Involvement of nigrotecto-reticulospinal pathways in the iminodipropionitrile (IDPN) model of spasmodic dyskinesias: a 2-deoxy-D-[1-14C]glucose study in the rat

Effects of iminodipropionitrile on cerebral amino acid levels

Iminodipropionitrile (IDPN), a compound that causes dyskinetic symptoms in animals and has possible use as a model for human dyskinesia, was tested in mice and rats for its effect on cerebral amino acids. In mice, 2 h after IDPN administration, the level of total brain alanine was reduced; after 5 h the levels of aspartic acid and glutamic acid were also reduced, and the level of glutamine was increased. In rats, after chronic administration of IDPN, the level of glutamic acid in the total brain tissue was reduced. After acute administration of IDPN using microdialysis, extracellular GABA and extracellular glutamine levels in the striatum were elevated. This study shows that IDPN causes alterations in total and extracellular levels of neurotransmitter amino acids in the brain, which could have a role in IDPN-induced dyskinesia.

Transneuronal pathways to the vestibulocerebellum

The alpha-herpes virus (pseudorabies, PRV) was used to observe central nervous system (CNS) pathways associated with the vestibulocerebellar system. Retrograde transneuronal migration of alpha-herpes virions from specific lobules of the gerbil and rat vestibulo-cerebellar cortex was detected immunohistochemically. Using a time series analysis, progression of infection along polyneuronal cerebellar afferent pathways was examined. Pressure injections of > 20 nanoliters of a 10(8) plaque forming units (pfu) per ml solution of virus were sufficient to initiate an infectious locus which resulted in labeled neurons in the inferior olivary subnuclei, vestibular nuclei, and their afferent cell groups in a progressive temporal fashion and in growing complexity with increasing incubation time. We show that climbing fibers and some other cerebellar afferent fibers transported the virus retrogradely from the cerebellum within 24 hours. One to three days after cerebellar infection discrete cell groups were labeled and appropriate laterality within crossed projections was preserved. Subsequent nuclei labeled with PRV after infection of the flocculus/paraflocculus, or nodulus/uvula, included the following: vestibular (e.g., z) and inferior olivary nuclei (e.g., dorsal cap), accessory oculomotor (e.g., Darkschewitsch n.) and accessory optic related nuclei, (e.g., the nucleus of the optic tract, and the medial terminal nucleus); noradrenergic, raphe, and reticular cell groups (e.g., locus coeruleus, dorsal raphe, raphe pontis, and the lateral reticular tract); other vestibulocerebellum sites, the periaqueductal gray, substantia nigra, hippocampus, thalamus and hypothalamus, amygdala, septal nuclei, and the frontal, cingulate, entorhinal, perirhinal, and insular cortices. However, there were differences in the resulting labeling between infection in either region. Double-labeling experiments revealed that vestibular efferent neurons are located adjacent to, but are not included among, flocculus-projecting supragenual neurons. PRV transport from the vestibular labyrinth and cervical muscles also resulted in CNS infections. Virus propagation in situ provides specific connectivity information based on the functional transport across synapses. The findings support and extend anatomical data regarding vestibulo-olivo-cerebellar pathways.

Dipyridamole attenuates the development of iminodipropionitrile-induced dyskinetic abnormalities in rats

The present investigation was undertaken to study the effect of dipyridamole on experimental dyskinesia in rats. The movement disorders were produced by intraperitoneal administration of iminodipropionitrile (IDPN) in the dose of 100 mg/kg per day for 12 days. Dipyridamole was administered orally, daily 30 min before IDPN in the doses of 0.5 g/kg, 1 g/kg, and 1.5 g/kg bodyweight in three different groups of rats. Twenty-four hours after the last dose of IDPN, animals were observed for neurobehavioral changes including vertical and horizontal head weaving, circling, backwalking, grip strength, and righting reflex. Immediately after behavioral studies brain specimens were collected for analysis of vitamin E, conjugated dienes, and lipid hydroperoxides as indices of oxygen-derived free radical (OFR) production. Our results showed that concurrent use of dipyridamole significantly protected rats against IDPN-induced neurobehavioral changes in a dose-dependent manner. Treatment of rats with dipyridamole inhibited IDPN-induced decrease of vitamin E and increase in conjugated dienes and lipid hydroperoxides in brain. These findings suggest the involvement of OFR in dipyridamole induced protection against the development of IDPN dyskinesia. Further studies are warranted to determine the role of dipyridamole as a prophylactic agent against the drug induced dyskinetic abnormalities.

beta,beta'-Iminodipropionitrile-induced persistent dyskinetic syndrome in mice is transiently modified by MPTP

Chronic administration of iminodipropionitrile (IDPN) is known to produce a persistent dyskinetic syndrome. Recent neurochemical reports seem to point out the dopaminergic system as having an important role in mediating IDPN syndrome. In order to identify a possible role for the nigrostriatal dopaminergic pathway in determining at least some aspects of the IDPN-induced dyskinetic syndrome, we used the neurotoxin, 1-methyl, 4-phenyl,1,2,3,6-tetrahydropyridine (MPTP), as a tool for investigating which aspects of the IDPN-related syndrome could be due to enhanced dopaminergic activity in the neostriatum. In mice made permanently dyskinetic with IDPN, MPTP administration produced dramatic and biphasic effects on all behavioral patterns characteristic of the dyskinetic syndrome. Six weeks after the syndrome occurred, IDPN failed to produce any change in striatal DA levels with respect to controls. By contrast, IDPN seems to reduce striatal levels of extraneuronal metabolites of DA. These data suggest that the activity of the nigrostriatal dopaminergic pathway does not play a leading role in the maintenance of IDPN-related syndrome. The transient modification of all behavioral parameters immediately after MPTP administration could be explained by acute effects of MPTP on other dopaminergic areas which are not permanently lesioned by this neurotoxin, or by the acute effects of MPTP on the release of other neurotransmitters.

The intrastriatal 6-hydroxydopamine model of hemiparkinsonism: quantitative receptor autoradiographic evidence of correlation between circling behavior and presynaptic as well as postsynaptic nigrostriatal markers in the rat

Unilateral injections of 6-hydroxydopamine into the striatum resulted in almost immediate ipsilateral amphetamine (AMPH)- and delayed contralateral apomorphine (APO)-induced circling behavior in rats. APO-induced rotation correlated positively with that caused by AMPH. In these animals, there was an almost complete disappearance of dopamine uptake sites as well as increases in DA D2 receptors in specific subdivisions of the ipsilateral caudate-putamen (CPu). Both the rate of AMPH- and APO-induced rotation correlated with the percentage of DA terminal loss in the total aspect and in various quadrants of the striatum. In contrast, AMPH- and APO-induced rotation correlated with the percentage increase in striatal D2 receptors only in the dorsolateral (DL) aspect of the CPu. These results indicate that both AMPH- and APO-induced rotation can be used to determine the extent of DA terminal loss in the rat basal ganglia. The positive correlation of circling behavior to only changes in DA D2 receptors observed in the DL striatal subdivision provides further evidence for the heterogeneity of the basal ganglia. This model of hemiparkinsonism in the rat which uses a distant intrastriatal approach to the destruction of nigral DA cell bodies may be a more appropriate model to study the regenerative properties of the nigrostriatal DA system. This approach could also be used to more specifically localize peptidergic receptors on midbrain dopamine cell bodies.

Asymmetric elevation of striatal dopamine D2 receptors in the chakragati mouse: neurobehavioral dysfunction in a transgenic insertional mutant

We have previously reported the discovery of a transgenic insertional mutant, recently named the chakragati (ckr) mouse, which displays lateralized circling, locomotor hyperactivity, hyperreactivity, as well as body weight deficits. Since lateralized dopamine function is associated with circling behavior we sought to determine whether dopamine (DA) D1 and D2 receptors were asymmetrically distributed in the striata of adolescent and adult ckr mice using receptor autoradiography. Stereotypic and rotational responses to quinpirole served as behavioral indices of D2 receptor function. The ckr mice showed hemispherically asymmetric elevations in DA D2 receptors in the lateral subregions of the striatum whereas medial regions of the striatum were symmetrically and bilaterally elevated (overall elevation = 30%). As a group, ckr mice had higher D2 receptor levels on the side which was contralateral to the preferred direction of spontaneous nocturnal rotation. Striatal D1 receptors and mesolimbic D2 and D1 receptors of ckr mice were neither elevated nor differentially asymmetric. Young adult ckr mice showed dose-dependent increases in net rotations in response to quinpirole whereas normal mice showed no change from baseline levels. Both groups showed similar stereotypic responses. Older adult ckr mice, however, showed dose-dependent reductions in rotation after quinpirole whereas normal mice turned at baseline levels. Older ckr mice also displayed significantly greater stereotyped sniffing behavior. This unique mutant provides a novel genetic model of basal ganglia dysfunction, and may be useful in studying aspects of neuropsychiatric disorders associated with dopaminergic abnormalities.

Auditory deficits and motor dysfunction following iminodipropionitrile administration in the rat

The behavioral effects of 3,3'-iminodipropionitrile (IDPN) were studied using reflex modification of the acoustic startle response and figure-eight maze activity. A number of experiments were conducted with separate groups of adult male Long-Evans hooded rats exposed to saline or 50-500 mg/kg IDPN for 3 consecutive days. Auditory thresholds (reflex modification), motor activity, and grip strength were measured 1 day, and 1, 3, and 9 weeks postdosing. Reflex inhibition was monitored daily, prior to, during, and for 7 days following exposure. Auditory thresholds for 5- and 40-kHz tones were elevated approximately 25 dB and 50 dB, respectively. The onset of this auditory dysfunction in the 200-mg/kg/day group, as demonstrated by a loss of reflex inhibition, was 2 days for the 40-kHz tone and 4 days for the 5-kHz tone. Motor activity was increased up to 400% in the 200-mg/kg group, whereas there was no alteration in hindlimb grip strength. These data demonstrate dosage- and time-dependent alterations in auditory and motor function following IDPN exposure.

Quantitative autoradiographic changes in 5-[3H]HT-labeled 5-HT1 serotonin receptors in discrete regions of brain in the rat model of persistent dyskinesias induced by iminodipropionitrile (IDPN)

Chronic injections of iminodipropionitrile (IDPN) to rat cause a persistent motor hyperactivity, lateral and vertical sustained twisting movement of the neck, random circling and increased startle response. These abnormalities are similar to those observed after the acute administration of serotonin (5-HT) agonists in rodents. Significant changes in 5-HT concentration and in 5-HT2 receptor density in several motor-related brain regions have been observed in IDPN-treated rats. The present quantitative autoradiographic study was undertaken to assess the possibility that IDPN may also affect 5-HT1 receptors in rat brain. IDPN caused significant increases of 5-[3H]HT binding in the oriens and pyramidal layers of the CA3 field of hippocampus. In contrast, there were significant decreases of 5-[3H]HT binding in the frontal and cingulate cortices, the olfactory tubercle, the ventromedial aspect of the caudate-putamen, the nucleus accumbens, the superior colliculus, and the lateral septal nuclei. These results provide further evidence for the involvement of the 5-HT system in the development of the IDPN-induced dyskinetic syndrome.

Regional changes in brain 5-HT1A serotonin receptors in the rat model of persistent spasmodic dyskinesias induced by iminodipropionitrile

Chronic injection of iminodipropionitrile (IDPN) to rats causes persistent motor abnormalities such as hyperactivity, lateral and vertical dyskinesia of the neck, and random circling. These behavioral changes are very similar to those observed after the acute administration of serotonin (5-HT) agonists in rodents. Moreover, some aspects of this syndrome are reproduced by stimulation of 5-HT1A receptors. The present quantitative autoradiographic study revealed a number of changes in 8-hydroxy-2-[di-n-propylamino-3H]tetralin (8-OH[3H]DPAT)-labeled 5-HT1A receptors in the brains of IDPN-treated rats. There were significant increases of 8-OH[3H]DPAT binding in the frontal cortex and in the caudate-putamen. In contrast, there were significant decreases in the interpeduncular nucleus, the pyramidal layer of the CA3 field of hippocampus, the superior colliculus and the pars reticulata of the substantia nigra. These results provide further evidence for the involvement of the 5-HT system in the development of the IDPN-induced dyskinetic syndrome.

Autoradiographic evidence of [3H]neurotensin binding changes in discrete regions of brain in the rat model of persistent spasmodic dyskinesia induced by iminodipropionitrile

Chronic injection of iminodipropionitrile (IDPN) to rats causes a persistent set of abnormalities which includes hyperlocomotion, hyperexcitability, and dyskinetic movements of the neck. These behavioral changes are very similar to those observed after the acute administration of the dopamine (DA) agonist, amphetamine, in rodents. Because of the anatomical and functional evidence that neurotensin (NT) can modulate DA neurotransmission, the present receptor autoradiographic study investigated the binding of [3H]NT in the brains of IDPN-treated rats. There were significant decreases in binding in the frontal and cingulate cortices, the rhinal sulcus, the dorsolateral aspect of the caudate-putamen, and in the ventral tegmental area. These results provide the first evidence for the possible participation of the NT system in the manifestations of the IDPN-induced syndrome.