Corticofugal projection inhibits the auditory thalamus through the thalamic reticular nucleus.
Electrical stimulation of the auditory cortex (AC) causes both facilitatory and inhibitory effects on the medial geniculate body (MGB). The purpose of this study was to identify the corticofugal inhibitory pathway to the MGB. We assessed two potential circuits: 1) the cortico-colliculo-thalamic circuit and 2) cortico-reticulo-thalamic one. We compared intracellular responses of MGB neurons to electrical stimulation of the AC following bilateral ablation of the inferior colliculi (IC) or thalamic reticular nucleus (TRN) in anesthetized guinea pigs. Cortical stimulation with intact TRN could cause strong inhibitory effects on the MGB neurons. The corticofugal inhibition remained effective after bilateral IC ablation, but it was minimized after the TRN was lesioned with kainic acid. Synchronized TRN neuronal activity and MGB inhibitory postsynaptic potentials (IPSPs) were observed with multiple recordings. The results suggest that corticofugal inhibition traverses the corticoreticulothalamic pathway, indicating that the colliculi-geniculate inhibitory pathway is probably only for feedforward inhibition.
Zhang
Zhuo
Z
Department of Rehabilitation Sciences, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong.
Liu
Chun-Hua
CH
Yu
Yan-Qin
YQ
Fujimoto
Kenji
K
Chan
Ying-Shing
YS
He
Jufang
J
D000161:Acoustic Stimulation / Q000379:methods; D000818:Animals; D001303:Auditory Cortex / Q000502:physiology*; D001306:Auditory Pathways / Q000502:physiology; D001931:Brain Mapping; D004307:Dose-Response Relationship, Radiation; D004558:Electric Stimulation / Q000379:methods; D005829:Geniculate Bodies / Q000502:physiology*; D006168:Guinea Pigs; D008564:Membrane Potentials / Q000502:physiology / Q000528:radiation effects; D009433:Neural Inhibition / Q000502:physiology*; D013787:Thalamic Nuclei / Q000502:physiology*