Objective To observe the collateral projection of the central medial thalamic nucleus(CM)to different cortical regions in mice and to provide morphological evidence for its involvement in the transmission of nociceptive information.Methods Fluoro-Gold(FG)was injected into the prefrontal cortex(PFC)or insular cortex(IC),respectively,and a complete Freund's adjuvant(CFA)model of inflammatory pain was established to observe the distributions of FG retrogradely labeled neurons in CM and whether neurons projecting to PFC or IC in CM were involved in the transmission of nociceptive information.Subsequently,FG was injected into PFC,while tetramethylrhodamine(TMR)was injected into IC,and a CFA model was established to observe the distribution of double-labeled neurons of FG and TMR and their co-labeling with FOS proteins in CM.Results ① After injection of FG into PFC,a substantial number of retrogradely labeled neurons were observed in the rostral and medial parts of CM,with a relatively small number of FG retrogradely labeled neurons present in the caudal part.After injection of FG into IC,a considerable number of FG retrogradely labeled neurons were observed in the medial and caudal parts of CM,with less in the rostral part of CM.②Activated neurons were observed in both CM-IC and CM-PFC pathway in CFA model,with a larger number of activated neurons present in the former.(3)A small number of neurons in the rostral and medial parts of the CM could send collateral projections to both PFC and IC,but co-labeled neurons were occasionally seen to be activated in the pain state.Conclusion CM can send a large number of projections to PFC and IC,respectively,and is involved in the transmission of nociceptive information.However,the collateral projections are less common.
central medial thalamic nucleuscollateral projectionprefrontal cortexinsular cortexpainneural pathway
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