Physiological Properties of the Lamina I Spinoparabrachial Neurons in the Rat

Abstract

Single-unit extracellular recordings of spino-parabrachial (spino-PB) neurons (n = 53) antidromically driven from the contralateral parabrachial (PB) area were performed in the lumbar cord in anesthetized rats. All the spino-PB neurons were located in the lamina I of the dorsal horn. Their axons exhibited conduction velocities between 2.8 and 27.8 m/s, in the thin myelinated fibers range. They had an extremely low spontaneous activity (median = 0. 064 Hz) and a small excitatory receptive field (</=2 toes or pads). They were all activated by both peripheral A (mainly Adelta) and C fibers after intense transcutaneous electrical stimulation. Their discharge always increased in response to noxious natural stimuli of increasing intensities. The great majority (75%) of spino-PB neurons were nociceptive specific, i.e., they were excited only by noxious stimuli. The remaining (25%) still were excited primarily by noxious stimuli but also responded moderately to innocuous stimuli. Almost all spino-PB neurons (92%, 49/53) were activated by both mechanical and heat noxious stimuli. Among them, 35% were in addition moderately activated by noxious cold (thresholds between +20 and -10 degrees C). Only (8%, 4/53) responded exclusively to noxious heat. Spino-PB neurons clearly encoded the intensity of mechanical (n = 39) and thermal (n = 38) stimuli in the noxious range, and most of the individual stimulus-response functions were monotonic and positive up to 40/60 N. cm(-2) and 50 degrees C, respectively. For the mechanical modality, the mean threshold was 11.5 +/- 1.25 N. cm(-2) (mean +/- SE), the response increased almost linearly with the logarithm of the pressure between 10 and 60 N. cm(-2), the mean p(50) (pressure evoking 50% of the maximum response) and the maximum responsiveness were: 30 +/- 2.4 N. cm(-2) and 40.5 +/- 5 Hz, respectively. For the thermal modality, the mean threshold was 43.6 +/- 0.5 degrees C, the mean curve had a general sigmoid aspect, the steepest portion being in the 46-48 degrees C interval, the mean t(50) and the maximum responsiveness were: 47.4 +/- 0.3 degrees C and 40 +/- 4.4 Hz, respectively. Most of the spino-PB neurons tested (13/16) had their noxiously evoked responses clearly inhibited by heterotopic noxious stimuli. The mean response to noxious stimuli during heterotopic stimuli was 31.7 +/- 6.1% of the control response. We conclude that the nociceptive properties of the lamina I spino-PB neurons are reflected largely by those of PB neurons that were suggested to be involved in autonomic and emotional/aversive aspects of pain.

Posterior Triangular Thalamic Neurons Convey Nociceptive Messages to the Secondary Somatosensory and Insular Cortices in the Rat

“…Indeed the main properties of lamina I neurons are close to those of PoT nociceptive neurons: (1) numerous lamina I neurons respond strongly and specifically to noxious stimuli (Christensen and Perl, 1970;Bester et al, 2000), and (2) the slope of the stimulus-response curve of lamina I neurons is maximum between 46 and 50°C (Kenshalo et al, 1979;Bester et al, 2000). However, the receptive fields of lamina I neurons were generally small or very small (typically one digit) (Kenshalo et al, 1979;Bester et al, 2000), whereas those of PoT neurons were markedly larger (one to three portions of the body). This last point likely reflects a strong convergence of lamina I projections within the PoT (Gauriau and Bernard, 2004).…”

“…Because lamina I neurons are involved primarily in nociceptive processing (Christensen and Perl, 1970;Kenshalo et al, 1979;Bushnell et al, 1984;Craig and Kniffki, 1985;Bester et al, 2000), it is probable that they provide the main nociceptive input to PoT NS neurons. Indeed the main properties of lamina I neurons are close to those of PoT nociceptive neurons: (1) numerous lamina I neurons respond strongly and specifically to noxious stimuli (Christensen and Perl, 1970;Bester et al, 2000), and (2) the slope of the stimulus-response curve of lamina I neurons is maximum between 46 and 50°C (Kenshalo et al, 1979;Bester et al, 2000). However, the receptive fields of lamina I neurons were generally small or very small (typically one digit) (Kenshalo et al, 1979;Bester et al, 2000), whereas those of PoT neurons were markedly larger (one to three portions of the body).…”

ATP receptors gate microglia signaling in neuropathic pain

“…A major ascending nociceptive (pain-related) pathway arises from neurons in lamina I of the spinal dorsal horn (Bester et al, 2000). The action potential discharge of these neurons, that is to say the output of these neurons, is normally evoked only in response to noxious peripheral stimulation, such as pinch to the skin (Keller et al, 2007) (Figure 1).…”

Arousal from hibernation and BAT thermogenesis against cold: central mechanism and molecular basis

“…Although the majority of the PBN neurons respond to noxious stimuli, a sub set appears to respond to innocuous thermal stimuli from spinal sensory neurons (Menendez et al, 1996;Bester et al, 2000).…”