N. Suzan Nadi

Mapping rat brain structures activated during ethanol withdrawal: role of glutamate and NMDA receptors

Brain structures activated during ethanol withdrawal have been mapped by visualizing c-fos mRNA expression. The regional distribution of c-fos mRNA in brain during ethanol withdrawal can be mimicked by acute injection of N-methyl-D-aspartic acid (NMDA) and is stereospecifically blocked by the NMDA receptor antagonist, MK-801. The findings reveal that the dentate gyrus and piriform cortex are selectively activated during ethanol withdrawal and suggest that this may be mediated by glutamate activation of NMDA receptors.

Behavioral, physiological, and neuroendocrine responses to arecoline in normal twins and “well state” bipolar patients

Cholinergic supersensitivity has been postulated to be an etiologic factor in affective disorder. After several pilot dose-response studies, we administered 8 mg of the cholinergic agonist arecoline subcutaneously to eight pairs of normal volunteer identical twins and eight bipolar patients currently euthymic and unmedicated. During the hour following arecoline administration, the Profile of Mood States (POMS) showed an increase in total mood disturbance in both patient and control groups. Mean systolic blood pressure, pulse, plasma cortisol, prolactin, and growth hormone also increased. Anger and elation scores on the POMS showed significant concordance in identical twins, as did change in prolactin, implying that these are the components of drug response possibly influenced by genetic factors. None of these responses differentiated well state patients from controls. Thus, mood, behavioral, and neurochemical responses to arecoline, which appears to have nonspecific neurochemical effects at the dose employed, are not markers of vulnerability to affective illness.

Quinolinic Acid Concentrations in Brain and Cerebrospinal Fluid of Patients with Intractable Complex Partial Seizures

Summary Quinolinic acid (QUIN) is a neurotoxin and convulsant when injected directly into the brains of experimental animals and as such has been implicated in the etiology of human seizure disorders. In the present study, we quantified QUIN in cerebrospinal fluid (CSF) and in spiking (focus) and nonspiking (nonfocus) regions of surgically resected human temporal neocortex. l‐tryptophan (L‐TRP), the putative precursor of QUIN, was also measured in brain, along with CSF concentrations of L‐TRP, 5‐hydroxyindoleacetic acid (5‐HIAA), and homovanillic acid (HVA). In brain tissue, no differences were found in the concentrations of QUIN and L‐TRP between focus and nonfocus regions in 15 pairs of samples. No differences were found in CSF, L‐TRP, 5‐HIAA, or HVA concentrations between 11 neurologically normal controls and 15 interictal (no seizures for >24 h) and 20 postictal (within 50 min of seizure) samples from epileptic patients. However, CSF QUIN concentrations were significantly lower (32%) in the epileptic patients as compared with controls, which may indicate a generalized disturbance in brain QUIN metabolism or perhaps a response to antiepileptic drugs.

Levels of Catechols in Epileptogenic and Nonepileptogenic Regions of the Human Brain

Abstract: Recent reports about tyrosine hydroxylase and α1‐adrenoceptors in epileptic foci have suggested increased regional catecholaminergic activity, which may serve a compensatory, inhibitory role. We measured levels of catechols, including the precursor 3,4‐dihydroxyphenylalanine (Dopa) and the catecholamines dopamine (DA) and nor‐epinephrine (NE), in surgically removed foci identified by electrocorticography and in nonepileptogenic sites from 23 patients with intractable temporal lobe epilepsy. The following values (mean ± 1 SD) were obtained: DOPA = 142 ± 60 ng/g of protein in the focus vs. 115 ± 39 ng/g in the nonfocus (p < 0.01); DA = 168 ± 85 vs. 106 ± 54 ng/g (p < 0.001); and NE = 267 ± 117 vs. 181 ± 80 ng/g (p < 0.001). The results are consistent with increased catecholaminergic activity in epileptic foci.

Separate mechanisms for behavioral, cardiovascular, and hormonal responses to dextroamphetamine in man

The neurochemical specificity of physiological, biochemical, and psychological responses to dextroamphetamine was tested by pretreating volunteers with haloperidol (0.014 mg/kg IM), proparonol (0.1 mg/kg IV), thymoxamine (0.1 mg/kg IV), or placebo prior to 0.3 mg/kg IV amphetamine. Healthy volunteers (N=12) participated in the studies, but not all volunteers received each drug combination. Haloperidol prevented dextroamphetamine-induced behavioral excitation, but did not significantly affect plasma norepinephrine or pressor responses, whereas propranolol inhibited norepinephrine and pressor responses without influencing excitation or other behavioral responses. Thymoxamine did not affect any of the responses measured. None of the agents significantly affected plasma cortisol or growth hormone responses. The prolactin rise following dextroamphetamine was potentiated by haloperidol. The results are consistent with the hypothesis that behavioral excitation after dextroamphetamine occurs through a dopaminergic mechanism, and pressor responses through a noradrenergic mechanism.

Amygdaloid kindling of rats increases preprosomatostatin mRNA and somatostatin without affecting glutamic acid decarboxylase (GAD) mRNA or GAD

The levels of preprosomatostatin (preproSS) mRNA, somatostatin-like immunoactivity (SS-LI) (also known as somatotropin-release inhibitory factor, or SRIF), glutamic acid decarboxylase (GAD) activity and GAD mRNA were determined in several brain regions of amygdaloid-kindled rats. SS mRNA and SS increased in the cortex and striatum, while only SS increased in the hippocampus. No changes were detected in either GAD activity or GAD mRNA in any brain region. The data suggest that somatostatin may be one of the factors involved in the chain of events leading to kindled seizures.

Kynurenine pathway metabolites in cerebrospinal fluid and serum in complex partial seizures.

Summary: The kynurenine pathway metabolites, quinolinic acid (QUIN) and L‐kynurenine are convulsants, whereas kynurenic acid (KYNA) is an antagonist of excitatory amino acid receptors. Imbalances in the concentrations of these metabolites have been implicated in the etiology of human seizure disorders. In the present study, L‐kynurenine and QUIN concentrations in both cerebrospinal fluid (CSF) and serum were reduced in patients with intractable complex partial seizures (CPS) in both the postictal period (15–75 min after a seizure) and the interictal period (absence of seizure for >24 h) as compared with neurologically normal control subjects. Linear regression analyses and analysis of covariance showed that the reductions in serum QUIN and L‐kynurenine were correlated to blood antiepileptic medication. L‐Tryptophan (L‐TRP) levels also tended to be lower in both CSF and serum of the seizure patients. CSF KYNA and serum 3‐hydroxykynurenine concentrations were not affected in seizure patients, whereas serum levels of KYNA were reduced. 3‐Hydroxykynurenine was not detected in the CSF of either control or seizure patients. The results do not support a role for a generalized reduction in KYNA concentrations or an increased ratio of QUIN:KYNA, or increases in CSF L‐kynurenine in initiation and maintenance of intractable CPS humans.

Alterations in somatostatin and proenkephalin mRNA in response to a single amygdaloid stimulation versus kindling

Previous studies have shown changes in both somatostatin (SS)- and proenkephalin(PE)-derived peptides in the brains of amygdaloid-kindled rats, suggesting possible roles for the peptides in the kindling process. In this study, we have extended this analysis by looking at the time course of changes in SS and PE mRNAs at various times after kindling, in comparison with a single non-convulsive stimulation. Blot analysis of total RNA showed increases in SS mRNA in striatum, frontal cortex and hippocampus of animals receiving only a single stimulation as well as kindled animals--the increase occurred 1-3 days following stimulation and levels were back to basal by 1 week. PE mRNA did not change. In situ hybridization analysis, one day after the last kindling stimulation, showed significant elevations of SS mRNA in CA1, CA2 and dentate gyrus of hippocampus and of PE mRNA in olfactory cortex that were specific to kindling. However, both a single stimulation and kindling increased PE mRNA in olfactory tubercle and arcuate nucleus. In contrast, a single electrical stimulus increased PE mRNA in ventral striatum and SS mRNA in cingulate cortex and olfactory tubercle. These data support the idea that changes of SS mRNA in hippocampus and of PE mRNA in olfactory cortex may be related to kindling, and point out the importance of using animals which receive a single electrical stimulus, rather than sham-operated animals, as controls.

Cerebrospinal fluid and serum levels of dopa, catechols, and monoamine metabolites in patients with epilepsy.

Summary: We measured CSF and serum concentrations of monoamines and monoamine metabolites in normal control subjects and in patients with partial epilepsy between and less than 2 h after complex partial seizures (CPS) or secondarily generalized tonic‐clonic seizures (SGTCs). After SGTCs, concentrations of norepinephrine in CSF were significantly higher (p < 0.05) than interictal concentrations, concentrations after PSs, and concentrations in control subjects. Serum epinephrine levels also were significantly higher after SGTCs than interictal and control subjects’levels. CSF HVA levels were significantly higher after PSs than interictal or control subjects’levels. CSF concentrations of norepinephrine and its intraneuronal metabolite, dihydroxyphenylglycol, were highly correlated, both interictally and following SGTCs, whereas correlations between serum and CSF levels of these catechols generally were not statistically significant. The results indicate that seizures are associated with release of catecholamines in the central nervous system.

Cerebrospinal Fluid Levels of Neuropeptides, Cortisol, and Amino Acids in Patients with Epilepsy

Summary: We measured lumbar cerebrospinal fluid (CSF) levels of somatostatin, cholecystokinin, neurotensin, atrial natriuretic factor, vasoactive inhibitory peptide, neuropeptide Y, adrenocorticotrophic hormone, corticotropin releasing hormone, β‐endorphin, metenkephalin, cortisol, alanine, glycine, aspartate, glutamate, taurine, and γ‐aminobutyric acid in 25 inpatients with epilepsy at known interictal and postictal times and in 11 neurologically normal volunteers. There were no significant differences between interictal or postictal complex partial seizures (CPS), postictal generalized tonic‐clonic seizures (GTC), and control CSF neuropeptide, cortisol, and amino acid (AA) levels. However, there were nonsignificant trends for CSF levels of several neuropeptides to be increased after CPS and GTC as compared with interictal baseline levels. There were significant correlations between levels of certain CSF neuropeptides or (AAs) and serum antiepileptic drug (AED) levels. Several correlations were noted between CSF levels of AAs, including a correlation between the excitatory neurotransmitters aspartate and glutamate identified only after CPS.