Nociceptive neurones in rat superior colliculus. I. Antidromic activation from the contralateral predorsal bundle

Area of Science:

• Neuroscience
• Sensory processing
• Motor control

Background:

• The superior colliculus (SC) integrates sensory information for orientation, approach, and avoidance behaviors.
• Tectofugal pathways are segregated: crossed for orientation/approach, uncrossed for avoidance/defense.
• Nociceptive neurons were presumed to only connect to the uncrossed pathway for defensive responses.

Purpose of the Study:

• To investigate if nociceptive neurons in the SC project to the crossed descending pathway.
• To determine if nociceptive neurons can initiate orientation towards noxious stimuli.

Main Methods:

• Electrophysiological identification of nociceptive and wide-dynamic-range neurons in rat SC.
• Application of noxious mechanical and thermal stimuli.
• Antidromic activation from brainstem stimulation of the crossed descending pathway.

Main Results:

• 82% nociceptive-specific and 18% wide-dynamic-range SC neurons were identified.
• Most nociceptive neurons were in intermediate SC layers, origin of the crossed projection.
• 44.9% of nociceptive neurons projected via the crossed descending pathway with a conduction velocity of 9.02 m/s.

Conclusions:

• A significant proportion of rat SC nociceptive neurons project contralaterally via the crossed descending pathway.
• Nociceptive neurons can utilize the same output pathway as low-threshold neurons for orientation.
• SC nociceptive neurons may mediate orientation responses to noxious stimuli, not just defensive behaviors.