The Role of Dopaminergic and Serotonergic Mechanisms in the Development of Swimming Ability of Young Rats

Abstract

Neonatal swimming behavior was studied after a single subcutaneous injection of L-dopa methyl ester (50 mg/kg; 200 mg/kg) apomorphine (0.1 mg/kg; 1.0. mg/kg), DL-amphetamine (0.5 mg/kg; 10 mg/kg), haloperidol (0.5 mg/kg; 1.0 mg/kg), L-tryptophan (50 mg/kg; 100 mg/kg), methysergide (1.0 mg/kg; 5.0 mg/kg) as well as intraventricular injection of 100 µg 6-OHDA. 1-, 3-, 5- and 7-day-old rats were placed into a temperature-controlled aquarium (37°C) and the pattern of motor coordination, latency time to swimming (LTS) and the number of foreleg strokes for 10 s (FS) were measured. When compared to the physiological saline-injected controls, rats that received L-dopa showed a striking increase of FS at all ages but the most striking improvement of motor coordination was found in newborn rats. On day 1 both doses of DL-amphetamine induced increases in FS and improvement of motor coordination, whereas apomorphine failed to show any effect at this age. On days 3, 5 and 7 low doses of DL-amphetamine and apomorphine increased the FS. However, high doses resulted in a decrement in swimming performance. Haloperidol impaired swimming on day 1 but produced a significant increase of FS on days 5 and 7. Neonatal injection of 6-OHDA delayed development of motor coordination, reduced FS and increased LTS. On days 3,5 and 7 high doses of L-tryptophan elicited an increase of FS, while high doses of methysergide caused significant impairment of performance. It is suggested that the brain rapidly converts the administered L-dopa to dopamine during the first week of life and there appears to be a strong dependent relationship between the pattern of motor coordination and the amount of available dopamine in the developing brain.

Brain Catecholamine Concentration during the First Week of Development in Rats

“…The results of these biochemical studies extend our recent observations concerning swimming behavior after treatment with drugs which effect brain dopamine systems during the first postnatal week [20]. In that study, we suggested that exogenous L-DO-PA was converted to dopamine during the first week of life and that there was a conse quent strong relationship between the pat tern of motor coordination exhibited during swimming and the amount of available do pamine in the developing brain.…”

“…On postnatal days 1 and 7 the effects of L-DOPA on the enhancement of brain DA and swimming behavior were roughly proportional. In addition to the greater (p<0.025) elevation in brain DA on day 1 versus day 7 after L-DOPA, there was also a relatively (to saline controls) greater im provement in swimming behavior after LDOPAon day 1 versus 7 [20]. During the first week of rodent postnatal life, the administra tion of L-DOPA (50-100 mg/kg) is reported to result in a specific increase in brain DA concentration [11], the density of DA-containing terminals, as well as hasten the adult appearance of histochemically demonstrable DA [13].…”

“…Although there is ample data available which demonstrates a selective elevation of brain DA levels after L-DOPA treatment [5,8,11,15], the relationship between elevated brain DA and motor stimulation is not a sim ple one with regard to specific amines and the time course of their effects [11,15,20], Our recent study on swimming behavior in the neonate revealed that administration of L-DOPA (50 mg/kg) 30 min before behavioral testing on either postnatal days 1 or 7 im proved motor coordination, as well as the rate of foreleg stroking and latency before swimming [20]. The present study demon strated parallel change in brain DA concen trations.…”

“…Littermate male and female rats were selected at ran dom on either postnatal day 1 or day 7 to receive the fol lowing substances subcutaneously in 0.05 ml saline [20] at approximately 10.00 h: (1) L-DOPA (L-3.4-dihydroxyphenylalanine methyl ester (Sigma), 50 mg/kg; (2) haloperidol (4-[4-(4-chlorophenyl)-4-hydroxy-I-piperidinyl]-l-(4-fluorophenyl)-l-butanone) (McNeil Laborato ries), I mg/kg; (3) ¿»-amphetamine (/3-phenyl-isopropyl amine) sulfate (Sigma), 0.5 mg/kg; (4) haloperidol. 1 mg/ kg 30 min before L-DOPA, 50 mg/kg; (5) saline injec tion; (6) no treatment.…”

“…We have recently studied dopaminergic and serotonergic mechanisms in the postnatal development of swimming behavior during the first week of life in the rat [20]. The results of that study demonstrated (1) that substan ces known to influence dopaminergic brain mechanisms were capable of altering the de velopmental pattern of coordination evident in swimming behavior [9]; (2) administration of substances known to primarily effect the serotonergic system had no apparent influ ence on the motor coordination involved in swimming, although there were indications of enhanced adaptive capabilities in the neo nates [20].…”