Gianfranco Ricci

Behavioral and electrographic patterns induced by systemic administration of kainic acid in developing rats

Abstract Behavioral and electrographic changes induced by systemic injection of 3–6 mg/kg of kainic acid (KA) have been studied during development in 1- to 28-day-old rats. In the first week of life, a few minutes after the administration of the toxin, animals developed motor signs such as scratching movements, hypo- and hyperactivity, loss of postural control, tremors and hyperextension of the limbs. No changes of the electrical cortical and hippocampal activity were detected. Similar, but more accentuated motor signs occur when KA was injected during the second week of postnatal life. In this case, on the electroencephalogram (EEG), bursts of spikes or polispikes localized in the cortex appeared. These bursts became more and more frequent and after only 20 min spread to the hippocampus. No correlation between the electrical and behavioral changes were observed. By the third week of life, in addition to motor signs, systemic kainic acid induced wet dog shakes (WDS) and limbic seizures. These were characterized by rearing, loss of postural control, masticatory movements and forepaw tremors. The EEG was characterized by primary hippocampal discharges that may spread to the cortex. Usually the limbic seizures become more and more frequent, leading to a status epilepticus. In another group of experiments, higher doses of KA (6–12 mg/kg) have been injected in curarized and artificially respirated animals of the same age. During the first days of life (1–7), unlike in the corresponding group of freely moving animals, KA induced sequences of slow spikes localized in the cortex and after 10–20 min spread to the hippocampus. In the following age-groups no differences between the curarized and free moving animals were detected. The different sensitivity of systemic KA to induce limbic seizures in neonatal rats may be related to the immaturity of pre- and post-synaptic glutamergic receptors in the hippocampus. Moreover, a different degree of maturity of cortical versus hippocampal glutamergic receptors may account for the preferential activation of the cortex versus hippocampus during the first period of life.

Seizure susceptibility in immature rats with micrencephaly induced by prenatal exposure to methylazoxymethanol acetate

The administration of the alkylating neurotoxin methylazoxymethanol acetate (MAM) to pregnant rats on day 15 of gestation induces, in the offspring, a marked micrencephaly, characterized by an impaired formation of interneurons at cortical, hippocampal and striatal levels. Since in man developmental CNS malformations are often associated with severe epileptogenic encephalopathies with seizures appearing in the first months or years of life, we have studied the development of kainic-acid- and bicuculline-induced seizures in 15- and 30-day-old rats, prenatally exposed to MAM. Compared to controls, a higher susceptibility to seizures has been found in micrencephalic rats aged 15 days, while no significant differences have been observed in those aged 30 days. It is hypothesized that the cerebral global anatomical dysgenesis caused by MAM underlies the higher seizure susceptibility shown by animals during the first periods of life. Successively, the processes of adjustment occurring between the cerebral regions affected by the neurotoxic action of MAM and the afferent and efferent pathways spared by the substance may re-establish adequate interneuronal relationships and, therefore, a normal convulsive susceptibility.

Bicuculline- and allylglycine-induced epilepsy in developing rats

The development of bicuculline- and allylglycine-induced epilepsy has been studied in developing rats (6 to 30 days old). The results showed that during the first period of life, in both experimental models, the behavioral modifications were atypical and poorly correlated to corresponding epileptic EEG changes. Successively, a gradual evolution of the electroclinical patterns was observed, with similar characteristics in both bicuculline- and allylglycine-treated animals. Only from the 3rd week did electroclinical patterns similar to those of adult animals and more specific for the type of the convulsant agent appear. These data suggest that during the 1st 2 weeks after birth, the level of global cerebral immaturity, rather than the type of the epileptogenic substance, is the prominent element in the characterization of epileptic manifestations. From the 3rd week, the more advanced level of anatomical, biochemical, and neurophysiologic maturation of the CNS allows a more selective involvement of various cerebral structures with subsequent well defined epileptic features.

Long‐Term Effects of Early Status Epilepticus on the Acquisition of Conditioned Avoidance Behavior in Rats

Summary: The acquisition of active avoidance behavior in a shuttle‐box apparatus was studied in 45‐day‐old rats. In these animals a single episode of status epilepticus had been induced by the systemic administration of kainic acid (KA) or pentylenetetrazole (PTZ), when they were 10 or 25 days old. The results were compared with those obtained from animals in which, at the same ages, only saline solution had been injected. In KA‐treated rats a decrement of right responses and a prolonged reaction time were observed, with these results more evident in animals treated earlier (10 days). Parallel with the behavioral alterations, the histological, morphometric and morphological examinations revealed neuronal and glial abnormalities at the neocortical level, while no lesions were found in the hippocampus. PTZ‐treated rats showed no behavioral alteration nor histological abnormality. The different findings obtained after KA and PTZ injection suggest that not only status epilepticus per se, but the mechanism of action and the neurotoxicity of the convulsant agent, are very important in impairing late performances.

Intracortical and intrahippocampal injections of kainic acid in developing rats: an electrographic study.

Electrographic patterns induced by neocortical and hippocampal microinjections of kainic acid (KA) have been studied in curarized 4-30-day-old rats. In younger (4-6-day-old) animals, both hippocampal and neocortical KA application induced, with a long delay, the appearance of sequences of slow spikes, simultaneously occurring in the cortex and hippocampus. The same pattern was observed in about 60% of animals 7-9 days old. In the remaining 40% of the rats of this age, epileptic abnormalities, initially localized in the neocortical or hippocampal injection site were obtained. The latter pattern always appeared in 10-14-day-old rats. In some of these status epilepticus was also reached. In older (15-30 days) animals, the hippocampal injection caused the appearance of hippocampal seizures, always evolving into status epilepticus. In neocortically injected animals, cortical bursts of polyspikes appeared, with or without hippocampal involvement. After 40-60 min, typical hippocampal seizures occurred, later leading to status epilepticus. The simultaneous hippocampal and neocortical response observed in younger rats is attributed to a massive activation of the immature brain structures. The focal response seems to be correlated with a maturational process of glutamate and/or kainate receptors at both hippocampal and neocortical levels. This process is completed during the third week, when a typical selective activation of the limbic structures is obtained.

Changes in Interictal Focal Activity and Spike‐Wave Paroxysms during Motor and Mental Activity

The number of focal spikes or sharp waves was studied in 5 epileptic children during movement of the limbs and during psychological tests. Another patient studied had frequent petit mal absences.

Effects of progabide on bicuculline-induced epileptic seizures in developing rats

The effects of progabide, a direct gamma-aminobutyric acid (GABA) receptor agonist, on bicuculline-induced seizures have been tested in developing rats, ages 7-28 days, to study the correlation between the antiepileptic effectiveness of this drug and the level of functional maturation of the GABAergic system. The incidence, latency of appearance, and behavioral characteristics of the epileptic manifestations, their evolution toward status epilepticus, and the percentage of recovery from status epilepticus have been evaluated in rats that had received a single injection (treatment) or three successive daily administrations (pretreatment) of progabide. The results have been compared with those obtained in a control group of animals in which only bicuculline had been injected. In rats ages 7-14 days the treatment appears to be substantially ineffective in protecting animals against bicuculline seizures and their consequences, probably because of the substantial immaturity of the GABAergic system at birth and during the first days of life. At this age, repetitive administrations of progabide cause a protective anticonvulsant action more remarkable than the single injection, particularly when using the higher doses of the substance. In 15-28-day-old rats, the treatment significantly reduces the lethality from status epilepticus but does not substantially modify the incidence of seizures, their latency of appearance, or their evolution toward status epilepticus. As in younger animals, in these rats also pretreatment is more effective than treatment against bicuculline seizures, whatever dose of progabide is used. At this age, therefore, the anticonvulsant properties of progabide appear to be more remarkable than in the previous age, probably because of a higher level of development of the GABAergic system, according to biochemical data on the GABAergic system ontogenesis.

A simple method for implanting electrodes in freely moving neonatal rats.

A simple method for implanting cortical and subcortical electrodes in very young rats is described, which does not interfere with the behavior of the animal during the experiment. The cortical electrodes are anchored to the skull by a spiral whose first loop is introduced between the inner layer of the skull and the dura mater. The subcortical electrodes have a loop which rests above the skull. Both the spirals of the cortical electrodes and the loops of subcortical electrodes are then embedded in dental acrylic.

Age-related anticonvulsant activity of NMDA in the rat caudate-putamen

Striatal pathways are important for modulating the threshold for seizures in the rat forebrain. N-Methyl-D-aspartate (NMDA), an excitatory amino acid derivative and powerful anticonvulsant agent, when injected into the brain, has been shown to protect adult rats against kindling and pilocarpine-induced seizures when injected into the caudate-putamen. The present study examines whether the anticonvulsant action of NMDA in the caudate-putamen varies with age. Bilateral striatal administration of NMDA was effective in suppressing bicuculline-induced seizures in rats older than 23 days of age. The results suggest that striatal pathways involved in the anticonvulsant activity of NMDA in the caudate-putamen are not functionally active in developing rats before the 4th week of life.

Status epilepticus and brain maturation.

The development of a limbic and a generalized tonic-clonic form of epilepsy, induced by systemic injections of kainic acid and pentylenetetrazol respectively, has been studied in developing rats. The purpose of this research was to investigate the correlations between the maturational stages of the CNS and the electro-clinical manifestations of epilepsy and status epilepticus. In both models of epilepsy, the electro-clinical patterns of seizures typical of the adult animal were reached as early as the third week of life. During the first weeks, atypical behavioural and EEG epileptic manifestations were observed. An attempt has been made to compare the experimental results with the electro-clinical epileptic signs of the infant, in order to suggest some neurophysiological explanations of the peculiar aspects of infantile epilepsy.