Effect of cutting or crushing the rat sciatic nerve on synthesis of substance P by isolated L5 dorsal root ganglia

Plasticity of developing and adult dorsal root ganglion neurons as revealed in vitro

We review recent data on the plasticity of dorsal root ganglion (DRG) neurons as revealed during cultivation in vitro. Some experiments on cultured developing DRG neurons and on adult DRG neurons in vivo are also mentioned. Cultured developing and adult DRG neurons can be switched from an apolar to a multipolar phenotype by fetal calf serum or fibronectin. The effect is concentration dependent and occurs through an early modification of cell-substratum interaction. Adult DRG neurons synthesize and release within hours after injury TGF beta-1, which is a mitogen and a differentiation factor for Schwann cells. Finally, adult DRG neurons express in vitro neurotransmitters that are not expressed in vivo. This neurotransmitter plasticity can be modulated in vitro by some growth factors and in vivo by distal or proximal axotomy.

Axotomy alters putative neurotransmitters in visceral sensory neurons of the nodose and petrosal ganglia

Acute peripheral axotomy of the visceral sensory neurons of the vagus and glossopharyngeal nerves removes peripheral depolarizing and trophic influences to their sensory ganglia. To study axotomy-induced changes in the putative neurotransmitters of visceral sensory neurons, rats were sacrificed 1, 3, 7 or 14 days after transection of either the cervical vagus and superior laryngeal nerves (to affect peripheral axotomy of the nodose ganglion) or the glossopharyngeal and carotid sinus nerves (to affect peripheral axotomy of the petrosal ganglion). The numbers of tyrosine hydroxylase (TH)-immunoreactive (ir), vasoactive intestinal peptide (VIP)-ir, calcitonin-gene-related peptide (CGRP)-ir, and substance P (SP)-ir neurons in the respective ganglia were analyzed in axotomized and control ganglia. In the nodose ganglion, axotomy of the cervical vagus resulted in a rapid (by 1 day) reduction in the number of TH-ir cells, whereas VIP-ir neurons were dramatically increased in number by 3 days. CGRP- and SP-ir cells in the nodose ganglion were relatively unaffected by axotomy. In the petrosal ganglion, axotomy of the glossopharyngeal and carotid sinus nerves greatly reduced the number of TH-ir cells but did not alter the number VIP-ir neurons. CGRP- and SP-ir neurons in the petrosal ganglion were reduced in number by axotomy. Thus, axotomy of visceral sensory neurons differentially changed the content and perhaps the expression of putative transmitters. Differential changes were seen among transmitters in a single ganglia and between ganglia. These data demonstrate the plasticity of putative neurotransmitter systems in visceral afferent systems of adult rats.

Further studies on galanin-, substance P-, and CGRP-like immunoreactivities in primary sensory neurons and spinal cord: effects of dorsal rhizotomies and sciatic nerve lesions

The peptides galanin (GAL), substance P (SP), and calcitonin gene-related peptide (CGRP) were analyzed with immunohistochemistry and radioimmunoassay in the spinal cord, dorsal root ganglia, dorsal roots, and sciatic nerve of normal rats and rats subjected to several experimental procedures, including ligation, crush, and/or sectioning of nerves. The results show that peripheral nerve transection induces a dramatic increase in GAL content both in dorsal roots and sciatic nerve, demonstrating that this lesion causes an increased out-transport of the newly synthesized peptide both into the central and peripheral branches of the primary sensory neurons. In contrast evidence was obtained for decreased out-transport of SP and CGRP. The functional significance of these findings remains to be analyzed.

Saphenous nerve injury and regeneration on one side of a rat suppresses the ability of the contralateral nerve to evoke plasma extravasation

Leakage of Evans blue dye from the circulation into the skin has been used to measure plasma extravasation evoked by antidromic nerve stimulation of the saphenous nerves in anaesthetised rats. Normal animals and ones in which one saphenous nerve had been cut and left to regenerate some time before were studied. Saphenous nerve injury on one side of a rat significantly reduced the ability of the contralateral, uninjured nerve to evoke plasma extravasation compared with the response measured in totally uninjured control animals. This suppression of plasma extravasation was not dependent on activation of nerve fibres in the regenerated nerve. The effect was evident by 6 weeks after injury and persisted for at least another 20 weeks. At the moment the mechanism underlying this suppression of neurogenic plasma extravasation is unknown.

Trophic influence of the distal nerve segment on GABAA receptor expression in axotomized adult sensory neurons

The depolarizing action of gamma-aminobutyric acid (GABA), or the GABAA receptor agonist muscimol, on rat dorsal root (L4 and L5) fibers is attenuated following transection, but not crush, of the sciatic nerve. Following discrete nerve crush, axons actively regenerate and contact both the distal nerve segment and the peripheral target tissues. The aim of the present study was to distinguish between these two regions as possible sources of trophic support for retrograde maintenance of dorsal root GABA receptor sensitivity. A surgical procedure was employed to permit a delimited segment of axonal regeneration while prohibiting reestablishment of end organ innervation; the sciatic nerve was crushed and a ligature was placed 3 cm distal to the crush site. Under these conditions, the injury-induced decrement in the dorsal root GABA response, observed between 12 and 21 postoperative days, was significantly attenuated relative to that of ligated nerves, in which regeneration into the distal stump does not occur. The data suggest that nerve transection by ligation restricts trophic support for maintenance of GABA receptor expression in dorsal root ganglion (DRG) neurons. Furthermore, during regeneration the denervated distal nerve segment assumes a neurotrophic role in the maintenance of dorsal root GABA sensitivity, consistent with the hypothesis that growth factors derived from reactive Schwann cells may positively regulate the expression of receptors on axotomized sensory neurons.

Plasticity of the peptidergic mediation of spinal reflex facilitation after peripheral nerve section in the rat

The effects of the tachykinin antagonist Spantide II (D-Nic-Lys1,3-Pal3,D-Cl2Phe5,Asn6,D-Trp7,9,Nl e11)-substance P (SP) and the vasoactive intestinal peptide (VIP) antagonist (Ac-Tyr1,D-Phe2)-GRF(1-29)-NH2 on the excitability of the spinal nociceptive flexor reflex to intrathecally (i.t.) applied SP and VIP, respectively, as well as the facilitation evoked by activation of cutaneous C-afferent was examined. Both antagonists blocked the effects of the respective neuropeptides in rats with both intact and sectioned sciatic nerves. Spantide II antagonised C-afferent induced reflex facilitation in rats with intact nerves, but the degree of antagonism declined after axotomy. In contrast, the VIP antagonist did not block C-afferent induced facilitation in rats with intact nerves, but did so after axotomy. The results indicate that the role of tachykinins in mediating C-afferent-induced reflex facilitation is taken over by VIP after axotomy.

The expression of different cytochemical markers in normal and axotomised dorsal root ganglion cells projecting to the nucleus gracilis in the adult rat

Rat lumbar dorsal root ganglion neurones projecting to the nucleus gracilis in the brainstem were retrogradely labelled with Fluoro-Gold and analysed immunocytochemically for their expression of substance P-, calcitonin gene-related peptide-, galanin-, galanin message-associated peptide-, neuropeptide Y-, nitric oxide synthase- and carbonic anhydrase-like immunoreactivity as well as affinity to Griffonia (bandeiraea) simplicifolia lectin I--isolectin B4, RT97 and to choleragenoid. The analysis was made both in uninjured rats and in rats which had been subjected to unilateral sciatic nerve transection and partial resection 3 weeks earlier. The data showed that 6% of the L4 and L5 lumbar dorsal root ganglion cells that projected to the nucleus gracilis showed substance P-like immunoreactivity. Following nerve injury, none of the nucleus gracilis-projecting dorsal root ganglion cells showed substance P-like immunoreactivity. Nineteen per cent of the investigated cell population showed calcitonin gene-related peptide-like immunoreactivity in uninjured rats, but no nucleus gracilis-projecting calcitonin gene-related peptide-positive cells were found after nerve injury. Galanin- and galanin message-associated peptide-like immunoreactivity were found in 2% and 3%, respectively, of the Fluoro-Gold-labelled cell population normally and in 22% and 14%, respectively, after injury. No neuropeptide Y-positive cells were found in the Fluoro-Gold-labelled cell population normally, but after nerve injury, 96% of this population became neuropeptide Y-positive. Nitric oxide synthase-like immunoreactivity was found in 2% of the Fluoro-Gold-labelled cells normally and in 10% after injury. Two per cent of the Fluoro-Gold-labelled cells in the normal cases were stained by Griffonia (bandeiraea) simplicifolia lectin I--isolectin B4. After injury, however, no such double labelling was found. Thirty-four per cent of the Fluoro-Gold-labelled cell population was carbonic anhydrase positive normally, and 42% after injury. Seventy-five per cent of the Fluoro-Gold-labelled cells showed RT97 immunoreactivity normally and 12% after injury. Choleragenoid-like immunoreactivity was found in 99% of the Fluoro-Gold-labelled dorsal root ganglion cells normally and 81% after injury. Immunohistochemical visualisation of choleragenoid transganglionically transported from the injured sciatic nerve combined with neuropeptide Y immunocytochemistry showed that primary afferent fibres and terminals in the nucleus gracilis contain neuropeptide Y following peripheral nerve transection. Taken together, the results indicate that peripherally axotomised nucleus gracilis-projecting neurones undergo marked alterations in their cytochemical characteristics, which may be significant for the structural and functional plasticity of this system after injury.

Expression of beta-preprotachykinin mRNA and tachykinins in rat dorsal root ganglion cells following peripheral or central axotomy

The changes in gene expression and protein synthesis induced in neurons by axotomy usually lead to increased production of axon constituents and decreased production of molecules related to neurotransmission. Exceptions to this generalization occur, however, and it is unclear whether the injury itself changes the pattern of synthesis or whether individual mechanisms regulate the synthesis of the various axonal components. We used in situ hybridization histochemistry and immunocytochemistry to compare the changes in L4 and L5 rat dorsal root ganglion neuron levels of preprotachykinin mRNA and tachykinin peptides caused by sciatic nerve injury with those caused by dorsal root injury. Both lesions elicit regeneration, although only the axotomized peripheral processes re-establish functional contact with their targets. In the contralateral, intact dorsal root ganglia approximately 17% of neurons contained detectable levels of both mRNAs and peptides. Sciatic nerve section decreased by 70% the number of neurons labeled for preprotachykinin mRNA at three days post-operatively. Not all cells in the ganglion are axotomized by the sciatic nerve lesion; grain counts over the cells spared by the lesion showed an increased level of labeling, possibly a result of collateral sprouting by these spared cells. By two weeks, the number of cells labeled for preprotachykinin mRNA had decreased to 80% of control levels. The numbers of neurons labeled for tachykinin peptides decreased more slowly and reached approximately 50% of control numbers at two weeks. By six months post-operatively, when regeneration is largely complete, the number of neurons containing both mRNAs and peptides returned to normal. In contrast, dorsal root section did not elicit a decrease in the number of neurons labeled either for the mRNAs or the peptides at any of the post-operative intervals examined. These results indicate that axotomy is not the stimulus that elicits changes in the expression of genes coding for tachykinins. Evidence is considered indicating that interruption of the supply of peripherally derived nerve growth factor may be responsible for the changes in gene expression for tachykinins after axotomy.

Reciprocal regulation of tachykinin- and vasoactive intestinal peptide-gene expression in rat sensory neurones following cut and crush injury

The relative abundance of preprotachykinin- (PPT), actin- and vasoactive intestinal peptide- (VIP) mRNA's was measured in L5 dorsal root ganglia of rats after resecting or crushing the sciatic nerve. PPT-mRNA levels fell to 40% of control values 3, 6 and 9 days following nerve resection. Crushing produced a lesser fall at 3 and 6 days with a partial recovery at 9 days. Following resection actin-mRNA levels transiently rose to twice control values and had returned to normal by day 9. VIP-mRNA was not detectable in control ganglia but increasing amounts of VIP-mRNA were present 3, 6 and 9 days after nerve injury. The results are discussed in terms of the control mechanisms operating.

Neuropeptide expression in rat dorsal root ganglion cells and spinal cord after peripheral nerve injury with special reference to galanin

The temporal course of changes in peptide expression in the dorsal root ganglia L4 and L5 and in the dorsal horn of the spinal cord has been studied in rats subjected to a sciatic nerve transection at a mid-thigh level following different survival times. Galanin-, substance P-, vasoactive intestinal polypeptide-, peptide histidine-isoleucine- and calcitonin gene-related peptide-like immunoreactivities have been studied both by immunohistochemistry and radioimmunoassay. Galanin messenger ribonucleic acid has also been studied by in situ hybridization in the dorsal root ganglia of normal and lesioned animals. In addition, a group of animals with a sciatic nerve crush was studied to compare possible differences in peptide expression after both types of lesions. The results show that the transection induces an increase in the number of cell bodies expressing galanin-like immunoreactivity in the ganglia, and that the galanin levels rise about 120-fold after three and 14 days of survival. This increase reflected increased synthesis of the peptide, since there was a rise in the galanin messenger ribonucleic acid already at 24 h post-lesion, which was maintained for at least 60 days. In the spinal cord there was an increase of staining in the midportion of the outer layers of the dorsal horn that corresponded to fibers thought to arise from cells of the dorsal root ganglia affected by the transection. Also a depletion of substance P-like and an increase in vasoactive intestinal polypeptide- and peptide histidine-isoleucine-like immunoreactivities in the dorsal root ganglia were confirmed. These changes were shown to be rapidly detectable and were paralleled by similar changes in the dorsal horn of the spinal cord. For calcitonin gene-related peptide the immunohistochemistry was inconclusive, and the radioimmunoassay showed no detectable changes. After nerve crush a transient increase in the number of galanin immunoreactive neurons was observed, as well as a decrease in the number of neurons showing substance P-like immunoreactivity. These changes were most noticeable between six and 14 days of survival. After this, peptide expression seemed to return slowly to normal, that is by day 45 post-crush only a few cells showed galanin-like, and many sensory neurons expressed substance P-like immunoreactivity. The results demonstrate that when primary sensory neurons are peripherally lesioned they respond in a complex manner, altering their normal production of peptides by increasing or decreasing their synthesis.(ABSTRACT TRUNCATED AT 400 WORDS)