Esa Koivisto

A new model of chronic temporal lobe epilepsy induced by electrical stimulation of the amygdala in rat

Spontaneous seizures are the hallmark of human epilepsy but they do not occur in most of the epilepsy models that are used to investigate the mechanisms of epilepsy or to test new antiepileptic compounds. This study was designed to develop a new focal epilepsy model that mimics different aspects of human temporal lobe epilepsy (TLE), including the occurrence of spontaneous seizures. Self-sustained status epilepticus (SSSE) lasting for 6-20 h was induced by a 20-30 min stimulation of the lateral nucleus of the amygdala (100 ms train of 1 ms, 60 Hz bipolar pulses, 400 microA, every 0.5 s). Stimulated rats (n = 16) were monitored with a video-EEG recording system every other day (24 h/day) for 6 months, and every other video-EEG recording was analyzed. Spontaneous epileptic seizures (total number 3698) were detected in 13 of the 15 animals (88%) after a latency period of 6 to 85 days (median 33 days). Four animals (31%) had frequent (697-1317) seizures and 9 animals (69%) had occasional seizures (1-107) during the 6-months follow-up period. Fifty-seven percent of the seizures occurred during daytime (lights on 07:00-19:00 h). At the end of the follow-up period, epileptic animals demonstrated impaired spatial memory in the Morris water-maze. Histologic analysis indicated neuronal loss in the amygdala, hippocampus, and surrounding cortical areas, and mossy fiber sprouting in the dentate gyrus. The present data indicate that focal stimulation of the amygdala initiates a cascade of events that lead to the development of spontaneous seizures in rats. This model provides a new tool to better mimic different aspects of human TLE for investigation of the pathogenesis of TLE or the effects of new antiepileptic compounds on status epilepticus, epileptogenesis, and spontaneous seizures.

Loss of synaptophysin-like immunoreactivity in the hippocampal formation is an early phenomenon in alzheimer's disease

We studied a synatophysin-like immunoreactivity in the hippocampal formation of patients with definite Alzheimers disease, multi-infarct dementia, patients with no evidence of clinical dementia with neuropathological findings fulfilling the criteria of possible Alzheimers disease, and age-matched nondemented controls. Possible Alzheimers disease cases were of special interest because they were considered to represent early Alzheimers disease. We also studied the spatial relationship of synaptophysin-like immunopositivity with amyloid-beta-protein immunopositive senile plaques and anti-paired helical filament immunopositive degenerating neurons locally as well as considering the intrinsic circuits in the hippocampal formation. The synaptophysin-like immunoreactivity was decreased in the hippocampus and the entorhinal cortex in patients with definite and possible Alzheimers disease but not in multi-infarct dementia patients compared to controls. Equal loss of synapses in possible and definite Alzheimers disease patients supports the hypothesis that synaptic loss is an early phenomenon in Alzheimers disease. Unchanged synaptophysin-like immunopositivity in patients with multi-infarct dementia suggests that the loss of synapses is centrally involved in the pathogenesis of Alzheimers disease and not dementia per se. There was no spatial correlation between loss of synapses and amyloid-beta-protein positive senile plaques. Moreover, we could not find a strict spatial relationship between senile plaques and degenerating neurons. Our results do not support the amyloid cascade hypothesis of Alzheimers disease that local accumulation of amyloid-beta-protein leads to the loss of synapses.

Guanfacine, but not clonidine, improves planning and working memory performance in humans

The present study compares, using a double-blind, placebo controlled design the effects of two α2-agonists, clonidine (0.5, 2, and 5 μg/kg) and guanfacine (7 and 29 μg/kg) on spatial working memory, planning and attentional set-shifting, functions thought to be dependent on the “central executive” of the prefrontal cortex. Blood pressure and the subjective feeling of sedation were affected equally by clonidine and guanfacine. The 0.5 μg/kg and 5 μg/kg doses of clonidine disrupted spatial working memory, but the medium dose had no effect. The 0.5 and 2 μg/kg doses of clonidine increased impulsive responding in the planning test. The 5 μg/kg dose of clonidine slowed responding at effortful levels of planning and attentional set-shifting tests. The 29 μg/kg dose of guanfacine improved spatial working memory and planning. Guanfacine had no effect on attentional set-shifting. These data indicate that guanfacine improved planning and spatial working memory, but clonidine dose-dependently disrupted performance. It is possible that the greater selectivity of guanfacine for α2A-adrenoceptor subtype may underlie its differences from clonidine.

Behavioral and pharmacological studies on the validation of a new animal model for attention deficit hyperactivity disorder.

Childhood hyperactivity (attention deficit hyperactivity disorder, ADHD) is a common behavior disorder among grade-school children. The characteristic symptoms are attentional problems and hyperkinesia. A number of animal models for ADHD syndrome have been developed, but very few of these models are truly representative in that they rarely describe both hyperactivity and attentional problems. Frequently the disorder has been induced in animals by pharmacological manipulations or exogenous brain lesions which are distinct from the disturbances in normal developmental processes which ultimately lead to ADHD. The main purpose of the present research was to develop a new animal model of ADHD, such that it would include an attention deficit, hyperactivity and alleviation by treatment with a psychostimulant. We used rats trained for a 5-choice serial reaction time task which assessed sustained attention. In this behavioral paradigm, rats are required to discriminate spatially a short visual stimulus that will occur randomly in one of five locations and have to maintain an adequate activity level. The ability of a rat to maintain its attention on the task can be measured by counting choice accuracy (percent correct responses), whereas percentage of premature responses indicates the level of motoric activity. According to the present results, rats performing poorly in the task have poorer choice accuracy and they make more premature responses than well performing individuals, i.e., a clear correlation was observed between these parameters (r = -0.59, p < .001). Interestingly, choice accuracy of poorly performing rats was found to be better at the beginning of testing, but it became impaired toward the end of testing session. It was also found that the deficiency was not due to impaired visual discrimination, since a reduction in the intensity of the visual stimulus impaired to a similar extent the performance of normal and poorly performing subjects. Equally, no relationship was observed between choice accuracy and the latencies to collect earned food pellets after the correct responses, indicating that motivational factors do not underlie the attention deficit or excessive activity of poorly performers. Furthermore, methylphenidate hydrochloride at doses of 100 and 1000 micrograms/kg slightly improved the attentional performance of poorly performing animals. At the dose 100 micrograms/kg, methylphenidate slightly decreased the probability of premature responses (impulsivity) in these rats, but 1000 micrograms/kg methylphenidate increased the impulsivity of both normal and poorly performing rats. However, methylphenidate did not affect the choice accuracy of normal animals tested at the baseline conditions or with the reduced stimulus duration which impaired their performance. The present data indicate that rats showing poor performance when trained and tested in a 5-choice serial reaction time task may be a model for ADHD.

Activation of 5-HT2A receptors impairs response control of rats in a five-choice serial reaction time task.

The present experiments investigated the effects of agents acting at serotonin (5-HT)-2 receptors on the performance of rats in a choice serial reaction time (5-CSRT) task in order to examine the role of 5-HT2 receptors in the modulation of attention and response control. The results indicate that DOI, [(+/-)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane hydrochloride; 0.05, 0.1 and 0.2 mg/kg, subcutaneously], a 5-HT(2A/2C) agonist, slightly impaired the choice accuracy of the well performing rats and markedly increased their premature responding. DOI (0.05 and 0.1 mg/kg) had no effect on the latency to collect earned food pellets or to respond correctly, indicating that these lower doses of DOI did not reduce motivation for the food reward in this task. The selective effect of a low dose of DOI (0.1 mg/kg) on premature responding was completely blocked by ketanserin (0.2 mg/kg), a 5-HT2A antagonist, and ritanserin (0.3 mg/kg), a 5-HT(2A/2C) antagonist, but only partially blocked by a high dose of SER082 (1.0 mg/kg), a 5-HT2C antagonist. In contrast to DOI, mCPP, [1-(3-phenyl)piperazine; 0.05 and 0.15 mg/kg], a 5-HT2C agonist, had no effect on choice accuracy or premature responding, but it reduced behavioral activity and/or arousal as indicated by the decreased number of trials completed and increased the probability of omissions. SER082 (1.0 mg/kg) blocked the effects of mCPP on performance. These data suggest that the overactivation of 5-HT2A receptors impairs response control in a 5-CSRT task, whereas the overactivation of 5-HT2C receptors can affect behavioral activity and/or arousal state of the animals for this food rewarded task.

Guanfacine and Clonidine, Alpha2-Agonists, Improve Paired Associates Learning, but not Delayed Matching to Sample, in Humans

The present study compares the effects of two alpha2-agonists, clonidine (0.5, 2, and 5 μg/kg, PO) and guanfacine (7 and 29 μg/kg, PO) in young healthy volunteers on their performance in visual paired associates learning (PAL) and delayed matching to sample (DMTS) visual short-term recognition memory tests. In the PAL test, clonidine 2 and guanfacine 29 μg/kg improved the subjects’ performance. In the DMTS test, clonidine at 5 μg/kg delay-dependently impaired performance accuracy, and at 2 and 5 μg/kg it also slowed responses. Guanfacine had no effect on DMTS test performance. Clonidine 5 and guanfacine 29 μg/kg equally increased subjective feelings of sedation and reduced blood pressure. The results suggest that both clonidine and guanfacine facilitated PAL learning by improving “frontal strategies,” but only clonidine disrupted “mnemonic processing” decreasing DMTS accuracy. The greater selectivity of guanfacine for alpha2A-adrenoceptor subtype may explain the different profile of action of the drugs.

Estimation of the Total Number of Cholinergic Neurons Containing Estrogen Receptor-α in the Rat Basal Forebrain

This study was undertaken to estimate the total number of cholinergic cells and the percentage of cholinergic cells that contain estrogen receptor-α (ERα) in the rat basal forebrain. Double immunostaining for choline acetyltransferase (ChAT) and ERα was carried out on 50-μm-thick free-floating sections. Because routine mounting method causes considerable flattening of the sections, we embedded immunostained sections in Durcupan, an epoxy resin known to cause virtually no shrinkage. When this procedure was used the section thickness was well preserved, individual cells could be clearly identified, and subcellular localization of ERα immunoreactivity was easy to verify. Cell counting in these sections revealed that the rat basal forebrain contains 26,390 ± 1097 (mean ± SEM) cholinergic neurons. This comprises 9674 ± 504 in the medial septum-vertical diagonal band of Broca, 9403 ± 484 in the horizontal diagonal band of Broca, and 7312 ± 281 in the nucleus basalis. In these nuclei, 60%, 46%, and 14% of the cholinergic neurons were colocalized with ERα, respectively. We believe that our results are an improvement on existing data because of the better distinction of individual neurons that the Durcupan embedding method brings.

Changes in absolute power values of EEG spectra in the follow‐up of Alzheimer's disease

We have studied the absolute and relative power and amplitude of EEG spectra (T6–02) of 24 patients with “probable” Alzheimers disease at the early stage of the disease and 1 year later and also compared the values to those of normal elderly controls. A remarkable variability of the absolute values was evident both for the patients and for the controls. The AD patients had significantly higher absolute theta amplitude and power and the absolute beta values tended to decrease compared to controls. Absolute delta and alpha values did not differ from those of the controls. The relative delta, theta and alpha power and amplitude, and beta amplitude showed significant changes in AD patients, whereas the relative beta power was unchanged. In the follow‐up of AD patients at 1 year, absolute alpha values decreased and delta values tended to increase. As to relative values, both the alpha and the delta significantly changed but the theta and the beta were unaltered. We conclude that both absolute and relative power and amplitude values should be considered in EEG studies of dementia patients. Absolute values are especially useful in follow‐up.

Coexistence of parvalbumin and GABA in nonpyramidal neurons of the rat entorhinal cortex

The possible coexistence of the calcium-binding protein, parvalbumin, with the major inhibitory neurotransmitter, gamma-aminobutyric acid (GABA), and its synthesizing enzyme, glutamate decarboxylase (GAD), was studied in nonpyramidal cells of the rat medial and lateral entorhinal cortex. The material was analyzed by two different methods, the first of which was a mirror techniques where the possible coexistence of two different antigens was analyzed from cells cut in half at the surface of the adjacent section. The other method consisted of analyzing double immunofluorescent-stained sections with a confocal microscope. The colocalization analysis revealed that all parvalbumin-immunoreactive neurons (mirror technique n = 688 and confocal microscopy n = 644) in all layers of the medial and lateral entorhinal cortex were also immunopositive for GABA or GAD. Parvalbumin-cells made up 52% of the GABA cells in most of the layers in the medial and lateral entorhinal cortex. In layer III of the entorhinal cortex, the proportion was about 40%. Thus, parvalbumin-containing neurons in the entorhinal cortex represent a large GABAergic cell population, which is likely to play an important role in controlling both the input and the output of the entorhinal cortex.

Blockade of muscarinic, rather than nicotinic, receptors impairs attention, but does not interact with serotonin depletion.

Abstract Rationale: The cholinergic system is considered to be essential for attention and the degeneration of the cholinergic system in Alzheimer’s disease (AD) correlates with the cognitive decline seen in AD patients. The serotonergic system also degenerates in AD, but its role in the modulation of cognitive functions, especially attention, is somewhat unclear. Objectives: The present study investigated possible differences between cholinergic muscarinic and nicotinic receptor mediated mechanisms, the role of serotonin (5-HT) and the interaction between the cholinergic and serotonergic systems in the modulation of attention and response control. Methods: The influences of cholinergic receptor blockade and 5-HT lesions on the performance of rats in the five-choice serial reaction time task were assessed. The 5-HT lesions were neurochemically verified. Results: The neurochemical analysis indicated that the levels of 5-HT and 5-hydroxyindoleacetic acid were reduced quite specifically in the hippocampi, parieto-occipital and frontal cortices, and in the striatum of both p-chloroamphetamine (pCA) and 5,7-dihydroxytryptamine (5,7-DHT) lesioned rats. The behavioural results showed that the pCA lesion caused a transient increase in impulsivity whereas the 5,7-DHT lesion temporarily reduced the motor activity and slightly impaired choice accuracy. Furthermore, the blockade of central muscarinic receptors by scopolamine (0.075 and 0.150 mg/kg), but not nicotinic receptors by mecamylamine (1.0 or 3.0 mg/kg), impaired the choice accuracy, whereas the blockade of both muscarinic and nicotinic receptors interfered with motor activity, though possibly via peripheral mechanisms. Interestingly, mecamylamine (3.0 mg/kg) reduced impulsivity, whereas scopolamine slightly increased it. Serotonergic lesions did not make the rats more susceptible to the effects of cholinolytics on choice accuracy. Conclusions: 5-HT system is not essential for the modulation of attention, but it is important in the modulation of response control. Central muscarinic receptors are important in the modulation of attention, whereas central nicotinic receptors may be more essential in response control. The results do not support there being an interaction between the serotonergic and the cholinergic systems in the modulation of attention.