Intracellular and current source density analysis of pretectal input to the optic tectum of the frog.
OBJECTIVE
Electrophysiological examination of the ipsilateral pretectotectal projection has proved that pretectal cells elicit strong suppressive responses to the ipsilateral tectum. However, the neural mechanisms underlying the contralateral pretectotectal prejection are still obscure. The present study aimed to examine the synaptic nature of pretectal nuclei and contralateral tectal cells, and to demonstrate the spatiotemporal pattern of neuronal activity in the 2 main brain structures.


METHODS
Intracellular recording and current source density (CSD) analysis were used to test the complexity of neuronal mechanism of pretectotectal information transfer.


RESULTS
The pretectal stimulation elicited only one type of response on the contralateral tectum, the inhibitory postsynaptic potential (IPSP). The majority of contra-induced IPSPs were assumed to be polysynaptically driven. In the CSD analysis, only one sink with short latency was observed in each profile. The ipsilateral projection produced a prominent monosynaptic sink in layer 8 of tectum. Recipient neurons were located in layers 6 and 7 of tectum. The result confirmed former findings from ipsilateral intracellular recordings.


CONCLUSIONS
These results suggest the following neuronal circuit: afferents from the pretectal nuclei broadly inhibit both tectal neuron, and since no second sink occurs in tectal layers, the pretectotectal excitatory afferents probably do not extend over the whole tectum, but are within limited state. The results of intracellular recording and CSD analysis further provide evidence of how pretectal afferent activity flows within the tectal laminae.
Li
Xiao-Hong
XH
Kyushu Institute of Technology, Graduate School of Life Science of Systems Engineering, Department of Brain Science and Engineering, Fukuoka 808-0196, Japan. xiaohongli01@yahoo.com
Kang
Hong-Jian
HJ
Xu
Mao-Lin
ML
Mastumoto
Nobuyoshi
N
D000344:Afferent Pathways / Q000502:physiology; D000818:Animals; D004553:Electric Conductivity; D005260:Female; D053444:Inhibitory Postsynaptic Potentials / Q000502:physiology; D007424:Intracellular Fluid / Q000502:physiology*; D008297:Male; D009475:Neurons, Afferent / Q000502:physiology; D011892:Rana catesbeiana / Q000502:physiology*; D013477:Superior Colliculi / Q000166:cytology / Q000502:physiology*; D014795:Visual Pathways / Q000166:cytology / Q000502:physiology*