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Multifaceted microglial functions in the developing brain, such as promoting the differentiation of neural progenitors and contributing to the positioning and survival of neurons, have been progressively revealed. Although previous studies have noted the relationship between vascular endothelial cells and microglia in the developing brain, little attention has been given to the importance of pericytes, the mural cells surrounding endothelial cells. In this study, we attempted to dissect the role of pericytes in microglial distribution and function in developing mouse brains. Our immunohistochemical analysis showed that approximately half of the microglia attached to capillaries in the cerebral walls. Notably, a magnified observation of the position of microglia, vascular endothelial cells and pericytes demonstrated that microglia were preferentially associated with pericytes that covered 79.8% of the total capillary surface area. Through in vivo pericyte depletion induced by the intraventricular administration of a neutralizing antibody against platelet-derived growth factor receptor (PDGFR)β (clone APB5), we found that microglial density was markedly decreased compared with that in control antibody-treated brains because of their low proliferative capacity. Moreover, in vitro coculture of isolated CD11b + microglia and NG2 + PDGFRα - cells, which are mostly composed of pericytes, from parenchymal cells indicated that pericytes promote microglial proliferation via the production of soluble factors. Furthermore, pericyte depletion by APB5 treatment resulted in a failure of microglia to promote the differentiation of neural stem cells into intermediate progenitors. Taken together, our findings suggest that pericytes facilitate microglial homeostasis in the developing brains, thereby indirectly supporting microglial effects on neural progenitors. SIGNIFICANCE STATEMENT This study highlights the novel effect of pericytes on microglia in the developing mouse brain. Through multiple analyses using an in vivo pericyte depletion mouse model and an in vitro coculture study of isolated pericytes and microglia from parenchymal cells, we demonstrated that pericytes contribute to microglial proliferation and support microglia in efficiently promoting the differentiation of neural stem cells into intermediate progenitors. Our present data provide evidence that pericytes function not only in the maintenance of cerebral microcirculation and blood brain barrier (BBB) integrity but also in microglial homeostasis in the developing cerebral walls. These findings will expand our knowledge and help elucidate the mechanism of brain development both in healthy and disease conditions., (Copyright © 2022 the authors.)

In the developing cortex, postmigratory neurons accumulate in the cortical plate (CP) to properly differentiate consolidating subtype identities. Microglia, despite their extensive surveying activity, temporarily disappear from the midembryonic CP. However, the mechanism and significance of this absence are unknown. Here, we show that microglia bidirectionally migrate via attraction by CXCL12 released from the meninges and subventricular zone and thereby exit the midembryonic CP. Upon nonphysiological excessive exposure to microglia in vivo or in vitro, young postmigratory and in vitro-grown CP neurons showed abnormal differentiation with disturbed expression of the subtype-associated transcription factors and genes implicated in functional neuronal maturation. Notably, this effect is primarily attributed to interleukin 6 and type I interferon secreted by microglia. These results suggest that "sanctuarization" from microglia in the midembryonic CP is required for neurons to appropriately fine-tune the expression of molecules needed for proper differentiation, thus securing the establishment of functional cortical circuit.

To identify neuron-specific genes, we performed gene expression profiling, cDNA microarray and in silico ESTs (expressed sequence tags) analyses. We identified a human neuron-specific gene, KIAA1110 (homologue of rat synArfGEF (Po)), that is a member of the guanine nucleotide exchange factor (GEF) for the ADP-ribosylation factor (ARF). RT-PCR analysis showed that the KIAA1110 gene was expressed specifically in the brain among adult human tissues, whereas no apparent expression was observed in immature neural tissues/cells, such as fetal brain, glioma tissues/cells, and neural stem/precursor cells (NSPCs). The KIAA1110 protein was shown to be expressed in mature neurons but not in undifferentiated NSPCs. Immunohistochemical analysis also showed that KIAA1110 was expressed in neurons of the human adult cerebral cortex. Furthermore, the pull-down assay revealed that KIAA1110 has a GEF activity toward ARF1 that regulates transport along the secretion pathway. These results suggest that KIAA1110 is expressed specifically in mature neurons and may play an important role in the secretion pathway as a GEF for ARF1.

Increased levels of endothelin-1 have been demonstrated in the ischemic brain, and endothelin receptor antagonism has been shown to improve the outcome of cerebral ischemia. However, it remains unknown what the relative receptor distribution in the brain of the spontaneously hypertensive stroke-prone rat (SHR-SP) is and whether it is changed by endothelin antagonism. The present study aimed to investigate the expression of the two endothelin receptors in the frontal cortex of SHR-SP after 12 weeks of treatment with an endothelin-A/endothelin-B dual receptor antagonist, SB209670, or saline (vehicle) starting from the prehypertensive stage (6 weeks old). A 50% increase in the endothelin-A receptor was found in the vehicle-treated brain of SHR-SP compared with that of the age-matched Wistar-Kyoto control, but endothelin antagonism reversed this upregulation completely. A 20% decrease in endothelin-B receptor was found in the vehicle-treated brain of SHR-SP compared with Wistar-Kyoto and was recovered by endothelin antagonism. This is the first study to explore the relative endothelin receptor distribution in the frontal cortex of SHR-SP at the typical hypertensive stage and changes resulting from long-term endothelin antagonism starting from the prehypertensive stage.

Spontaneously hypertensive stroke-prone rats suffer spontaneous strokes partly as a result of abnormal cerebrovascular development. This model exhibits prehypertensive, typical hypertensive and malignant hypertensive stages. We had observed that vascular endothelial growth factor and its receptors, kinase domain region (KDR) and fms-like tyrosine kinase (Flt-1), were upregulated in the frontal cortex of spontaneously hypertensive stroke-prone rats at the typical hypertensive stage. The current study therefore investigated whether the long-term treatment with an endothelin-A/endothelin-B dual receptor antagonist, SB209670, or saline (vehicle) starting at the prehypertensive stage (6 weeks old) could reverse the upregulated vascular endothelial growth factor and its receptors; this upregulation is believed to be a compensatory adaptation for hypertension in the brain of spontaneously hypertensive stroke-prone rats. A 40% upregulation of vascular endothelial growth factor was observed in the brain of vehicle-treated spontaneously hypertensive stroke-prone rats compared with the age-matched genetic control, Wistar-Kyoto rat, and this upregulation was markedly reversed by endothelin antagonism. A similar change was found in KDR and Flt-1 expression. It is worth noting that the vascular endothelial growth factor/KDR signaling system was upregulated in the brain of spontaneously hypertensive stroke-prone rats treated with vehicle at the typical hypertensive stage, whereas the cerebral blood flow did not differ between Wistar-Kyoto and spontaneously hypertensive stroke-prone rats. We concluded that endothelin antagonism reversed the upregulated vascular endothelial growth factor and its receptors in the frontal cortex of spontaneously hypertensive stroke-prone rats at the typical hypertensive stage, and it is suggested that endothelin antagonism can reverse the hypertension-induced neurovascular remodeling in the brain of these rats.

Spontaneously hypertensive stroke-prone rats (SHR-SP) suffer spontaneous stroke in part as a result of abnormal cerebrovascular development. Reduction of regional cerebral blood flow in this model has already been demonstrated. This model has three distinct stages of hypertension: pre-hypertensive, typical hypertensive and malignant hypertensive. We investigated the level of endothelin-1 and its receptor expression in the frontal cortex of SHR-SP at the malignant hypertensive stage (35-40 weeks of age), during which time the rats suffer strokes. The cerebral endothelin-1 level, as determined by enzyme-linked immunosorbent assay, was highly increased at this severely hypertensive stage compared to their genetic control, normotensive Wistar-Kyoto rats. This upregulation was associated with an increased expression of endothelin-A receptor, however, another endothelin-1 receptor, endothelin-B, was downregulated. The regional cerebral blood flow in the frontal cortex was reduced by 60% in 40-week-old malignantly SHR-SP as compared to age-matched Wistar-Kyoto rats. Thus, cerebral endothelin-1 expression increased in malignant hypertension in SHR-SP. The enhanced endothelin-1 may activate the endothelin-A receptor, which would, in turn, result in reduced cerebral blood flow. Downregulation of the endothelin-B receptor may cause suppression of endothelium-derived relaxing factors in the brain of SHR-SP and be an underlying factor in their stroke susceptibility.

The accumulation of calcium ions (Ca) was examined in the rat brain by means of 45Ca autoradiography following the application of a weak anodal direct current to the surface of the sensorimotor cortex. Repetition of the anodal polarization with 3.0 microA for 30 min caused more Ca to accumulate in the cerebral cortex. The degree and extent of accumulation was greater in the hemisphere ipsilateral to the polarization than in the other. Accumulation was also noted in the hippocampus and thalamus. Ca accumulation was detected after 24 h and it remained virtually constant up to 72 h after the last polarization. The results suggest that a long-lasting disturbance of Ca homeostasis is involved in the cortical plastic changes seen following anodal polarization.

c-Fos protein-like immunoreactivity (IR) was investigated in the rat brain following an application of weak anodal direct current to the surface of the unilateral sensorimotor cortex in an attempt to elucidate the cellular and molecular bases of central plasticity. Anodal polarization resulted in a massive increase in c-Fos protein-like IR in neurons of the cingulate, piriform, frontoparietal cortices, and hippocampus ipsilateral to the polarization. The effects were dependent upon the duration and intensity of currents applied. The time-dependent induction of c-Fos protein-like IR was maximal at 1 h, became weaker by 6 h, and almost returned to the baseline within 24 h following polarization. When MK-801 [(+)-5-methyl-10,11-di-hydro-5H- dibenzo[a,d]cyclohepten-5,10-imine hydrogen maleate], a noncompetitive antagonist for N-methyl-D-aspartate (NMDA) receptors, was injected intraperitoneally, the induction of this nuclear protein was reduced or completely blocked in both hemispheres, except around the polarized point itself, as a function of the time and dosage. These results suggest that the proto-oncogene c-fos is rapidly and transiently activated in the brain following anodal polarization and this activation is mediated by NMDA receptors.

Protein kinase C gamma (PKC gamma)-like immunoreactivity was examined in the rat brain, employing the monoclonal antibody 36G9 raised against purified PKC gamma, after an application of weak anodal direct current to the surface of the sensorimotor cortex. Anodal polarization with 3.0 microA for 30 min resulted in a pronounced increase in the number of PKC gamma-like-positive neurons in accordance with the intensity of PKC gamma-like immunostaining in the neocortex, cingulate cortex and piriform cortex ipsilateral to the polarization. The number of PKC gamma-like-positive neurons began to increase at 1 h after polarization, peaked at 3 h, and thereafter decreased to the control levels by 72 h. The increase in expression of PKC gamma-like immunoreactivity in specific areas of the cerebral cortex is suggested to serve as a basis for the long-lasting hyperexcitability in situ following anodal polarization.

A unilateral 30-min application of anodal direct current to the promotor cortex of rabbits was repeated 10 times, and cyclic AMP accumulation in response to histamine was investigated in slices of different cortical areas. Polarization with 1.0 microA decreased the cyclic AMP accumulation in the cortical area contralateral to the polarization, by which regional dominance in cyclic AMP accumulation was produced in the polarized cortex. In contrast, the regional difference in cyclic AMP accumulation was reversed when 10.0 or 30.0 microA was applied. The histamine-elicited accumulation of cyclic AMP was almost completely inhibited by the selective H2-receptor antagonist cimetidine. These results suggest that repeated anodal polarization regionally alters H2-receptor-mediated cyclic AMP generation in the cortex depending on the intensity of the polarizing currents and this pattern of cyclic AMP accumulation is responsible for the characteristic motor behavior induced by anodal polarization.

An anodal direct current of 3.0 microA or 30.0 microA was unilaterally applied for 30 min or 3 h to the surface of the sensorimotor cortex of rats, and the effects of polarization on the morphology of brain cells were examined by light microscopy. After five repeated anodal polarization trials, dark neurons appeared mainly in the polarized neocortex regardless of the intensity and duration of the polarizing currents. Such dark neurons were scarce in the control animals or the animals receiving only one trial of polarization. The dark neurons were most abundant in the second to fourth layers of the ipsilateral superior-lateral convexity of the frontal cortex, but a few were present in the contralateral cortex. The dark neurons began to appear 24 h after the last polarization; thereafter almost all of these neurons gradually reverted to their normal morphological profiles through a transitory state within 1 month of the last trial of repeated polarization. No morphological changes were apparent in any of the brain structures other than the cerebral cortex. These findings indicate that repeated anodal polarization has reversible morphological effects on the cortical neurons, suggesting that the appearance of dark neurons after anodal polarization is an important index for evaluation of cortical plastic change induced by polarization.

An injection of cobalt chloride solution into the unilateral sensorimotor cortex of rats induced electrographic epileptic activity, which was followed by a peripheral motor disturbance. Brain slices were prepared from the cortical region including the injection site and from the other cortical regions of rats between 8 and 50 days after the injection. In the cortical slices, we examined cyclic AMP accumulations elicited by adenosine and its stable analogue 2-chloroadenosine. Adenosine and 2-chloroadenosine at their maximal dose increased cyclic AMP accumulation six- to 10-fold and 10-15-fold, respectively, and the elicitation was markedly inhibited by the adenosine antagonist 8-phenyltheophylline. The cyclic AMP accumulation was increased in the primary epileptic region of the cortex adjacent to the injection site of cobalt chloride solution, whereas it was unchanged in the other cortical regions. The increase in cyclic AMP accumulation was observed regardless of the presence or absence of the adenosine uptake inhibitor dipyridamole, the phosphodiesterase inhibitor DL-4-(3-butoxy-4-methoxybenzyl)-2-imidazolidinone, and adenosine deaminase. Such an increased accumulation of cyclic AMP in the primary epileptic cortex was detected as early as 8 days after the injection. The cyclic AMP accumulation continued to increase and reached a peak level 17-19 days after the injection, and it returned to the control levels after 40-50 days, in correspondence with the electrographic and behavioral findings. It is concluded that alterations in adenosine receptor-mediated generation of cyclic AMP in the primary epileptic cortex are closely associated with the central process of cobalt-induced epilepsy.(ABSTRACT TRUNCATED AT 250 WORDS)

Cyclic AMP accumulations elicited by adenosine analogues 2-chloroadenosine (2-CADO), R-N6-phenylisopropyladenosine (R-PIA), and N6-cyclohexyladenosine (CHA) were investigated in cortical slices of chronic iron-induced epileptic rats. Cyclic AMP accumulation was elicited 9- to 18-fold by 2-CADO and it was elicited 5- to 7-fold by either R-PIA or CHA; 2-CADO was more potent than R-PIA or CHA in eliciting cyclic AMP accumulation. The adenosine analogues elicited cyclic AMP accumulation in a dose-dependent manner, and the elicitation was inhibited by the adenosine antagonist 8-phenyltheophylline. The 2-CADO-elicited accumulation of cyclic AMP was greatly increased in the cortical region on the primary epileptic side, while the R-PIA- or CHA-elicited accumulation did not change in any cortical region. The deviation detected only in the 2-CADO-elicited accumulation of cyclic AMP may be due to the difference in relative potency for adenosine receptors of the adenosine analogues. The results suggest that adenosine receptor-mediated generation of cyclic AMP is altered in the primary region of iron-induced epileptic cortex, in which heterogeneous alterations in different adenosine receptor subtypes may occur in the epileptic process.

Anodal direct currents of 1 or 10 microA were unilaterally applied for 30 min once a day to the premotor area of the cerebral cortex in rabbits, in which the current application was repeated 10 times at intervals of 2-3 days. Peripheral motor behavior was observed during and after each polarization trial, and was compared with that before polarization. The motor manifestations were classified into two types: gentle flexion of either forelimb and struggle with violent movement of forelimbs. Flexion of the forelimb contralateral to the polarized cortical side was clearly increased by polarization at an intensity of 1 microA, but not at 10 microA. Forelimb struggle of both sides decreased only when 10 microA was applied. These results suggest that the passage of 1 microA current activates the polarized local area of the cortex, while 10 microA has an inhibitory effect on cortical activity.

Unilateral injection of ferrous chloride solution into the rat sensorimotor cortex produced epileptic discharges in the electrocorticograms (ECoGs). The discharges were isolated spikes and spike and wave complexes, and the epileptic activity lasted for more than 12 months after the injection. Isolated spike activity often appeared on the left or right side of the cortex, whereas spike and wave complex activity appeared bilaterally. In rats showing dominant isolated spike activity in the secondary epileptic cortex, there was a deviation in somatosensory evoked potentials (SEPs). Rats showing isolated spikes and spike and wave complexes exhibited vibrissa tremors and head nodding. Rats showing only isolated spikes exhibited no abnormal behavior, but their convulsion thresholds to pentylenetetrazol were lowered. The results including ECoGs, SEPs, behavior and convulsion threshold were characterized with reference to the development of iron-induced epilepsy. The profiles of ECoG discharge activity and SEP configuration suggest that the process of iron-induced epilepsy consists of 3 stages.

Cyclic AMP accumulation in brain slices incubated with adenosine or the adenosine analogue 2-chloroadenosine was examined in different areas of rat cerebral cortex following a unilateral injection of FeCl2 solution into the sensorimotor cortex to induce chronic epileptic activity. In the epileptic cortex, cyclic AMP accumulation in cortical slices was elicited three- to 11-fold by adenosine. The elicitation by adenosine of cyclic AMP accumulation was markedly inhibited by the adenosine antagonist 8-phenyltheophylline. In anterior cortical areas of rats in which the appearance of electrographic isolated spikes was dominant either ipsilateral or contralateral to the injection site 8 days or more after the injection, the adenosine-elicited accumulation of cyclic AMP was greater on the side of dominant spike activity than on the other. In anterior cortical areas of rats showing nearly equal spike activity on the two sides 19 days or more after the injection, the cyclic AMP accumulation was greater on the side ipsilateral to the injection site than on the other. In anterior and posterior cortical areas of rats showing spike-and-wave complexes and isolated spikes 1 month or more after the injection, the cyclic AMP accumulation was greater on the ipsilateral side than on the other. Similar regional differences in the adenosine-elicited accumulation of cyclic AMP were detected in the presence of the adenosine uptake inhibitor dipyridamole or the phosphodiesterase inhibitor DL-4-(3-butoxy-4-methoxybenzyl)-2-imidazolidinone (Ro 20-1724). The cyclic AMP accumulation was elicited five- to 17-fold by 2-chloroadenosine, in which case the elicitation was markedly inhibited by 8-phenyltheophylline. Regional differences in the 2-chloroadenosine-elicited accumulation of cyclic AMP were similar to those with adenosine and were detected in the presence of Ro 20-1724 or adenosine deaminase. The regional differences which correlated with the electrographic discharge patterns were due mainly to persistent changes in cyclic AMP accumulation on the primary epileptic side. These results suggest that alterations in adenosine-sensitive cyclic AMP generation in the cortex are associated with the neurochemical process leading to chronic iron-induced epilepsy.

Cyclic AMP accumulation elicited by adenosine was investigated in cortical slices of rats following the application of a weak anodal direct current (anodal polarization) to the unilateral sensorimotor cortex. Anodal polarization with 3.0 microA for 30 min caused an increase in the adenosine-elicited accumulation of cyclic AMP in the polarized cortex, in which case the increase in the polarized cortical region was highlighted by repeated applications of the currents. Polarization with 0.3 microA for 30 min decreased the cyclic AMP accumulation, and polarization with 30.0 microA for 30 min had no effect. When applied for 3 h, the polarizing currents at all of the intensities tested decreased the cyclic AMP accumulation. The results indicate that anodal polarization has biphasic effects on adenosine-elicited accumulation of cyclic AMP in the cortex. Alterations in the cyclic AMP generation are suggested to form the neurochemical basis of central and behavioral activity induced by anodal polarization.

Rotational behavior was examined in rats after unilateral application of an anodal direct current (3 microA, 30 min) to the substantia nigra pars compacta (SNC). The current application increased contralateral rotation in two stages. One was during the period immediately after the current application, in which the increase in rotation declined within 30 min. The other period was long lasting, in which rotation increased 2 hr after the application and persisted for 24 hr or more. These results suggest that anodal direct currents induce transient and long-lasting activation of the SNC neurons, resulting in increases in rotational behavior.

Electrocorticograms were recorded from rats which were unilaterally injected with ferrous chloride solution into the sensorimotor cortex to induce chronic epileptic activity. All of the iron-injected rats showed isolated spikes near the injection site and in the contralateral cortex immediately after the injection. The injection produced 3 kinds of responses in the rats according to the frequency of the isolated spikes. Spike and wave complexes appeared bilaterally approximately 30 days or more after the injection in the rats in which the frequency of the isolated spikes was dominant on the side ipsilateral to the injection site or nearly equal on the two sides. These results suggest that there are at least 2 stages in the development of chronic iron-induced epilepsy.

Responsiveness of norepinephrine (NE)-sensitive cyclic AMP (cAMP)-generating systems was determined in slices from different areas of the rat cerebral cortex in which FeCl2 solution was injected unilaterally into the sensorimotor cortex to induce epileptic activity. In anterior cortical areas of rats in which the appearance of electrographic isolated spikes was dominant either ipsilaterally or contralaterally to the injection site 8-10 days after the injection, the cAMP accumulations elicited by NE and an NE-phentolamine combination were greater on the side of dominant spike activity than on the other. In anterior cortical areas of rats showing dominant spike activity on either side of the cortex 31-60 days after the injection, the cAMP accumulation elicited by NE was smaller on the dominant side than on the other. In anterior cortical areas of rats showing nearly equal spike activity on the two sides 31-60 days after the injection, the cAMP accumulations elicited by NE and an NE-phentolamine combination were greater on the side ipsilateral to the injection site than on the other. In anterior and posterior cortical areas of rats in which the appearance of spike and wave complexes, as well as isolated spikes, was detected 31-60 days after the injection, the cAMP accumulations elicited by NE and combinations of NE and phentolamine or propranolol were greater on the side ipsilateral to the injection site than on the other. The elicitation by an NE-propranolol combination, but not by an NE-phentolamine combination, of cAMP accumulation was almost completely inhibited by 8-phenyltheophylline.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of prolonged weak anodal direct current (DC) on the electrocorticogram (ECoG) were investigated in awake rabbits. When the current (20-40 microA) was applied to the motor region of the cerebral cortex, seizure activity in the ECoG appeared from the frontal cortex. Repeated application of the DC decreased the threshold current for producing the seizure activity. Diazepam significantly elevated the threshold of the seizure activity. In contrast to the marked changes in the ECoG, no behavioral changes were observed during or after the application of weak anodal DC. The changes in the ECoG are discussed in relation to the intensity and duration of the DC.

Ferrous chloride solution was injected unilaterally into the sensorimotor cortex of rats to induce a chronic epileptic focus. Accumulation of cyclic AMP elicited by depolarizing agents was determined in slices from different cortical areas of rats 30-60 days after the injection. In anterior cortical areas which include the sensorimotor cortex, the cyclic AMP accumulation elicited by ouabain or a high concentration of potassium ion was greater in electrographic spike activity on the dominant side than on the other. In posterior cortical areas, no difference in cyclic AMP accumulation was detected. The regional difference in the depolarization-elicited accumulation of cyclic AMP is discussed with regard to the process of epileptic focus.

The effect of L-glutamate of cyclic AMP levels in different areas of rat cerebral cortex was examined during the development of an iron-induced focus in the left sensorimotor cortex. The addition of L-glutamate resulted in increased cyclic AMP levels in slices from the quarter of cortex with the iron-induced focus. The levels lowered in slices from the quarter of cortex most remote from the focus. Thus L-glutamate showed stimulatory and inhibitory effects on the accumulation of cyclic AMP.

An epileptic focus not resulting in generalized convulsions was induced by a microinjection of ferric chloride solution into the left anterior cortex of rats. The formation of the epileptic focus was confirmed by the appearance of bilateral spike and slow wave complexes as well as focal isolated spikes in electrocorticograms (ECoGs). The effect of glutamate on cyclic AMP accumulation was examined in incubated slices prepared from four quadrants of the epileptic cortex. In animals showing isolated spikes 8 to 10 days after the microinjection, the effect of glutamate on cyclic AMP accumulation was stimulatory. It was greatest in the left anterior quadrant which included the injection site, but only slight in the left and right posterior quadrants. In animals showing spike and slow wave complexes 30 to 60 days after the microinjection, the stimulatory effect of glutamate was also most pronounced in the left anterior quadrant. In the right anterior and the left posterior quadrants glutamate had almost no effect, while in the right posterior quadrant, glutamate was inhibitory.

Accumulation of cyclic AMP elicited by glutamate was examined in slices from different cortical areas of rats 30 to 60 days after ferrous chloride solution was injected into the left sensorimotor cortex to induce an epileptic focus. In the anterior cortex of rats showing dominant electrographic spike activity on either side of the cortex, the glutamate-elicited accumulation of cyclic AMP was greater on the dominant side than on the other. In the anterior cortex of rats showing nearly equal spike activity on either side, the accumulation was greater on the side ipsilateral to the injection site than on the other. Different inhibitory effects of 3-isobutyl-1-methylxanthine on the elicitation of cyclic AMP accumulation by glutamate was observed in relation to the patterns of spike activity.

A chronic epileptic focus was induced by a microinjection of ferric chloride solution into the sensorimotor cortex of rats. Two types of somatosensory evoked potentials (SEPs) were recorded from the cortex near the injection site. In animals showing an initial positive-negative biphasic SEP, spikes appeared in electrocorticograms (ECoGs) more frequently on the side ipsilateral to the injection site than on the contralateral side, whereas in animals showing an initial negative monophasic SEP, spikes appeared more frequently on the contralateral side.

The appearance of epileptiform discharges in electrocorticograms was induced by a unilateral injection of CoCl2 solution into the sensorimotor cortex of rats. Accumulation of cyclic AMP elicited by ouabain or a high concentration of potassium ions was determined in slices from different cortical areas of rats 9 or 10 days after the injection. In the anterior cortex, the depolarization-elicited accumulation of cyclic AMP was significantly higher in the cortical area ipsilateral to the injection site than in the contralateral cortical area. In the posterior cortex, a similar but not significant difference in the accumulation of cyclic AMP was noted.

Cyclic AMP accumulation in response to norepinephrine was examined in slices of rat cerebral cortex the day after a unilateral application of anodal current of 0.3, 3.0 or 30 microA to the surface of the sensorimotor cortex. When 3.0 microA was applied, the norepinephrine-elicited accumulation of cyclic AMP was greater in the cortical area including the application point than in either the contralateral cortical area or non-polarized control cortical slices. The changes in cyclic AMP accumulation are discussed in relation to the role of the direct current in producing functional changes in the cortex.

Responsiveness of norepinephrine-sensitive cyclic AMP-generating systems was examined in slices of different cortical areas of rats showing electrographic spike and wave complexes after unilateral injection of ferrous chloride solution into the sensorimotor cortex. Accumulation of cyclic AMP elicited by norepinephrine was greater on the injection side of the cortex than on the other. Similar lateral differences were detected in cyclic AMP levels antagonized by phentolamine or propranolol, in which 8-phenyltheophylline almost completely inhibited the elicitation of cyclic AMP accumulation by a norepinephrine-propranolol combination but not by a norepinephrine-phentolamine combination. These results suggest that alterations in cyclic AMP generation through the beta-adrenoceptor-coupled adenylate cyclase system and through alpha-adrenergic activation of the adenosine receptor-coupled adenylate cyclase system are closely related to the electrographic activity of iron-induced epilepsy.

Noradrenaline-elicited accumulation of cyclic AMP and effects of an alpha-, beta-adrenoceptor, or adenosine receptor antagonist on the accumulation were examined in slices of different areas of rat cerebral cortex in which ferrous chloride solution was injected unilaterally into the sensorimotor cortex to induce epileptiform activity. The cyclic AMP accumulation was altered regionally in relation to both lateral dominance of electrographic isolated spike activity and variance of the epileptic process. Involvement of a beta-adrenergic, and possibly alpha-adrenergic, mechanism in the alterations in the cyclic AMP accumulation was indicated.

A microinjection of ferric chloride solution into the left frontal cortex of rats induced epileptic discharges which were recorded by electrocorticography. In animals having such electrographic seizure activity 30 to 60 days after the injection, the accumulation of cyclic AMP elicited by norepinephrine was examined in slices from four cortical regions. The accumulation was significantly greater in the left anterior area, into which region the ferric chloride solution was injected, than in the right anterior area. There was also a tendency for greater norepinephrine-elicited accumulation of cyclic AMP to occur in the left posterior area than in the right posterior area.

A chronic epileptic focus not resulting in generalized convulsions was induced by a microinjection of FeCl3 solution into the left anterior cortex of rats. Cyclic AMP accumulation in response to adenosine was examined in incubated slices from the cerebral cortex of animals that showed bilateral spike and slow wave complex in an electrocorticogram (ECoG) 30 to 60 days after the microinjection. Cyclic AMP accumulation after incubation with adenosine was most marked in slices from the left anterior quadrant of the cortex including a FeCl3-injected site. A medium response was observed in both the left posterior and the right anterior quadrants, but little or no response in the right posterior quadrant of the cortex.