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

Neurovestibular toxicities of acrylonitrile and iminodipropionitrile in rats: a comparative evaluation of putative mechanisms and target sites

This investigation was aimed to study the effects of individual and concomitant exposures of the two nitrile compounds, the industrially important acrylonitrile (ACN; 5, 15, 45 mg/kg/day) and the positive control iminodipropionitrile (IDPN; 100 mg/kg/day) in rats. The six treatment groups were 1 (control), 2 (ACN 5), 3 (ACN 15), 4 (ACN 45), 5 (IDPN), and 6 (IDPN + ACN 15). Both the drugs were started on the same day and continued for 9 days (IDPN was given daily 30 min before ACN but stopped a day earlier). The animals were daily observed for neurobehavioral abnormalities including dyskinetic head movements, circling, tail hanging, air righting reflex, and contact inhibition of righting reflex. There was no dyskinetic behavioral abnormality in the animals treated with any of the three doses of ACN whereas all the rats in IDPN alone treated group developed clear symptoms of excitation, circling, and chorea syndrome (ECC syndrome) on day 9. Concomitant treatment of rats with ACN significantly attenuated the severity of IDPN-induced behavioral deficits. Administration of ACN significantly depleted glutathione (GSH) in striatum, hippocampus and cerebral cortex; IDPN significantly reduced the GSH only in striatum. The anterior striatum showed intense tyrosine hydroxylase (TH) expression in IDPN alone treated rat as compared to control and ACN alone treated rat. Cotreatment with ACN reduced the intensity of TH immunostaining in IDPN-treated rats. Administration of IDPN alone caused massive loss of vestibular sensory hair cells in the crista ampullaris whereas the sensory epithelium appeared intact in ACN alone treated groups. The animals receiving the combination of ACN and IDPN showed comparatively less degeneration of sensory hair cells than IDPN alone group. These findings suggest that ACN and IDPN produce different behavioral effects that are exerted through entirely different mechanisms; the nervous and vestibular systems appear to be the major target sites of these toxins, respectively.

Neurotensin: role in psychiatric and neurological diseases

Neurotensin (NT), an endogenous brain-gut peptide, has a close anatomical and functional relationship with the mesocorticolimbic and neostriatal dopamine system. Dysregulation of NT neurotransmission in this system has been hypothesized to be involved in the pathogenesis of schizophrenia. Additionally, NT containing circuits have been demonstrated to mediate some of the mechanisms of action of antipsychotic drugs, as well as the rewarding and/or sensitizing properties of drugs of abuse. NT receptors have been suggested to be novel targets for the treatment of psychoses or drug addiction.

Expression of neurotransmitter genes in motor regions of the dyskinetic rat after iminodipropionitrile

Rats treated with iminodipropionitrile develop a neurobehaviour syndrome with dyskinesia. Searching for the molecular correlates, we have examined the expression of selected genes involved in neurotransmission in motor regions using hybridization histochemistry. Frontal cortical and thalamic vasoactive intestinal peptide (VIP) expression, and striatal dynorphin, enkephalin (ENK) and substance P expression were increased. No change in cortical cholecystokinin (CCK), ENK, glutamic acid decarboxylase (GAD) and somatostatin (SRIF) expression, in striatal GAD, SRIF, nitric oxide synthase (NOS) and guanylate cyclase expression, and in thalamic CCK, GAD and thyrotropin-releasing hormone expression was found. NOS expression in the subthalamic nucleus as well as tyrosine hydroxylase, GAD and CCK expression in the substantia nigra were unchanged. These results confirm the involvement of striatal projection neurons in dyskinesia and suggest a novel role for VIP.

Effect of bimoclomol (N-[2-hydroxy-3-(1-piperidinyl) propoxy]-3 pyridine-carboximidoyl-chloride) on iminodipropionitrile-induced central effects

Dyskinesia is frequently seen in neurological disorders affecting the basal ganglia. Iminodipropionitrile (IDPN) produces a somewhat similar motor syndrome in rodents, one that is a possible model for dyskinesia. Because in previous studies the compound (N-[2-hydroxy-3-(1-piperidinyl) propoxy]-3 pyridine-carboximidoyl-chloride) (Bimoclomol, BRLP-42) was shown to provide protection against IDPN-induced retinopathy; we investigated the effect of BRLP-42 on IDPN-induced motor changes and on IDPN-induced cerebral amino acid level changes in rats and mice. IDPN had a biphasic effect on motor activity in C57BL/6 mice: it was a depressant for 24 days and a stimulant after 30 days. Bimoclomol inhibited the motor depressant effect and enhanced the stimulatory effect of IDPN in this mouse strain. In BALB/cBy mice and Sprague Dawley rats IDPN produced persistent vertical head movements and changes in the level of glutamic acid in brain. Bimoclomol reduced the effect of IDPN on head movements and blocked the effect on cerebral glutamate; by itself it had no effect on motor activity in either species. Bimoclomol inhibited ischemia-induced [3H]norepinephrine release from rat hippocampal slices. Our findings indicate that Bimoclomol could have a beneficial effect on some dyskinesias, and on drug-induced vertical head movements.

Bilateral modulation of [3H]neurotensin binding by unilateral intrastriatal 6-hydroxydopamine injections: evidence from a receptor autoradiographic study

The present study was carried out in order to re-evaluate the issue of the localization of neurotensin receptors in the caudate-putamen and in the nucleus accumbens of rat. Intrastriatal injections of 6-hydroxydopamine which cause almost complete destruction of the mesostriatal dopaminergic pathway also caused a marked loss of neurotensin receptors in the caudate-putamen (CPu), the nucleus accumbens (NAc) and in the olfactory tubercle (OT). These decreases corresponded to a mean loss of 98, 93 and 41% in the CPu, the NAc, and the OT, respectively. There were corresponding decreases in the substantia nigra pars compacta (SNpc) (-94%) and pars reticulata (SNpr) (-97%), and in the ventral tegmental area (-78%). Moreover, there were also decreases in neurotensin receptors on the contralateral side of the intrastriatal injections which occurred in the CPu but not in the NAc nor in the OT. These results indicate that almost all NT receptors measured within the CPu and the NAc are located on the terminals of dopaminergic neurons within those structures. The bilaterality of the changes which occur in the CPu provide further support for the notion of the interdependence of the two nigrostriatal dopaminergic projections and the peptidergic systems with which they interact.

Neurotensin receptors in human meningiomas

We have investigated the presence of neurotensin receptors in human meningiomas by in vitro binding autoradiography. Ten of the 12 meningiomas tested displayed specific [3H]neurotensin binding. All meningothelial (n = 3) and transitional (n = 5) meningiomas were positive, whereas only 2 of the 4 fibroblastic meningiomas showed measurable concentrations of neurotensin binding sites. Within the tumors, [3H]neurotensin binding was preferentially observed in syncytial areas. Saturation experiments showed that the maximal binding capacity (Bmax) greatly varied among tumors, ranging from low values to more than 290 fmol/mg of protein. All positive tumors had neurotensin binding sites with a dissociation constant (kd) within the nanomolar range and a pharmacological specificity for [3H]neurotensin similar to neurotensin receptors.