Tyrosine hydroxylase-immunoreactive neurons in the temporal lobe in complex partial seizures

Memory, emotional and vocational impairments before and after anterior temporal lobectomy for complex partial seizures

PURPOSE

To assess the pre- and postsurgical frequency of memory, emotional, and vocational impairments in patients who underwent anterior temporal lobectomy (ATL), and to assess the relationship between emotional disturbance and memory abilities after ATL.

METHODS

Retrospective analysis of data was performed on 90 patients with medically intractable complex partial seizures who underwent ATL between 1981 and 2003. Patients were evaluated an average of 5 months before surgery and 11.3 months after surgery.

RESULTS

A moderate to high frequency of memory impairment (44.4%; verbal or nonverbal), emotional disturbance (38.9%) and unemployment (27.8%) existed in the same individuals both before and after surgery. There were small to moderate rates of new onset memory (18.9%), emotional (11.1%), and vocational (7.8%) difficulties after surgery often regardless of seizure control outcome. Patients who underwent left-ATL and had emotional disturbance after surgery had the lowest verbal memory test scores.

CONCLUSIONS

Results highlight the importance of taking into account emotional status when assessing memory abilities after ATL. Results replicate the finding of moderate to high frequencies of memory impairment, emotional disturbance, and unemployment both before and after ATL. Results provide support for the rationale that cognitive, psychiatric and vocational interventions are indicated to mitigate the problems that exist before and persist after ATL.

Epilepsy-induced microarchitectural changes in the brain

Our understanding of the pathogenesis of the neuropathology of epilepsy has been challenged by a need to separate the "lesions" that cause epilepsy from the "lesions" that are produced by the epilepsy. Significant clinical, genetic, pathologic, and experimental studies of Ammon horn sclerosis (AHS) suggest that AHS is the result and cause of seizures. The data support the idea that seizures cause alterations in cell numbers, cell shape, and organization of neuronal circuitry, thus setting up an identifiable seizure-genic focus. As such, AHS represents a slowly progressive lesion and a search for the cause of the initiating seizure has led to the identification of ion channel mutations. In this report, the neuropathology of other conditions associated with intractable epilepsy is considered, suggesting that in them similar epilepsy-produced alterations in microarchitecture can be observed. The idea is important to define the optimum time for epilepsy surgery and the underlying etiology of these seizure-genic lesions.

L-phenylalanine selectively depresses currents at glutamatergic excitatory synapses

To explore the hypothesis that L-phenylalanine (L-Phe) depresses glutamatergic synaptic transmission and thus contributes to brain dysfunction in phenylketonuria (PKU), the effects of L-Phe on spontaneous and miniature excitatory postsynaptic currents (s/mEPSCs) in rat and mouse hippocampal and cerebrocortical cultured neurons were studied using the patch-clamp technique. L-Phe depressed the amplitude and frequency of both N-methyl-D-aspartate (NMDA) and non-NMDA components of glutamate receptor (GluR) s/mEPSCs. The IC(50) of L-Phe to inhibit non-NMDAR mEPSC frequency was 0.98 +/- 0.13 mM, a brain concentration seen in classical PKU. In contrast, D-Phe had a significantly smaller effect, whereas L-leucine, an amino acid that competes with L-Phe for brain transporter, had no effect on mEPSCs. Unlike GluR s/mEPSCs, GABA receptor mIPSCs were not attenuated by L-Phe. A high extracellular concentration of glycine prevented the attenuation by L-Phe of NMDAR current, activated by exogenous agonist, and of NMDAR s/mEPSC amplitude, but not of NMDAR s/mEPSC frequency. On the other hand, L-Phe significantly depressed non-NMDAR current activated by low but not high concentrations of exogenous agonists. Glycine-independent attenuation of NMDAR s/mEPSC frequency suggests decreased presynaptic glutamate release caused by L-Phe, whereas decreased amplitudes of NMDAR and non-NMDAR s/mEPSCs are consistent with competition of L-Phe for the glycine- and glutamate-binding sites of NMDARs and non-NMDARs, respectively. The finding that GluR activity is significantly depressed at conditions characteristic of classical PKU indicates a potentially important contribution of impaired GluR function to PKU-related mental retardation and provides important insights into the potential physiological consequences of impaired GluR function.

Seizure control and cognitive outcome after temporal lobectomy: a comparison of classic Ammon's horn sclerosis, atypical mesial temporal sclerosis, and tumoral pathologies

PURPOSE

Neuropathologic examination of resected tissue after anterior temporal lobectomy (ATL) for treatment of complex partial seizures revealed several distinct histologic substrates. Our study examined the relation between neuropathology, seizure control, and cognition in ATL patients and described preliminary profiles to aid in the prediction of outcome.

METHODS

Of the 149 patients who underwent ATL from 1980 to 1999, long-term follow-up was available for 145. Specimens from 124 of the 145 patients had histologic findings consistent with one of three diagnoses: classic Ammon's horn sclerosis (cAHS; n = 75), atypical mesial sclerosis (Atypical; n = 21), or low-grade tumor (Tumor; n = 28). The other 20 patients had diverse pathologies that were insufficient for analysis. ATL patients underwent a complete preoperative and 68 underwent a postoperative neuropsychological evaluation.

RESULTS

Of the 145 patients, 84% of cAHS, 57% of Tumor, and 29% of Atypical patients had a > or =95% reduction in seizure frequency. Neuropsychological testing suggested that cAHS patients demonstrate more generalized preoperative cognitive impairment than do the Atypical or Tumor patients. The Atypical group recalled significantly less nonverbal material after surgery than did the cAHS or Tumor groups. Stratification by both pathology and surgery side revealed that the right Atypical patients declined more on information processing and set shifting.

CONCLUSIONS

Patients with cAHS or Tumor demonstrated better seizure control and fewer declines in cognitive functioning after ATL than did the Atypical patients, highlighting the need to investigate this group as a distinct entity.

Corpora amylacea and heat shock protein 27 in Ammon's horn sclerosis

Increased numbers of corpora amylacea have been observed in the resected mesial temporal lobe of many patients with complex partial seizures (CPS) and Ammon's horn sclerosis (AHS). Several heat shock proteins (HSPs) are induced by seizures and have been suggested as an etiologic factor in the formation corpora amylacea. We quantified corpora amylacea and HSP27-immunoreactive astrocytes in temporal lobe specimens from patients with CPS (28 AHS; 10 non-AHS) and in 5 autopsy controls. Corpora amylacea were increased in each sector of Ammon's horn in the AHS group, significantly so in CA1 and CA3 (p < 0.0001 and p = 0.0097, respectively), compared with the non-AHS group, although there was considerable variability among the specimens. We found HSP27 to be significantly but nonspecifically increased in the resected temporal lobe specimens from all patients with CPS, regardless of the underlying pathology. HSP27 was not, however, expressed within the corpora amylacea, and did not correlate with the number of corpora amylacea in any of the 9 mesial and lateral temporal lobe areas examined.

Muscarinic receptor loss and preservation of presynaptic cholinergic terminals in hippocampal sclerosis

PURPOSE

Prior single-photon emission tomography studies showed losses of muscarinic acetylcholine receptor (MAChR) binding in patients with refractory mesial temporal lobe epilepsy. Experimental animal studies demonstrated transient losses of MAChR due to electrically induced seizures originating in the amygdala. However, the relations between cholinergic synaptic markers, seizures, and underlying neuropathology in human temporal lobe epilepsy are unknown. We tested the hypotheses that human brain MAChR changes are attributable to hippocampal sclerosis (HS), and that HS resembles axon-sparing lesions in experimental animal models.

METHODS

We measured MAChR binding-site density, an intrinsic neuronal marker, within the hippocampal formation (HF) in anterior temporal lobectomy specimens from 10 patients with HS and in 10 autopsy controls. Binding-site density of the presynaptic vesicular acetylcholine transporter (VAChT) was measured as a marker of extrinsic cholinergic afferent integrity. MAChR and VAChT results were compared with neuronal cell counts to assess their relations to local neuronal losses.

RESULTS

Reduced MAChR binding-site density was demonstrated throughout the HF in the epilepsy specimens compared with autopsy controls and correlated in severity with reductions in cell counts in several HF regions. In contrast to MAChR, VAChT binding-site density was unchanged in the epilepsy specimens compared with autopsy controls.

CONCLUSIONS

Reduction in MAChR binding in HS is attributable to intrinsic neuronal losses. Sparing of afferent septal cholinergic terminals is consistent with the hypothesis that an excitotoxic mechanism may contribute to the development of HS and refractory partial epilepsy in humans.

Transcripts of the transposon mariner are present in epileptic brain

Mobile genetic elements termed transposons have been increasingly implicated in human disease. The small transposon mariner is widespread within non-vertebrate genomes and causes mutation by replication, excision, and insertion of itself without an RNA intermediate. We find that human DNA contains about 60 copies of this gene. Mariner transcripts are abundant in RNA prepared from sclerotic epileptic hippocampi. In contrast, typically no mariner-specific RNA is detected in non-sclerotic hippocampi from other epileptic patients or from autopsies. A complete but non-functional copy was obtained using rapid amplification of cDNA ends (RACE). This human mariner transcript is approximately 45% homologous to a functional counterpart active in Drosophila, with a coding region of 1035 bases flanked by 32 base inverted terminal repeats. The differential expression of mariner transcripts within sclerotic hippocampi suggests the probable activity of an autonomous element which by mutating critical genes could establish an epileptogenic substrate in the hippocampus.

Pathologic basis of the symptomatic epilepsies in childhood

The epilepsies in childhood are classified as primary (or idiopathic) and secondary (or symptomatic). The primary epilepsies account for two thirds of all childhood epilepsies and are presumed to be genetically determined. In the remaining one third of cases, a neuropathologic lesion can be identified. This paper summarizes the etiologies of the symptomatic epilepsies. They are classified according to the pathologic processes; malformative, metabolic, neoplastic and phakomatoses, hypoxic-ischemic, infectious, and of unknown pathologic process.

Dynorphin and the kappa 1 ligand [3H]U69,593 binding in the human epileptogenic hippocampus

The distribution of dynorphin (DYN), one of its binding sites (kappa 1 receptor) and their relationship to neuronal loss and granule cell hyperexcitability was examined in hippocampi from patients with temporal lobe epilepsy (TLE). In hippocampi that were not the seizure focus (mass associated temporal lobe epilepsy, MaTLE; and paradoxical temporal lobe epilepsy, PTLE) DYN-like immunoreactivity was localized in the dentate granule cells and their mossy fiber terminals within the hilus and area CA3. In hippocampi that were the seizure focus (MTLE), 89% showed an additional band of immunoreactivity confined to the inner molecular layer (IML) of the dentate gyrus, representing recurrent mossy fiber collaterals. In 11% of MTLE patients no staining was found in the IML (MTLE/DYN-). The MTLE/DYN- hippocampi were also characterized by a significantly lower degree of cell loss than in MTLE hippocampi in the dentate granule cell layer, the hilus and CA3. Both MTLE and MTLE/DYN- hippocampi showed evoked epileptiform bursting in granule cells while MTLE showed greater polysynaptic EPSPs and spontaneous excitatory activity. Thus granule cell recurrent collateral sprouting may account for only some aspects of hyperexcitability. In 30% of the MTLE group, hilar neurons of a variety of morphological types expressed DYN immunoreactivity in their somata and dendrites. The density of [3H]U69,593 binding sites in MaTLE and PTLE patients was highest in areas CA1 and the subiculum-regions having little or no DYN-staining. In the dentate molecular layer, hilus and CA3--regions with the most DYN immunoreactivity--there was a low density of ligand binding. The significance of this transmitter/receptor mismatch is yet unknown.

Connections of the hippocampal formation in humans: I. The mossy fiber pathway

The hippocampal formation has been one of the most extensively studied cortical regions in rats, yet little is known about the anatomical connections of the hippocampus in primates, especially humans. With the use of an antibody against the calcium-binding protein, calbindin-D28K, in normal autopsy tissue and the neuronal tracers biocytin or biotinylated dextrans in in vitro slice preparations from tissue removed during surgery for intractable epilepsy, we examined the human hippocampal mossy fiber pathway. The injections of biocytin into the dentate granule cell layer labeled neurons in a Golgi-like manner, revealing the presence of basal dendrites on about 30% of the granule cells. The granule cell axons, the mossy fibers, initially formed a diffuse plexus of fibers in the polymorphic layer before organizing into fiber fascicles in the hilar pyramidal region. These fiber fascicles were much more prominent rostrally than caudally. Within the hilus and proximal portions of the extrahilar CA3 field, the mossy fibers ran through the pyramidal cell layer, and while near the transition to field CA2, the fibers turned superficially and crossed the pyramidal layer to run in the stratum lucidum. All of these features, seen following injections of tracer into hippocampal slices from the brains of epileptics, were confirmed by calbindin-staining of mossy fibers in normal brains. Biocytin-labeled mossy fiber axons revealed two characteristic types of enlargements: small varicosities and larger expansions. The expansions were found throughout the neuropil and were highly irregular, diaminobenzidine-dense profiles that had pleiomorphic modes of attachment to the parent axon. Electron microscopic images of these biocytin labeled expansions revealed that they were large synaptic boutons bearing asymmetric synapses. This study indicates that the human mossy fiber pathway shows some minor deviations from the rodent brain but little difference from monkeys. We argue that these changes mirror a phylogenetic growth of the CA3 pyramidal neurons (subfield CA3c) into the hilus rather than an evolutionary change of the mossy fiber pathway. This growth of subfield CA3c and the increase in mossy fibers running through the pyramidal layer (and a presumed accompanying increase in proximal basal dendritic contacts) may reflect a growing role of the projection from the dentate granule cells to subfield CA3c and from there to field CA1 in the primate hippocampus.

The pathogenic and progressive features of chronic human hippocampal epilepsy

To design useful experimental models of epilepsy, it is necessary to clearly understand the known clinical-pathologic features of the disease process. Studies of mesial temporal lobe epilepsy (MTLE) patients have identified several distinctive clinical and pathophysiologic characteristics and many of these can be analyzed in experimental models. For example, patients with typical MTLE have medical histories that often contain an initial precipitating injury (IPI), are likely to have hippocampal sclerosis in the surgical specimen, and have better seizure outcomes than patients with typical idiopathic temporal seizures (i.e. cryptogenic). Hippocampal from children as young as age 1 year with IPI histories also demonstrate neuron damage similar to adults with hippocampal sclerosis. Compared to IPI patients without seizures (i.e. trauma, hypoxia, etc.), IPI cases with severe seizures showed younger ages at the IPI, shorter latent periods, and longer durations of habitual MTLE. Hippocampal damage is often bilateral, however, the epileptogenic side shows hippocampal sclerosis and the opposite side usually shows only mild neuron losses. Moreover, MTLE patients show declines in hippocampal neuron densities with very long histories of habitual seizures (15 to 20 years), however, the additional neuron loss adds to the template of hippocampal sclerosis and occurs in limited subfields (granule cells, CA1 and prosubiculum). Hippocampal axon and synaptic reorganization is another pathologic feature of MTLE, and involves granule cell mossy fibers and axons immunoreactive for neuropeptide upsilon, somatostatin, and glutamate decarboxylase (which synthesizes GABA). Finally, MTLE patients with hippocampal sclerosis show increased granule cell mRNA levels for brain derived neurotropic factor, nerve growth factor, and neurotrophin-3 that correlate with mossy fiber sprouting or with declines in Ammon's horn neuron densities. Taken together, our data support the following concepts: (1) The pathogenesis of MTLE is associated with IPI histories that probably injure the hippocampus at some time prior to habitual seizure onsets, (2) most of the damage seems to occur with the IPI, (3) there can be additional neuron loss associated with long histories, (4) another pathologic feature of MTLE is axon reorganization of surviving fascia dentata and hippocampal neurons, and (5) reorganized axon circuits probably contribute to seizure or propagation.

Adrenocorticotropic hormone immunoreactivity in the hippocampal formation of temporal lobe epilepsy patients

PURPOSE

We wished to identify immunocytochemically the distribution of proopiomelanocortin-related peptides in the hippocampal formation of patients with epilepsy.

METHODS

Surgical hippocampal specimens from temporal lobe epilepsy (TLE) patients and autopsy control tissue were examined immunocytochemically for ACTH, alpha-melanocyte-stimulating hormone (alpha-MSH) and beta-endorphin.

RESULTS

There was a dense distribution of ACTH-immunoreactive neurons in the hippocampal formation of patients with mesial TLE syndrome (MTLE). These hippocampal specimens showed significant cell loss. ACTH-positive neurons were most prominent in the subiculum, with scattered ACTH-immunoreactive neuronal elements distributed in the cornu ammonis fields and hilus. Light ACTH immunoreactivity was detected in the tumor-related epileptic hippocampal specimens, which showed minimal cell loss. Although autopsy control tissue from the hypothalamus showed intense ACTH staining patterns in cells and fibers, there was little or no ACTH immunoreactivity in the autopsy hippocampal tissue. The expression of ACTH immunoreactive elements was correlated with patterns of cell loss. No alpha-MSH- or beta-endorphin-immunoreactive neurons were detected in any of the hippocampal specimens.

CONCLUSIONS

ACTH has anticonvulsant properties, and its novel expression in the glutamatergic subicular neurons, which provide the main outflow of the hippocampal formation, may represent an attempt by the damaged hippocampal circuit to restore the balance of excitatory/inhibitory neurotransmission in TLE.

Distribution of AMPA receptor subunits in the hippocampal formation of temporal lobe epilepsy patients

The immunocytochemical distribution of the AMPA-selective receptor subunits GluR1 and GluR2/3 were mapped in the human hippocampal formation obtained from surgery for medically intractable temporal lobe epilepsy. GluR2/3 immunoreactivity was detected in all principal cell types of the hippocampal formation, including hilar neurons, granule cells of the dentate gyrus, and pyramidal cells of the cornu ammonis fields and subiculum. GluR2/3 immunostaining typically filled the cell bodies and processes of neurons. A comparison of GluR2/3 immunoreactivity in a sclerotic specimen versus a non-sclerotic specimen demonstrated a profound loss of staining, specifically in the areas where neuronal dropout was occurring, including CA1, CA3 and the hilus. An analysis of GluR1 immunoreactivity in non-sclerotic specimens revealed that it was predominantly localized to cellular processes throughout the cornu ammonis fields, with a sparse staining of the dentate gyrus outer molecular layer and little to no staining of the dentate gyrus inner molecular layer. Similar to the GluR2/3-immunostained patterns, GluR1 immunoreactivity was lost in the cornu ammonis fields of sclerotic hippocampal specimens, corresponding to patterns of neuronal dropout. Our most compelling finding was a unique extensive pattern of GluR1 and Glu2/3 immunoreactivity throughout the molecular layers of the dentate gyrus of severely compromised hippocampi. The altered staining of GluR1 and GluR2/3 complements some of the patterns of axonal sprouting already described for the dentate gyrus, with a conjecture that their anatomy and distribution pattern underlies to some degree the reorganization of the sclerotic hippocampus. A combination of enhanced glutamatergic transmission and changes in neuropeptides that modulate hippocampal circuitry could greatly affect the degree of excitability in the hippocampal formation. The alterations of GluR1 and GluR2/3 immunoreactivity in the dentate gyrus add another component to the concept of reorganization in the epileptic sclerotic hippocampus.

Neurochemical and morphological changes associated with human epilepsy

To date a multitude of studies into the morphology and neurochemistry of human epilepsy have been undertaken with variable, and often inconsistent, results. This review summarises these studies on a range of neurotransmitters, neuromodulators, neuropeptides and their receptors. In addition to this, novel changes in cell viability and sprouting have been identified and are discussed. Whether the alterations observed are a result of the seizures or are a contributory factor is unclear. However, it may be that following an initial insult (such as febrile convulsions, status epilepticus or head injury) secondary processes occur both of an anticonvulsant nature in an attempt to compensate for seizure activity, and in a kindling type of fashion, resulting in an increased susceptibility to seizures, leading to future seizures. Many of the alterations documented in this study probably represent one or both of these processes. Clearly no single chemical abnormality or morphological alteration is going to explain the clinically diverse disorder of epilepsy. However, by drawing together the neurochemistry and morphology of epilepsy, we may begin to understand the mechanisms involved in seizure disorders.

Altered patterns of catecholaminergic fibers in focal cortical dysplasia in two patients with partial seizures

We present the histologic study of two patients who underwent cerebral cortex resection for partial seizures linked with cortical dysplasia. The distinction of areas of seizure origin from areas of seizure propagation was made according to stereoelectroencephalographic criteria. Samples of epileptogenic tissue were studied by using cytoarchitectonic and immunohistochemical stainings. We mapped the catecholaminergic afferents by employing antisera directed against tyrosine hydroxylase and dopamine-beta-hydroxylase enzymes. The epileptic activity was correlated with the underlying patterns of cytoarchitectonic and immunohistochemical changes. The neuropathological features were focal and consisted of large neurons dispersed through all but the first cortical layer (associated in one case to giant glial cells), of variable disturbance of lamination, of neuronal ectopia in the white matter and of moderate proliferation of small glial cells. Areas of seizure onset coincided with that of dysplastic zones. Both laminar distribution and density of catecholaminergic fibers were altered in the dysplastic cortices (area of seizure onset) and there was an increase in the density of tyrosine hydroxylase-immunoreactive fibers in the surrounding areas of seizure propagation. Our results indicate that these developmental epileptogenic lesions were associated with abnormal neuronal circuitry. They provide evidence at the structural level of the increase in tyrosine hydroxylase activity previously reported in spiking areas of human epileptogenic cerebral cortex and they suggest that catecholamines may contribute toward limiting seizure activity propagation.

Development of a model for Parkinson's disease in sheep using unilateral intracarotid injection of MPTP via slow continuous infusion

The effects of unilateral intracarotid administration of MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) in sheep were studied with the goal of producing a non-primate, large animal model of Parkinson's Disease. Adult female sheep were given an acute (over 30 min) or chronic (over 1 week) injection of MPTP (0.4-5.0 mg/kg) via the common carotid artery. Both methods produced parkinsonian-like behavior. Turning contralateral to the side of injection was induced by apomorphine (APO) in both groups. However, amphetamine (AMP) induced ipsilateral turning only in the chronic treatment group. Acute and chronic MPTP treatment resulted in a loss of substantia nigra tyrosine hydroxylase immunoreactive (THIR) neurons with a significantly greater loss ipsilateral to the injection in each treatment group (acute p < 0.05; chronic p < 0.01). Caudate dopamine (DA) was depleted in both treatment groups, although the difference between ipsilateral and contralateral DA content was significant only in the chronic treatment group (p < 0.05). The best results were seen in those animals with chronic infusion with the occipital artery occluded to prevent entry of drug into the posterior circulation with subsequent bilateral distribution. Use of slow and continuous intracarotid administration of MPTP with the ipsilateral occipital artery occluded can prevent some of the bilateral effects of acute treatment, and results in statistically significant ipsilateral reduction of THIR neurons in the substantia nigra and reduction of tissue levels of DA in the caudate nucleus. Such treatment produces appropriate turning responses to both AMP and APO challenge not seen in the acute treatment group, and appears to be an effective method of producing parkinsonian-like behavior in a large animal.

Differential modulation by dopamine of responses evoked by excitatory amino acids in human cortex

The responses of human neocortical neurons to iontophoretic application of excitatory amino acids and their modulation by dopamine (DA) were studied in vitro. Brain slices were obtained from children undergoing surgery for intractable epilepsy. Application of N-methyl-D-aspartate (NMDA) to the slices induced slow depolarizations accompanied by decreased input conductances and sustained action potentials in cortical neurons. Glutamate produced rapid depolarizations and firing with few changes in input conductances. Quisqualate also induced depolarization and firing, but input conductances increased during the rising phase of the membrane depolarization. Iontophoretic application of DA alone produced no change in membrane potential or input conductance. However, when DA was applied in conjunction with the excitatory amino acids, it produced contrasting effects. With either bath application of DA or when iontophoresis of DA preceded application of NMDA, the amplitude of the membrane depolarizations and the number of action potentials were increased, whereas the latency of these responses decreased. In contrast, DA decreased the amplitude of the depolarizations and the number of action potentials evoked by glutamate or quisqualate. The fact that DA affects responses to NMDA and glutamate or quisqualate in opposite directions is of considerable importance to the understanding of cellular mechanisms of neuromodulation and the role of DA in cognitive processing and in epilepsy.

Neuropathologic asymmetries in the brain of a patient with a unilateral status epilepticus

Autopsy study of a patient who died after an episode of prolonged unilateral status epilepticus revealed neuronal loss in the hippocampus on the epileptic side, with gliosis confined to the CA1 and CA3 fields. There was loss of the parvalbumin-immunoreactive gamma-aminobutyric acid (GABA)-ergic interneurons in the hippocampus on that side. There was also loss of the normal laminar pattern of substance P staining with increased substance P immunoreactivity in the supragranular plexus on that side. Met-enkephalin immunoreactivity was also increased in the outer molecular layer of the dentate gyrus on the epileptic side. Mossy fibers on the epileptic side stained more strongly with the Hicks' silver stain and with antibodies against glutamate and taurine, but less intensely with antibodies against calbindin. In the contralateral cerebellum, there was Purkinje cell loss, injury to the remaining Purkinje cells, and increased prominence of the Bergmann glia. Our observations show that prolonged unilateral seizure activity can be associated with specific histochemical changes in the human hippocampus.