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Dor (2002) 10
Dor (2002) 10

The Medullary Dorsal Reticular Nucleus

(DRt) Enhances the Responses of

Spinal Nociceptive Neurons to

Peripheral Stimulation: a Role in

Central Sensitization?

Christophe Dugast

Resumo
Utilizaram-se técnicas de registo extracelular da actividade neuronal combinadas com a aplicação de
glutamato no núcleo reticular dorsal do bolbo raquidiano (DRt) para estudar a acção facilitatória deste
núcleo sobre os neurónios nociceptivos da medula espinhal. O glutamato aumentava significativamente a
post-discharge induzida nos neurónios nociceptivos pela estimulação eléctrica do nervo ciático, mas as
respostas directas à estimulação das fibras C e A não sofriam alterações. Estes resultados confirmam os
estudos anteriores que demonstraram uma acção facilitatória do DRt sobre a percepção da dor, e sugerem
que este núcleo possa estar envolvido na sensibilização central.

Palabras chave: DRt. Medullary dorsal reticular nucleus. WDR, wide dynamic range.

Summary
Single-unit recordings associated with local applications of glutamate into the medullary dorsal reticular
nucleus (DRt) were used to assess the putative descending facilitatory action of this nucleus upon spinal
nociceptive neurons. Glutamate dramatically increased the post-discharge of nociceptive neurons induced
by the noxious electrical stimulation of the sciatic nerve, whereas A- and C-fibre mediated responses
remained unchanged. This data indicates that the DRt enhances the capacity of spinal nociceptive neurones
to respond to noxious stimulation by prolonging their discharge. This result is in agreement with previous
studies showing a descending facilitation of the DRt upon pain perception and suggests the implication of
the DRt in central sensitization.

Key words: Electrophysiology. Facilitation. Glutamate. Pain. Sensitization.

Introduction plate tests (Almeida, et al., 1996), decreased the time
spent in pain behaviour during the formalin test and
The medullary dorsal reticular nucleus has been spinal c-fos induction, a reliable marker of spinal neu-
shown to be involved in pain modulation by exerting ronal nociceptive activation (Lima, et al., 1994; Almei-
pronociceptive actions upon spinal nociceptive trans- da, et al., 1999). On the other hand, anatomical studies
mission. Its activation by local application of an excita- aimed at devising the neuronal circuitry underlying the
tory amino acid decreased pain threshold in tail-flick
test (Almeida, et al., 1996). In contrast, its lesion DRt nociceptive facilitating action showed that the DRt
is reciprocally connected with the spinal dorsal horn,
increased the pain threshold in both tail-flick and hot-
through a putatively excitatory bi-directional feed-back
loop (Almeida, et al., 1993, 2000).
In order to get physiological support to the putative
descending pronociceptive action of the DRt upon spi-
DOR Instituto de Histologia e Embriologia nal neurons, we analysed the effect of DRt stimulation
upon the activity of wide dynamic range (WDR) neurons
Faculdade de Medicina e IBMC
16 Universidade do Porto, 4200-319 Porto, Portugal using extracellular single unit recordings.