Monosynaptic excitatory inputs to spinal lamina I anterolateral-tract-projecting neurons from neighbouring lamina I neurons.
Spinal lamina I receives nociceptive primary afferent input to project through diverse ascending pathways, including the anterolateral tract (ALT). Large projection neurons (PNs) form only a few per cent of the cell population in this layer, and little is known about their local input from other lamina I neurons. We combined single-cell imaging in the isolated spinal cord, paired recordings, 3-D reconstructions of biocytin-labelled neurons and computer simulations to study the monosynaptic input to large ALT-PNs from neighbouring (somata separated by less than 80 μm) large lamina I neurons. All 11 connections identified were excitatory. We have found that an axon of a presynaptic neuron forms multiple synapses on an ALT-PN, and both Ca(2+)-permeable and Ca(2+)-impermeable AMPA receptors are involved in transmission. The monosynaptic EPSC latencies (1-12 ms) are determined by both post- and presynaptic factors. The postsynaptic delay, resulting from the electrotonic EPSC propagation in the dendrites of an ALT-PN, could be 4 ms at most. The presynaptic delay, caused by the spike propagation in a narrow highly branched axon of a local-circuit neuron, can be about 10 ms for neighbouring ALT-PNs and longer for more distant neurons. In many cases, the EPSPs evoked by release from a lamina I neuron were sufficient to elicit a spike in an ALT-PN. Our data show that ALT-PNs can receive input from both lamina I local-circuit neurons and other ALT-PNs. We suggest that lamina I is a functionally interconnected layer. The intralaminar network described here can amplify the overall output from the principal spinal nociceptive projection area.
Luz
Liliana L
LL
Instituto de Biologia Molecular e Celular, Universidade do Porto, Rua do Campo Alegre 823, 4150-180 Porto, Portugal.
Szucs
Peter
P
Pinho
Raquel
R
Safronov
Boris V
BV
D000818:Animals; D000870:Anterior Horn Cells / Q000502:physiology*; D019706:Excitatory Postsynaptic Potentials / Q000502:physiology*; D009434:Neural Pathways / Q000166:cytology / Q000502:physiology; D009474:Neurons / Q000145:classification / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D012023:Reflex, Monosynaptic / Q000502:physiology; D013116:Spinal Cord / Q000166:cytology / Q000502:physiology; D013376:Substantia Gelatinosa / Q000502:physiology; D013569:Synapses / Q000502:physiology*