l-Prolyl-l-leucyl-glycinamide (MIF-1) is known to attenuate apomorphine-induced stereotypies in adult rats that are lesioned as neonates with 6-hydroxydopamine (6-OHDA). To test whether MIF-1 would affect dopamine (DA) agonist-induced and serotonin (5-HT) agonist-induced oral activity, both intact and neonatal 6-OHDA-treated rats were studied. Rats at 3 days from birth were injected with desipramine (20 mg/kg, IP), 1 h before 6-OHDA HBr (100 μg, salt form, in each lateral ventricle) or its vehicle, saline-ascorbic acid (0.1%). At approximately 6 months rats were treated with MIF-1 (0.1, 1.0, or 10.0 mg/kg, IP), 10 min before SKF 39393 HCl (1.0 mg/kg, IP) or m-chlorophenylpiperazine 2HCl (m-CPP 2HCl; 0.5 mg/kg, IP), DA D1 and 5-HT1C,2 receptor agonists, respectively. Although both agonists increased oral activity in control and neonatal 6-OHDA-treated rats, MIF-1 did not modify the response. In rats that received either of the three doses of MIF-1 for 21 consecutive days, there was still no observed effect of MIF-1 on the oral response of control and 6-OHDA-lesioned rats to SKF 38393 and m-CPP. These findings indicate that MIF-1 does not modify the oral activity response of supersensitized D1 and 5-HT1C receptors in adult rats that are lesioned neonatally with 6-OHDA.

To determine if greater amounts of hydroxyl radical (·OH) are formed by dopamine (DA) denervation and treatment with L-dihydroxyphenylalanine (L-DOPA), the neostriatum was DA denervated (99% reduction in DA content) by 6-hydroxydopamine treatment (134μg icv, desipramine pretreatment) of neonatal rats. At 10 weeks the peripherally restricted dopa decarboxylase inhibitor carbidopa (12.5mg/kg i.p.) was administered 30min before vehicle, L-DOPA (60mg/kg i.p.), or the known generator of reactive oxygen species, 6-hydroxydopa (6-OHDOPA) (60mg/ kg i.p.); and this was followed 30min later (and 15 min before termination) by the spin trap, salicylic acid (8 μmoles icv). By means of a high performance liquid chromatographic method with electrochemical detection, we found a 4-fold increase in the non-enzymatically formed spin trap product, 2,3-dihydroxybenzoic acid (2,3-DHBA), with neither L-DOPA nor 6-OHDOPA having an effect on 2,3-DHBA content of the neostriatum. Basal content of 2,5-DHBA, the enzymatically formed spin trap product, was 4-fold higher vs. 2,3-DHBA in the neostriatum of untreated rats, while L-DOPA and 6-OHDOPA each reduced formation of 2,5-DHBA. We conclude that DA innervation normally suppresses ·OH formation, and that the antiparkinsonian drug L-DOPA has no effect (2,3-DHBA) or slightly reduces (2,5-DHBA) ·OH formation in the neostriatum, probably by virtue of its bathing the system of newly formed ·OH.

Tardive dyskinesia (TD), a movement disorder produced by long-term treatment with a classical antipsychotic drug, is generally considered to be a disorder of dopamine (DA) systems, since classical antipsychotics are potent DA D2 receptor blockers. Also, acute DA D1 agonist treatment of rats is known to produce vacuous chewing movements (VCMs), a behavioral feature resembling the oral dyskinesia that is so prominent in most instances of TD. In this paper we outline a series of studies in a new animal model of TD in which DA D1 receptor supersensitivity was produced by neonatal 6-hydroxydopamine (6-OHDA)-induced destruction of nigrostriatal DA fibers. In rats so-lesioned 5-HT receptor supersensitivity is additionally produced, and in fact 5-HT receptor antagonists attenuate enhanced DA D16-lesioned rats treated with haloperidol for one year, there is a 2-fold increase in numbers of VCMs (versus intact rats treated with haloperidol); and this high frequency of VCMs persists for more than 6 months after discontinuing haloperidol treatment. During this stage, 5-HT2 receptor antagonists, but not DA D1 receptor antagonists, attenuate the incidence of VCMs. This series of findings implicates the 5-HT neuronal phenotype in TD, and promotes 5-HT2 receptor antagonists, more specifically 5-HT2C receptor antagonists, as a rational treatment approach for TD in humans.

Hyperactivity is thought to be associated with an alteration of dopamine (DA) neurochemistry in brain. This conventional view became solidified on the basis of observed hyperactivity in DA-lesioned animals and effectiveness of the dopaminomimetics such as amphetamine (AMP) in abating hyperactivity in humans and in animal models of hyperactivity. However, because AMPreleases serotonin (5-HT) as well as DA, we investigated the potential role of 5-HT in an animal model of hyperactivity. We found that a greater intensity of hyperactivity was produced in rats when both DA and 5-HT neurons were damaged at appropriate times in ontogeny. Therefore, previously we proposed this as an animal model of attention deficit hyperactivity disorder (ADHD) - induced by destruction of dopaminergic neurons with 6-hydroxydopamine (6-OHDA (neonatally) and serotoninergic neurons with 5,7-dihydroxytryptamine (5,7-DHT) (in adulthood). In this model effects similar to that of AMP(attenuation of hyperlocomotion) were produced by m-chlorophenylpiperazine (m-CPP) but not by 1-phenylbiguanide (1-PG), respective 5-HT2 and 5-HT3 agonists. The effect of m-CPP was shown to be replicated by desipramine, and was largely attenuated by the 5-HT2 antagonist mianserin. These findings implicate 5-HT neurochemistry as potentially important therapeutic targets for treating human hyperactivity and possibly childhood ADHD.

No description available.

The role that norepinephrine plays in regulating the concentration of different proteins in the parietal cortex, hippocampus and cerebellum was assessed by investigating the effects of either a bilateral lesion of the locus coeruleus or neonatal administration of 6-hydroxydopamine. Two weeks after lesioning the locus coeruleus, the concentration of two different proteins was elevated in the hippocampus; a third protein was reduced in concentration in this brain area as a result of the lesion. Three proteins were affected in concentration in the cerebellum after the locus coeruleus lesion - two were elevated in concentration and one was reduced in concentration. No proteins were altered in concentration in the parietal cortex as a result of the lesion. Seventy days after neonatal treatment with 6-hydroxydopamine, a total of 6 proteins were found to be changed. Four of these (one in the hippocampus and 3 in the parietal cortex) were reduced in concentration while two proteins (both in the cerebellum) were elevated in concentration after neonatal treatment with the catecholamine neurotoxin. There was little overlap between those proteins affected in concentration by the bilateral lesion of the locus coeruleus and those changed by neonatal treatment with 6-hydroxydopamine. These results suggest that the concentration of a number of different proteins may, under normal physiological conditions, be regulated in vivo by norepinephrine in the brain.

To determine whether prolonged supersensitization of dopamine D-1 receptors could be produced during ontogeny, rats were treated daily, from birth, for 33 consecutive days with the D-1 receptor agonist, SKF 38393 HC1 (3.0 mg/kg per day i.p.). These rats were additionally treated at 3 days after birth with the neurotoxin, 6-hydroxydopamine HBr (6-OHDA; 200 μg, i.c.v., half in each lateral ventricle) or its vehicle. At 6 to 7 weeks from birth a challenge dose of SKF 38393 HCl (3.0 mg/kg i.p.) increased stereotypy scores for a number of behaviors in 6-OHDA-lesioned rats that were treated repeatedly during ontogeny with SKF 38393. These accentuated behaviors included licking, grooming, taffy pulling, jumping, paw treading and locomotion. Although the findings demonstrate an increased sensitivity of D-1 receptors to an agonist, there was no change in the Bmax or Kd for D-1 receptors in the striatum. In rats that were treated during postnatal development with SKF 38393, but not lesioned with 6-OHDA, SKF 38393-induced stereotyped behaviors were not substantially different from control. The neonatally primed rat model may be useful for probing mechanisms of receptor supersensitivity.

Abstract: To study potential biochemical correlates of dopamine (DA) and serotonin receptor supersensitivity, rats were lesioned at 3 days after birth with 6‐hydroxydopamine (6‐OHDA; 67 µg in each lateral ventricle; desipramine pretreatment, 20 mg/kg i.p., 1 h) and then sensitized with the DA D1 agonist, SKF 38393 HCl (3.0 mg/kg i.p. per day) either ontogenetically (daily, for 28 consecutive days from birth) and/or in adulthood (four weekly injections, 6–9 weeks from birth). Controls received vehicle in place of 6‐OHDA or SKF 38393. Enhanced locomotor responses were observed after SKF 38393 at 6 weeks, only in rats that received SKF 38393 + 6‐OHDA in ontogeny. Locomotor responses were further enhanced in this group after the last of four weekly SKF 38393 injections at the 9th week. These weekly SKF 38393 treatments also produced enhanced responses in 6‐OHDA rats that did not receive SKF 38393 in ontogeny. When striata were studied at 11 weeks, the percentages of high and low affinity DA D1 binding sites were not altered. Basal as well as DA‐, NaF‐, and forskolin‐stimulated adenylyl cyclase activities also were not changed. Dot blot analysis showed that there was a reduction of mRNA levels for DA D1, but not serotonin1C, receptors in the 6‐OHDA groups. However, SKF 38393 at 6–9 weeks eliminated this alteration. Based on these findings it can be proposed that supersensitization may be a consequence of altered neuronal cross talk rather than an imbalance of receptor elements per se.

The locus coeruleus (LC) of the rat was lesioned by microinjection of selective neurotoxins into the brainstem. 6‐Hydroxydopamine (6‐OHDA), 3 μg/μl, given unilaterally at two sites 0.6 mm apart on the rostro‐caudal axis of the LC, was used to lesion catecholamine‐containing neuronal elements. Ibotenic acid, 2.5 μg/0.5 μl, administered similarly was used to lesion nerve cell bodies. Two weeks after administration of the neurotoxin, lesion efficacy was determined based on the norepinephrine content of the cerebral cortex ipsi‐ and contralateral to the lesion. 6‐OHDA lesions of the LC caused a 46% reduction in ipsilateral cortical norepinephrine and a 60% reduction in specific 125I‐[Sar1, Ile8]‐angiotensin II (125I‐SIAII) binding in the LC. Ibotenic acid lesions of the LC caused a 73% reduction in ipsilateral cortical norepinephrine and a 81% reduction in specific 125I‐SIAII binding in the LC. These results indicate that All receptor binding sites in the LC are localized on noradrenergic nerve cell bodies or their dendritic and axonal ramifications within the LC.

Thèse numérisée par la Direction des bibliothèques de l'Université de Montréal.