The dorsolateral thalamus as a relay in the retino-wulst pathway in pigeon (Columba livia)

Summary In 4 dorsolateral thalamic nuclei (LA, DLAmc, DLLd and DLLv) short latency evoked responses were recorded after electrical or photic stimulation of the contralateral eye. Electrical stimulation of these 4 nuclei led to bilaterally evoked responses in the wulst, where previous experiments had demonstrated an oligosynaptic projection from the retina.Cooling in DLL, while stimulating the contralateral optic nerve, leads to a severe decrement of both wulst responses suggesting that the thalamus functions as a relay within the retino-thalamo-hyperstriatal pathway. When the optic nerve ipsilateral to the cooled thalamus is stimulated the ipsilateral wulst response is unchanged while the contralateral wulst response is enhanced, suggesting a disinhibition. Similarly an inhibitory effect of the thalamus on one side upon the contralateral wulst response was found after concomitant stimulation of one optic nerve and a delayed stimulation of the ipsilateral thalamus.The dorsolateral thalamic group is the origin of bilateral wulst projections, the pathway to the contralateral telencephalon was demonstrated to pass via the supraoptic decussation DSO. Cooling DSO diminished the inhibitory thalamic effect upon the contralateral wulst. DSO was corroborated as part of the ipsilateral retino-wulst system.Abbreviations DLAmc Nucleus dorsolateralis anterior, thalami, pars magnocellularis - DLL Nucleus dorsolateralis anterior thalami, pars lateralis - DLLd DLL, pars dorsalis - DLLv DLL, pars ventralis - DSO Decussatio supraoptica - E Ectostriatum - GLv Nucleus geniculatus lateralis, pars ventralis - LA Nucleus lateralis anterior thalami - N Neostriatum - ON Optic nerve - Rt Nucleus rotundus - TeO Tectum opticum - W WulstSupported by Grants Nos. 3.329.70 and 3.823.72 of the Swiss National Foundation for Scientific Research and by the Dr. Eric Slack-Gyr Foundation.A preliminary report was given at the Union Schweizerischer Gesellschaften für Experimentelle Biologie, May 6, 1972 in Geneva (Meier et al., 1972b).