P. Keen

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) mRNAs 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.

Synthesis, and central and peripheral axonal transport of substance P in a dorsal root ganglion-nerve preparation in vitro.

A preparation of the rat L5 dorsal root ganglion with 6 mm lengths of dorsal root and peripheral branch attached was incubated in vitro over a 9 h period. The substance P-like immunoreactivity (SPLI) of the preparation increased linearly with time and SPLI was transported down both branches. The turnover-time of ganglion SPLI was 3.6 h. Four times as much SPLI accumulated in the peripheral branch as in the dorsal root. When axonal transport was inhibited by demecolcine, SPLI was formed at the same rate but accumulated in the ganglion. Anisomycin inhibited SPLI synthesis after a delay of 2 h. It was apparent that the SPLI of the preparation was contained in two pools, only one of which underwent rapid axonal transport. The mobile pool of axonal SPLI comprised 30% of the total and moved with a velocity of 4.9 mm . h-1.

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

Following cutting or crushing the rat sciatic nerve, synthesis of substance P by L5 dorsal root ganglia in vitro was reduced respectively to 20 and 40 per cent of control values. By day 64 the ability to synthesise substance P had been fully restored in crushed neurones but in cut neurones remained at a low level. We conclude that substance P synthesis is a more sensitive index of the effect of nerve injury than is substance P content and further that regenerating axons are able to support substance P synthesis before they reach their target tissue.

Localization of chromatographically characterized oxytocin and arginine-vasopressin to sensory neurones in the rat

Following treatment with colchicine 50-60% of all neurones in rat trigeminal and L5 spinal ganglia showed oxytocin (OXT)- and arginine-vasopressin (AVP)-like immunoreactivity. Further, OXT and AVP, together with their associated neurophysins, could be isolated from trigeminal ganglia by reversed-phase high-performance liquid chromatography followed by radioimmunoassay.

Essential fatty acid treatment — effects on nerve conduction, polyol pathway and axonal transport in streptozotocin diabetic rats

SummaryThis study was designed to examine the effect of dietary supplementation with essential fatty acids (evening primrose oil — 5% weight:weight added to the diet) on acute neurophysiological and neurochemical defects in streptozotocin-diabetic rats. Diabetic rats, which were not given evening primrose oil, showed highly significant elevations of nerve sorbitol and fructose combined with a depletion of nerve myo-inositol. In those animals there was also a 40% reduction (p<0.02) in the accumulation of axonally transported substance P-like immunoreactivity proximal to a 12 h sciatic nerve ligature together with reduced motor nerve conduction velocity (13% [p<0.001] and 20% [p<0.001] in two separate experiments). Treatment of other diabetic rats with evening primrose oil prevented completely the development of the motor nerve conduction velocity deficit without affecting sorbitol, fructose or myo-inositol levels or the deficit in axonal transport of substance P. In a second experiment, treatment of diabetic rats with evening primrose oil was associated with significant attenuation of the conduction velocity deficit, but not complete prevention.

Deficient Axonal Transport of Substance P in Streptozocin-Induced Diabetic Rats: Effects of Sorbinil and Insulin

This study measured the accumulation of substance P–like immunoreactivity (SPLI) proximal and distal to 12-h constricting ligatures applied to rat sciatic nerves. There were three separate experiments, and the baseline for each consisted of control and age-matched rats with 3 wk of untreated streptozocin-induced diabetes. We compared the effects of twice-daily insulin treatment, daily sorbinil (25 mg · kg−1 · day−1 p.o.), and a combination of both treatments. In untreated diabetic rats the anterograde accumulation of SPLI was reduced by 30–40%. This deficit was unaffected by sorbinil alone but was attenuated by insulin and prevented completely by insulin and sorbinil combined. There were also indications that diabetes caused reductions in retrograde accumulation of SPLI and its content in unconstricted nerve and the L4 dorsal root ganglion. The fraction of SPLI undergoing net anterograde or retrograde movement and the velocities of accumulation were unaffected by diabetes or the treatment regimens. These findings indicate a reduction in the amount of substance P moved by axonal transport in diabetic rats that is related partly to aldose reductase activity and partly to some other insulin-correctable consequence of experimental diabetes.

The distribution of free amino acids in subdivisions of rat and frog retinae obtained by a new technique

A technique is described for splitting intact rat and frog retinae into laminae. These laminae have been examined histologically and the distribution of free amino acids in the laminae has been determined by the dansylation technique. In both rat and frog retinae, taurine was selectively concentrated in the photoreceptor cells and their processes. In the rat, glycine, glutamine and GABA were especially abundant in a lamina which contained the ganglion, inner plexiform and inner neuronal layers. High concentrations of GABA were also present in the outer plexiform layer. These results are discussed in terms of a possible transmitter function for these amino acids in the retina.

Substance P levels in peripheral nerve, skin, atrial myocardium and gastrointestinal tract of rats with long-term diabetes mellitus. Effects of aldose reductase inhibition.

This study measured the content of substance P-like immunoreactivity (SPLI) in peripheral nervous tissue (lumbar dorsal root ganglia, sciatic nerve), skin (snout, foot), gastrointestinal tract (stomach, terminal ileum) and in the atria of the heart. Animals studied were long-term (11 months) streptozotocin-diabetic rats compared with age-matched control rats. All diabetic rats were given a very long acting insulin preparation twice weekly to reduce morbidity. Half of the diabetic rats were given the aldose reductase inhibitor, sorbinil (mean dose 30 mg/kg/day body weight by dietary admixture) over the entire protocol. Diabetic rats (given insulin only) showed marked accumulation of sorbitol and fructose together with myo-inositol depletion in their sciatic nerves. The sciatic nerves of the sorbinil-treated diabetic rats contained amounts of sorbitol, fructose and myo-inositol which were similar to those of non-diabetic rats, in spite of large amounts of nerve glucose in the sorbinil-treated animals. Thus, the inhibition of aldose reductase was successful. The L4 and L5 dorsal root ganglia of the diabetic rats showed reduced SPLI (63% and 72% respectively of control ganglia; P less than 0.05). There was also numerical reduction in sciatic nerve SPLI (84% of control nerve). There were no effects of sorbinil treatment on the reduced SPLI levels in ganglia or sciatic nerve. In the gastrointestinal tract the levels of SPLI were reduced in diabetic rats even when data were adjusted to take account of tissue hypertrophy (diabetic SPLI/whole stomach was 60% controls, P less than 0.01 and SPLI/cm ileum was 78%, though the latter did not attain statistical significance). In skin SPLI/unit area was raised in the diabetic rats to 145% of controls for foot skin and 151% for snout skin. Changes in SPLI content of gastrointestinal tract were unaffected by sorbinil treatment; in the skin the elevations were enhanced to 188% and 270% of respective control values for foot and snout skin. The SPLI content of the atria was unaffected by diabetes or sorbinil. These data are not consistent with a generalised impairment of delivery of substance P by axonal transport in experimental diabetes; special factors appear to influence the levels in neurones innervating different tissues. Exaggerated flux through the polyol pathway appears to be uninvolved.

The effect of a conditioning lesion on the regeneration rate of peripheral nerve axons containing substance P.

The regeneration rate of peripheral nerve axons containing substance P-like immunoreactivity (SPLI) was measured in rat sciatic nerve by radioimmunoassay of SPLI in nerve segments 2, 4 and 6 days after a test lesion made by briefly crushing the nerve at the hip. The regeneration rate of the fastest growing sensory axons was also measured in the same nerves using the pinch-reflex procedure. Three groups of animals were compared: group S, which received only the single test lesion, had regeneration rates of 3.57 +/- 0.26 (S.E.) mm/day for SPLI-containing axons and 3.53 +/- 0.14 mm/day for the fastest growing sensory axons. Group A/H, which received a conditioning lesion on the tibial nerve at the ankle 7 days prior to the test lesion at the hip, had a regeneration rate for SPLI-containing axons which was not significantly different from group S, of 3.35 +/- 0.17 mm/day. However, the regeneration rate for the sensory axons was significantly increased to 4.60 +/- 0.23 mm/day. Group H/H, which received both conditioning and test lesions at the hip, once again separated by 7 days, showed a significant increase in regeneration rate of SPLI-containing axons to 5.50 +/- 0.33 mm/day and a further increase over group A/H in the regeneration rate of sensory axons to 6.70 +/- 0.25 mm/day. We conclude that the small-diameter, unmyelinated axons containing SPLI in peripheral nerve normally regenerate at the same rate as the fastest growing sensory axons.(ABSTRACT TRUNCATED AT 250 WORDS)

Axonal transport of substance P-like immunoreactivity in ganglioside-treated diabetic rats

This study examined the effect of treatment of control and streptozotocin-diabetic rats with a mixture of gangliosides, derived from bovine brain, on parameters of axonal transport of substance P-like immunoreactivity (SPLI) and its levels in sciatic nerve and lumbar spinal ganglia. Rats were treated daily (10 mg/kg i.p.) for 28 days and compared with untreated control and diabetic groups. The duration of diabetes was 28 days in both cases. Untreated diabetic rats showed deficits in accumulation of axonally transported SPLI proximal (59% of controls) and distal (34% of controls) to sciatic nerve ligations (left in place for 12 h). Rates of accumulation were unaltered by diabetes. There were small numerical reductions in the SPLI content of unconstricted sciatic nerve and of L4 and L5 dorsal root ganglia in diabetic rats. None of these diabetes-associated changes was altered by ganglioside treatment, nor was there any indication of an effect of gangliosides on substance P in non-diabetic rats. The implications are discussed in relation to the possible pathogenesis of diabetic neuropathy.