Neuronal sparing and behavioral effects of the antiapoptotic drug, (-)deprenyl, following kainic acid administration

(-)Deprenyl is an irreversible inhibitor of monoamine oxidase B (MAO-B) frequently used as an adjunct therapy in the treatment of Parkinson's Disease. Recent evidence, however, has found that deprenyl's metabolites are associated with an antiapoptotic action within certain neuronal populations. Interestingly, deprenyl's antiapoptotic actions appear not to depend upon the inhibition of MAO-B. Due to a paucity of information surrounding (-)deprenyl's ability to spare neurons in vivo, a series of studies was conducted to further investigate this phenomenon within an apoptotic neuronal death model: kainic acid induced excitotoxicity. Results indicated that (-)deprenyl increased hippocampal neuronal survival compared to saline-matched controls following kainic acid insult. Furthermore, it was discovered that (-)deprenyl treatment could be stopped 14 days following CNS insult by kainate, with evidence of neuronal sparing still present by day 28. In open-field locomotor activity testing of kainate-treated animals, those given subsequent (-)deprenyl treatment showed habituation curves similar to control subjects, while saline-treated animals did not. Given deprenyl's antiapoptotic actions, it is proposed that (-)deprenyl may be beneficial in the treatment of a variety of neurodegenerative diseases where evidence of apoptosis exists, such as Parkinson's and Alzheimer's Disease, by slowing the disease process itself.

Neuronal stress and injury in C57/BL mice after systemic kainic acid administration

Kainate-induced seizures are widely studied as a model of human temporal lobe epilepsy due to behavioral and pathological similarities. While kainate-induced neuronal injury is well characterized in rats, relatively little data is available on the use of kainate and its consequences in mice. The growing availability of genetically altered mice has focused attention on the need for well characterized mouse seizure models in which the effects of specific genetic manipulations can be examined. We therefore examined the kainate dose-response relationship and the time-course of specific histopathological changes in C57/BL mice, a commonly used founder strain for transgenic technology. Seizures were induced in male C57/BL mice (kainate 10-40 mg/kg i.p.) and animals were sacrificed at various time-points after injection. Seizures were graded using a behavioral scale developed in our laboratory. Neuronal injury was assayed by examining DNA fragmentation using in situ nick translation histochemistry. In parallel experiments, we examined the expression an inducible member of the heat shock protein family, HSP-72, another putative marker of neuronal injury, using a monoclonal antibody. Seizure severity paralleled kainate dosage. At higher doses DNA fragmentation is seen mainly in hippocampus in area CA3, and variably in CA1, thalamus and amygdala within 24 h, is maximal within 72 h, and is largely gone by 7 days after administration of kainate. HSP-72 expression is also highly selective, occurring in limbic structures, and it evolves over a characteristic time-course. HSP-72 is expressed mainly in structures that also manifest DNA fragmentation. Using double-labeling techniques, however, we find essentially no overlap between neurons expressing HSP-72 and DNA fragmentation. These findings indicate that DNA fragmentation and HSP-72 expression are complementary markers of seizure-induced stress and injury, and support the notion that HSP-72 expression is neuroprotective following kainate-induced seizures.

Vagal mechanisms underlying gastric protection induced by chemical activation of raphe pallidus in rats

Peripheral mechanisms involved in kainic acid injected into the raphe pallidus (Rpa)-induced gastric protection were investigated in urethan-anesthetized rats. Gastric mucosal blood flow (GMBF), acid secretion, and gastric injury induced by intragastric ethanol (60%) were measured in response to kainic acid (25 pg) injected into the Rpa. Kainic acid reduced ethanol-induced gastric lesions by 57%. The protective effect was blocked by vagotomy, capsaicin deafferentation, and intravenous injection of the calcitonin gene-related peptide (CGRP) antagonist CGRP-(8-37) and NG-nitro-L-arginine methyl ester (L-NAME). L- but not D-arginine reversed the L-NAME action. Kainic acid injected into the Rpa, unlike outside sites, increased basal GMBF but not acid secretion. Indomethacin unmasked an acid secretory response to kainic acid. These results show that kainic acid injected into the Rpa at a dose that did not stimulate acid secretion, due to the inhibitory effect of prostaglandins, protects against ethanol-induced gastric injury through vagal-dependent activation of CGRP contained in capsaicin-sensitive afferents and nitric oxide-mediated gastric vasodilatory mechanisms.

Seizure activity is increased in endocrine states characterized by decline in endogenous levels of the neurosteroid 3 alpha,5 alpha-THP

To examine the role of progesterone (P) and its 5alpha-reduced metabolite, the neurosteroid 5alpha-pregnan-3alpha-ol-20-one (3alpha, 5alpha-THP), in endogenous variations in ictal activity rats were tested for kainic acid-induced seizures in different hormonal milieu. Corresponding plasma and central P and 3alpha,5alpha-THP levels were measured. Cycling Long-Evans rats in estrus and proestrus had seizures of significantly shorter duration and more central and plasma 3alpha,5alpha-THP and P than animals in metestrus or diestrus. Females with luteal functioning had seizures of significantly shorter duration and increased central and plasma 3alpha,5alpha-THP and P compared to animals that recently had luteal functioning discontinued. Pregnant rats had significantly shorter seizures and greater central and plasma 3alpha,5alpha-THP and central P than animals tested 1-2 days postparturition. In all test paradigms, seizure activity was increased in animals that had decreased 3alpha, 5alpha-THP or P; overall, central 3alpha,5alpha-THP was more inversely related to ictal activity than central P or plasma P and 3alpha,5alpha-THP. To investigate a causal relationship between 3alpha,5alpha-THP and seizures, a 5alpha-reductase inhibitor, finasteride, or vehicle was administered to pregnant rats. Finasteride administration significantly decreased central and plasma 3alpha,5alpha-THP, but had no significant effect on plasma or central P of pregnant rats. Finasteride, but not vehicle administration, to pregnant rats significantly increased seizure duration. These findings support the hypothesis that variations in seizure threshold over endogenous hormonal milieu may be related to endogenous 3alpha,5alpha-THP. Of all of the endocrine conditions, seizure durations were greatest in diestrus animals; this group did not experience the lowest or the greatest decrease in 3alpha, 5alpha-THP concentrations; however, of all of the endocrine conditions, cycling rats experienced the most rapid cycles of 3alpha, 5alpha-THP variation. This suggests that cycles of endogenous variations in 3alpha,5alpha-THP may influence seizure threshold.

Mineralocorticoid receptors regulate bcl-2 and p53 mRNA expression in hippocampus

The present study addressed the hypothesis that the neuronal mineralocorticoid receptor (MR) regulates genes associated with cell death, such as bax and p53, and cell viability, including bcl-2, BDNF, and NT-3. Rats were pretreated with either oil vehicle or the MR antagonist spironolactone (SPIRO) and subsequently injected with saline or kainic acid (KA). MR blockade significantly decreased basal mRNA expression of bcl-2 in CA1 of saline-treated animals and attenuated KA-induced increases in p53 mRNA levels in CA3. SPIRO pretreatment had no significant effect on expression of bax, NT-3, or BDNF mRNAs. The data suggest that the neuronal MR contributes to regulation of select cell survival and cell death-related genes in hippocampal pyramidal neurons.

Estradiol prevents kainic acid-induced neuronal loss in the rat dentate gyrus

The neuroprotective role of 17beta-estradiol in the hippocampal dentate gyrus of adult rats treated with kainic acid has been investigated. The systemic injection of a single low dose (7 mg/kg) of kainic acid to ovariectomized rats produced a marked loss of Nissl-stained and somatostatin-immunoreactive hilar neurons. A single simultaneous systemic dose of estradiol (150 microg per animal) prevented the kainic acid-induced decrease in Nissl-stained and somatostatinergic hilar neurons. These results indicate that estradiol may protect adult hilar neurons in vivo from neurotoxic-induced cell death.

Stimulation of the neostriatum induces jaw-opener muscle activity, but not jaw-closer muscle activity: an electromyographic study in the rat

Microstimulation was carried out at 36 sites in the dorsal striatum in lightly anesthetized rats. Only at two sites, microstimulation of 40 microA induced a considerable EMG activity in the jaw-opener (anterior digastric muscle). No activity was evoked in the jaw-closers (masseter and temporalis muscles). The effective sites were confirmed to be localized in a small central region of the striatum at a level corresponding to the caudal end of the anterior commissure. The effect was ascribed to excitation of a small cluster of striatal neurons, rather than to antidromic activation of cerebral cortical neurons through their axons within the striatum. (1) The effect was abolished after destruction of neurons in the striatal region by injecting kainic acid. (2) The effect was not influenced by ablation of the neocortex. (3) Microinjection of kainic acid into the striatal region also induced the similar muscle activity in the jaw-opener, but not in the jaw-closers.

The effects of kainic acid in rats with spontaneous recurrent seizures

1. Rats with spontaneous recurrent seizures (SRS) were obtained by injection of kainic acid (KA; 10 mg/kg SC) to drug-naive rats that regularly developed wet-dog shakes followed by complex partial seizures and status epilepticus. Three to five weeks later, the rats with manifest SRS were selected. 2. The SRS rats were challenged with KA (10 mg/kg SC). The seizures induced in SRS rats by KA were similar to SRS regarding their clinical stage and duration (mean duration of seizures: 44 sec and 43 sec, respectively). The frequency of seizures was, however, increased compared with the frequency of SRS in control, vehicle-treated SRS rats (mean frequency of seizures: 12.9 and 0.4 per 3 hr, respectively). The KA-induced seizures in SRS rats differ behaviorally from KA-induced seizures in naive rats-namely, neither wet-dog shakes nor the status epilepticus could be induced. 3. Repeated injection of an equal dose of KA, applied to the SRS rats 1 day after the previous KA challenge, did not induce seizures. The loss of seizure susceptibility to KA was only temporary, as shown after a 7-day drug-free period, when the repeated injection of KA regained its seizure-triggering capacity. 4. The results indicate that reactivity to the seizure-inducing agent kainic acid changes in rats with spontaneous recurrent seizures.

Protective effects of cortistatin (CST-14) against kainate-induced neurotoxicity in rat brain

Cortistatin (CST-14) is a recently discovered endogenous peptide which shares similarity to somatostatin and binds to somatostatin receptors. In this study, we show that CST-14 exhibits anticonvulsive and neuroprotective effects in rats. Injection of rats with kainic acid (KA; 10 mg/kg; i.p.) generated a strong seizure activity which was attenuated by the i.c.v. application of 1 and 10 nmol CST-14 when given 10 min before KA. Moreover, 3 days after KA injection, a marked loss of neurons in cortex and hippocampus of rats was observed which was inhibited by pretreatment with CST-14. An immunohistochemical analysis using specific antibodies revealed that KA reduced immunoactive sst2A and sst3 somatostatin receptors in the hippocampus-an effect which was largely prevented by pretreatment with CST-14. Superfusion of hippocampal slices with CST-14 also reduced the stimulated release of 3H-d-aspartate. We conclude that CST-14 exerts neuroprotective effects by binding to somatostatin receptors which in turn leads to a reduced release of excitotoxic neurotransmitters.

Characteristics of acute and chronic kainate excitotoxic damage to the optic nerve

Macroglial cells express ionotropic glutamate receptors. In the adult optic nerve, reverse transcription-PCR showed that the native receptors are formed by subunits belonging to the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and kainate classes. Because activation of AMPA and kainate receptors can be toxic to oligodendrocytes in vitro, I examined the nature of the damage caused by kainate, an agonist of both receptor classes, applied directly onto the optic nerve. Acute infusion or chronic slow delivery of the agonist caused massive nerve damage that was more extensive in the latter. Interestingly, chronic delivery also produced inflammation and demyelination in well circumscribed areas of the nerve, together with other pathological features that closely resemble those observed in multiple sclerosis patients. Acute and chronic kainate lesions were both prevented by the non-N-methyl-D-aspartate receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione. However, GYKI53655, a specific AMPA receptor antagonist, did not significantly reduce the size of the lesion, suggesting that the kainate toxicity was mainly mediated through activation of kainate-preferring glutamate receptors. These observations suggest that alterations in glutamate signaling may be detrimental to oligodendrocytes and may be involved in the pathogenesis of multiple sclerosis and other demyelinating diseases.

Kainic acid induction of heme oxygenase in vivo and in vitro

Heme oxygenase, catalyses oxidation of the heme molecule in concert with NADPH-cytochrome P450 reductase and then specifically cleaves heme into biliverdin, carbon monoxide, and iron. Biliverdin and its product, bilirubin, are known to be strong antioxidants. Kainic acid is a potent neurotoxin, and induces selective neuronal loss in the rat hippocampus. Kainic acid acts on the kainate receptors, and kainic acid neurotoxicity may be in part mediated by oxidative stress. In this study, we examined whether or not heme oxygenase was activated in kainic acid-induced neurotoxicity. After intracerebroventricular injection of kainic acid, the heme oxygenase-1 protein level was strongly enhanced, although the constitutive heme oxygenase (heme oxygenase-2) protein level was not changed. One day after treatment, the protein level of heme oxygenase-1 reached a maximum and then gradually decreased over a period of three to seven days. In the rat hippocampus, cells expressing heme oxygenase-1 in vivo were predominately microglia and only a few astrocytes. In addition, heme oxygenase-1 immunoreactivity was predominantly co-localized with major histocompatibility complex class II-, and partly co-localized with class I-immunoreactive microglia. In cultured glial cells in vitro, heme oxygenase- protein was expressed in the microglia even with the vehicle treatment, and was strongly induced in astrocytes by kainic acid treatment. These results suggest that ameboid microglia, which express both heme oxygenase-1 and major histocompatibility complex antigens, may play a key role in a delayed episode of kainic acid-induced microglial activation and neurodegeneration.

Effect of a subconvulsant dose of kainic acid on thresholds for phenomena elicited by electrical stimulation of sensorimotor cortex in rats

Electrical stimulation of sensorimotor cortex was used to study early and late effects of administration of kainic acid in a dose (6 mg/kg i.p.) eliciting only nonconvulsive seizures in rats. Thresholds for elicitation of four phenomena--movements directly related to stimulation; epileptic afterdischarges (ADs) of the spike-and-wave type; clonic seizures accompanying these ADs; and mixed type of ADs where spike-and-wave activity transgresses into limbic type of epileptic phenomena--were measured. Acute administration of kainic acid resulted in a decrease of the threshold for elicitation of mixed type of ADs. In contrast, 1 week after kainic acid administration, the thresholds for stimulation-bound movements, spike-and-wave ADs and concomitant clonic seizures were increased, but the threshold for mixed type of ADs remained unchanged. The changes in thresholds tended to decrease 2 weeks after kainic acid but statistical significance was reached only for stimulus-bound movements. In addition, repetition of stimulation series after 1 as well as 2 weeks markedly influenced the thresholds.

High-frequency stimulation of the subthalamic nucleus suppresses absence seizures in the rat: comparison with neurotoxic lesions

High-frequency electrical stimulation of deep brain structures has recently been developed for the surgical approach of neurologic disorders. Applied to the thalamus in tremors or to the subthalamic nucleus in Parkinson's disease, high-frequency stimulation has been demonstrated to exert a local inhibiting influence, leading to symptoms alleviation. In the present study, bilateral high-frequency stimulations (130 Hz) of the subthalamic nuclei suppressed ongoing spontaneous absence seizures in rats. This effect was dissociated from motor side-effects and appears specific to the subthalamic nucleus. Bilateral excitotoxic lesions of the subthalamic nuclei only partially suppressed absence-seizures. These results confirm the involvement of the basal ganglia system in the control of generalized seizures and suggest that high-frequency stimulations could be used in the treatment of some forms of seizures.

Recurrent spontaneous motor seizures after repeated low-dose systemic treatment with kainate: assessment of a rat model of temporal lobe epilepsy

Human temporal lobe epilepsy is associated with complex partial seizures that can produce secondarily generalized seizures and motor convulsions. In some patients with temporal lobe epilepsy, the seizures and convulsions occur following a latent period after an initial injury and may progressively increase in frequency for much of the patient's life. Available animal models of temporal lobe epilepsy are produced by acute treatments that often have high mortality rates and/or are associated with a low proportion of animals developing spontaneous chronic motor seizures. In this study, rats were given multiple low-dose intraperitoneal (i.p.) injections of kainate in order to minimize the mortality rate usually associated with single high-dose injections. We tested the hypothesis that these kainate-treated rats consistently develop a chronic epileptic state (i.e. long-term occurrence of spontaneous, generalized seizures and motor convulsions) following a latent period after the initial treatment. Kainate (5 mg/kg per h, i.p.) was administered to rats every hour for several hours so that class III-V seizures were elicited for > or = 3 h, while control rats were treated similarly with saline. This treatment protocol had a relatively low mortality rate (15%). After acute treatment, rats were observed for the occurrence of motor seizures for 6-8 h/week. Nearly all of the kainate-treated rats (97%) had two or more spontaneous motor seizures months after treatment. With this observation protocol, the average latency for the first spontaneous motor seizure was 77+/-38 (+/-S.D.) days after treatment. Although variability was observed between rats, seizure frequency initially increased with time after treatment, and nearly all of the kainate-treated rats (91%) had spontaneous motor seizures until the time of euthanasia (i.e. 5-22 months after treatment). Therefore, multiple low-dose injections of kainate, which cause recurrent motor seizures for > or = 3 h, lead to the development of a chronic epileptic state that is characterized by (i) a latent period before the onset of chronic motor seizures, and (ii) a high but variable seizure frequency that initially increases with time after the first chronic seizure. This modification of the kainate-treatment protocol is efficient and relatively simple, and the properties of the chronic epileptic state appear similar to severe human temporal lobe epilepsy. Furthermore, the observation that seizure frequency initially increased as a function of time after kainate treatment supports the hypothesis that temporal lobe epilepsy can be a progressive syndrome.

Amyloid precursor protein proteoglycan is increased after brain damage

The beta-amyloid peptide (Abeta or A4) is produced by proteolytic cleavage from amyloid precursor protein (APP). The progressive cerebral deposition of this peptide is one of the most important features of Alzheimer's disease. From the study of normal and transfected cells, two APP processing pathways have been proposed as physiological alternatives. One of these can produce Abeta or amyloidogenic peptides, whereas the second does not. However, it is not completely clear how APPs are post-translationally modified, proteolytically processed and metabolized in the brain. We report here that APPs also exist as proteoglycan, chondroitin-sulfate (ChS). We have identified in normal rat brain a complex pool of 8 to 130 kDa ChS-core proteins. The main portion of these proteoglycan (PGs) APPs contains complete amyloidogenic sequence, suggesting a novel proteolytic processing of APP from the amino-terminal to the transmembrane region. This population appears augmented after brain damage. These findings may have significant implications in understanding the initial deposition and kinetics of amyloid aggregation in a pathological situation like Alzheimer's disease.

Increased transcription of glutamate-aspartate transporter (GLAST/GluT-1) mRNA following kainic acid-induced limbic seizure

Expression of mRNA for glutamate-aspartate transporter (GLAST/GluT-1/EAAT1) was studied in the brain of the rat which presented recurrent limbic seizure following systemic administration of kainic acid (KA) by in situ hybridization and Northern blot analysis. The expression of GLAST mRNA was markedly increased after 12 h and peaked after 48 h in animals which demonstrated limbic seizure. The induction of the mRNA were observed in the small non-neuronal cells in the hippocampus, especially around CA3 region and hilus. In contrast, there was no change in GLAST mRNA levels in KA injected seizure-free animals. These findings suggest that GLAST mRNA is induced by seizure and increased extracellular glutamate levels during seizure may be important for induction of GLAST mRNA.

Kainic acid lesions in adult rats as a model of schizophrenia: changes in auditory information processing

Previous studies have suggested that intracerebroventricular kainic acid injections alter brain anatomy and neurochemistry in a manner similar to what is observed in schizophrenic patients. Disturbances in sensory information processing are one of the major symptoms of schizophrenia. Thus, the present experiments were designed to evaluate the hypothesis that hippocampal damage, induced by administration of kainic acid, would alter the processing of auditory stimuli in a paired-click paradigm. Adult male Sprague-Dawley rats were implanted for surface recording of auditory evoked potentials. At the time of electrode implantation, the rats also received bilateral injections of either kainic acid or the vehicle solution. In vehicle-treated rats, the midlatency N40 component of the auditory evoked potential was diminished in amplitude by approximately 60% in response to the second of a pair of clicks delivered 0.5 s apart. By contrast, no reduction of the N40 wave evoked by the second click was observed in kainate-treated rats. Further, administration of haloperidol, a prototypical neuroleptic agent, did not improve this auditory processing dysfunction in kainate-treated animals. Loss of auditory filtering in the paired-click paradigm and a lack of response to haloperidol in this test are typically observed in schizophrenic humans. Thus, the present results demonstrate that kainate-lesioned rats possess a functional schizophrenia-like abnormality, further reinforcing the utility of this model system for studying the basic neurobiology of schizophrenia-induced sensory processing deficits.

The messenger RNA encoding VGF, a neuronal peptide precursor, is rapidly regulated in the rat central nervous system by neuronal activity, seizure and lesion

The VGF gene encodes a neuronal secretory-peptide precursor that is rapidly induced by neurotrophic growth factors and by depolarization in vitro. VGF expression in the animal peaks during critical periods in the developing peripheral and central nervous systems. To gain insight into the possible functions and regulation of VGF in vivo, we have used in situ hybridization to examine the regulation of VGF messenger RNA by experimental manipulations, and have found it to be regulated in the CNS by paradigms that affect electrical activity and by lesion. Inhibition of retinal electrical activity during the critical period of visual development rapidly repressed VGF messenger RNA in the dorsal lateral geniculate nucleus of the thalamus. In the adult, kainate-induced seizures transiently induced VGF messenger RNA in neurons of the dentate gyrus, hippocampus, and cerebral cortex within hours. Cortical lesion strongly induced VGF messenger RNA in ipsilateral cortex within hours, and strongly repressed expression in ipsilateral striatum. Ten days postlesion there was a delayed induction of VGF messenger RNA in a portion of deafferented striatum where compensatory cortical sprouting has been detected. Expression of the neuronal secretory-peptide precursor VGF is therefore modulated in vivo by monocular deprivation, seizure, and cortical lesion, paradigms which lead to neurotrophin induction, synaptic remodeling and axonal sprouting.

Antinociception mediated by the periaqueductal gray is attenuated by orphanin FQ

Orphanin FQ or nociceptin (OFQ/N(1-17)) is a recently discovered peptide which, upon intracerebroventricular administration, reverses opioid-mediated analgesias. OFQ/N(1-17) terminals are located in the periaqueductal gray (PAG), a structure known to be involved in pain modulation, suggesting that the functional anti-opioid effects of OFQ/N(1-17) are mediated by PAG neurons. To test this, subsequent microinjections of morphine or kainic acid and OFQ/N(1-17) were made into the PAG of awake rats. Administration of OFQ/N(1-17) attenuated the tail flick inhibition produced by both morphine and kainic acid microinjection. OFQ/N(1-17) attenuation of antinociception produced by a neuroexcitant indicates that OFQ/N(1-17) reverses opioid antinociception by inhibiting PAG output neurons.

Ventral and dorsal striatal cholinergic neurons have different sensitivities to kainic acid

The present study was conducted to investigate the sensitivity of the cholinergic elements of ventral and dorsal striatal regions of the rat brain to the neurotoxin kainic acid (KA). Cholinergic activity was assessed by determining choline-acetyltransferase activity (CAT) and by measurements of acetylcholine (Ach) release from slices prelabeled with [3H]-choline. Direct stereotaxic injections of high-dose KA (4 micrograms/2 microliters) into specific brain regions, reduced CAT in caudate putamen (CP) by 91 +/- 1%, in nucleus accumbens (Nac) by 71 +/- 6%, but CAT in the olfactory tubercle (OT) was not affected by KA. The effects of KA on CP CAT were dose- and volume-dependent. In the OT, KA failed to affect CAT at low, moderate or high doses. Slices obtained from CP injected with KA (3 days prior) showed a 90% reduction in the electrically evoked release of [3H]-transmitter release; however, KA had no effect on transmitter release from OT. These results indicate that KA spares the cholinergic elements of the OT, and reveal the existence of marked differences in excitotoxic action of KA between ventral and dorsal striatal regions and among regions of the ventral striatum. Kainic acid preferentially damages neuronal cell bodies, dendrites and terminals intrinsic within the structures injected, with little or no effect on afferent axons and terminal boutons. Therefore, we propose that most of the Ach present in the OT may be within afferent axons and axon terminals. In the CP and NAc, KA lesions reflect loss of intrinsic cholinergic neurons. In addition, variable levels of excitatory inputs and of excitatory receptors, of the mechanisms available to reduce elevated intracellular calcium concentrations and of the levels of free-radical scavenging resources, also could account for the differences in KA neurotoxicity between OT and CP.

In vivo electrochemical measurement of the long-lasting release of dopamine and serotonin induced by intrastriatal kainic acid

Intrastriatal injection of the glutamate agonist kainic acid (KA) in rats has been used to produce an animal model to investigate the mechanism of acetylcholine and GABA cell death associated with Huntington's disease. In the present study, the time course of low (10(-5) M) and high (5 x 10(-3) M) concentrations of KA on striatal dopamine and serotonin release was studied in freely moving rats by using in vivo voltammetry. The response to low concentrations of KA varied between animals, either increasing dopamine release during the injection or increasing dopamine and serotonin after the injection for an extended time, suggesting that 10(-5) KA is near the threshold for KA toxicity in the striatum in rats. High concentrations of KA suppressed dopamine release during injection, with both dopamine and serotonin release increasing and remaining elevated for 1-4 and 7-21 days, respectively. KA-induced changes were inhibited by 6-cyano-7-nitroquinoxaline-2,3-dione and bicuculline increased the release of dopamine but not serotonin. These findings suggest that KA-induced changes in dopamine release resulted from a disinhibition of dopamine neurons due to KA-mediated toxicity of striatal GABA neurons. An alternate possibility is that the change in dopamine and serotonin release may have arisen from a functional modification or degeneration of presynaptic terminals.

Repeated independent exposures to domoic acid do not enhance symptomatic toxicity in outbred or seizure-sensitive inbred mice

Domoic acid (DA) is an environmental neurotoxin to humans. This work examines whether repeated exposure to subsymptomatic or symptomatic nonlethal doses of domoic acid leads to enhanced symptomatic toxicity in ICR outbred and DBA inbred strains of laboratory mice. A multiple independent exposure paradigm was designed in which doses were administered intraperitoneally every other day for 7 days to achieve four separate exposures to domoic acid. We first examined the effect of repeated exposure on serum clearance of domoic acid. Serum domoic acid levels did not differ following a single or repeated exposure. We next examined the effect of repeated exposure on symptomatic toxicity. The mean toxicity scores did not show a significant difference between single and repeated exposures of either subsymptomatic (0.5 mg/kg) or symptomatic sublethal (2.0 mg/kg) doses of domoic acid. We then examined the effects of repeated domoic acid exposure on a second strain of mouse. DBA mice were chosen based upon their sensitivity to kainic acid-induced seizures; however, the ICR mice were more sensitive to low-dose domoic acid toxicity, particularly in terms of onset and duration of stereotypic scratching behavior. Our results indicate that both strains of mice have comparable concentration-dependent toxic responses to domoic acid; however, differences exist in the magnitude of the response and in specific symptoms. The mean toxicity scores did not show a significant difference when a single exposure (1.0 and 2.0 mg/kg domoic acid) and repeated exposure of the same dose were compared in the DBA mice. This study provides no evidence that short-term repeated exposure to domoic acid in laboratory mice alters domoic acid clearance from the serum, or leads to a more sensitive or a greater neurotoxic response.

Kainate microinjection into the dorsal raphe nucleus induces 5-HT release in the amygdala and periaqueductal gray

Earlier results obtained in one of our laboratories showed that microinjection into the dorsal raphe nucleus (DRN) of the excitatory amino acid kainic acid, the benzodiazepine (BZD) inverse agonist FG 7142, and the 5-HT1A receptor agonist 8-OHDPAT changed the behavior of rats in the elevated T-maze, an animal model of anxiety. The present study investigates biochemical correlates of these results in awake rats by measuring 5-HT release with in vivo microdialysis in two brain structures innervated by the DRN-the amygdala (Am) and the dorsal periaqueductal gray matter (DPAG)-that have been implicated in anxiety. Microinjection of kainic acid (60 pmol) into the DRN significantly increased 5-HT release in both the Am and the DPAG. In the DPAG, the increase was 14-fold higher with respect to the baseline and occurred only at the first sample, which was collected 30 min after the injection. In the Am, the increase was less pronounced (nearly fourfold) but persistent, lasting until the fourth sample, which was collected 120 min from the injection. FG 7142 (40 pmol) and 8-OH-DPAT (8 nmol) were ineffective. Because only intra-DRN kainate both increased inhibitory avoidance and decreased one-way escape in the elevated T-maze, the present behavioral results support the suggestion that 5-HT facilitates conditioned fear in the Am and inhibits unconditioned fear in the DPAG.

Effects of chronic lithium treatment on ornithine decarboxylase induction and excitotoxic neuropathology in the rat

Young adult rats were chronically treated with lithium (2.5 mmol/kg/day) for 16 days. The day after the last lithium administration, rats were injected s.c. with the excitotoxic convulsant kainic acid (10 mg/kg). As compared to saline controls, lithium-treated rats had no apparent attenuation of convulsions. Furthermore, the induction of brain ornithine decarboxylase and the consequent increase of putrescine levels, an index related to the convulsant effects of kainic acid, were similar in saline- and lithium-treated rats. Other rats were unilaterally injected with ibotenic acid into the nucleus basalis magnocellularis: no differences were measured in cortical choline acetyltransferase (ChAT) decrease among saline- and lithium-treated rats. In both the above experiments, apoptotic cell death was monitored in relevant brain regions of saline- or lithium-treated rats through a specific in situ labeling method for fragmented DNA. Whilst morphological evidence for a reduced damage in the olfactory cortex and hippocampus of kainic acid-injected rats was not obtained, lithium-treated rats showed a lower decrease of specific neurochemical markers: [3H]D-aspartate uptake and glutamate decarboxylase. This result suggests that mechanisms of recovery, absent in saline-treated animals, are elicited by the excitotoxic insult in lithium-treated rats.