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Synaptic input of rat spinal lamina I projection and unidentified neurones in vitro
Author(s) -
Dahlhaus Anne,
Ruscheweyh Ruth,
Sandkühler Jürgen
Publication year - 2005
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.2005.088567
Subject(s) - excitatory postsynaptic potential , neuroscience , inhibitory postsynaptic potential , postsynaptic potential , kainate receptor , ampa receptor , postsynaptic current , chemistry , biology , anatomy , nmda receptor , receptor , biochemistry
Spinal lamina I projection neurones that transmit nociceptive information to the brain play a pivotal role in hyperalgesia in various animal models of inflammatory and neuropathic pain. Consistently, activity‐dependent long‐term potentiation can be induced at synapses between primary afferent C‐fibres and lamina I projection neurones but not unidentified neurones in lamina I. The specific properties that enable projection neurones to undergo long‐term potentiation and mediate hyperalgesia are not fully understood. Here, we have tested whether lamina I projection neurones differ from unidentified neurones in types or strength of primary afferent input and/or action potential‐independent excitatory and inhibitory input. We used the whole‐cell patch‐clamp technique to record synaptic currents in projection and unidentified lamina I neurones in a transverse lumbar spinal cord slice preparation from rats between postnatal day 18 and 37. Lamina I neurones with a projection to the parabrachial area or the periaqueductal grey were identified by retrograde labelling with a fluorescent tracer. The relative contribution of NMDA receptors versus AMPA/kainate receptors to C‐fibre‐evoked excitatory postsynaptic currents of lamina I neurones significantly decreased with age between postnatal day 18 and 27, but was independent of the supraspinal projection of the neurones. We did not find a significant contribution of kainate receptors to C‐fibre‐evoked excitatory postsynaptic currents. Lamina I projection and unidentified neurones possessed functional GABA A and glycine receptors but received scarce action potential‐independent spontaneous GABAergic and glycinergic inhibitory input as measured by miniature inhibitory postsynaptic currents. The miniature excitatory postsynaptic current frequencies were five times higher in projection than in unidentified neurones. The predominance of excitatory synaptic input to projection neurones, taken together with the previous finding that their membranes are more easily excitable than those of unidentified neurones, may facilitate the induction of synaptic long‐term potentiation.