Electrophysiological and pharmacological characterisation of ascending anterolateral axons in the in vitro mouse spinal cord.

Here we describe a procedure to obtain electrophysiological recordings from cut ends of ascending axons of the spinal cord white matter. This procedure involves the use of an in vitro preparation of the neonate mouse spinal cord and suction microelectrodes of about 10 microm tip diameter. Using this procedure, we have recorded from axons of the anterolateral quadrant at the thoracic level which responded to electrical stimulation of a lumbar dorsal root. Using adequate stimulation parameters, we have identified axons responding exclusively to activation of C-fibres and axons responding to activation of A- and C-fibres. These axons are likely to originate at dorsal horn second order sensory neurons of different functional types. Simultaneous recordings from a lumbar ventral root and from ascending axons were used to assess the effects of noradrenaline and sevoflurane on motor and sensory pathways. The results obtained show that noradrenaline can potentiate responses of motor neurons to dorsal root stimulation while depressing responses of ascending axons to the same stimulus. In contrast both motor and sensory pathways were inhibited by sevoflurane. We believe that the procedures developed here may be of great interest to assess spinal nociceptive and antinociceptive mechanisms in vitro.