Organization of the crossed tecto-reticulo-spinal projection in rat--II. Electrophysiological evidence for separate output channels to the periabducens area and caudal medulla.
The previous paper (Redgrave et al., Neuroscience 37, 571-584, 1990) presented anatomical evidence indicating there are at least two largely segregated components of the crossed tecto-reticulo-spinal pathway which project to the periabducens area and caudal medulla. An immediate question arising from this finding is whether tectal cells which project either to the periabducens area or to the caudal medulla have different electrophysiological response properties. An answer to this question would be relevant to the issue of whether different components of the tecto-reticulo-spinal system are specialized for the production of different classes of orienting movement. Accordingly, extracellularly recorded units in the superior colliculus of urethane anaesthetized rats were tested for antidromic activity following electrical stimulation of the periabducens area or the caudal medulla. When antidromic potentials were successfully recorded the sensory properties of the units were tested with a range of unimodal visual, somatosensory and auditory stimuli. The following results were obtained. (i) Tectal cells antidromically activated by stimulation of the caudal medulla were preferentially sensitive to somatosensory stimuli from the perioral region, while cells activated from the periabducens area were more frequently responsive to auditory stimuli. (ii) Tectal fibres activated by stimulation of the caudal medulla had significantly higher conduction velocities than the fibres activated by electrodes in the periabducens region. (iii) More than 90% of antidromically activated cells were located in stratum album intermediale or dorsal stratum profundum. These electrophysiological findings confirm and extend previous anatomical observations which indicate that components of the crossed descending projection of the colliculus may be functionally specialized for the production of different classes of orienting movements.
Keay
K
K
Department of Psychology, University of Sheffield, U.K.
Westby
G W
GW
Frankland
P
P
Dean
P
P
Redgrave
P
P
D000161:Acoustic Stimulation; D000818:Animals; D004558:Electric Stimulation; D004567:Electrodes, Implanted; D004594:Electrophysiology; D005260:Female; D008526:Medulla Oblongata / Q000033:anatomy & histology / Q000166:cytology / Q000502:physiology*; D009475:Neurons, Afferent / Q000502:physiology; D010775:Photic Stimulation; D010812:Physical Stimulation; D051381:Rats; D012154:Reticular Formation / Q000033:anatomy & histology / Q000502:physiology; D013116:Spinal Cord / Q000033:anatomy & histology / Q000502:physiology; D013477:Superior Colliculi / Q000033:anatomy & histology / Q000166:cytology / Q000502:physiology