Functional damage of dopamine nerve terminals following intrastriatal kainic acid injection

Longitudinal characterization of cognitive and motor deficits in an excitotoxic lesion model of striatal dysfunction in non-human primates

As research progresses in the understanding of the molecular and cellular mechanisms underlying neurodegenerative diseases like Huntington's disease (HD) and expands towards preclinical work for the development of new therapies, highly relevant animal models are increasingly needed to test new hypotheses and to validate new therapeutic approaches. In this light, we characterized an excitotoxic lesion model of striatal dysfunction in non-human primates (NHPs) using cognitive and motor behaviour assessment as well as functional imaging and post-mortem anatomical analyses. NHPs received intra-striatal stereotaxic injections of quinolinic acid bilaterally in the caudate nucleus and unilaterally in the left sensorimotor putamen. Post-operative MRI scans showed atrophy of the caudate nucleus and a large ventricular enlargement in all 6 NHPs that correlated with post-mortem measurements. Behavioral analysis showed deficits in 2 analogues of the Wisconsin card sorting test (perseverative behavior) and in an executive task, while no deficits were observed in a visual recognition or an episodic memory task at 6 months following surgery. Spontaneous locomotor activity was decreased after lesion and the incidence of apomorphine-induced dyskinesias was significantly increased at 3 and 6 months following lesion. Positron emission tomography scans obtained at end-point showed a major deficit in glucose metabolism and D2 receptor density limited to the lesioned striatum of all NHPs compared to controls. Post-mortem analyses revealed a significant loss of medium-sized spiny neurons in the striatum, a loss of neurons and fibers in the globus pallidus, a unilateral decrease in dopaminergic neurons of the substantia nigra and a loss of neurons in the motor and dorsolateral prefrontal cortex. Overall, we show that this robust NHP model presents specific behavioral (learning, execution and retention of cognitive tests) and metabolic functional deficits that, to the best of our knowledge, are currently not mimicked in any available large animal model of striatal dysfunction. Moreover, we used non-invasive, translational techniques like behavior and imaging to quantify such deficits and found that they correlate to a significant cell loss in the striatum and its main input and output structures. This model can thus significantly contribute to the pre-clinical longitudinal evaluation of the ability of new therapeutic cell, gene or pharmacotherapy approaches in restoring the functionality of the striatal circuitry.

The effect of acute kainic acid treatment on dopamine D2 receptors in rat brain

Acute exposure to kainic acid (KA) induces neurochemical changes in dopaminergic systems in the brain and the aim of the present study was to investigate the acute toxicity of KA upon dopamine D2 receptors. Adult rats were injected intraperitoneally with either saline or 16 mg/kg KA. Brains were removed after 4 h. Membrane homogenates were prepared from seven brain regions and in addition, frozen coronal sections were sectioned for comparative quantitative autoradiographic analysis. Dopamine D2 receptors were characterised by saturation studies using [125I]iodosulpiride, [3H]raclopride and [3H]spiperone. KA produced a 2-fold decrease in receptor affinity for [125I]iodosulpiride and a 2-fold increase in receptor density in all regions studied except striatum. Quantitative autoradiography with [125I]iodosulpiride showed similar increases in D2 labelling following KA except in caudate putamen, nucleus accumbens and olfactory tubercle. In contrast, there was no change in [3H]spiperone binding in whole brain minus striatum nor in striatum alone after KA treatment. KA produced a significant increase in Bmax for [3H]raclopride in whole brain minus striatum and in striatum alone with minimal changes in affinity. These findings demonstrate acute changes in rat brain dopamine D2 receptors labelled with [125I]iodosulpiride and [3H]raclopride but not [3H]spiperone after KA treatment predominantly in extra striatal regions.

Generators of the brainstem auditory evoked potential in cat. II. Correlating lesion sites with waveform changes

Brainstem regions involved in generating the brainstem auditory evoked potential (BAEP) were identified by examining the effects of lesions on the click-evoked BAEP in cats. An excitotoxin, kainic acid, was injected into various parts of the cochlear nucleus (CN) or into the superior olivary complex (SOC). The locations of the resulting lesions were correlated with the changes produced in the various extrema of the BAEP waveforms. The results indicate that: (1) the earliest BAEP extrema (P1, N1 (recorded between vertex and the earbar ipsilateral to the stimulus) and P1a, P1b, (vertex to contralateral earbar)) are generated by cells with somata peripheral to the CN; (2) P2 is primarily generated by posterior anteroventral CN (AVCNp) and anterior posteroventral CN (PVCNa) cells; (3) SOC, anterior anteroventral CN (AVCNa), AVCNp, and PVCNa cells are involved in generating P3; (4) AVCNa cells are the main CN cells involved in P4, N4, and P5 generation; (5) both ipsilateral and contralateral SOC cells have a role in generating monaurally evoked P4 and P5; and (6) P5 is generated by cells with characteristic frequencies below 10 kHz. From (2) and (4), it is clear that P2 and P4-P5 are generated by cells in distinct, parallel pathways.

Generators of the brainstem auditory evoked potential in cat. I. An experimental approach to their identification

This paper is the first in a series aimed at identifying the cellular generators of the brainstem auditory evoked potential (BAEP) in cats. The approach involves (1) developing experimental procedures for making small selective lesions and determining the corresponding changes in BAEP waveforms, (2) identifying brainstem regions involved in BAEP generation by examining the effects of lesions on the BAEP and (3) identifying specific cell populations involved by combining the lesion results with electrophysiological and anatomical information from other kinds of studies. We created lesions in the lower brainstem by injecting kainic acid which is generally toxic for neuronal cell bodies but not for axons and terminals. This first paper describes the justifications for using kainic acid, explains the associated problems, and develops a methodology that addresses the main difficulties. The issues and aspects of the specific methods are generally applicable to physiological and anatomical studies using any neurotoxin, as well as to the present BAEP study. The methods chosen involved (1) measuring the BAEP at regular intervals until it reached a post-injection steady state and perfusing the animals with fixative shortly after the last BAEP recordings were made, (2) using objective criteria to distinguish injection-related BAEP changes from unrelated ones, (3) making control injections to identify effects not due to kainic acid toxicity, (4) verifying the anatomical and functional integrity of axons in lesioned regions, and (5) examining injected brainstems microscopically for cell loss and cellular abnormalities indicating dysfunction. This combination of methods enabled us to identify BAEP changes which are clearly correlated with lesion locations.

Evaluation of the mechanisms underlying the kainate-induced impairment of [3H]dopamine release in the rat striatum

Kainic acid caused a marked decrease of the electrically evoked release of [3H]dopamine from rat striatal slices 4 days after its injection (10 nmol/microliters) into the corpus striatum. This damage was prevented by the non-N-methyl-D-aspartate (non-NMDA) receptor antagonist 6,7-dinitroquinoxaline-2,3-dione (DNQX) when co-injected with kainic acid into the striatum. Prior systemic administration of the NMDA selective antagonists (cis-4-phosphonomethyl-2-piperidine carboxylic acid (CGS 19755), dizocilpine (MK-801) and ketamine did not alter the kainate effect. Previous destruction of the cortico-striatal pathway abolished the kainate-induced decrease of [3H]dopamine release. When injected into the striatum, domoic acid or alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) mimicked kainic acid and damaged the dopaminergic nigro-striatal afferents. The [3H]dopamine release evoked by electrical stimulation of slices of frontal cortex was unaffected following local injections of kainic acid. Taken together, the results indicate that AMPA/kainate receptors play a key role in the impairment of [3H]dopamine release caused by kainate in the striatum. However, the kainic acid effect is probably indirect since it appears to require the availability of endogenous glutamate originating from cortico-striatal afferents.

GM1 ganglioside treatment promotes recovery of electrically-stimulated [3H]dopamine release in striatal slices from rats lesioned with kainic acid

The electrically-evoked release of [3H]dopamine ([3H]DA) from rat striatal slices was studied after a monolateral intrastriatal injection of kainic acid (KA). The release in the KA-lesioned striatum measured 4 days after the lesion was largely reduced (by 80%) with respect to the contralateral striatum. Administration of GM1 ganglioside (GM1) beginning on the day of the lesion resulted in restoration of the catecholamine release. Significant recovery was observed when GM1 was administered i.p. daily at the dose of 3 mg/kg for 6 days. The ganglioside given for 6 days at 30 mg/kg restored to near normal the electrically-evoked [3H]DA release. Similar recovery from the KA-induced injury occurred spontaneously but required 50 days.

Terminal excitability of the corticostriatal pathway. II. Regulation by glutamate receptor stimulation

The influence of impulse activity and glutamate receptor stimulation on the electrical excitability of the corticostriatal terminal field was explored. Antidromic responses were recorded from prefrontal cortical neurons the electrical stimulation of their terminal field in the contralateral striatum. Terminal excitability was assessed by determining the percentage of subthreshold current stimulus presentations eliciting an antidromic response. Terminal excitability was found to be positively correlated with variations in spontaneous firing rate: increases and decreases in firing rate were accompanied by corresponding changes in the percentage of antidromic responses elicited by a subthreshold stimulus. Drugs were applied to the striatal stimulation site in a volume of 312 nl delivered over 5 min. Striatal administration of either the competitive NMDA antagonist D-alpha-aminoadipate (DAA) or D-2-amino-7-phosphonoheptanoate (AP-7) or the competitive non-NMDA antagonist 6-cyano-7-nitroquinoxaline-2,3 dione (CNQX) blocked the correlation between excitability and firing rate. Further examination revealed that the terminal field was rendered more excitable for a period of 20-80 ms following the arrival of an action potential. This post-impulse facilitation of terminal excitability was attenuated after local application of AP-7 (10 microM) or CNQX (20 microM). At half these doses, AP-7 or CNQX produced a non-significant effect, however when administered simultaneously a significant attenuation was observed. The participation of interneurons in these excitability effects was ruled out since they were still seen following kainic acid lesions. We propose that this impulse-dependent enhancement in terminal excitability results from the release of glutamate induced by the action potential in the terminal field and the subsequent stimulation of glutamate autoreceptors on the terminals.

Terminal excitability of the corticostriatal pathway. I. Regulation by dopamine receptor stimulation

Glutamatergic cortical and dopaminergic nigral afferents converge onto neurons of the neostriatum forming synapses in close proximity. Studies, mainly using pharmacological methods, suggest presynaptic interactions between these afferents. The influence of dopaminergic transmission on the cortical terminal fields in the striatum was assessed electrophysiologically using the terminal excitability method. Antidromic action potentials recorded from neurons in the prefrontal cortex were elicited by bipolar electrical stimulation (250 microns wire, 0.5 mm tip separation) of the cortical terminal field in the contralateral dorsomedial neostriatum. Threshold excitability was defined as the minimum current sufficient to elicit 95-100% antidromic response on non-collision trials. Under control conditions, the mean threshold current was 1.7 +/- 0.2 mA. Drugs were applied in a volume of 312 nl delivered over 5 min to the striatal stimulation site. Following local striatal administration of amphetamine (10 microM) or electrical stimulation of the nigrostriatal pathway (1-2 pulses, 1.5 mA/0.5 ms/1 Hz) an increase in striatal stimulating current was required in order to reinstate threshold levels of antidromic response. This decrease in the excitability of corticostriatal afferents could be reversed by local infusion of haloperidol (1 microM) or L-sulpiride (10 nM) and did not occur following depletion of dopamine stores with alpha-methylparatyrosine and reserpine. The possible participation of postsynaptic dopamine receptor stimulation was ruled out as these effects were still seen in animals with kainic acid induced lesions of the striatum. In addition, terminal excitability was not modified by the muscarinic agonist carbachol (10 microM). Striatal administration of apomorphine (10 microM) decreased terminal excitability similar to amphetamine. The specific D-2 agonist, quinpirole (10-20 microM) did not affect excitability. These results indicate that manipulations which have been shown to increase the release of endogenous dopamine decrease the excitability of prefrontal corticostriatal afferents by stimulation of presynaptic dopamine receptors which are insensitive to low doses of quinpirole but sensitive to L-sulpiride and apomorphine. The mechanisms underlying dopamine-induced changes in terminal excitability are likely to be similar to those which have been shown to alter conductance at postsynaptic sites.

Selectivity of kainic acid as a neurotoxin within the dorsal lateral geniculate nucleus of the cat: a model for transneuronal retrograde degeneration

In situ injections of the cytotoxin kainic acid were used to make localized lesions of the dorsal lateral geniculate nucleus in the adult cat to produce a model for studying the effects of postsynaptic target loss. Kainic acid has been used extensively to produce lesions of neuronal cell bodies within the central nervous system. However, the selectivity of kainic acid has been questioned, as it may also affect afferent terminals or axons of passage. Retinal projections to degenerated geniculate nuclei were visualized 1 week after kainate injection using anterograde labelling with horseradish peroxidase and electron microscopy. The results demonstrate the presence of afferent terminals within regions of neuronal loss, and hence the selectivity of kainic acid for intrinsic geniculate neurons.