Effects of leucine on brain serotonin.
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Using mass fragmentographic techniques, the synthesis of dopamine (DA) and norepinephrine (NE) was studied in five functional regions in the spinal cord of the developing rat. Norepinephrine was first detectable in the whole cord on fetal day (FD) 16. Thereafter, there was a rapid increase in synthesis. The fastest rate occurred in the ventral horn. The peak concentration was recorded in the latter half of neonatal life, followed by a decline back to the levels found in the adult cord. The capacity of the developing cord to synthesize NE from injected L-dihydroxyphenylalanine (L-DOPA) increased in concert with its normal synthetic capacity. There was no clear consistent pattern in the development of DA synthesis, with two exceptions: (1) in the cervical dorsal horn (CDH), cervical ventral horn ( CVH ), and thoracic zona intermedia ( TZI ), there was a peak of DA on the day of birth; (2) in all regions there was a peak of DA on neonatal day (ND) 20. At FD 16 (the earliest time studied) the developing cord was capable of considerable synthesis (6.0 nmol/g) of DA from injected L-DOPA. This synthetic capacity developed rapidly, peaked at ND 4, and declined back to the adult levels by ND 20. Control experiments indicate that only about 10% (at best) of the DA synthesized from injected L-DOPA occurs in monoaminergic nerve terminals. Norepinephrine is synthesized exclusively in noradrenergic nerve terminals. The newly synthesized DA and NE are both extensively metabolized in the cord. The results are discussed in relationship to current attempts to understand the functional importance of spinal monoaminergic nerves.(ABSTRACT TRUNCATED AT 250 WORDS)
Male Sprague-Dawley rats (325-350 g) were anesthetized with urethane (1.5 g/kg i.p.) and treated with physiological saline, Aspartame (APM; 552 mumols/kg), or tyrosine (Tyr; 552 mumols/kg). Ganglionic transmission and the synthesis of dopamine (DA) and norepinephrine (NE) were measured in the superior cervical ganglion (SCG) following electrical stimulation of the cervical sympathetic trunk (CST). When the CST was stimulated with single pulses, neither APM nor Tyr affected the synthesis of NE or DA. However, in response to low- (5 Hz, 20 s) and high- (20 Hz, 20 s) frequency pulses, the metabolism of DA was increased (p less than 0.05), but to the same extent after saline, APM, or Tyr. In rats stimulated with similar low- and high-frequency pulses, the synthesis of NE was increased significantly (p less than 0.05) after Tyr, but not after APM or saline. In saline-treated controls, ganglionic transmission was not changed in response to single pulses, or low- or high-frequency stimulation. However, after treatment with APM, ganglionic transmission was depressed significantly (p less than 0.01) in response to high-frequency stimulation (single: 0.46 +/- 0.09 mV; low: 0.39 +/- 0.07 mV; high: 0.27 +/- 0.07 mV). After treatment with Tyr, ganglionic transmission was depressed significantly (p less than 0.05) in response to both low- and high-frequency stimulation (single: 0.44 +/- 0.04 mV; low: 0.22 +/- 0.12 mV; high: 0.26 +/- 0.07 mV). In the nonstimulated SCG, L-3,4-dihydroxy-phenylalanine (25 mg/kg) caused a rapid, significant (p less than 0.01) increase in the synthesis and metabolism of DA, but not of NE.(ABSTRACT TRUNCATED AT 250 WORDS)
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