Spinal input to thalamic VL neurons: evidence for direct spinothalamic effects

Area of Science:

• Neuroscience
• Spinal Cord Physiology
• Thalamic Function

Background:

• The ventrolateral nucleus of the thalamus (VL) plays a crucial role in motor control by relaying cerebellar information to the motor cortex.
• Understanding the somatosensory inputs to VL is essential for comprehending how motor commands are modulated during movement.

Purpose of the Study:

• To investigate the postsynaptic actions of afferents ascending in the ventrolateral quadrant and dorsal columns of the spinal cord on VL neurons.
• To determine the extent of monosynaptic and polysynaptic transmission from the spinal cord to the VL.

Main Methods:

• Intracellular recordings were performed on 138 neurons in the VL of anesthetized cats.
• Neurons were identified by cerebellar input and/or antidromic activation from the motor cortex.
• Monosynaptic transmission was assessed by intrathalamic delay times and responses to double-shock stimulation.

Main Results:

• 86% of VL neurons responded to spinal cord stimulation with excitatory or inhibitory postsynaptic potentials.
• Evidence for monosynaptic excitation from ventrolateral quadrant afferents was found in 30 neurons, with estimated delays <1 ms.
• Approximately 19-39% of sampled neurons may receive monosynaptic input, with spinal conduction velocities ranging from 10-35 m/s.
• Much of the ascending input was polysynaptic, with shorter latency responses originating from direct spinothalamic projections.

Conclusions:

• VL neurons receive somatosensory input from the spinal cord through both direct and indirect pathways.
• This ascending information likely contributes to the adjustment of cerebellar commands relayed by the VL to the motor cortex during movement execution.