Reg-2 expression in dorsal root ganglion neurons after adjuvant-induced monoarthritis

Reg-2 is a secreted protein that is expressed de novo in motoneurons, sympathetic neurons, and dorsal root ganglion (DRG) neurons after nerve injury and which can act as a Schwann cell mitogen. We now show that Reg-2 is also upregulated by DRG neurons in inflammation with a very unusual expression pattern. In a rat model of monoarthritis, Reg-2 immunoreactivity was detected in DRG neurons at 1 day, peaked at 3 days (in 11.6% of DRG neurons), and was still present at 10 days (in 5%). Expression was almost exclusively in the population of DRG neurons that expresses the purinoceptor P2X(3) and binding sites for the lectin Griffonia simplicifolia IB4, and which is known to respond to glial cell line-derived neurotrophic factor (GDNF). Immunoreactivity was present in DRG cell bodies and central terminals in the dorsal horn of the spinal cord. In contrast, very little expression was seen in the nerve growth factor (NGF) responsive and substance P expressing population. However intrathecal delivery of GDNF did not induce Reg-2 expression, but leukemia inhibitory factor (LIF) had a dramatic effect, inducing Reg-2 immunoreactivity in 39% of DRG neurons and 62% of P2X(3) cells. Changes in inflammation have previously been observed predominantly in the neuropeptide expressing, NGF responsive, DRG neurons. Our results show that changes also take place in the IB4 population, possibly driven by members of the LIF family of neuropoietic cytokines. In addition, the presence of Reg-2 in central axon terminals implicates Reg-2 as a possible modulator of second order dorsal horn cells.

(S)-AMPA inhibits electrically evoked calcitonin gene-related peptide (CGRP) release from the rat dorsal horn: reversal by cannabinoid receptor antagonist SR141716A

Previous studies in the hippocampus and cerebellum demonstrate that depolarisation of postsynaptic neurones stimulates the rapid synthesis and release of an endocannabinoid that retrogradely interacts with pre-synaptic CB(1) to modulate neurotransmitter release. This study evaluated whether depolarisation of second order neurones in the dorsal horn of the spinal cord by the AMPA receptor agonist, (S)-AMPA, would modulate sensory neurotransmission via release of endocannabinoids. Using an isolated rat dorsal horn with dorsal root attached in vitro preparation the release of calcitonin gene-related peptide (CGRP) after electrical stimulation of the dorsal roots was measured. Superfusion of either WIN55,212-2 (1 microM) or (S)-AMPA (1 microM) significantly attenuated CGRP release in a CB(1)-dependent manner (SR141716A, 5 microM). This provides indirect pharmacological evidence for an AMPA-evoked release of endogenous cannabinoids inhibiting peptide release from primary afferent neurons. This study confirms that CGRP release from the dorsal horn is modulated via CB(1) activation. Furthermore a depolarising stimulus also modulates CGRP release, potentially via the release of endogenous cannabinoids.

Nerve growth factor induces mechanical allodynia associated with novel A fibre-evoked spinal reflex activity and enhanced neurokinin-1 receptor activation in the rat

A single dose of nerve growth factor (NGF, 1 microgram/g, i.p.) administered to rats aged between postnatal days (PND) 12 and 14 resulted in a behavioural hypersensitivity of the hindlimb flexion withdrawal reflex to mechanical stimuli which developed 2 h after NGF and remained significant for 24 h. Heat hyperalgesia occurred some 4 h following NGF injection and lasted for 24 h. Isolated spinal cords were prepared from animals treated with NGF and were maintained in vitro for physiological and pharmacological analysis of lumbar spinal reflex activity. Repetitive, low-frequency group I/II A beta-fibre stimulation evoked a novel wind-up response after NGF injection similar to that produced by C-fiber group III/IV stimulation in normal animals. The neurokinin-1 (NK1) receptor antagonist RP67580 reduced the C fiber-evoked responses following NGF treatment but not in naive preparations. The novel A beta fiber-evoked wind-up response was also reduced by RP67580. The NGF-induced changes in NK1 receptor responses occurred in the absence of any detectable changes in either spinal cord NK1 receptor dose-response relationships or NK1 receptor mRNA levels. These findings are likely to be related to the behavioural allodynia observed in the present study and to central excitability changes observed after chronic inflammation where NGF levels are increased.