title: Diverse firing properties and Aβ-, Aδ-, and C-afferent inputs of small local circuit neurons in spinal lamina I.
abstract: Spinal lamina I is a key element of the pain processing system, which integrates primary afferent input and relays it to supraspinal areas. More than 90% of neurons in this layer are local circuit neurons, whose role in the signal processing is poorly understood. We performed whole-cell recordings in a spinal cord preparation with attached dorsal roots to examine morphological features and physiological properties of small local circuit neurons (n = 47) in lamina I. Cells successfully filled with biocytin (n = 17) had fusiform (n = 10), flattened (n = 4), and multipolar (n = 3) somatodendritic morphology; their axons branched extensively and terminated in laminae I-III. Intrinsic firing properties were diverse; in addition to standard tonic (n = 16), adapting (n = 7), and delayed (n = 6) patterns, small local circuit neurons also generated rhythmic discharges (n = 6) and plateau potentials (n = 10), the latter were suppressed by the L-type Ca(2+)-channel blocker nifedipine. The neurons received monosynaptic inputs from Aδ and C afferents and could generate bursts of spikes on the root stimulation. In addition, we identified lamina I neurons (n = 7) with direct inputs from the low-threshold Aβ afferents, which could be picked up by ventral dendrites protruding to lamina III. Stimulation of afferents also evoked a disynaptic inhibition of neurons. Thus, small local circuit neurons exhibit diverse firing properties, can generate rhythmic discharges and plateau potentials, and their dendrites extending into several laminae allow broad integration of Aβ-, Aδ-, and C-afferent inputs. These properties are required for processing diverse modalities of nociceptive inputs in lamina I and may underlie spinal sensitization to pain.
authors.affiliation: Instituto de Investigação e Inovação em Saúde, Universidade do Porto, Porto, Portugal Neuronal Networks Group, Instituto de Biologia Molecular e Celular (IBMC), Universidade do Porto, Porto, Portugal MTA-DE-NAP B-Pain Control Research Group, Debrecen, Hungary Department of Physiology, University of Debrecen, Debrecen, Hungary.
authors.forename: Elisabete C
authors.initials: EC
authors.lastname: Fernandes
authors.forename: Liliana L
authors.initials: LL
authors.lastname: Luz
authors.forename: Oleh
authors.initials: O
authors.lastname: Mytakhir
authors.forename: Nikolai V
authors.initials: NV
authors.lastname: Lukoyanov
authors.forename: Peter
authors.initials: P
authors.lastname: Szucs
authors.forename: Boris V
authors.initials: BV
authors.lastname: Safronov
mesh_terms: D000200:Action Potentials / Q000502:physiology*; D000818:Animals; D000831:Animals, Newborn; D001703:Biophysics; D004558:Electric Stimulation; D019706:Excitatory Postsynaptic Potentials / Q000502:physiology; D007839:Functional Laterality; D066298:In Vitro Techniques; D007395:Interneurons / Q000502:physiology*; D009413:Nerve Fibers, Myelinated / Q000502:physiology*; D036421:Nerve Fibers, Unmyelinated / Q000502:physiology*; D009415:Nerve Net / Q000166:cytology; D018408:Patch-Clamp Techniques; D051381:Rats; D017208:Rats, Wistar; D066148:Spinal Cord Dorsal Horn / Q000166:cytology*