Evidence for fibroblast growth factor-2 as a mediator of amphetamine-enhanced motor improvement following stroke.

Previously we have shown that addition of amphetamine to physical therapy results in enhanced motor improvement following stroke in rats, which was associated with the formation of new motor pathways from cortical projection neurons of the contralesional cortex. It is unclear what mechanisms are involved, but amphetamine is known to induce the neuronal release of catecholamines as well as upregulate fibroblast growth factor-2 (FGF-2) expression in the brain. Since FGF-2 has been widely documented to stimulate neurite outgrowth, the present studies were undertaken to provide evidence for FGF-2 as a neurobiological mechanism underlying amphetamine-induced neuroplasticity. In the present study rats that received amphetamine plus physical therapy following permanent middle cerebral artery occlusion exhibited significantly greater motor improvement over animals receiving physical therapy alone. Amphetamine plus physical therapy also significantly increased the number of FGF-2 expressing pyramidal neurons of the contralesional cortex at 2 weeks post-stroke and resulted in significant axonal outgrowth from these neurons at 8 weeks post-stroke. Since amphetamine is a known releaser of norepinephrine, in vitro analyses focused on whether noradrenergic stimulation could lead to neurite outgrowth in a manner requiring FGF-2 activity. Primary cortical neurons did not respond to direct stimulation by norepinephrine or amphetamine with increased neurite outgrowth. However, conditioned media from astrocytes exposed to norepinephrine or isoproterenol (a beta adrenergic agonist) significantly increased neurite outgrowth when applied to neuronal cultures. Adrenergic agonists also upregulated FGF-2 expression in astrocytes. Pharmacological analysis indicated that beta receptors and alpha1, but not alpha2, receptors were involved in both effects. Antibody neutralization studies demonstrated that FGF-2 was a critical contributor to neurite outgrowth induced by astrocyte-conditioned media. Taken together the present results suggest that noradrenergic activation, when combined with physical therapy, can improve motor recovery following ischemic damage by stimulating the formation of new neural pathways in an FGF-2-dependent manner.

Long-term motor improvement after stroke is enhanced by short-term treatment with the alpha-2 antagonist, atipamezole.

Drugs that increase central noradrenergic activity have been shown to enhance the rate of recovery of motor function in pre-clinical models of brain damage. Less is known about whether noradrenergic agents can improve the extent of motor recovery and whether such improvement can be sustained over time. This study was designed to determine if increasing central noradrenergic tone using atipamezole, an alpha-2 adrenoceptor antagonist, could induce a long-term improvement in motor performance in rats subjected to ischemic brain damage caused by permanent middle cerebral artery occlusion. The importance of pairing physical "rehabilitation" with enhanced noradrenergic activity was also investigated. Atipamezole (1 mg/kg, s.c.) or vehicle (sterile saline) was administered once daily on Days 2-8 post-operatively. Half of each drug group was housed under enriched environment conditions supplemented with daily focused activity sessions while the other half received standard housing with no focused activity. Skilled motor performance in forelimb reaching and ladder rung walking was assessed for 8 weeks post-operatively. Animals receiving atipamezole plus rehabilitation exhibited significantly greater motor improvement in both behavioral tests as compared to vehicle-treated animals receiving rehabilitation. Interestingly, animals receiving atipamezole without rehabilitation exhibited a significant motor improvement in the ladder rung walk test but not the forelimb reaching test. These results suggest that a short-term increase in noradrenergic activity can lead to sustained motor improvement following stroke, especially when paired with rehabilitation.

Motor recovery and axonal plasticity with short-term amphetamine after stroke.

BACKGROUND AND PURPOSE: There is considerable debate regarding the efficacy of amphetamine to facilitate motor recovery after stroke or experimental brain injury. Different drug dosing and timing schedules and differing physical rehabilitation strategies may contribute to outcome variability. The present study was designed to ascertain (1) whether short-term amphetamine could induce long-term functional motor recovery in rats after an ischemic lesion modeling stroke in humans; (2) how different levels of physical rehabilitation interact with amphetamine to enhance forelimb-related functional outcome; and (3) whether motor improvement was associated with axonal sprouting from intact corticoefferent pathways originating in the contralesional forelimb motor cortex. METHODS: After permanent middle cerebral artery occlusion, rats received vehicle or amphetamine during the first postoperative week (2 mg/kg, subcutaneously on Postoperative Days 2, 5, and 8). In both treatment groups, separate cohorts of rats were exposed to different levels of "physical rehabilitation" represented by a control environment, enriched environment, or enriched environment with additional sessions of focused activity. Skilled forelimb performance was assessed using the forelimb reaching task and ladder rung walk test. Anterograde tracing with biotinylated dextran amine was used to assess new fiber outgrowth to denervated motor areas. RESULTS: All treatment groups showed significant motor improvement as compared with control-housed, vehicle-treated animals. However, animals housed in an enriched environment that received amphetamine paired with focused activity sessions performed significantly better than any other treatment group and was the only group to achieve complete motor recovery (ie, reached preoperative performance) by 8 weeks. This recovery was associated with axonal sprouting into deafferentated subcortical areas from contralesional projection neurons. CONCLUSIONS: This study suggests that, after stroke, short-term pairing of amphetamine with sufficiently focused activity is an effective means of inducing long-term improvement in forelimb motor function. The anatomic data suggests that corticoefferent plasticity in the form of axonal sprouting contributes to the maintenance of motor recovery.

Postsynaptic 5-HT1A receptor stimulation increases motor activity in the 6-hydroxydopamine-lesioned rat: implications for treating Parkinson's disease.

RATIONALE: We have shown that the 5-HT1A agonist R-(+)-hydroxy-2-(di-n-propylamino)tetralin [R-(+)-8-OHDPAT] enhances motor activity in the monoamine-depleted rat, an acute model of Parkinson's disease. The present work extends these findings by investigating motor effects of R-(+)-8-OHDPAT in the unilateral 6-hydroxydopamine-lesioned rat, a chronic model of Parkinson's disease. OBJECTIVE: The objectives of the present study were to assess the motor response to R-(+)-8-OHDPAT in rats with unilateral destruction of the nigrostriatal dopamine system and to determine the involvement of postsynaptic 5-HT1A receptors in this response. MATERIALS AND METHODS: Rotational behavior after R-(+)-8-OHDPAT was investigated in rats that received 6-hydroxydopamine unilaterally into the median forebrain bundle 2 weeks before testing. RESULTS: A dose of 0.3 mg/kg subcutaneously (s.c.) R-(+)-8-OHDPAT induced significant ipsilateral turning in unilateral 6-OHDA-lesioned rats. Pretreatment with the selective 5-HT(1A) antagonist N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-2-pyridinyl-cyclohexanecarboxiamide maleate (WAY-100635, 0.1 mg/kg, s.c.) blocked turning. Blockade of 5-HT synthesis and 5-HT depletion caused by the tryptophan hydroxylase inhibitor DL: -p-chlorophenylalanine did not decrease R-(+)-8-OHDPAT-induced turning. Finally, a subset of animals were tested for their turning response to the dopamine agonist apomorphine after tests with R-(+)-8-OHDPAT had been completed. Correlation analysis indicated no relationship existed between the turning response to apomorphine and the turning response to R-(+)-8-OHDPAT. CONCLUSION: R-(+)-8-OHDPAT induces ipsilateral turning in unilateral 6-OHDA lesioned rats by stimulating postsynaptic 5-HT1A receptors, not by altering 5-HT synthesis and release. The mechanism underlying the motor effects of R-(+)-8-OHDPAT appears to differ from classic dopaminergic anti-parkinsonian agents suggesting that 5-HT1A agonists might prove useful adjunctive therapy in the treatment of Parkinson's disease.

Enhanced 5-HT2C receptor signaling is associated with haloperidol-induced "early onset" vacuous chewing in rats: implications for antipsychotic drug therapy.

RATIONALE: Haloperidol is a representative of typical antipsychotics that are still in clinical use and which can lead to abnormal motor activity following repeated administration. The mechanisms underlying antipsychotic-induced dyskinesias are not well understood but are widely held to be related to excessive loss of dopamine function. In several models of dopamine hypofunction, serotonin 5-HT2C receptors have been shown to mediate vacuous chewing movements (VCM), a form of abnormal motor activity. It is well established that repeated haloperidol administration also elicits VCM, but there is no information on how repeated haloperidol administration affects 5-HT2C receptor signaling. OBJECTIVES: In the present study, we tested the hypothesis that repeated daily administration of haloperidol leads to enhanced serotonin 5-HT2C receptor signaling that is associated with increased 5-HT2C-mediated VCM. METHODS: Rats were treated by subcutaneous injection once daily for 21 days with either vehicle, a low dose of haloperidol (0.1 mg kg(-1) day(-1)), or a high dose of haloperidol (1.0 mg kg(-1) day(-1)). Following 1-day withdrawal, rats were either used for behavioral scoring of VCM or sacrificed for biochemical assessment of 5-HT2 receptor-mediated phospholipase C activity and radioligand binding. VCM were scored following two successive "drug" challenges. The first challenge was an injection of vehicle (0.9% saline), and the second challenge was an injection of the 5-HT2C agonist meta-chlorophenylpiperazine (1.0 mg/kg). In this manner, a measure of "spontaneous" and "5-HT2C-elicited" orofacial activity could be made while minimizing animal use. RESULTS: Following 21-day haloperidol treatment at either dose, there was an increase in expression of meta-chlorophenylpiperazine-induced VCM. In a separate experiment, meta-chlorophenylpiperazine-induced VCM were shown to be mediated through 5-HT2C receptors. Striatal 5-HT2C receptor-mediated phospholipase C (PLC) activity and high-affinity agonist-labeled 5-HT2C receptors were also increased following either dose of haloperidol as compared to vehicle treatment. GTP-stimulated PLC activity and striatal Gq proteins were unchanged by haloperidol suggesting that enhanced signaling could be accounted for by alterations at the level of the receptor and not at downstream mechanisms. CONCLUSIONS: Repeated daily administration of haloperidol leads to an adaptive increase in 5-HT2C signaling which may contribute to abnormal motor function associated with antipsychotic use.

8-hydroxy-2-(di-n-propylamino)tetralin reduces striatal glutamate in an animal model of Parkinson's disease.

Using in-vivo microdialysis, we examined the effect of the serotonin 5-HT1A agonist R-(+)-8-hydroxy-2-(di-n-propylamino)tetralin on striatal extracellular excitatory amino acids in an animal model of Parkinson's disease. Extracellular glutamate and aspartate in the dopamine-denervated striatum of unilateral 6-hydroxydopamine-lesioned rats were significantly decreased by acute subcutaneous injection of R-(+)-8-hydroxy-2-(di-n-propylamino) tetralin (0.3 mg/kg). Although not quantified in the present study, a concomitant increase in locomotor activity was anecdotally observed following R-(+)-8-hydroxy-2-(di-n-propylamino)tetralin. These results suggest that systemic administration of a 5-HT1A agonist can reduce glutamate neurotransmission in the dopamine-denervated striatum. The results are discussed with respect to the treatment of Parkinson's disease.

SLV-308. Solvay.

Solvay is developing SLV-308 (SME-308), a partial dopamine D2 agonist and noradrenergic agonist with serotonin 5-HT1A agonist properties, for the potential oral treatment of Parkinson's disease (PD), panic and depression. By January 2001, SLV-308 had entered phase II trials for PD and phase I trials for anxiety and depression.

Postsynaptic 5-HT(1A) receptors mediate an increase in locomotor activity in the monoamine-depleted rat.

RATIONALE: In animal models of reduced dopamine transmission, such as haloperidol-induced catalepsy or monoamine-depleted animals, serotonin (5-hydroxytryptamine; 5-HT) 5-HT(1A) agonists appear to enhance motor activity. However, the exact mechanism remains unclear. OBJECTIVE: The objective of the present study was to demonstrate that 5-HT(1A) agonists can increase locomotor activity by activation of postsynaptic 5-HT(1A) heteroreceptors without the involvement of somatodendritic 5-HT(1A) autoreceptors which are known to regulate 5-HT neuronal activity. METHODS: The effects of the 5-HT(1A) full agonist R-(+)-8-hydroxy-2-(di- n-propylamino)tertralin ( R-(+)-8-OHDPAT) on locomotor activity in reserpinized (i.e., monoamine-depleted) rats were studied. RESULTS: The present data demonstrate that R-(+)-8-OHDPAT significantly increased locomotor activity in monoamine-depleted animals at a dose as low as 0.01 mg/kg. The partial 5-HT(1A) agonist/D(2) antagonist buspirone (3 mg/kg) also elevated locomotor activity. The effects of these 5-HT(1A) compounds were found to be similar to the locomotor-stimulating effect of the dopamine precursor 3,4-dihydroxyphenylalanine (150 mg/kg, 15 min after 50 mg/kg benserazide). The 5-HT(1A) antagonist N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-2-pyridinyl-cyclohexanecarboxamide maleate (WAY 100635; 0.2 mg/kg) blocked the R-(+)-8-OHDPAT (0.03 mg/kg)-mediated increase in locomotion. Blockade of 5-HT synthesis with DL- p-chlorophenylalanine (pCPA), a tryptophan hydroxylase inhibitor, prior to reserpinization did not affect R-(+)-8-OHDPAT-induced locomotion. CONCLUSIONS: The present data indicate that R-(+)-8-OHDPAT can increase motor activity in monoamine-depleted rats through postsynaptic 5-HT(1A) receptors and not necessarily through 5-HT(1A) autoreceptor-mediated alterations in 5-HT synthesis and release. A potential mechanism of 5-HT(1A)-mediated modulation of non-monoaminergic motor circuits in the brain is discussed. Taken together, the results suggest that 5-HT(1A) agonists would provide a novel approach to the amelioration of antipsychotic-induced side effects and the symptomatic treatment of Parkinson's disease.