Intracerebroventricular 4-methylcatechol (4-MC) ameliorates chronic pain associated with depression-like behavior via induction of brain-derived neurotrophic factor (BDNF).

Neuropathic pain concurrent with mood disorder from peripheral nerve injury is a serious clinical problem that significantly affects quality of life. Recent studies have suggested that a lack of brain-derived neurotrophic factor (BDNF) in the limbic system may cause this pain-emotion. BDNF is induced in cultured neurons by 4-methylcatechol (4-MC), but the role of 4-MC-induced BDNF in pain-emotion is poorly understood. Thus, we assessed the possible involvement of BDNF in brain in depression-like behavior during chronic pain following peripheral nerve injury. In addition, we examined whether intracerebroventricular (i.c.v.) 4-MC prevents chronic pain in rats and produces an antidepressant effect. Sprague-Dawley rats implanted intracerebroventricularly with a PE-10 tube were subjected to chronic constriction injury (CCI). Pain was assessed by a reduction in paw withdrawal latency (PWL) to heat stimuli after CCI. We also used a forced swimming testing (FST; time of immobility, in seconds) from day 14 to day 21 after CCI. Modulation of pain and emotional behavior was performed by injection of PD0325901 (a MEK1/2 inhibitor). 4-MC (100 nM) was continuously administered i.c.v. for 3 days during the period from day 14 to day 21 after CCI. To block analgesic and antidepressant effects, anti-BDNF antibody or K252a (a TrkB receptor inhibitor) was injected in combination with 4-MC. Naloxone was also coadministered to confirm the analgesic effect of 4-MC. During the chronic stage after CCI, the rats showed a sustained decrease in PWL (thermal hyperalgesia) associated with extension of the time of immobility (depression-like behavior). PD0325901 significantly reduced the decrease in PWL and the increased time of immobility after CCI. The decreased PWL and increased time of immobility were also reduced by 4-MC and by treatment with an ERK1/2 inhibitor. These effects of 4-MC i.c.v. were reversed by anti-BDNF and K252a. The analgesic effect of 4-MC i.c.v. was also antagonized by naloxone. Based on these results, we suggest that a lack of BDNF and activation of ERK1/2 in the pain-emotion network in the CNS may be involved in depression-like behavior during chronic pain. 4-MC i.c.v. ameliorates chronic pain and depression-like behavior by producing of BDNF and normalization of ERK1/2 activation. Therefore, enhancement of BDNF may be a new treatment strategy for chronic pain associated with depression.

Effects of actinomycin D and cycloheximide on zinc status in marginally zinc-deficient rats.

During deficient zinc intake, rats are liable to suffer zinc deficiency under the following conditions: higher protein diet, diet containing higher quality (higher nutritive value) protein, and higher dietary intake. This suggests that a higher protein nutritional status (rapid increase in body protein) in rats leads to a lower zinc nutritional status (higher zinc requirement). In contrast, it is expected that a lower protein nutritional status (lowered body protein biosynthesis) is not liable to result in a lower zinc nutritional status. Therefore, the effects of protein biosynthesis inhibitors on zinc status were studied. Actinomycin D and cycloheximide were administered to rats under a marginally zinc-deficient condition. The growth of rats was depressed and serum and femur zinc concentrations were increased by administration of protein biosynthesis inhibitors. The carcasses of rats administered protein synthesis inhibitors had a higher zinc/protein ratio than those of the respective pair-fed (calorically equivalent to the zinc-deficient group) rats. Results suggest that zinc deficiency in rats is mainly alleviated by decreased food intake with administration of protein synthesis inhibitors. Furthermore, protein biosynthesis inhibition alone alleviated zinc deficiency.

Effects of dietary protein levels on body composition of zinc-deficient rats.

This study examined why decreased protein intake retards zinc deficiency in zinc-deficient rats. Rats were freely provided zinc-deficient diets with either 10 or 20% protein. Experimental groups consisted of five rats that were fed experimental diets for 0, 3, 4, 12 and 25 d in Experiment 1. The body protein content in rats fed the 10% protein diet was similar to those fed the 20% protein diet for the duration of the experiment. The body zinc content in both dietary groups slowly decreased in a similar manner. Eventually, the body zinc/protein ratio in the 10% protein diet group decreased more slowly than that in the 20% protein diet group. Ingestion of the 10% protein diet also reduced the zinc/protein ratio in bone more slowly compared with that of the 20% protein diet, under zinc-deficient conditions, at 12 d in Experiment 2. However, there was no difference in the zinc/protein ratio of carcass total soft tissue between the two zinc-deficient groups. Decreased protein intake eventually slowed the reduction in both the body and bone zinc/protein ratios in zinc-deficient rats, resulting in retardation of zinc deficiency.

Growth of zinc-deficient rats during intra-gastric tube feeding.

This study aimed to examine the reasons for the lack of growth in rats fed a zinc-deficient (ZnD) diet via gastric tube. Four days after rats were given free access to the ZnD diet (0.3 mg/kg Zn), their food intake had decreased, and their growth had stopped. Rats were then fed via gastric tube; growth was restored in rats fed a control diet (25 mg/kg Zn; restored group) but not in those fed the ZnD diet (ZnD group). In the ZnD group, there was no reduction in the apparent absorption of dry matter, protein, or ash during 3 days of tube feeding. Dry matter in urine was markedly higher on day 3 and mainly consisted of glucose. Urinary nitrogen was also elevated in the ZnD group, but nitrogen balance remained positive; i.e., bodily protein continued to increase during the 3 days of tube feeding. Drinking water consumption in the ZnD group was markedly reduced from the second day of tube feeding. On the other hand, urine volume in the ZnD group was comparable to that in the restored group. Water content in the bodies of the ZnD group was reduced. These observations demonstrate that the ZnD group was dehydrated. In conclusion, rats fed a ZnD diet via gastric tube did not grow because their drinking water consumption decreased with progression of zinc deficiency, thereby, decreasing bodily water content. Administration of water led to growth in the ZnD group.

Relationship between zinc parameters and either body weight gain, protein intake or survival time in zinc-deficient rats.

This study was undertaken to examine the relationships between zinc parameters (serum alkaline phosphatase activity, and zinc concentration in serum and femur) and either body weight gain, protein intake or survival time in zinc deficient rats. Demineralized soy protein (DP) and alkali-treated soy protein (AP) were used as dietary protein sources in order to make zinc deficient diets (< 0.5 mg zinc/kg diet). The same diets (DP and AP diets) supplemented with lysine or cystine were also given freely to rats. Moreover, in other experiments, the above relationships were examined. During the early stages, a significant negative correlation between body weight gain and survival time in zinc-deficient rats was demonstrated. The significant negative correlation coefficient between protein intake and survival time increased gradually, and the maximum value of this correlation coefficient was higher than that between body weight gain and survival time. The significant correlations between protein intake and femur zinc concentration were recognized throughout the longer periods. These results show that the number of zinc-deficient rats which survive decreases as protein intake increases throughout the feeding period, that the influence of protein intake is greater than that of body weight in early stages, and that the zinc requirements of rats rise with the increase in protein intake.

Influences of dietary protein levels and phytate contents on zinc requirement in rats.

This study investigates whether the effects of increased dietary levels of soy protein on zinc-deficient rats are due to the dietary protein content. Rats were fed two levels of demineralized soy protein (DP) diets and two levels of egg albumin (EA) diets including 7 ppm zinc (Experiment 1). Growth was depressed in rats fed a 20% DP diet (0.43% phytate) but not in those fed a 10% EA diet containing 7 ppm zinc. Zinc concentrations in the serum, femur and kidney were lower in rats fed the 20% DP diet than those fed a 10% DP (0.20% phytate) diet, and they were also lower in rats fed the 10% EA diet than those fed a 5% EA diet. Zinc concentrations in the serum and femur of rats fed the 10% DP diet or the 20% DP diet were decreased compared with those fed the 5% EA diet or the 10% EA diet, respectively. Under zinc-deficient conditions (< 0.4 ppm Zn), the survival time shortened (Experiment 2) and the zinc concentration in the serum and femur decreased faster (Experiment 3) in rats fed the 10% EA diet compared with those fed the 5% EA diet. The survival times and time courses of these parameters show that the zinc requirements of rats increased with the dietary protein level. The increased zinc requirement of rats that accompanied increasing dietary soy protein was due to the dietary protein content as well as the dietary phytate content.