Neural circuits and temporal plasticity in hindlimb representation of rat primary somatosensory cortex: revisited by multi-electrode array on brain slices

Abstract

Objective The well-established planar multi-electrode array recording technique was used to investigate neural circuits and temporal plasticity in the hindlimb representation of the rat primary somatosensory cortex (S1 area).Methods Freshly dissociated acute brain slices of rats were subject to constant perfusion with oxygenated artificial cerebrospinal fluid (95% O 2 and 5% CO 2 ), and were mounted on a Med64 probe (64 electrodes, 8×8 array) for simultaneous multi-site electrophysiological recordings. Current sources and sinks across all the 64 electrodes were transformed into twodimensional current source density images by bilinear interpolation at each point of the 64 electrodes. Results The local intracortical connection, which is involved in mediation of downward information flow across layers II-VI, was identified by electrical stimulation (ES) at layers II-III. The thalamocortical connection, which is mainly involved in mediation of upward information flow across layers II-IV, was also characterized by ES at layer IV. The thalamocortical afferent projections were likely to make more synaptic contacts with S1 neurons than the intracortical connections did. Moreover, the S1 area was shown to be more easily activated and more intensively innervated by the thalamocortical afferent projections than by the intracortical connections. Finally, bursting conditioning stimulus (CS) applied within layer IV of the S1 area could successfully induce long-term potentiation (LTP) in 5 of the 6 slices (83.3%), while the same CS application at layers II-III induced no LTP in any of the 6 tested slices. Conclusion The rat hindlimb representation of S1 area is likely to have at least 2 patterns of neural circuits on brain slices: one is the intracortical circuit (ICC) formed by interlaminar connections from layers II-III, and the other is the thalamocortical circuit (TCC) mediated by afferent connections from layer IV. Besides, ICC of the S1 area is spatially limited, with less plasticity, while TCC is spatially extensive and exhibits a better plasticity in response to somatosensory afferent stimulation. The present data provide a useful experimental model for further studying microcircuit properties in S1 cortex at the network level in vitro.

The mTOR Signaling Pathway Regulates Pain-Related Synaptic Plasticity in Rat Entorhinal-Hippocampal Pathways

“…Here, we explored these changes during persistent peripheral nociceptive stimuli using a planar microelectrode array. Previous work has successfully applied the MED64 probe (Panasonic, Japan) to multiple brain regions responsible for nociception [28] and confirmed its stability and reliability [34]. Persistent peripheral nociceptive stimuli can alter both spatial and temporal plasticity in the EC - hippocampal pathway [28].…”

Use of multi-electrode array recordings in studies of network synaptic plasticity in both time and space

“…These two commerciallyavailable MEA systems make possible the wide use of the technique on various biological preparations, including acutely-dissociated brain slices (e.g., hippocampus, cortex, hypothalamus, substantia nigra, amygdala, superior colliculus, and brain stem), cultured slices (e.g., hippocampus, spinal cord, suprachiasmatic nucleus, cerebellum, and septohippocampal co-culture), retina, myocardial (ventricular and atrial slices) and smooth muscle from mammals [2,[17][18][19][20][21][22] .…”

“…4B), implying a functional rearrangement of synaptic connections due to micro-circuit damage in the state of persistent nociception. In addition, the 2D-CSD image analysis can be used to map spatial patterns of synaptic connections and functions not only in hippocampal slices but also in cerebral cortex slices such as anterior cingulate cortex (ACC) and primary somatosensory cortex [21,22,31] .…”

“…Subsequently, Shimono et al [38] made chronic recordings of LTP in hippocampal slices cultured on MED64 probes and demonstrated that LTP in this condition can last for up to 48 h. Next, using the same MED64 system, our group addressed the LTP induction property in different neuronal circuits of the primary somatosensory cortex and found that the thalamocortical circuit was much more plastic than the intracortical circuit [22] . We also explored the effects of different TBS protocols on the induction rate of LTP in brain slices containing the ACC [21] .…”

“…(4) evaluation of network physiological properties and the pharmacological effects of compounds [16,22,45,46] ; (5) stable recording that is less sensitive to factors such as mechanical vibration [42,43] ; and (6) a tremendous variety of research applications involving acute brain slices [10,16,45,47] , organotypic slice cultures [38,44,46,48] and dissociated cell cultures [7,17] . It is well-suited for studying synaptic plasticity [21,[31][32][33] , single unit activity [49,50] , rhythmic activity [17,45,51] , and pharmacological drug testing [23,46,52] .…”