  
Jacques Näsström
Keyword(s):  
Spinal Cord ◽  
Nmda Receptor ◽  
Dorsal Horn ◽  
Physiological Role ◽  
Kainate Receptors ◽  
Superficial Dorsal Horn ◽  
Electrophysiological Recordings

Sequeira, Sandra and Jacques Näsström. Low-affinity kainate receptors and long-lasting depression of NMDA-receptor–mediated currents in rat superficial dorsal horn. J. Neurophysiol. 80: 895–902, 1998. In an in vitro spinal cord slice preparation whole cell electrophysiological recordings of rat superficial dorsal horn neurons responding differentially to glutamate (Glu) and N-methyl-d-aspartate (NMDA) were investigated systematically for the role of kainate (KA) receptors in modulating their activity. In these neurons, coapplication of Glu and NMDA, as well as application of Glu immediately before NMDA, induced long- and short-lasting depressions of NMDA-induced currents as well as depression of NMDA-receptor–mediated excitatory postsynaptic currents. KA applied before NMDA mimicked Glu-induced attenuating effects. Furthermore, the low-affinity KA receptor antagonist 5-nitro-6,7,8,9- tetrahydrobenzo[G]indole-2,3-dione-3-oxime potentiated Glu-induced NMDA-receptor–mediated currents in neurons responding differentially to Glu and NMDA. These results provide evidence for a novel mechanism, which may relate to classical long-term depression, involving low-affinity KA receptors in long-lasting modulation of NMDA-receptor–mediated currents. This implies a physiological role of KA receptors in long-term modulation of sensory transmission in the superficial dorsal horn of rat spinal cord.

Electrotonic Structure of Motoneurons in the Spinal Cord of the Turtle: Inferences for the Mechanisms of Bistability

2001 ◽  
Vol 85 (1) ◽  
pp. 391-398 ◽  
Author(s):  
Gytis Svirskis ◽  
Aron Gutman ◽  
Jørn Hounsgaard
Keyword(s):  
Spinal Cord ◽  
Classical Method ◽  
Current Injection ◽  
Membrane Properties ◽  
Resting Membrane Potential ◽  
Synaptic Membrane ◽  
Field Stimulation ◽  
The Difference ◽  
Dendritic Branches

Understanding how voltage-regulated channels and synaptic membrane conductances contribute to response properties of neurons requires reliable knowledge of the electrotonic structure of dendritic trees. A novel method based on weak DC field stimulation and the classical method based on current injection were used to obtain two independent estimates of the electrotonic structure of motoneurons in an in vitro preparation of the turtle spinal cord. DC field stimulation was also used to ensure that the passive membrane properties near the resting membrane potential were homogeneous. In two cells, the difference in electrotonic lengths estimated with the two methods in the same cell was 6 and 9%. The majority of dendritic branches terminated at a distance of 1 electrotonic unit from the recording site. The longest branches reached 2 λ. In the third cell, the difference was 36%, demonstrating the need to use both methods, field stimulation and current injection, for reliable measurements of the electrotonical structure. Models of the reconstructed cells endowed with voltage-dependent conductances were used to explore generation mechanisms for the experimentally observed hysteresis in input current-voltage relation of bistable motoneurons. The results of modeling suggest that only some dendrites need to possess L-type calcium current to explain the hysteresis observed experimentally and that dendritic branches with different electrotonical lengths can be bistable. Independent bistable behavior in individual dendritic branches can make motoneurons complex processing units.

scholarly journals Serotonergic Modulation of Nociceptive Circuits in Spinal Cord Dorsal Horn

2019 ◽  
Vol 17 (12) ◽  
pp. 1133-1145 ◽  
Author(s):  
Rita Bardoni
Keyword(s):  
Spinal Cord ◽  
Dorsal Horn ◽  
Pain Modulation ◽  
Spinal Cord Dorsal Horn ◽  
Pain Transmission ◽  
Spinal Cord Dorsal ◽  
Spinal Cord Level ◽  
Serotonergic Modulation

Background: Despite the extensive number of studies performed in the last 50 years, aimed at describing the role of serotonin and its receptors in pain modulation at the spinal cord level, several aspects are still not entirely understood. The interpretation of these results is often complicated by the use of different pain models and animal species, together with the lack of highly selective agonists and antagonists binding to serotonin receptors. Method: In this review, a search has been conducted on studies investigating the modulatory action exerted by serotonin on specific neurons and circuits in the spinal cord dorsal horn. Particular attention has been paid to studies employing electrophysiological techniques, both in vivo and in vitro. Conclusion: The effects of serotonin on pain transmission in dorsal horn depend on several factors, including the type of receptors activated and the populations of neurons involved. Recently, studies performed by activating and/or recording from identified neurons have importantly contributed to the understanding of serotonergic modulation on dorsal horn circuits.

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