Abstract
The functional significance of neuropeptide Y in the rat spinal cord is unclear
and there have been no reports of the stimuli needed to produce release of this peptide
in vivo. When a peripheral nerve is injured a de novo synthesis of neuropeptide Y
occurs in many large and some medium sized dorsal root ganglion neurones. The
experiments in this thesis employed the antibody microprobe technique to study both in
normal rats and in those with a peripheral mononeuropathy the spinal release of
extracellular immunoreactive neuropeptide Y and to determine the origin of such
release.
In the initial experiments, microprobes bearing immobilised antibodies to
neuropeptide Y were inserted into the lumbar spinal cord of urethane anaesthetised
normal rats. In the absence of peripheral stimuli microprobes detected a high basal
presence of immunoreactive NPY throughout the entire dorsal and ventral hom.
Electrical stimulation of large diameter afferents of the ipsilateral sciatic nerve and
unmyelinated primary afferents did not significantly alter the spinal release of
immunoreactive neuropeptide Y in the spinal cord. Transection of the spinal cord at
a low thoracic level resulted in increased levels of immunoreactive neuropeptide Y
only in the lower ventral horn. The predominant failure of electrical stimulation and
of spinalisation to significantly alter the basal levels of immunoreactive neuropeptide
Y suggests that the latter results from spontaneous activity in intrinsic neurones.
For studies of rats with a peripheral mononeuropathy, the model of Bennett
& Xie was used. Postoperatively the development of mechanical allodynia and
hyperalgesia were assessed and animals used at 10-14 days only ifthey displayed the
characteristic behavioural signs associated with this model. Sham experiments were
carried out in separate animals as controls for the effect of surgery per se. In sham
animals both sides of the lumbar spinal cord showed a significant spinal release of
immunoreactive neuropeptide Y throughout the entire dorsal horn. The site of greatest extracellular levels was the superficial dorsal horn. A similar distribution
was also found in the neuropathic animal on the side contralateral to the nerve
ligation. On the ipsilateral side of the neuropathic rat however there was a further
zone of spontaneous release of immunoreactive neuropeptide Y in the mid and lower
dorsal horn (approximating to laminae III, IV and V). Additionally, electrical
stimulation of large diameter afferents of the ipsilateral sciatic nerve resulted in an
increase in the spinal release over the entire dorsal and upper ventral horn.
Stimulating both large diameter myelinated afferents and small unmyelinated
afferents did not increase release of immunoreactive neuropeptide Y above that
observed by stimulating large myelinated fibres alone. Thus, the additional zone of
spontaneous release found on the ipsilateral side of the neuropathic rat probably
represents spontaneous activity in damaged and/or regenerating primary afferents.
This may represent central release of a neuroactive compound by ectopic impulses in
such fibres.
