Non-NMDA receptor-mediated vibrotactile responses of neurons from the hindpaw representation in the rat SI cortex

Abstract

Non-NMDA receptor-mediated vibrotactile responses of neurons from the hindpaw representation were investigated in the rat SI cortex. We recorded single-unit spikes evoked by sinusoidal (duration: 500 ms; frequency: 5, 40, and 250 Hz; amplitude: 100 μm peak-to-peak) stimulation of the glabrous skin. The responses were obtained with microinjection of aCSF (sham), bicuculline, and AMPA near the isolated neurons in anaesthetized rats. Blocking most of the NMDA receptors by ketamine revealed local dynamics differentially modulated by each drug. The responses were generally suppressed after the initial 100-ms period of the 40- and 250-Hz stimulus, but not at 5 Hz. Both drugs increased average firing rates (AFRs) only during vibrotactile stimulation, and increased entrainment as measured by the vector strength (VS) of spike phases. However, bicuculline was more effective on the AFR in the late period particularly at 40 Hz. Complex interactions were found with AMPA; late activity increased only for fast spiking neurons at 40 Hz, and more for regular spiking neurons at 5 Hz. The increase of VS by bicuculline was much higher in layer IV. In addition to thalamocortical feed-forward inhibition, vibrotactile information seems to be suppressed after 100 ms by longer-latency inhibitory networks tuned to mid-frequency inputs. Combined with the presumed AMPA-receptor desensitization, those two inhibitory factors could limit the excitatory flow mostly to lower frequencies. The frequency dependence of the drug effects highlights the role of local cortical dynamics in the hindpaw area.

Keywords:

• Cortical neuron
• glabrous skin
• microinjection
• somatosensory
• touch

Acknowledgements

We are indebted to Professor Gülay Barbarosoğlu for her efforts to advance the university infrastructure by Ministry of Development DPT project no. 09K120520. Dr Güçlü thanks Professor Ehud Ahissar (Weizmann Institute of Science), Dr Sebastian Haidarliu, and Dr Knarik Bagdasarian for early discussions on the methods used in the study.

Disclosure statement

No conflicts of interest, financial or otherwise, are declared by the authors.

Additional information

Funding

This work was supported by Boğaziçi University Research Fund [BAP no. 13XP8] granted to Burak Güçlü.