Insulin-like growth factor-II increases and IGF is required for postnatal rat spinal motoneuron survival following sciatic nerve axotomy.

The prolonged disconnection of nerve from muscle results in the death of motoneurons and permanent paralysis. Because clinical nerve injuries generally involve postbirth motoneurons, there is interest in uncovering factors that may support their survival. A rich history of research dating back to the time of Santiago Ramon y Cajal and Viktor Hamburger supports the inference that there are soluble neurotrophic factors associated with nerve and muscle. However, the endogenous factors normally required for motoneuron survival following nerve injury have eluded identification. Two interrelated hypotheses were tested: (1) administration of insulin-like growth factor-II (IGF-II) can support the survival of postbirth motoneurons, and (2) endogenous IGFs are essential for motoneuron survival following nerve injury. We report that IGF-II locally administered close to the proximal nerve stump prevented the death of motoneurons (estimated by relative numbers of neuronal profiles) which ordinarily follows sciatic nerve transection in neonatal rats. By contrast, anti-IGF antiserum, as well as IGF binding proteins-4 and -6, significantly increased (P < 0.01) motoneuron death. This report shows that IGF-II can support survival, and contains the novel observation that endogenous IGF activity in or near nerves is required for motoneuron survival. Other studies have determined that IGF gene and protein expression are increased in nerve and muscle following sciatic nerve crush, and that IGFs are required for nerve regeneration. Taken together, these data show that IGFs are nerve- and muscle-derived soluble factors that support motoneuron survival as well as nerve regeneration.

Time-dependent alteration of insulin-like growth factor gene expression during nerve regeneration in regions of muscle enriched with neuromuscular junctions.

Insulin-like growth factors (IGFs) increase the rate of motor axon elongation, prevent motoneuron death, and may support the reestablishment of synapses following nerve injury. In situ hybridization was used in the present study to examine the temporal and spatial distribution of IGF gene expression in soleus muscle following sciatic nerve crush in rats. In intact muscle, IGF-II gene expression was generally low, and localized to interstitial cells, possibly fibroblast and Schwann cells. These cells were found in the middle of muscle which is enriched in neuromuscular junctions. IGF-II gene expression, 4-6 days postcrush, was increased in interstitial cells. Thereafter, IGF-II gene expression was also increased in muscle cells or cells closely associated with muscle fibers, such as satellite cells. IGF-II gene expression was increased to a much greater extent in the midregion of muscle enriched in end-plates than in the two ends of muscle, but returned towards normal following the reestablishment of functional synapses. On the other hand, IGF-I gene expression was only slightly increased following nerve crush, and this increase was associated with interstitial, but not muscle cells. These results show that the IGF-I and IGF-II genes are regulated by independent signals and may play separate roles during nerve regeneration. For example, a regional increase in IGF-II gene expression may support preferential nerve terminal sprouting in the middle of muscle enriched in neuromuscular junctions, thereby increasing the probability for the reestablishment of synapses.

Insulin-like growth factors reverse or arrest diabetic neuropathy: effects on hyperalgesia and impaired nerve regeneration in rats.

Diabetic neuropathy is a debilitating disorder whose causation is poorly understood. A new theory proposes that neuropathy may arise as a consequence of loss of neurotrophic insulin-like growth factor (IGF) activity due to diabetes, superimposed on a slow continual loss due to aging. The prediction that IGF-I and IGF-II gene expression are reduced in diabetic nerves was recently tested and validated. Here we tested the prediction that IGF administration can prevent or reverse diabetic sensory neuropathy. Subcutaneous infusion of IGF-I or IGF-II, but not vehicle, halted (P < 0.01) the progression of hyperalgesia in streptozotocin-diabetic rats. Moreover, impaired sensory nerve regeneration was partially reversed within 2 weeks after treatment of diabetic rats with IGFs (P < 0.01). Impaired regeneration could also be prevented by daily subcutaneous IGF injections. The low replacement doses of IGFs were effective despite unabated hyperglycemia and weight loss. These results show that IGF replacement therapy can reverse or prevent diabetic sensory neuropathy independently of hyperglycemia or weight loss.

Differential spatio-temporal expression of the insulin-like growth factor genes in regenerating sciatic nerve.

Previous studies have demonstrated that the regeneration of mammalian peripheral nerves is dependent on endogenous insulin-like growth factors (IGFs). In the present study, in situ hybridization was used to examine the temporal and spatial expression of the IGF-I and IGF-II genes in rat sciatic nerve after crush. Such expression was characterized in relation to Schwann cell proliferation and the presence of neurofilaments in returning axons during regeneration. The results show that both IGF-I and IGF-II mRNAs were increased in the sciatic nerve distal to the crush site. However, each transcript had a distinctly different temporal and spatial distribution during regeneration. IGF-I gene expression was intensely increased at the crush site within 4 days after nerve crush. Along the portion of the nerve distal to the crush site, a moderate increase was observed to reach maximal levels 10 days postcrush, and was decreased thereafter back towards baseline at 20 days postcrush. Furthermore, this increase was associated with the proliferation of Schwann cells, and the return toward baseline with the regeneration of axons containing neurofilaments. By contrast, IGF-II gene expression was unchanged at or near the site of injury, but unexpectedly was increased in more distal, intramuscular reaches of the nerves. This had a slower time course beginning 10 days postcrush, and was further increased at 20 days postcrush. These results show that the IGF-I and IGF-II genes are regulated by independent signals and probably play different roles during nerve regeneration. They support the hypotheses that IGF-I contributes to the initial sprouting and subsequent elongation of axons in nerves, whereas IGF-II enhances the regeneration of certain axons into neuromuscular branches of nerves, and/or the re-establishment of neuromuscular synapses.

Cholecystokinin octapeptide (CCK-8) antagonizes morphine analgesia in nucleus accumbens of the rat via the CCK-B receptor.

The analgesic effect of systemic morphine (4 mg/kg, s.c.) was antagonized in a dose-dependent manner by cholecystokinin octapeptide (CCK-8) (0.1-0.5 ng) administered bilaterally to the nucleus accumbens of the rat. This effect of CCK-8 could be reversed by devazepide, a CCK-A receptor antagonist, at 50 ng and 200 ng and by L-365,260, a CCK-B receptor antagonist, at 5 ng administered bilaterally to the nucleus accumbens. A marked potentiation of morphine analgesia was achieved by intra-nucleus accumbens injection of 200 ng devazepide or 5 ng L-365,260. Since the effect of L-365,260 in antagonizing the anti-opioid effect of CCK-8 in the nucleus accumbens is 40 times more potent than devazepide, it is suggested that the anti-opioid effect of CCK-8 is mediated by CCK-B receptors. In conclusion, nucleus accumbens is a strategic site where CCK-8 exerts an anti-opioid activity, most probably via the CCK-B receptors.

Role of insulin-like growth factors in peripheral nerve regeneration.

Prolonged denervation results in atrophy of target organs and increased risk of permanent paralysis. A better understanding of the mechanism responsible for nerve regeneration may one day lead to improved rates of nerve regeneration and diminished risk of loss of function. Neurobiologists have known for decades that soluble neurotrophic activity is present in nerves and nerve targets. Until recently, the soluble molecules that regulate the rate of nerve regeneration have eluded identification. Insulin-like growth factor (IGF) gene expression is correlated with synapse formation during development and regeneration. IGFs are now identified as the first soluble nerve- and muscle-derived neurotrophic factors found to regulate the rate of peripheral nerve regeneration. The roles of IGFs and other neurotrophic factors in peripheral nerve regeneration, motor nerve terminal sprouting and synapse formation are reviewed.

Effect of electroacupuncture tolerance by different frequencies on the opioid inhibition to cardiovascular activity in the spinal cord of rats.

Continuous 2-15 Hz or 2 Hz electroacupuncture (EA) of 6 h applied to rats resulted in electroacupuncture tolerance (ET). The effect of 2-15 Hz ET on the recovery of mean arterial blood pressure (MAP) and heart rate (HR) of rats after hemorrhagic shock, and the effect of intrathecal (i.t.) injection of [D-ala2, D-leu5]enkephalin (DADLE) on MAP and HR of 2 Hz ET rats were observed. The results were as follows: 1) there was no dramatic difference between the 2-15 Hz ET group and the control group in the recovery of MAP and HR from hemorrhagic shock; 2) DADLE (25 micrograms) caused almost the same depressor effect in the 2 Hz ET group as that in the control group. These data suggest that the spinal lateral horn cells (supposed to be involved in regulating blood pressure) are insensitive to EA and cannot be made tolerant to continuous EA, which is different from the dorsal horn cell (supposed to be involved in analgesia).

[Cholecystokinin octapeptide (CCK-8) antagonizes morphine analgesia in amygdala of the rat].

CCK-8 administered bilaterally to the amygdala at 0.1-1.0 ng dose-dependently antagonized the analgesia induced by morphine (4 mg/kg, s. c.) as measured by the changes in tail flick latency (TFL). This effect of CCK-8 could be reversed by Devazepide, a CCK-A receptor antagonist dose-dependently at 50 ng and 200 ng, and by L-365, 260, a CCK-B receptor antagonist at 5 ng and 8 ng administered to the same site. The effect of morphine analgesia was potentiated by 200 ng Devazepide or 8 ng L-365, 260 administered bilaterally to amygdala. Devazepide and L-365, 260 per second showed no significant influence on basal TFL. The results indicate that amygdala is a strategic site where CCK-8 exerts an antiopioid activity. Since the effect of L-365, 260 was 25 times more potent than Devazepide, it suggests that the anti-opiod effect of CCK in amygdala is mediated by CCK-B receptors.