ABSTRACT
BACKGROUND: The nucleus tractus solitarius (NTS), the region of the brain stem in which primary baroreceptor afferents teminate, is critically important in the normal regulation of arterial pressure (AP). In the NTS, excitatory amino acids such as L-glutamate serve as the main neurotransmitter in the regulation of AP. However, the function of GABA in the NTS has not been established. To test the function of GABA, we applied GABAergic agents to the NTS. METHODS: The experiments were conducted on adult male Sprague-Dawley rats weighing 300-500g. A cannula (PE-50 tubing filled with heparinized saline) was inserted into the femoral artery for recording of AP and heart rate(HR). Another cannula was inserted into the femoral vein for administration of nitroprusside or phenylephrine. After rats were placed on a sterotaxic instrument, the dorsal surface of the medulla was exposed, and with the aid of a surgical microscope, the NTS was visualized. Drug injections were made into the NTS using single- or three-barreled grass micropipettes pulled to an outer diameter of 80-100(micro)m and connected to a 1(micro)l Hamilton syringe. RESULTS: The follwing results were obtained in this experiment. Injection into the NTS of 10 or 20 nmol nipecitic acid, a selective inhibitor of GABA untake, produced an increase in AP. The pressor responses evoked by two doses of nipecotic acid were not significantly different. Injection of GABA(A) agonist, musciml(5 pmol in 80 nl artificial CSF) and GABA(B) agonist, baclofen (20 pmol in 80 nl) into the NTS of urethane-anesthetized rats prodused an increase in AP of 16.6+/-1.3 and 27.6+/-1.5 mmHg, respectively. Thus the pressor response to GABA(B) agonist was greater than to GABA(A) agonist. On the other hand, microinjection of GABA(A) antagonist, bicuculline and GABA(B) antagonist, phaclofen into the NTS decreased AP by approximately 13.4+/-1.0 and 20.9+/- mmHg, respectively. Thus injection of nipecotic acid into the NTS was greater in control group compared with the muscimiol or baclofen groups. The AP changes caused by i.v. injection of nitroprusside or phenylephrine were smallest in control group and greatest in the baclofen group. When calculated as baroreflex sensitivity, the change was greatest in control group and smallest in the baclofen group. CONCLUSION: From these results it was concluded that GABA in the NTS plays an important role in the regulation of AP, especially through GABA(B) receptors, and have an inhibitory effect on baroreceptor reflex.
Subject(s)
Adult , Animals , Humans , Male , Rats , Arterial Pressure , Baclofen , Baroreflex , Bicuculline , Blood Pressure , Brain Stem , Catheters , Excitatory Amino Acids , Femoral Artery , Femoral Vein , GABA Agents , gamma-Aminobutyric Acid , Glutamic Acid , Hand , Heart , Heparin , Microinjections , Neurotransmitter Agents , Nitroprusside , Phenylephrine , Poaceae , Pressoreceptors , Rats, Sprague-Dawley , Solitary Nucleus , SyringesABSTRACT
PURPOSE: This study was conducted to get baseline data to establish a guideline for the infant nutrition by observing the feeding practice and nutritional intake during infancy and evaluationg the nutritional status of iron and lipids at 12-month-old infants. METHODS: This survery was cnducted from July to November, 1992. Subjects were healthy infants who were brought to Yeungnam University Hospital for vaccination. We followed up feeding methods for 6 months in 120 infants, and laboratory tests which include hemoglobin, fematocrit, MCHC, ferritin, total cholesterol, HDL-cholesterol, triglyceride and urea nitrogen/creatinine ratio were done in 36 infants at 12 months of age. RESULTS: Male to female sex ratio was 1.6:1 in total 120 study infants. Among 36 infants who took laboratory tests, five infants were breast-fed, 25 were formula-fed, and 6 were mexed-fed. Percentage of the formula-fed infants increased as their monthly age increases. Although 54.2% of the studied infants were started weaning diet at four months of age, 10.8% of infants were not given any weaning diet until 6 month of age. Breastfed infnats had lower hemoglobin(10.6+/-1.8g/dl), hematocrit(32.6+/-3.6%), serum ferritin(13.6+/-13.1ng/ml)(p<0.05), and 15.6% of them had anemia and 16.7% of them had iron deficiency. Serum lipids levels except total cholesterol in breaset-fed female infants were comparable between groups. CONCLUSIONS: We confirm that the incidence of iron deficiency anemia was increased in breast fed infants and there was no difference in lipids levels according to different feeding methods. Adequate iron supplementation through weaning diets is one of the most important problems in breast milk feeding