title: Behavioral differences between neonatal and adult 6-hydroxydopamine-treated rats to dopamine agonists: relevance to neurological symptoms in clinical syndromes with reduced brain dopamine.
abstract: Administration of L-dopa or apomorphine to neonatal and adult 6-hydroxydopamine (6-OHDA)-treated rats resulted in different behavioral responses depending on the age at which dopaminergic fibers were destroyed. When neonatal 6-OHDA-treated rats were tested as adults, they exhibited marked stereotypies, self-biting and self-mutilation behavior (SMB) when given these dopamine agonists. Self-biting as well as the incidence of SMB in neonatal 6-OHDA-treated rats showed dose-related changes between 10 and 100 mg/kg of L-dopa. This SMB and self-biting after L-dopa was observed as early as 22 to 24 days of age. Adult 6-OHDA-treated rats did not exhibit SMB or self-biting to L-dopa (100 mg/kg) or apomorphine (10 mg/kg), but did display paw treading and head nodding--behaviors not observed in neonatal 6-OHDA-treated rats. In addition, the locomotor response to apomorphine (1 mg/kg) was significantly greater in adult 6-OHDA-treated rats than in neonatal 6-OHDA-treated rats. Brain dopamine was reduced markedly in striatum, nucleus accumbens and olfactory tubercles in both 6-OHDA treatment groups with the reduction being slightly greater in rats treated with 6-OHDA neonatally. Serotonin content was elevated in striatum of rats treated neonatally with 6-OHDA, but not in adult 6-OHDA-treated rats. SMB and behaviors observed after L-dopa in rats treated neonatally with 6-OHDA were not apparent after L-dopa in rats with brain serotonin or norepinephrine reduced. Rats with brain dopaminergic fibers destroyed neonatally exhibited self-biting and SMB after L-dopa, suggesting that neonatal reduction of this amine is responsible for the SMB and self-biting in neonatal 6-OHDA-treated rats. 5-Hydroxytryptophan administration to neonatal 6-OHDA-treated rats did not induce SMB, indicating that release of serotonin by L-dopa is not responsible for this behavior. Because inhibition of dopamine-beta-hydroxylase did not alter the SMB response to L-dopa observed in neonatal 6-OHDA-treated rats, norepinephrine synthesized from L-dopa does not appear to contribute to the response. High doses of a decarboxylase inhibitor sufficient to inhibit conversion of dopa to dopamine in brain did not reduce the incidence of SMB. Administration of haloperidol (1 mg/kg) reduced the incidence of SMB, but did not antagonize the self-biting or the taffy pulling exhibited by L-dopa. In contrast, cisflupentixol completely blocked the SMB and self-biting induced by L-dopa.(ABSTRACT TRUNCATED AT 400 WORDS)
mesh_terms: D000367:Age Factors; D000818:Animals; D014150:Antipsychotic Agents / Q000494:pharmacology; D065105:Aromatic Amino Acid Decarboxylase Inhibitors; D001522:Behavior, Animal / Q000187:drug effects*; D001923:Brain Chemistry / Q000187:drug effects*; D004298:Dopamine / Q000032:analysis*; D004299:Dopamine beta-Hydroxylase / Q000037:antagonists & inhibitors; D004305:Dose-Response Relationship, Drug; D005260:Female; D006801:Humans; D006892:Hydroxydopamines / Q000633:toxicity*; D007926:Lesch-Nyhan Syndrome / Q000209:etiology*; D007980:Levodopa / Q000494:pharmacology; D009043:Motor Activity / Q000187:drug effects; D009638:Norepinephrine / Q000032:analysis; D016627:Oxidopamine; D010302:Parkinson Disease, Secondary / Q000209:etiology*; D051381:Rats; D011919:Rats, Inbred Strains; D011954:Receptors, Dopamine / Q000187:drug effects*; D012701:Serotonin / Q000032:analysis
chemical_list: D014150:Antipsychotic Agents; D065105:Aromatic Amino Acid Decarboxylase Inhibitors; D006892:Hydroxydopamines; D011954:Receptors, Dopamine; D012701:Serotonin; D007980:Levodopa; D016627:Oxidopamine; D004299:Dopamine beta-Hydroxylase; D004298:Dopamine; D009638:Norepinephrine