Stepwise progression of kindling: Perspectives from the kindling antagonism model

What is the nature of the kindling process? We hypothesize that kindling is a discontinuous process involving discrete, stepwise transitions from one state of neural organization to another. Our data from the kindling antagonism paradigm argue that there are two critical transitions in the kindling process. These transitions constitute major steps in kindled seizure development. They act as "gates" controlling the ability of afterdischarge (AD) activity to effect the necessary reorganization of neural function which drives the kindling process. We identify two critical gates: 1) a forebrain gate which is dependent on norepinephrine (NE) and effects a discrete transition from nonconvulsive, stage 1 and 2 behaviors to stage 3 seizures, and 2) a brainstem gate which is also NE-dependent and effects a transition from stage 3 seizures to stage 4 and 5 seizures. These gates separate the kindling process into 3 "phases" which are different from, but overlap, the traditional behavioral stages of kindling defined by Racine. Current data suggest that these phases involve independent neural circuitry. They may also involve different physiological mechanisms, but this remains to be determined. This hypothesis is designed to provide a framework for the kindling process within which to search for kindling mechanisms.     

Human ventral mesencephalic xenografts to the catecholamine-depleted striata of athymic rats: ultrastructure and immunocytochemistry

On the basis of animal studies, grafts of fetal human dopaminergic cells have been suggested as a therapy for Parkinson's disease. The purpose of this study was to characterize the ultrastructure and immunocytochemistry of human ventral mesencephalic xenografts placed into the catecholamine-depleted striata of athymic "nude" rats. Human fetal tissue was obtained from tissue fragments derived from elective abortions during the first trimester of pregnancy. Small pieces of the basal mesencephalon were grafted into the catecholamine-depleted striata of four athymic nude rats. The rats were allowed to survive from 3 to 6 months after grafting; following fixation, the striatal tissue containing the grafts was labeled with antibodies against tyrosine hydroxylase and serotonin. Immunocytochemistry revealed tyrosine-hydroxylase-like-immunoreactive (THLI) and serotoninlike-immunoreactive (5HTLI) cell bodies within the human grafts. Both 5HTLI and THLI fibers crossed the graft-host interface and innervated the previously lesioned striatum. Both types of fibers also entered the host cortex from the adjacent human graft. At the ultrastructural level, THLI and 5HTLI fibers and synaptic terminals were observed in the host neuropil. THLI and 5HTLI dendrites and axon terminals were also observed in the neuropil of the grafts themselves. THLI axon terminals are not normally present in the substantia nigra. The results of our study indicate that human xenografts can survive in the neuropil of the host striatum and form morphologically appropriate synapses within the host brain.     

A glass/silicon composite intracortical electrode array

A new manufacturing technique has been developed for creating silicon-based, penetrating electrode arrays intended for implantation into cerebral cortex. The arrays consist of a 4.2 mm×4.2 mm glass/silicon composite base, from which project 100 silicon needle-type electrodes in a 10×10 array. Each needle is approximately 1,500 μm long, 80μm in diameter at the base, and tapers to a sharp point at the metalized tip. The technique used to manufacture these arrays differs from our previous method in that a glass dielectric, rather than ap-n-p junction, provides electrical isolation between the individual electrodes in the array. The new electrode arrays exhibit superior electrical properties to those described previously. We have measured interelectrode impedances of at least 10¹³ Ω, and interelectrode capacitances of approximately 50 fF for the new arrays. In this paper, we describe the manufacturing techniques used to create the arrays, focusing on the dielectric isolation technique, and discuss the electrical and mechanical characteristics of these arrays.     

Distribution of the largest neuron in mouse caudate-putamen nucleus: Its position in large-cell — Medium-cell clusters

Summary The position of the largest striatal neuron within territories delimited by medium-sized clustered neurons was charted in Nissl-stained sections through the mouse caudate-putamen nucleus. Medium-sized neuron somata occur in close proximity to this large cell at some point in the anteroposterior, mediolateral or dorsoventral extent of its soma. The size of the network of medium-sized neurons associated with the large cell may vary from two to 15 neurons. Even when this network is extensive, the large neuron is never completely surrounded. Most often, this cell also borders a fascicle of internal capsule fibers, and the entire cellular island may be aligned either parallel to or perpendicular to the orientation of these fibers. These findings suggest the hypothesis that cellular territories in the caudate-putamen nucleus have a very specific orientation in three dimensional space.     

Electrical properties of implant encapsulation tissue

The purpose of this study was to determine the electrical properties of the encapsulation tissue that surrounds electrodes chronically implanted in the body. Two four-electrode arrays, fabricated from either epoxy or silicone rubber, were implanted in each of six adult cats for 82 to 156 days.In vivo measurements of tissue resistivity using the four-electrode technique indicated that formation of the encapsulation tissue resulted in a significant increase in the resistivity of the tissue around the arrays.In vitro measurements of tissue impedance using a four-electrode cell indicated that the resistivity of the encapsulation tissue was a function of the tissue morphology. The tight layers of fibroblasts and collagen that formed around the silicone rubber arrays had a resistivity of 627±108 Ω-cm (mean ± SD; n=6), which was independent of frequency from 10 Hz to 100 kHz, and was significantly larger than the resistivity of the epoxy encapsulation tissue at all frequencies between 20 Hz and 100 kHz. The combination of macrophages, foreign body giant cells, loose collagen, and fibroblasts that formed around the epoxy arrays had a frequency-dependent resistivity that decreased from 454±123 Ω-cm (n=5) to 193±98 Ω-cm between 10 Hz and 1 kHz, and was independent of frequency between 1 kHz and 100 kHz, with a mean value of 195 ±88 Ω-cm. The results indicate that the resistivity of the encapsulation tissue is sufficient to alter the shape and magnitude of the electric field generated by chronically implanted electrodes.     

Immunohistochemical localization of nNOS in the skin and nerve fibers of the earthworm Lumbricus terrestris L. (Annelida Oligochaeta)

The epidermis of the earthworm Lumbricus terrestris is a multifunctional tissue. It is composed of supporting, mucous, neuroendocrine-like, sensory and basal cells. NO is considered to be a molecule that regulates numerous functional activities (also in non-neuronal cells) in vertebrates. In the earthworm epidermis, we found neuronal NO synthase immunopositivity in orthochromatic and metachromatic mucous cells, neuroendocrine-like cells and in epidermal and subepidermal nerve fibers and striated muscle fibers. It is suggested that NO has a multitude of biological actions, affecting functional activities of the epidermis such as tissue homeostasis, control of secretion, proliferation, respiration, defense, water-salt balance, as well as regulation of tonus in vascular and striated muscles.     

Fine Structure of A: Autonomic Nerve Fibers and Terminals in Human Myocardium; and B: Myocardial Changes in Congenital Heart Disease

In a histological and fine structural study of right atrial biopsy specimens from 31 patients with rheumatic heart disease (RHD), aged 7 to 46 years, and 11 patients with congenital heart disease (CHD), aged 3 to 36 years, nerve fibers or endings were seen by electron microscopy in 11 specimens. There was concurrence of ordinary axons along with terminals bearing pale cholinergic or dark adrenergic synaptic vesicles. Smaller and denser cholinergic vesicles suggested proliferation followed by exhaustion of such nerve endings. The closest proximity of nerve terminal to muscle fiber was about 100 nm. In one RHD specimen a “specific terminal cell” was present between a nerve ending and muscle fiber; in another a possible neuromuscular contact was developing at the surface of a regenerating small muscle fiber with a few myofilaments. Unmyelinated axons amidst increased subendocardial and subepicardial collagen, with prominent fibroblasts and depleted muscle fibers, were seen more frequently in specimens of CHD. Loss of myofibrils and accumulation of mitochondria, with infrequent formation of lipofuscin bodies, characterized degenerating muscle fibers in CHD also, although to a lesser degree than in RHD (reported earlier, 1985). The myocardial blood vessels in CHD tended to have pale swollen endothelial cells and narrowed lumen. The most severely affected cases of CHD were those with (1) a very wide atrial septal defect (ASD), (2) ventricular septal defect (VSD) with vegetations near the defect, (3) 1 infundibular pulmonary stenosis, and (4) Fallot's tetralogy.     

Morning to evening changes in the electrical and mechanical properties of human soleus motor units activated by H reflex and M wave

The aim of the present study was to compare the relative contribution of the soleus motor units (MUs) activated by H and M waves to the plantar-flexion torque in the morning and in the evening. Twelve healthy male subjects (physical education students) took part in this investigation. The electromechanical properties of the plantar flexor muscles were recorded at two different times of day: between 06:00 and 08:00 h and between 17:00 and 19:00 h. Plantar-flexion torque and concomitant electromyographic activity of soleus muscle were assessed under voluntary and evoked conditions. The results indicated a significant decrease in maximal voluntary muscle torque of triceps surae and associated soleus EMG in the evening as compared with the morning. The mean values of MVC ranged from 131.6±9.6 N m in the morning to 125.1±9.0 N m in the evening. Peak-to-peak values of soleus H _max and M _max potentials were comparable in the morning and in the evening (2.97 vs 3.18 mV and 7.95 vs 7.44 mV for H _max and M _max, respectively). The H _max/M _max ratio was not modified between the two experimental test sessions (34.8 vs 41.3%). The peak amplitude of the twitch produced by the H _max wave decreased significantly. When estimating the mechanical contribution to of the slowest and fastest-twitch MUs reflexively and directly activated, we observed that the contribution of the slowest MUs did not change while those of the fastest decreased significantly in the evening. To conclude, a weaker reflex twitch torque caused by higher fatigue state of the MUs directly activated by the M wave which accompanied H _max in the evening may be regarded as a possible explanation of the weaker plantar-flexion torque production in the evening.     

Survival and immunogenicity of dissociated allogeneic fetal neural dopamine-rich grafts when implanted into the brains of adult mice

Summary The survival of grafts of dissociated allogeneic fetal neural dopamine (DA) rich tissue in the striatum has been studied after transplantation between inbred strains of mice differing at defined immunogenetical loci between donor and recipient. Six to 7 weeks and 15 weeks after grafting, surviving grafted DA neurons were found in the brains of all the recipients, albeit with a large variation in numbers, located either within the striatum or within the adjacent lateral ventricle. The mean number of surviving DA neurons did not differ between the syngeneic controls and the histoincompatible donor-host combinations, and there was no difference in survival between grafts that differed at single or multiple major histocompatibility complex (MHC) loci, and those that differed at multiple non-MHC loci. The amount of inflammatory cells in the graft area did not differ between the groups, and none of the animals showed massive infiltration of inflammatory cells. The in situ immunogenicity of the grafted neural tissue after intracerebral implantation was monitored by means of Simonsen's alloimmunization test, at 6–7 weeks after transplantation, which provides a sensitive measure primarily of the cellular immunological response. Most, but not all, graft recipients showed immunization with a Spleen Index (S.I.) close to that seen in recipients of an orthotopical skin graft of the same histoincompatibility combination. In contrast to the prolonged survival of the intracerebral neural transplants, none of the skin grafts survived longer than 3 weeks, thus demonstrating the immunologically privileged status of the brain. We conclude that intracerebrally grafted allogeneic neural tissue is capable of provoking a cellular immune response. Despite host immunization, however, the dissociated fetal neural allografts survived for at least 15 weeks without any overt signs of rejection, regardless of the donor-host combination used.     

Xenografting of fetal pig ventral mesencephalon corrects motor asymmetry in the rat model of Parkinson's disease

Summary A suspension of cells from embryonic day 21 fetal pig ventral mesencephalon was transplanted into the striatum of 20 immunosuppressed rats with 6-hydroxydopamine-induced lesions of the nigrostriatal dopamine pathway. Of these rats, 15 showed reduction of amphetamine-induced ipsilateral rotation by 9 weeks and complete reversal of rotation by 14–17 weeks. Animals maintained stable reversal of rotations (contralateral direction) until cessation of Cyclosporin A (CyA) treatment at 15–20 weeks. Within 4–9 weeks after CyA removal, these rats showed exclusively ipsilateral rotations during behavioral testing which were comparable to pre-transplant levels, suggesting that the grafts were rejected upon cessation of CyA treatment. Rats were sacrificed and tyrosine hydroxylase (TH) immunohistochemistry was performed at several time points, both on and off CyA, to examine a possible correlation between the degree of rotational behavior and the number of TH- positive surviving grafted cells. Staining showed large numbers (230–12,329) of TH-positive surviving cells in animals displaying a high degree of rotational correction (1.6 to -9.6 net ipsilateral rotations/min) after cessation of CyA treatment. Two control groups, those transplanted with nonneuronal cells from the pig ventral mesencephalon (n=5) and those receiving only daily CyA injections (n=4) showed no significant reduction of net ipsilateral rotations throughout the experiment. No TH-positive surviving cells were seen in the one non-neuronal transplant analyzed. This data demonstrates long-term retention of xenografted tissue with immunosuppression and its concomitant restoration of normal motor behavior in the rat model of Parkinson's disease.