Distributions of different types of nociceptive neurons in thalamic mediodorsal nuclei of anesthetized rats
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Mediodorsal thalamic nucleus (MD) is a critical relay of nociception. This study recorded responses of MD neurons to noxious mechanical and thermal stimuli in isoflurane anesthetized rats. We found the threshold of noxious mechanical stimulation was 141 gw and that of noxious heat stimulation was 46 °C. A significantly higher percentage of noxious inhibitory neurons were found in the medial and central part of the MD, whereas a higher percentage of noxious excitatory neurons were found in the lateral part of the MD and adjacent intralaminar nuclei. The differential distribution of excitatory and inhibitory neurons implies functional differentiation between the medial and lateral part of the MD in nociception processing. Furthermore, by an analysis of the stimulus–response function (SRF), we found 80% of these excitatory neurons had a step-function or hat-shape-like SRF. This suggests that most of the MD neurons may serve as a system to distinguish innocuous versus noxious stimuli.
KeywordsMediodorsal thalamic nucleus Intralaminar thalamic nuclei Stimulus–response function Multiple single-unit recording
This research was supported by grants from the National Science Council (NSC100-2311-B-002-002-MY3, NSC100-2221-E-002-064, and NSC 100-2923-E-002-007-MY3) and National Health Research Institute (NHRI-EX101-10104NI), Taiwan.
PLL, MLT, FSJ, and CTY contributed to the conception and design of the experiments. PLL conducted the experiments. PLL and MLT analyzed the data. PLL and CTY drafted the manuscript. All authors participated in interpreting the data, revising the article, and approving the final version for publication. Experiments were conducted at the Department of Life Science, National Taiwan University, Taipei, Taiwan.
This study was funded by grants from the National Science Council (NSC 100-2311-B-002-002-MY3, NSC 100-2221-E-002-064, and NSC 100-2923-E-002-007-MY3) and National Health Research Institute (NHRI-EX101-10104NI), Taiwan.
Compliance with ethical standards
Conflict of interest
Author Pen-Li Lu declares that she has no conflicts of interest. Author Meng-Li Tsai declares that he has no conflicts of interest. Author Fu-Shan Jaw declares that he has no conflicts of interest. Author Chen-Tung Yen declares that he has no conflicts of interest.
All applicable international, national, and/or institutional guidelines for the care and use of animals were followed. This article does not contain any studies with human participants performed by any of the authors.
Informed consent was obtained from all individual participants included in the study.
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