The ontogeny of excitatory amino acid receptors in rat forebrain--I. N-methyl-D-aspartate and quisqualate receptors

Mesial temporal sclerosis: pathogenesis and significance

Mesial temporal sclerosis (MTS) is a common pathologic finding in patients with temporal lobe epilepsy. Rarely MTS can be detected in children during the first decade of life, but is not commonly found until adolescence. Although the etiology of MTS remains controversial, there is now a considerable amount of evidence demonstrating that MTS is both a result and a cause of seizures. Clinical studies suggest that prolonged seizures or complicated febrile seizures may result in MTS. A variety of epileptogenic agents administered to adult animals have resulted in MTS and spontaneous recurrent seizures. The mechanism of the lesions is due to excessive excitability secondary to release of excitatory amino acids, primarily glutamate. Glutamate, acting at a number of subreceptors on the postsynaptic membrane, leads to prolonged depolarization of neurons and results in the entry of cytotoxic amounts of calcium. Interestingly, the same agents that produce MTS in adult animals do not produce MTS in immature animals. Clinical and experimental evidence suggests that although prolonged seizures or complicated febrile seizures can place a child at risk for MTS, a period of time is required for the lesions to develop fully.

Expression and characterization of the alpha 2 subunit of the alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA)-selective glutamate receptor channel in a baculovirus system

Using a baculovirus expression vector system, the alpha 2 subunit of the mouse alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA)-selective glutamate receptor (GluR) channel was expressed in Spodoptera frugiperda insect cells. Immunoblotting using the antibody made to the synthetic peptide corresponding to the C-terminus of GluR alpha 2 and [35S]methionine/[35S]cysteine metabolic radiolabeling revealed the major 102-kDa and the minor 98-kDa protein bands. Metabolic radiolabeling with tunicamycin suggested that the two bands correspond to glycosylated and unglycosylated forms, respectively. The recombinant GluR alpha 2 proteins expressed in insect cells were also identified by immunofluorescence staining. The results of [3H]AMPA binding assay using whole cells suggested that, in infected Sf21 cells, binding sites of the GluR alpha 2 proteins were possibly located on the extracellular side. Scatchard analysis of AMPA binding showed the following parameters: Kd = 16 nM, Bmax = 1.9 x 10(5) binding sites per cell or 1 pmol/mg protein in the total particulate fraction. The ligand binding characteristics of the receptors expressed in insect cells were examined. From the effect of various agonists on [3H]AMPA binding of the receptors expressed in insect cells, the rank order potency of agonists was quisqualate > AMPA > L-glutamate > kainate. Thus, the baculovirus-insect cell expression system provides high-efficiency expression of the receptor sufficient to permit structural and functional analyses.

Long-term behavioral deficits following pilocarpine seizures in immature rats

The effect of seizures on subsequent long-term behavior was studied in immature rats. A similar severity of seizures were induced in 20-day old rats (P20) and 45-day old rats (P45) by intraperitoneal injections of pilocarpine at doses of 200 mg/kg and 380 mg/kg, respectively. Immediately after injection of pilocarpine, prolonged seizures with electroencephalographic ictal discharges were observed in both groups of rats. These seizures were followed by seemingly complete neurological recovery. In rats that received pilocarpine at P45 spontaneous recurrent seizures appeared after 4-10 days and persisted until completion of the study at P100. Behavioral tests performed when the rats were fully mature demonstrated that they were more aggressive when handled, more active in open field, and had deficits in learning platform position in the water maze as compared to controls. Furthermore, flurothyl seizure latency was significantly lower in pilocarpine-treated P45 rats than controls. Histology examination showed gross cell loss in the CA3 subfield of the hippocampus in four out of six pilocarpine-treated rats while no cell loss was found in control rats. Rats that received pilocarpine at P20, despite having more severe seizures than the P45 rats, had no histological lesions, did not develop spontaneous recurrent seizures, and had no significant difference in the flurothyl seizure latency test when compared to their controls. While there was no difference between the control and pilocarpine-treated rats in the handling and open field test, P20 rats receiving pilocarpine were slower in learning platform position in the water maze than the controls. Rats receiving pilocarpine at P45 performed significantly more poorly than rats treated at P20 in the water maze. These results suggest that prolonged seizures in immature rats can cause long-term behavioral deficits. However, the severity and nature of these deficits are highly age dependent.

Death of neurons in the neonatal rodent and primate globus pallidus occurs by a mechanism of apoptosis

We have examined the developing rat, mouse and marmoset globus pallidus for evidence of cells dying by a process of "naturally occurring" or programmed cell death. We have demonstrated that cells in the developing mammalian globus pallidus die by a process of apoptosis and that by day 7 after birth many of the apoptotic cells possess a neuronal phenotype. Light microscopic and ultrastructural evidence of apoptotic cell death included cell shrinkage, blebbing of the extracellular membrane and condensation of the nuclear chromatin. Additionally we used an in situ nick translation method to assess the integrity of the DNA within the dying cells. This revealed that cells with the morphological characteristics of apoptosis also possessed fragmented DNA typical of cells undergoing Type 1 programmed or apoptotic cell death. The lack of lysosomal enzyme activity within the dying cells and the frequent observations of phagocytosis by neighbouring cells also suggest that the form of programmed cell death is apoptosis and not Type 2 autophagic degeneration. We found no evidence for cells dying by Type 3 non-lysosomal degeneration since all dying cells examined under the electron microscope possessed intact intracellular organelles and cell membranes. We developed a sensitive silver stain which detected balls of condensed chromatin within the apoptotic cells. This enabled identification of apoptotic cells in the developing globus pallidus at low magnification and so allowed us to map the numbers and distribution of dying cells with time. The incidence of apoptotic cells in the neonatal globus pallidus was greatest at birth and then declined such that few cells were detected at one week and none was seen in the adult rat. Although the loss of large numbers of cells in the developing nervous system is a well documented phenomenon, there are only a limited number of reports of the mechanism by which neuronal cells die, and few of these are in the developing mammalian brain. There are at least four different morphological categories of neuronal cell death which are discriminated on morphological and biochemical criteria. Our analysis suggests that apoptotic or Type 1 cell death is the major form of programmed cell death occurring in the mammalian globus pallidus in the first week of life. This report also describes the use of two methods for the ready identification of apoptotic cells at the light microscope level. Because these methods are suitable for use on tissue sections they provide a means to assess the incidence of apoptotic cell death, in parallel with other analyses of the expression of gene products which control cell fate.

The development of epilepsy in the paediatric brain

The immature central nervous system (CNS) is more susceptible to the development of seizures than its adult counterpart. Developmental studies of experimental seizures have suggested that young animals have unique behavioural seizure patterns, including the presence of bilateral, though asymmetric, convulsions. There are differences in the mechanisms responsible for the generation of seizures, propagation patterns and seizure arrest and recurrences. These differences are due to local factors as well as factors that affect neural systems consisting of long neuronal circuits. The substantia nigra, a site involved in the control of seizures, will be used as an example to demonstrate how evolving neurobiological processes modulates the suppression or exacerbation of seizures with age. Evidence will also be presented indicating that early in life, seizures may not produce hippocampal damage. An understanding of the age-related differences is important for the development of rational approaches to treating seizures and their consequences.

NMDA receptor responses in adult hippocampal CA1 region after neonatal treatment with MK-801: comparison with NMDA receptor responses in the immature rat

Neonatal MK-801 treatment from postnatal day 8-19 leads to long-term effects on brain function, suggesting that exposure to this drug leads to the development of a brain with immature network properties. One aspect of this hypothesis, that the NMDA receptors preserve their immature state after the treatment, has been tested by measuring the potency of the competitive antagonist D-AP5 in hippocampal slices. We have previously shown that an increased potency to D-AP5 is a characteristic property of NMDA receptors during early life. In the present study we measured field potentials in the CA1 region of rat hippocampal slices evoked by iontophoretic NMDA application in the Schaffer-commissural synaptic fields. Agonist dose-response curves were constructed, followed by bath applications of increasing concentrations of the antagonist D-AP5. The maximum NMDA evoked field response was the same in slices of mature control (PND70-90; 18.9 +/- 1.2 mV) and MK-801 treated rats (PND70-90; 19.3 +/- 0.9 mV), but significantly larger in immature slices (PND10-16; 24.0 +/- 0.6 mV). The sensitivity to NMDA in hippocampal slices from each group was estimated by quantifying the ionotophoretic ejection current (= dose) which evoked 50% of the maximum field response (EC50). A significantly higher sensitivity to NMDA was found in hippocampal slices obtained from MK-801-treated rats (EC50 = 3.6 +/- 0.2 nA) than in slices from control (EC50 = 6.1 +/- 0.7 nA) or immature (EC50 = 5.9 +/- 0.5 nA) animals.(ABSTRACT TRUNCATED AT 250 WORDS)

The glutamate uptake inhibitor L-trans-2,4-pyrrolidine dicarboxylate is neurotoxic in neonatal rat brain

High-affinity glutamate uptake (HAGU) transporters rapidly remove released glutamate from the synaptic cleft. If HAGU is suppressed, neurotoxic concentrations of excitatory amino acids may accumulate. To seek further evidence in support of the neurotoxicity of endogenous glutamate in the developing brain, we assessed the neurotoxicity of the selective HAGU inhibitor L-trans-2,4-pyrrolidine dicarboxylate (L-PDC) in postnatal day 7 (PND 7) rats. The hippocampus of PND 7 rats is susceptible to EAA agonist-mediated injury; features of injury include atrophy and neuronal loss. Since HAGU is energy-dependent, we hypothesized that moderate hypoxia would increase L-PDC-mediated injury by further suppressing HAGU. L-PDC was stereotaxically injected into dorsolateral hippocampus of PND 7 rats (568 nmol, n = 20). Prior to return to the dam, rats were divided into two groups, one of which was subjected to moderate hypoxia (3 h, FiO2 = 0.08) (n = 11; 2 died acutely). On PND 12, hippocampal neuropathology was assessed by a blinded observer using a five-point scale and also by measuring hippocampal cross-sectional areas with computerized image analysis. Three brains were excluded from analysis, since markedly asymmetric tissue sectioning precluded valid side-to-side comparison of hippocampal areas. Injection of L-PDC alone elicited focal pyramidal cell loss (6/7); in the (L-PDC + hypoxia) group, injury was significantly increased (median scores: L-PDC = 2; [L-PDC + hypoxia] = 3.5; p < 0.005). Hippocampal atrophy was noted only after L-PDC + hypoxia (4/8) (percent right-left difference in mean hippocampal area [+/- SE]: L-PDC = 2.5% [+/- 2.6]; [L-PDC + hypoxia] = 8.9% [+/- 3.2]; p < 0.02). In tissue from PND 7 rats, L-PDC (10 microM) inhibited hippocampal synaptosomal HAGU by > 85%; at the same concentration, L-PDC did not displace [3H]glutamate from NMDA- or AMPA-sensitive hippocampal binding sites. These results support the hypothesis that increased synaptic accumulation of endogenous excitatory amino acid neurotransmitters may produce hippocampal injury in perinatal rodents.

Experimental models of epilepsy in young animals

Seizures occur more frequently early in life. Some of these early seizures may eventually become epilepsy. Others are reactive seizures due to excessive environmental stimuli that, in any other age group, might not have elicited a similar response. To understand the developmental aspects of seizures and epilepsy in humans, it is important to study these processes in animals of equivalent ages. In this paper, we describe several animal models of developmental seizures, including their electroclinical manifestations and their validity in respect to human epileptic syndromes. There are several factors that may account for the increased seizure susceptibility of the immature brain, including the delayed development of effective systems or synaptic networks that are involved in the suppression of seizures. A better insight of the basic pathophysiology of seizures as a function of age in animal models will lead to the development of new therapeutic approaches for the treatment of age-specific epileptic disorders in humans.

Postnatal ontogeny of GABAB binding in rat brain

The postnatal development of GABAB binding sites in rat brain was studied by quantitative receptor autoradiography using [3H]GABA under selective conditions. Binding levels peak at regionally specific times during the first three weeks of life and then decline to adult levels. GABAB binding peaked in the globus pallidus, vestibular and spinal trigeminal nuclei, and the CA3 region of the hippocampus at postnatal day 3; in the striatum, nucleus accumbens, inferior olive, septum, dentate gyrus and CA1 region of the hippocampus at postnatal day 7; in the neocortex and thalamus at postnatal day 14; and in the medial geniculate at postnatal day 21. Following these regionally specific peaks, binding decreased to postnatal day 28 levels. Further significant decreases in binding were observed in all regions examined between postnatal day 28 and adulthood. Comparisons of binding site pharmacology reveal equipotent displacement of GABAB binding by several competitive agonists and antagonists in postnatal day 7 and adult rat brain, indicating that immature and adult binding sites have similar pharmacological properties with regard to these compounds. The GABAB receptor antagonist CGP 54626A, however, inhibited binding more potently in the postnatal day 7 thalamus and neocortex than in these areas in the adult brain. The guanyl nucleotide analogue guanosine 5'-O-(3-thiotriphasphate) inhibited GABAB binding extensively in both postnatal day 7 and adult brain. The non-competitive antagonist zinc also inhibited GABAB binding at both ages and was more potent in postnatal day 7 brain than in adult brain. Saturation analyses reveal two binding sites with similar affinities in both immature and adult rat brain, indicating that postnatal modulation of GABAB binding reflects changes in binding site density rather than modulation of binding site affinity. While immature GABAB binding sites share most pharmacological characteristics with adult binding sites and appear to be coupled to G-proteins at an early age, their interactions with zinc and CGP 54626A suggest that GABAB binding sites in immature brain may have a distinct pharmacological profile. Our data suggest significant regional and pharmacological changes in GABAB binding during development. The implications of these findings are discussed with regards to a possible role of GABAB receptors in the development of the central nervous system.

Developmental changes of ketamine action against epileptic afterdischarges induced by hippocampal stimulation in rats

Action of ketamine (5-40 mg/kg) was tested against electrically induced hippocampal afterdischarges (four stimulations in one session; 8 Hz, 15 s) in rats 7, 12, 18, 25 and 90 days old. In control sessions, there was either stable afterdischarge (AD) duration and wet dog shakes (WDS) number or there was an increase in ADs' duration with repeated stimulations. Ketamine had dose-dependent and age-dependent effects. In 7-18-day-old rats, ketamine suppressed better WDS number than AD duration, with nearly absent action on AD duration in 18-day-old animals. Ketamine was equipotent for both phenomena in 25-day-old rats and, in contrast, it decreased more AD duration than WDS number in 90-day-old rats. The data suggest a differentiation induced by ketamine in the expression of motor and electrographic phenomena of the experimental seizures.

Induction of HSP70 mRNA and HSP70 protein in the hippocampus of the developing gerbil following transient forebrain ischemia

The effects of a 20-min transient episode of forebrain ischemia on the induction of HSP70 mRNA and protein, and the histopathological outcome in the hippocampus of the developing gerbil, were examined at postnatal days (P) 7, 15, 21 and 30 and in adulthood. 4 days after the ischemic episode, P7 gerbils did not show apparent histological abnormalities; however, from P15 onwards, ischemia resulted in necrosis in selected areas of the hippocampus. At P15 and P21, necrosis was observed in the base of the granular cell layer of the dentate gyrus and in the CA3 pyramidal cell layer, whereas at P30 and adult necrosis was apparent in the CA1 pyramidal cell layer. HSP70 mRNA induction was not found in ischemic P7 and P15 gerbils while, from P21 onwards, induction was observed in the dentate gyrus and CA1 pyramidal cell layer. In addition, at P30 and adult, HSP70 mRNA expression was also seen in CA3 pyramidal cell layer. Induction of HSP70 immunoreactivity was not seen at P7 but, from P15 onwards, ischemia induced HSP70 immunoreactivity in different areas: in dentate gyrus granular and molecular layers, from P15 onwards; in CA1 pyramidal cell layer, from P21 onwards; and in CA3 pyramidal cell layer, from P30 onwards. Results show selective age-dependent patterns of vulnerability to ischemia in the gerbil hippocampus which, overall, were not well-correlated to the corresponding HSP70 mRNA and protein induction patterns.

Distinct laminar differences in the distribution of excitatory amino acid receptors in adult ferret primary visual cortex

In order to explore the relative contributions of the different ionotropic excitatory amino acid receptor subtypes to signalling in primary visual cortex, we have mapped their distributions in area 17 of adult ferret cerebral cortex by quantitative in vitro autoradiography. D,L-alpha-amino-3-hydroxy-5-methoxy-4-isoxazole propionate (AMPA) and kainate receptors, gating fast, Na(+)-permeable channels, were localized with [3H]dizocilpine maleate ([3H]MK-801). All three radioligands bound to single sites, with KDs of 414 nM [3H]AMPA and [3H]kainate, respectively. Slower-acting N-methyl-D-aspartate receptors, which gate the influx of Ca2+ as well as Na+, were localized with ([3H]AMPA), 78 nM ([3H]kainate) and 16 nM ([3H]MK-801), and each receptor subtype displayed a different laminar distribution pattern within area 17. AMPA receptors were concentrated in superficial layers, with intermediate densities in deep layers and lowest levels in layer IV. Kainate receptor levels were high in layers V and VI and low in all other layers. N-methyl-D-aspartate receptors were more homogeneously distributed than AMPA or kainate receptors, but were expressed at highest levels in layers I and IV and lowest levels in layers V and VI. The binding site densities found in the layers containing most receptors were Bmax = 2812 fmol/mg for [3H]AMPA, Bmax = 626 fmol/mg for [3H]MK-801 maleate and Bmax = 278 fmol/mg for [3H]kainate. Thus, while AMPA receptors were predominant and kainate receptors least abundant in all cortical layers, a complementary relative distribution of excitatory amino acid receptors was apparent, with AMPA receptor density highest in superficial layers, kainate receptor density highest in inferior layers and N-methyl-D-aspartate receptor density highest in the middle granular layer, as well as in layer I. The results indicate that although AMPA receptors are principally involved in excitatory signalling in adult ferret primary visual cortex, kainate receptors in layers V and VI and N-methyl-D-aspartate receptors in layers I and IV may have particularly important roles in mediating synaptic transmission.

Persistent physiological effects caused by a single pentylenetetrazol induced seizure in neonatal rats

A single seizure was induced by pentylenetetrazol (PTZ; 150 mg/kg i.p.) in 1-day-old and 21-day-old rats; control littermates were given saline (i.p.) injections. In vitro recordings were made in hippocampal slices derived from adult (2-3.5-month-old) rats. The population responses in CA1, CA3 and dentate gyrus (DG) were recorded following double-pulse stimulation of Schaffer collateral (CA1 stratum radiatum, for CA1 and CA3 recordings) and perforant path (for DG recordings). Paired-pulse stimuli at an interpulse interval (IPI) of 10-200 ms and intensity of 1.5, 2 or 4 times the stimulus threshold were used. PTZ given on day 1 resulted in a highly significant increase in the paired-pulse facilitation (PPF) of the population EPSP, but not of the population spike, in CA1 at all stimulus intensities. In the DG, PPF of both the population EPSP and population spike was found at 1.5 x threshold intensity. PTZ given on day 21 decreased PPF of the population EPSP and spike in CA1 and had no significant effect in the DG. No significant difference was found in CA3 responses after seizures on day 1 or day 21. The slices from seized and control animals were not different in their stimulus thresholds or response to a single pulse. It is concluded that a single neonatal PTZ-induced seizure had long-lasting physiological consequences which depend on the age of seizure.(ABSTRACT TRUNCATED AT 250 WORDS)

Developmental alterations in NMDA receptor-mediated [Ca2+]i elevation in substantia gelatinosa neurons of neonatal rat spinal cord

Using spinal cord slices prepared from neonatal rats, the intracellular free Ca2+ concentration ([Ca2+]i) in neurons located in the dorsal horn substantia gelatinosa (SG) was measured with microscopic fluorometry by loading fura 2-AM into neurons. Developmental alterations in the elevation of [Ca2+]i elicited by the glutamate analogs, NMDA and AMPA, were investigated from postnatal day (PNDs) 1 to 17. During the 1st week of postnatal life, when neuronal maturation of the SG is known to take place, the NMDA response remained large or even slightly increased. It subsequently showed a gradual decline. This pattern of postnatal changes is consistent with previously reported autoradiographic studies on NMDA-binding sites. The affinity of receptors for NMDA was found to decrease constantly during the period examined. The AMPA response and resting [Ca2+]i showed no significant developmental changes. Neonatal treatment with capsaicin, which has been shown to degenerate fine primary afferent fibers terminating in the SG, delayed the developmental decline in the NMDA-induced [Ca2+]i response. It is suggested that the number and the molecular properties of NMDA receptors expressed in the SG change during early postnatal neuronal maturation. The temporal coincidence between postnatal alteration in NMDA-induced [Ca2+]i elevation and neuronal maturation of the SG may indicate that intracellular Ca2+ regulated by NMDA receptor activation is related to postnatal neuronal maturation. Activation of fine primary afferent fibers may contribute to the observed developmental alterations in the NMDA response of SG neurons.

Quisqualic acid-induced seizures during development: a behavioral and EEG study

Quisqualic acid (QA) is an excitatory amino acid analogue that binds to the glutamate ionotropic receptor subclass AMPA (alpha-amino-3 hydroxy-5 methyl-4 isoxazol propionic acid) and metabotropic receptor phospholipase C. To study its epileptogenic properties, we administered QA through an intraventricular cannula to 23-, 41-, and 60-day-old rats with recording electrodes implanted in amygdala, hippocampus, and neocortex. The frequency power spectra of the recorded EEG was computed by fast fourier transform (FFT), and coherence between anatomic sites was computed. Seizures occurred in all animals receiving QA. The behavioral manifestations of the seizures varied as a function of age, with younger rats demonstrating rigidity and immobility followed by circling activity and intermittent forelimb clonus and 60-day-old animals exhibiting severe, wild running followed by generalized clonus. Ictal electrical discharges occurred in all animals. Neocortical ictal discharges occurred more prominently in the younger animals, and amygdala ictal discharges were more prominent in the older animals. Marked increases in spectral power occurred during the seizures in all anatomic structures and at all frequencies. Our results demonstrate that the clinical manifestations of QA seizures vary during development; results of the neurophysiologic studies suggested that neocortex may play an important role in genesis of QA seizures in immature brain.

Regulation of D-aspartate release by glutamate and GABA receptors in cerebral cortical slices from developing and ageing mice

The basal release of D-[3H]aspartate, an unmetabolized analogue of glutamate, from cerebral cortical slices remained at the same level from three-day-old to 24-month-old mice, but the response to K+ stimulation (50 mM) was smaller in young than in adult or aged mice. Kainate, N-methyl-D-aspartate and quisqualate (0.1 mM) stimulated the basal release of D-aspartate in the cerebral cortex of seven-day-old mice, the effects of kainate and N-methyl-D-aspartate being reduced by their antagonists 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) and dizocilpine maleate, respectively, indicating that in the immature cerebral cortex the kainate and N-methyl-D-aspartate types of the glutamate receptor are involved in the basal release. The K(+)-stimulated release was not affected by glutamate agonists in developing mice, though they markedly attenuated the evoked release in adults. The inhibitory amino acids GABA, taurine and glycine depressed the K(+)-stimulated release only in the adult cerebral cortex. The action of GABA was abolished by bicuculline, demonstrating the involvement of presynaptic GABAA receptors. The glycine effect was strychnine-insensitive, characteristic of the glycine modulatory site in the N-methyl-D-aspartate receptor. This kind of regulation by both kainate and N-methyl-D-aspartate receptors could be of physiological significance, particularly in the immature cerebral cortex.

The susceptibility of CA1 pyramidal cells to cerebral ischemia is maintained after neonatal, lesion-induced reorganization of the hippocampal circuitry

Acute lesions of hippocampal pathways have been shown previously to ameliorate CA1 pyramidal cell loss after subsequent transient cerebral ischemia. In this study, we examined the effect of chronic neonatal lesion with reorganization of hippocampal circuitry on adult postischemic neuron loss in the hippocampus. Newborn rats were subjected to unilateral knife-cut lesions at various positions along the trisynaptic entorhino-dentato-hippocampal pathway. Seven months later, the rats were subjected to transient cerebral ischemia using the four-vessel occlusion technique. At the time of killing 4 days later, a Nissl stain was used to demonstrate neuronal degeneration, while connective reorganization resulting from the neonatal lesions was monitored by Timm staining. In one group of rats, neonatal lesions had caused severe depletion of entorhinal projections to the septodorsal fascia dentata and hippocampus (CA1 and CA3), without any direct damage to the dorsal hippocampus itself. Another group had extensive damage of the dorsal CA3, with removal of the Schaffer collaterals from these levels to CA1, and variable damage to the entorhinal afferents. In both groups, the extent and pattern of ischemia-induced degeneration of CA1 pyramidal cells were the same on the lesioned and nonlesioned sides of the brain, demonstrating that neonatal lesions and the subsequent connective reorganization did not have a sparing effect. Seen in relationship to previous observations in adult rats of the neuroprotective actions of acute, preischemic lesions of the trisynaptic hippocampal pathway, it is concluded that CA1 pyramidal cell loss requires the presence of intact excitatory afferents rather than an intact hippocampal circuitry.

Postnatal development of nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d) positive neurons in rat prefrontal cortex

First nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d)-positive perikarya in rat prefrontal cortex (PFC) are present at birth. On postnatal day (P) 1, there is an increase of NADPH-d-positive neurons in all developing layers of PFC. From P1 to P7, a further increase in the overall number of positive neurons is observed. First laminar and area shifts are noted on P21, while morphological maturation of NADPH-d-positive neurons is finished around P30. In conclusion, the postnatal development of NADPH-d neurons in PFC is in concordance with other developmental events in rat cerebral cortex.

Regional profile of developmental changes in the sensitivity of the N-methyl-D-aspartate receptor to polyamines

The NMDA receptor exhibits increased sensitivity to stimulation during early development compared with the adult. In this study, we examined modulation of the NMDA receptor by polyamines during development to see if it correlates with differences in the functional responsiveness of the NMDA receptor. [3H]MK-801 binding was measured in discrete brain regions in the presence and absence of polyamines in 3-, 7-, 15-, 25-, and 60-day-old Sprague-Dawley rats. [3H]MK-801 binding increased between postnatal days 3 and 15, with adult levels of binding being reached between days 15 and 25. Spermidine (75 microM) caused maximal stimulation of [3H]MK-801 binding during early development, ranging from 250% in the thalamus to 450% in the caudate putamen at postnatal day 3. This effect gradually declined to levels seen in the adult by postnatal days 15-25. During all developmental stages, the stimulation seen was greater in the caudate putamen compared with the hippocampus. Diethylenetriamine (1 mM) exhibited similar developmental and regional heterogeneity in its effects on [3H]MK-801 binding, producing substantial stimulation of binding in the neonate, but not in the adult. The EC50 and Emax values for the stimulatory effect of spermidine were significantly higher at day 7 compared with the adult. Unlike spermidine and diethylenetriamine, there was no regional variation in the effects of the putative "polyamine site" inverse agonist 1,10-diaminodecane at any age and only a slightly attenuated inhibition at postnatal day 3 compared with the adult.(ABSTRACT TRUNCATED AT 250 WORDS)

Postnatal development of NMDA, AMPA, and kainate receptors in individual layers of rat visual cortex and the effect of monocular deprivation

The postnatal development of the ligand binding to N-methyl-D-aspartate (NMDA), alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA), and kainate receptor sites was studied in individual layers of rat visual cortex with [3H]MK-801, [3H]CNQX and [3H]kainate, respectively. The studies were performed by quantitative receptor autoradiography in the different visual cortical layers from normally raised rats and from monocularly deprived animals. In normally raised rats, in all visual cortical layers, [3H]MK-801 and [3H]CNQX binding increased significantly from birth to around postnatal day 20, at which age already the adult values are reached. In contrast, the increase in [3H]kainate binding from day 1 to day 15 is followed by a significant decrease in binding sites up to day 25; at this age the adult binding level is nearly attained. Monocular deprivation, by unilateral eyelid suture at the age of 11 days onwards, leads to a transient decrease in [3H]CNQX binding in all visual cortical layers, whereas [3H]kainate binding results to a permanent decrease in AMPA receptor sites in cortical layers II to VI in both sides of the cortex. In contrast, only long-term monocular deprivation until the age of 90 days resulted in decreased [3H]MK-801 binding levels as compared to age-matched controls. The data suggest that the laminar development of glutamate receptor subtypes is differentially affected by visual experience during early brain maturation.

The effects of perinatal anoxia or hypoxia on hippocampal kindling development in rats

The effects of anoxia and hypoxia (3% oxygen) at 10-12 post days of age on the development of ventral hippocampal kindling and its transfer to the contralateral ventral hippocampus were studied in adult male Sprague-Dawley rats. During oxygen deprivation, the heart rate decreased to 15% of the prehypoxic value in the animals exposed to anoxia and 40% in those exposed to hypoxia. As is observed in asphyxia of human newborns, our study included both ischemia and hypoxia. The susceptibility to kindling, which was measured by kindling rate, afterdischarge threshold, generalized seizure threshold, and total afterdischarge duration to stage 5, had a tendency to be enhanced in rats exposed to hypoxia compared with controls. The facilitating effects on primary site kindling were enhanced in the animals exposed to hypoxia compared with those exposed to anoxia. Transfer, which was indicated by kindling rate and afterdischarge threshold, was also slightly facilitated in the rats exposed to anoxia or hypoxia in the perinatal period. These results reveal that perinatal oxygen deficiency may not be sufficient to lead to the development of temporal lobe epilepsy. However, it is possible that perinatal hypoxia results in some pathophysiological change in the brain which leads to greater seizure susceptibility in adulthood.

Unilateral naris closure and olfactory system development

In most animals there is bilateral access of odorants to the olfactory sensory epithelium. Air enters the nose through two external nares and passes back through the nasal cavity, which is divided down the midline by a cartilaginous nasal septum. The olfactory mucosa, a sheet of ciliated bipolar receptor cells, is found in the caudal two thirds of the nasal cavity. Axons from the sensory cells project to an ipsilateral extension of the telencephalon known as the olfactory bulb. If a single external naris of a rat pup is surgically closed (usually via brief cauterization) on the day after the day of birth (P1) and the subject is examined on P30, the size of the ipsilateral olfactory bulb is reduced by approximately 25%. The large reduction in size, coupled with the clear lamination and other features of the olfactory system, indicates that the manipulation is an ideal preparation for examining the regulation of early growth. We know that both olfactory bulbs are of equal size at the time of occlusion, but that 30 days later there is a large discrepancy. What series of events produces the changes? The present paper outlines what is known about the anatomical, biochemical and physiological changes introduced by naris occlusion in order to lay a framework for further work.

Developmental regulation of mRNAs encoding rat brain kainate/AMPA receptors: a northern analysis study

Functionally diverse kainate/alpha-amino-3-hydroxy-5-methyl-4- isoxazolepropionic acid (AMPA) receptors are generated by assembly of glutamate receptor (GluR)1, 2, and 3 subunits into homomeric and heteromeric channels. We examined GluR1, 2, and 3 gene expression in embryonic, neonatal, and adult rat brain by northern analysis under conditions of high stringency. In the adult, hybridization to a GluR1 riboprobe revealed the presence of an abundant RNA species, 5.2 kb in size, and minor bands of 3.2 and 3.9 kb. GluR2 hybridized to two species, 3.9 and 5.9 kb, of comparable abundance, presumably attributable to alternate splice products. Hybridization to the GluR3 riboprobe showed a major species of 5.2 kb. This pattern of RNA species was invariant over all the brain regions examined. Examination of GluR expression in development revealed that in the postnatal period, GluR1, 2, and 3 mRNAs are regulated as a function of age. In adult rat brain, GluR1 and 2 mRNA expression was highest in hippocampus; GluR3 was expressed at highest density in hippocampus and frontal cortex. The three transcripts were first detected at embryonic day 16 and then exhibited changes in expression levels in a region-specific manner. In hippocampus, all three transcripts exhibited elevated expression in the late neonatal period; in frontal cortex, elevated expression was observed for GluR2 and 3 only. In striatum, all three transcripts were expressed at relatively low levels throughout development, with a modest peak at postnatal day 14. In cerebellum, the GluR1 mRNA level was high from postnatal day 28 to adult.(ABSTRACT TRUNCATED AT 250 WORDS)

The segregation and expression of glutamate receptor subunits in cultured hippocampal neurons

The distribution and expression of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate-selective glutamate receptor subunits (GluR1-4) were studied in cultured hippocampal neurons using antibodies generated against peptides corresponding to the C-termini of GluR1, GluR2/3 and GluR4, and with a set of oligonucleotide probes designed complementary to specific pan, flip and flop GluR1-4 messenger RNA sequences. GluR1-4 subunit proteins were localized in fixed hippocampal neurons (2 h to three weeks after plating) by immunocytochemistry with light and electron microscopy. At early stages in culture, moderate staining with antibodies to GluR1 and GluR2/3 and very light staining with antibody to GluR4 was observed in cell bodies and proximal portions of all neurites of some neurons. Upon establishment of identified axons and dendrites by seven days in culture, staining was intense with specific antibodies to GluR1 and GluR2/3 and light with anti-GluR4 antibody in cell bodies and dendrites. Little or no staining was observed in axons. Cells at seven days in culture exhibited a variety of morphologies. However, we could not assign a pattern of staining to a particular type. As the cultures matured over two and three weeks, staining was limited to the somatodendritic compartment. The intensity of glutamate receptor subunit staining increased and the extent of staining proceeded to the distal extreme of many dendrites. Moreover, antibodies to GluR1-4 subunits were co-localized in neurons. Immunocytochemistry on living neurons did not result in any significant labeling, suggesting that the epitope is either not expressed on the surface of the neurons, or is present, but inaccessible to the antibody. Electron microscopy demonstrated receptor localization similar to that found in brain, with staining of postsynaptic membrane and density, dendritic cytoplasm and cell body, but not within the synaptic cleft. We examined the possible role of "cellular compartmentation" in the pattern of glutamate receptor expression in hippocampal neurons. Compartmentalization studies of the subcellular distribution of messenger RNAs encoding GluR1-4 subunits was determined in mature cultures by in situ hybridization. Significant silver grain appearance was restricted to the cell body, indicating that the synthesis of glutamate receptor subunits is limited largely to the neuronal cell body. The expression of microtubule-associated protein 2 was studied in parallel. Microtubule-associated protein 2 expression appeared 6 h after plating, while glutamate receptor subunit expression was present at 2 h. This indicates that microtubule-associated protein 2 does not regulate the initial distribution of glutamate receptor subunits into neurites.(ABSTRACT TRUNCATED AT 400 WORDS)

Potassium-induced changes in excitability in the hippocampal CA1 region of immature and adult rats

Orthodromic and spontaneous population spike activity was measured in vitro in the CA1 region of rat hippocampal slices to determine maturational differences in excitability and susceptibility to K(+)-induced seizures. Several indices of excitability in the CA1 region changed in a non-monotonic fashion during maturation, in response to step-wise increases in bath [K+]. Slices from rats 18-22 days old, showed a greater probability of both spontaneous epileptiform activity and episodes of seizure-like activity followed by spreading depression, and more prolonged durations of evoked seizure-like events. Elevation of [K+] in the bathing medium increased these indices in a similar manner in older rats but not to the same degree as in 18- to 22-day-old rats. However, the threshold level of bath [K+] resulting in evoked bursts of population spikes was lower in adult and 28- to 32-day-old rats than in 18- to 22-day-old rats, suggesting that excitability is not uniformly greater at any given age. In 10- to 15-day-old rats, elevation of bath [K+] either produced persistent blockade of population responses, or increased the amplitude of the initial population spike, without producing bursts. Basal levels of [K+] in the interstitium of the slices corresponded to the various levels of [K+] placed in the bathing medium and there were no differences among age groups. Therefore, differences in basal [K+]o cannot account for the maturational changes in excitability and seizure activity. The period from 18-22 days of age in the rat is a useful focal point for investigating mechanisms underlying maturational changes in propensity to develop seizures.

Differential regulation of c-fos expression after cortical brain injury during development

Unilateral cortical brain injury is accompanied by widespread expression of c-fos protein(s) throughout the wounded cortex, including areas far from the lesion site. Here we report that this phenomenon is differentially regulated during development. At postnatal day (PD) 10 or 15, when rats were sacrificed 1.5 h after a mechanical cortical injury, they did not show an increase in c-fos immunoreactivity far from the wound, despite the fact that some of these animals (PD 15) displayed a positive response close to the lesion. At PD 22, the same injury induced an increase in c-fos-immunoreactive nuclei in the piriform cortex ipsilateral, but not contralateral, to the lesion. This pattern was maintained up to at least PD 360. Similarly, the presence of c-fos-immunoreactive cells was observed in the ipsilateral cingulate cortex in animals 22 days old and older. The pattern of c-fos expression in adult animals after mechanical damage was compared with other models of focal brain injury: application of potassium to the cortical surface and devascularization. Though all models generated c-fos expression far from the lesion site, potassium application resulted in higher numbers of c-fos-positive cells, particularly in the cingulate cortex. This study shows that c-fos expression after cortical brain injury is regulated differently during development, and that dissimilar models of cortical injury induce qualitatively similar responses although c-fos-like protein expression differs quantitatively.

Expression of the gene coding for the NR1 subunit of the NMDA receptor during rat brain development

Expression of the gene coding for the NR1 subunit of the N-methyl-D-aspartate (NMDA)-type of glutamate receptor was investigated in the developing rat brain. Peak NR1 gene expression in the whole brain occurred at approximately postnatal day (P) 10 with a second increase in the adult. To determine the ontogenic expression in the various brain regions, the expression of NR1 at P2, P10 and P60 was compared. The regional studies indicated increased expression at P60 in the cerebellum. In the midbrain and diencephalon, levels of expression at P10 and P60 were higher than at P2, while in the hippocampus, expression at P10 was significantly higher than at either P2 or P60. Expression in the other brain regions was constant over the period studied. These data indicate a region-specific expression of NR1 in the central nervous system during ontogeny.

Age dependence of homosynaptic non-NMDA mediated long-term depression in field CA1 of rat hippocampal slices

It has been hypothesized that high levels of presynaptic activity that fail to activate postsynaptic N-methyl-D-aspartate (NMDA) receptors may lead to long-term depression (LTD). Therefore, we tested the ability of high-frequency (50 Hz) synaptic stimulation in the presence of a blocker of NMDA receptors to elicit homosynaptic LTD at Schaffer collateral-CA1 synapses in hippocampal slices from 15-, 30- and 60-day-old rats. In control slices, there were no developmental differences in the incidence of long-term potentiation (LTP) of either EPSP slope or population spike amplitude. However, while NMDA receptor blockade with the specific antagonist D-2-amino-5-phosphonopentanoic acid (AP5; 25 microM) completely eliminated LTP in 30 and 60-day-olds, a significant number of slices from 15-day-old rats displayed some non-NMDA LTP of synaptic transmission. Moreover, under NMDA receptor blockade, the same high-frequency stimulation now induced homosynaptic LTD of population spike amplitude in a significant number of slices from 15- and 60-day-old rats (47% and 42%, respectively) but not in 30-day-olds (7%). LTD of population spike amplitude was most pronounced in 15-day-old slices (27 +/- 6% of baseline), whereas, in 60-day-old slices, LTD was 81 +/- 3% of baseline. LTD of EPSP slopes occurred in 44% of 15-day-olds, 13% of 30-day-olds, and 33% of slices from 60-day-old rats; the magnitude of EPSP was similar in 15 and 60-day-old slices (70 +/- 9% versus 81 +/- 1% of baseline).(ABSTRACT TRUNCATED AT 250 WORDS)

A comparison of the perioperative neurologic effects of hypothermic circulatory arrest versus low-flow cardiopulmonary bypass in infant heart surgery

BACKGROUND

Hypothermic circulatory arrest is a widely used support technique during heart surgery in infants, but its effects on neurologic outcome have been controversial. An alternative method, low-flow cardiopulmonary bypass, maintains continuous cerebral circulation but may increase exposure to known pump-related sources of brain injury, such as embolism or inadequate cerebral perfusion.

METHODS

We compared the incidence of perioperative brain injury after deep hypothermia and support consisting predominantly of total circulatory arrest with the incidence after deep hypothermia and support consisting predominantly of low-flow cardiopulmonary bypass in a randomized, single-center trial. The criteria for eligibility included a diagnosis of transposition of the great arteries with an intact ventricular septum or a ventricular septal defect and a planned arterial-switch operation before the age of three months.

RESULTS

Of 171 patients with D-transposition of the great arteries, 129 (66 of whom were assigned to circulatory arrest and 63 to low-flow bypass) had an intact ventricular septum, and 42 (21 assigned to circulatory arrest and 21 to low-flow bypass) had a ventricular septal defect. After adjustment for diagnosis, assignment to circulatory arrest as compared with low-flow bypass was associated with a higher risk of clinical seizures (odds ratio, 11.4; 95 percent confidence interval, 1.4 to 93.0), a tendency to a higher risk of ictal activity on continuous electroencephalographic (EEG) monitoring during the first 48 hours after surgery (odds ratio, 2.5; 95 percent confidence interval, 1.0 to 6.4), a longer recovery time to the first reappearance of EEG activity (only in the group with an intact ventricular septum, P < 0.001), and greater release of the brain isoenzyme of creatine kinase in the first 6 hours after surgery (P = 0.046). Analyses comparing durations of circulatory arrest produced results similar to those of analyses comparing treatments.

CONCLUSIONS

In heart surgery in infants, a strategy consisting predominantly of circulatory arrest is associated with greater central nervous system perturbation in the early postoperative period than a strategy consisting predominantly of low-flow cardiopulmonary bypass. Assessment of the effect of these findings on later outcomes awaits follow-up of this cohort.

Postnatal development of central nervous alpha 2-adrenergic binding sites: an in vitro autoradiography study in the tree shrew

The postnatal development of the alpha 2-adrenoceptor pattern was investigated by in vitro receptor autoradiography with the antagonist [3H]rauwolscine in the brains of tree shrews (Tupaia belangeri). At birth, high numbers of [3H]rauwolscine binding sites are diffusely distributed in the whole brain with exception of the neocortex which is very weakly labeled at this time. While the number of [3H]rauwolscine binding sites in the cerebellum decreases to low levels during the first three postnatal weeks, several brain regions show a significant increase in binding sites which are progressively concentrated in distinct nuclei. In the medulla oblongata, the diffuse labeling pattern changes so that binding sites become centralized in the dorsomedial nuclei. In the pons, similar changes can be observed with a moderate labeling of the locus coeruleus on postnatal day 10 and a strong labeling in the adult. In the thalamus, a transient appearance of high numbers of [3H]rauwolscine binding sites can be observed during the second and third postnatal week in specific nuclei. In the preoptic area and hypothalamus, there are only minor postnatal changes but the numbers of [3H]rauwolscine binding sites decrease between postnatal day 5 and adulthood. The high number of binding sites in the limbic system does not significantly change after birth. In the neocortex and the superior colliculus, the [3H]rauwolscine labeling pattern which is characteristic for the adult is achieved not before the third postnatal week. Competition experiments demonstrate that [3H]RAUW binds with high affinity to alpha 2-adrenoceptors in the postnatal as well as in the adult brain. Therefore, this study demonstrates region specific developmental profiles of the pattern of alpha 2-adrenoceptors in the postnatal tree shrew brain.

Quantitation of NMDA receptor (NMDAR1) mRNA levels in the adult and developing rat CNS

A rapid and sensitive solution hybridization assay was used to quantitate N-methyl-D-aspartate (NMDA) receptor mRNA levels in the central nervous system (CNS) of rat, mouse and human. A riboprobe labelled with 32P was prepared from a plasmid containing a 1413 base sequence from the cDNA for the functional rat NMDA receptor subunit, NMDAR1. Using a full length sense transcript as the calibration standard, the assay reliably measures 8 pg of NMDAR1 mRNA. When expressed as pg of NMDAR1 mRNA/micrograms total cellular RNA, the highest levels in the adult rat CNS are in the olfactory bulb (20.9 pg/micrograms RNA) and the lowest levels are in the spinal cord (5.2 pg/micrograms RNA). Intermediate levels were found in frontal cortex, hippocampus, cerebellum and whole brain. In the mouse CNS the highest levels of NMDAR1 mRNA were found in the olfactory bulb (12.9 pg equivalents/micrograms RNA), followed closely by hippocampus, frontal cortex and cerebellum. Mouse spinal cord (4.4 pg equivalents/micrograms RNA) had the lowest levels of NMDAR1 mRNA. The NMDAR1 riboprobe hybridizes with the same size transcripts in Poly(A)+ RNA from rat, mouse and human brain. In the developing rat, NMDAR1 mRNA levels in frontal cortex and hippocampus increased nearly 3 fold from postnatal day 3 to day 15 and approximately doubled from day 15 to day 67 (adult). Therefore, from postnatal day 3 to adult (day 67) frontal cortex and hippocampus levels of NMDAR1 mRNA increased nearly 6 fold.(ABSTRACT TRUNCATED AT 250 WORDS)

Development of NMDA receptor-channel complex and L-type calcium channels in mouse hippocampus

In vitro binding autoradiography was used to examine the pattern and intensity of binding of [3H]glutamate to NMDA receptors, [3H]MK 801 to NMDA receptor associated channels, and [3H]PN-200 110 to L-type calcium channels in the hippocampus of mice aged 3-70 days. The distribution of NMDA receptors and NMDA receptor associated channels was similar but not identical at the tested ages. Beginning with postnatal day 8, high binding levels were confined mostly to the hippocampal strata: the oriens and radiatum (CA1 and CA3 with [3H]MK 801 labeling but only CA1 with NMDA displaced [3H]glutamate labeling), the moleculare (higher labeling with [3H]MK 801 than with NMDA displaced [3H]glutamate binding), and the lucidum. The binding values for NMDA receptor-channel complex rose in the examined period (especially within the second and third week), reaching a plateau at the end of the third postnatal week. Sharp growth of binding within the second and third week of life was about 50% greater with [3H]MK 801 than with NMDA displaced [3H] glutamate labeling. L-type calcium channels were found to be most abundant in the strata: the oriens of the CA3 field, the moleculare, and the lucidum. The time course of binding value changes for the calcium channel was similar to the time course found for the NMDA receptor-channel complex.

Profound, reversible energy loss in the hypoxic immature rat brain

The goal of this study was to compare the effects of oxygen deprivation on cellular energy state and pH in the developing and adult rat brain. Relative quantities of phosphocreatine (PC), inorganic phosphorus (P(i)), and nucleoside triphosphates (NTP), and intracellular pH, were determined using in vivo 31P NMR spectroscopy at different postnatal ages (postnatal day (P) 2-6, P9-13, P16-20, P23-27) in the hypoxic rat brain (7 min, 4% O2). While a significant increase in P(i) was seen at all ages during hypoxia, a severe but reversible reduction in concentrations of PC (80-100% decrease) and NTP (40-50% decrease) was observed only at P9-13. This dramatic response was not seen in older (> P16) or younger (< P6) animals. These latter groups responded with moderate decreases in brain PC (50-60% decrease) and NTP (20-40% decrease). In addition, the youngest animals showed much less intracellular brain acidosis than the other age groups. The transient period of development during which the brain exhibits heightened susceptibility to hypoxic energy failure coincides with known changes in brain energy production pathways and susceptibility to hypoxia-induced excitability.

Development of dopamine and N-methyl-D-aspartate systems in rat brain: the effect of prenatal phencyclidine exposure

Phencyclidine (PCP) inhibits the uptake of the neurotransmitter dopamine (DA), and blocks N-methyl-D-aspartate (NMDA) receptor-regulated ion channels. PCP also binds to sigma receptors in vivo and in vitro in rat brain. Prolonged exposure to PCP in adults has been observed to reduce the number of PCP binding sites in brain. We designed these experiments to evaluate whether prolonged prenatal exposure to PCP produces alterations in the development of DA and NMDA systems in brain. To do so, we characterized the normal course of development of basal and stimulated DA release in striatal slices, the ontogeny of striatal DA concentrations, and the development of NMDA receptor channels and associated glutamate binding sites in frontal cortex. We compared these developmental profiles to those in rats exposed to prenatal PCP, in an attempt to characterize the effect of prenatal PCP exposure on the pattern of brain development. Pregnant CD rats were injected s.c. with either 0, 10 or 20 mg/kg PCP daily on gestational days 8 through 20. On postnatal days (PND) 8, 21, 45, or 100, rats were sacrificed and brain tissues isolated for in vitro assessment. In vitro [3H]DA release from striatal slices evoked by either 40 microM glutamate or 15 mM K+ increased over 250% from PND 8 to PND 45, and glutamate-stimulated release was still significantly below adult levels at PND 45. In contrast, D-methamphetamine (D-METH)-evoked [3H]DA release, frontal cortical glutamate binding sites and NMDA channels developed early, reaching adult levels on or before PND 21.(ABSTRACT TRUNCATED AT 250 WORDS)

Phencyclidine-binding sites in mouse cerebral cortex during development and ageing: effects of inhibitory amino acids

The binding of N-[1-(2-thienyl)cyclohexyl]-[3H]piperidine ([3H]TCP) to the phencyclidine-binding sites in the N-methyl-D-aspartate (NMDA) receptor complex-associated ion channel was characterized in cerebral cortical membranes from 3-day-old to 24-month-old mice. The binding was saturable, exhibiting only one binding component during the whole life-span studied. The maximal binding capacity Bmax, calculated per protein content, decreased during postnatal development until 3 months of age, remaining thereafter constant in ageing mice, thus indicating the greatest availability of phencyclidine-binding sites in the immature cerebral cortex. The binding constant KD increased during the first postnatal week, remained thereafter unchanged and increased again during the second year of life, indicating a decreased affinity of the receptor sites for the ligand. The general properties of the binding; potentiation by glutamate and NMDA, as well as by glycine in a strychnine-insensitive manner, prevailed during development and ageing, certain of these effects being however less pronounced in the immature brain. Taurine and beta-alanine stimulated TCP binding, acting probably at the glycine modulatory site. The actions of these inhibitory amino acids were weak and inconsistent when compared to that of glycine. Since NMDA receptors have been suggested to be involved in neuronal plasticity and learning and memory processes, these modifications in the properties of cortical phencyclidine-binding sites might be of importance in the regulation of excitatory amino acid functions during development and ageing.

Postnatal changes in N-methyl-D-aspartate receptor binding and stimulation by glutamate and glycine of [3H]-MK-801 binding in human temporal cortex

1. Homogenates of human infant and adult temporal cortex were used to measure [3H]-TCP and [3H]-MK-801 binding to the N-methyl-D-aspartate (NMDA)-coupled ion channel phencyclidine site. 2. Both [3H]-TCP and [3H]-MK-801 binding increased in infant cortex by > 100% between term and 26 weeks suggesting that the numbers of NMDA receptors increase during postnatal brain development. 3. [3H]-MK-801 binding was measured under non-equilibrium conditions in temporal cortex homogenates with the addition of 100 microM of L-glutamate plus a range of concentrations (0.05 microM-100 microM) of glycine. Glutamate and glycine increased [3H]-MK-801 binding by stimulating NMDA receptors and improving [3H]-MK-801 access to ion channel binding sites; maximum stimulation in adult and infant temporal cortex was achieved with 100 microM glutamate plus 5 microM glycine; a higher concentration of glycine (50 microM) reduced [3H]-MK-801 binding to below maximum. 4. The stimulation by 100 microM glutamate plus 5 microM glycine of [3H]-MK-801 binding in infant temporal cortex was affected by postnatal age. For example, although the stimulation of [3H]-MK-801 binding in 5-6 week infant cortex (236% of basal) was similar to adult cortex (230% of basal), in samples taken from infants aged 5-6 months glycine (plus glutamate) stimulation of [3H]-MK-801 binding (392% of basal) was substantially greater than that measured in adult temporal cortex. 5. The binding of [3H]-glycine to the glycine modulatory site associated with the NMDA receptor in infant cortex also increased with postnatal age by > 100% between term and 26 weeks. 6. It is concluded that NMDA receptors in infant cortex increase to levels greater than those in adult cortex during postnatal development. The results do not exclude the possibility that the transiently increased NMDA receptor-ion channel complex in infant cortex shows enhanced responses to agonists and modulators.

Tetraethylammonium-induced epileptiform activity in young and adult rat hippocampus

Extracellular field potential recordings were used to study the epileptiform activity evoked by tetraethylammonium (TEA) in the CA3 subfield of hippocampal slices obtained from young (12-18 day-old) and adult (> 60-day-old) rats. During TEA application (5-10 mM), young slices generated both ictal-like (duration: up to 28 s, rate of occurrence 1-3 x 10(-2) s-1) and interictal-like (duration: 1.5-2 s; rate of occurrence: 1-3 x 10(-1) s-1) activity. In adult slices only interictal-like activity was induced by TEA (3-10 mM). Depending on the concentrations of TEA, these events lasted 80-600 ms and occurred at 5-60 x 10(-2) s-1. Both the N-methyl-D-aspartate (NMDA) receptor antagonist 3-3(2-carboxypiperazine-4-yl)propyl-1-phosphonate (5-10 microM; CPP) and the non-NMDA receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (5-10 microM; CNQX) were necessary to suppress ictal-likeand interictal-like discharges in young slices. By contrast, interictal-like activity in adult slices was reduced and eventually blocked by CNQX (0.5-3 microM) alone. Furthermore the pattern of epileptiform discharges seen in young slices was modified by CPP (i.e. decrease in the rate of occurrence of ictal events and reduction in the duration of interictal discharges), while the activity recorded in adult slices was resistant to this NMDA antagonist. Bicuculline methiodide (5 microM; BMI) enhanced the duration of epileptiform activities in both young and adult slices. Our data demonstrate that the epileptiform discharges induced by TEA in the CA3 subfield of the rat hippocampus display age-dependent patterns of activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Distribution of NMDA receptor binding in developing mouse spinal cord

The role of NMDA receptors in spinal sensorimotor processes has been studied in neonates and adults, while NMDA binding has previously been described only in mature spinal cord. In autoradiographs of mouse lumbar cord, NMDA-sensitive [3H]glutamate binding peaked transiently around postnatal days 6-10. Differentiation increased progressively from day 10 to adulthood. Mature levels were highest in substantia gelatinosa and moderate in dorsomedial dorsal horn. The results are described in relation to functional and anatomical features of developing spinal cord.

Behavioral effects of non-NMDA glutamate receptor antagonists

Non-NMDA receptor antagonists decrease motor activity in some situations, alter the sleep-wake cycle, possess anticonvulsant and neuroprotectant actions, and appear to impair some learning tasks but not others. NMDA receptor antagonists affect these same functions but often in different and even opposite ways. NMDA receptor antagonists impair many different spatial learning tasks, including the Morris water maze, the Olton radial maze, and the hole-board task. Non-NMDA receptor antagonists are either ineffective in these spatial tasks or have not yet been evaluated. However, non-NMDA receptor antagonists may impair associative processes required in a bar-press response and in discrimination learning. Further research is needed in the context of comparing NMDA as opposed to non-NMDA receptor antagonists within the same paradigm.

AMPA glutamate receptor subunits are differentially distributed in rat brain

To demonstrate the regional, cellular and subcellular distributions of non-N-methyl-D-aspartate glutamate receptors in rat brain, we generated antipeptide antibodies that recognize the C-terminal domains of individual subunits of the alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA)-preferring glutamate receptors (i.e. GluR1, GluR4, and a region highly conserved in GluR2, GluR3 and GluR4c). On immunoblots, antibodies detect distinct proteins with mol. wts ranging from 102,000 to 108,000 in homogenates of rat brain. Immunocytochemistry shows that glutamate receptor subunits are distributed abundantly and differentially within neuronal cell bodies and processes in cerebral cortex, basal ganglia, limbic system, thalamus, cerebellum and brainstem. The precise patterns and cellular localizations of glutamate receptor subunit immunoreactivities are unique for each antibody. In neocortex and hippocampus, pyramidal neurons express GluR1 and GluR2/3/4c immunoreactivities; many non-pyramidal, calcium-binding, protein-enriched neurons in cerebral cortex are selectively immunoreactive for GluR1. In striatum, the cellular localizations of GluR1, GluR2/3/4c and GluR4 immunoreactivities are different; in this region, GluR1 co-localizes with many cholinergic neurons but is only present in a minor proportion of nicotinamide adenine dinucleotide phosphate diaphorase-positive striatal neurons. GluR1 co-localizes with most dopaminergic neurons within the substantia nigra. In several brain regions, astrocytes show GluR4 immunoreactivity. Within the cerebellar cortex, cell bodies and processes of Bergmann glia express intense GluR4 and GluR1 immunoreactivities; perikarya and dendrites of Purkinje cells show GluR2/3/4c immunoreactivity but no evidence of GluR1 or GluR4. Ultrastructurally, GluR subunit immunoreactivities are localized within cell bodies, dendrites and dendritic spines of specific subsets of neurons and, in the case of GluR1 and GluR4, in some populations of astrocytes. This investigation demonstrates that individual AMPA-preferring glutamate receptor subunits are distributed differentially in the brain and suggests that specific neurons and glial cells selectively express glutamate receptors composed of different subunit combinations. Thus, the co-expression of all AMPA receptor subunits within individual cells may not be obligatory for the functions of this glutamate receptor in vivo.

Biochemical and immunocytochemical characterization of antipeptide antibodies to a cloned GluR1 glutamate receptor subunit: cellular and subcellular distribution in the rat forebrain

Antibodies were made to synthetic peptides corresponding to residues 253-367, 757-771 and 877-889 of the published amino acid sequence of the rat brain glutamate receptor GluR1 subunit [Hollmann et al. (1989) Nature 342, 643-648]. The peptides were synthesized both as multiple copies on a branching lysyl matrix (multiple antigenic peptides) and conventional linear peptides using solid-phase synthesis. Rabbits were immunized with these peptides either without conjugation (multiple antigenic peptides) or following coupling to ovalbumin with glutaraldehyde (monomeric peptides). The antibodies from immune sera were then purified by affinity chromatography using reactigel coupled monomeric peptides. All the rabbits produced good antipeptide responses, and were characterized by immunoprecipitation of solubilized alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate and kainate binding activity and by their staining patterns on immunoblots. Antibody to peptide 253-267 specifically immunoprecipitated 12 +/- 3, 50 +/- 3 and 44 +/- 4% of solubilized alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate binding activity from cortex, hippocampus and cerebellum, respectively. Under identical conditions, antibody against the 877-889 peptide removed 23 +/- 4, 9 +/- 4 and 15 +/- 9% of alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate binding sites from these areas. On immunoblots of rat brain membrane samples separated by sodium dodecyl sulphate-polyacrylamide gel electrophoresis, antibodies labelled a 105,000 mol. wt immunoreactive band. GluR1 was immunoaffinity-purified using subunit-specific antibodies against both N-terminal (253-267) and C-terminal (877-889) residues, covalently attached to protein A-agarose. Analysis of the purified product from each column showed a major immunoreactive band, recognized by both sera at 105,000 mol. wt and silver staining identified the same major protein. After exhaustive immunoprecipitation of solubilized membrane samples with antibody against the C-terminal of the subunit, a subpopulation of GluR1 was labelled with antibodies specific for the N-terminal part of the receptor. These observations suggest that the GluR1 subunit consists of at least two isoforms possessing a common N-terminal region but a distinct C-terminus. Immunocytochemistry, using immunoperoxidase staining, was performed for the GluR1 subunit in rat forebrain with antisera raised against the N-terminal (253-267) and the C-terminal parts (877-889) of the molecule. Both antisera gave a similar distribution of immunoreactivity at the light-microscopic level. Immunoreactivity for the GluR1 subunit was selectively distributed throughout the rat forebrain. The hippocampus, septum, amygdala and olfactory bulb exhibited the strongest immunoreactivity.(ABSTRACT TRUNCATED AT 400 WORDS)

Differences in c-fos immunoreactivity due to age and mode of seizure induction

The aim of this study was to determine whether the regional distribution and time course of immunoreactivity to the c-fos protein varies with maturation and method of seizure induction. The effect of the two chemical convulsants, pentylenetetrazol (PTZ) and flurothyl, on the spatial and temporal pattern of c-fos-like immunoreactivity in immature (postnatal day (P) 10) was compared to that in adult rats. Patterns of c-fos-like immunoreactivity following O2 deprivation were also evaluated at the 2 ages because hypoxia is acutely epileptogenic in immature animals but not adults. C-fos-like immunoreactivity was examined at 2, 4, and 6 h after onset of chemically induced seizures or O2 deprivation at both ages. After PTZ or flurothyl seizures, both ages exhibited similar patterns of IR in amygdala, pyriform cortex, and hypothalamus. Age-dependent regional differences were most prominent in cortex: superficial layers of retrosplenial, cingulate, and neocortex stained in adults; staining was confined to deep layers of neocortex in P10 rats. Intense staining of dentate gyrus and hippocampus occurred with more prolonged seizures, but not brief seizures. PTZ administration resulted in staining at 2 h after seizure onset and was reduced by 4 h in adults, but immunoreactivity was not seen until 4 and 6 h after seizure onset in immature rats, indicating an age effect on the time course of IR. In immature rats, immunoreactivity patterns after hypoxia were markedly different from PTZ or flurothyl: staining was confined to layer VI of neocortex in these animals, and rarely involved limbic structures. These differences in the pattern of c-fos immunoreactivity suggest that the neuronal populations involved in epileptogenesis are influenced by age as well as seizure phenotype and intensity.

Endogenous D-serine in rat brain: N-methyl-D-aspartate receptor-related distribution and aging

Recently, a substantial amount of free D-serine has been demonstrated in rat brain, although it has long been presumed that D-amino acids are uncommon in mammals. The anatomical distribution and age-related changes in endogenous D-serine have been examined here to obtain insight into its physiological functions. Free D-serine exclusively occurs in brains, with a persistent high content from birth to at least 86 postnatal weeks. The patterns of the regional variations and the postnatal changes in brain D-serine are closely correlated with those of the N-methyl-D-aspartate (NMDA)-type excitatory amino acid receptor. Because D-serine potentiates NMDA receptor-mediated transmission by selective stimulation of the strychnine-insensitive glycine site of the NMDA receptor, it is proposed that D-serine is a novel candidate as an intrinsic ligand for the glycine site in mammalian brain.

The differential expression patterns of messenger RNAs encoding non-N-methyl-D-aspartate glutamate receptor subunits (GluR1-4) in the rat brain

The messenger RNA expression of non-N-methyl-D-aspartate glutamate receptor subunits (GluR1-4), considered alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid type, was investigated in rat brain by in situ hybridization histochemistry using oligonucleotide probes specific to each subunit sequence. GluR1-4 subunit messenger RNAs were expressed widely and abundantly throughout the CNS. However, the combination of expression pattern varied notably according to location. GluR2 messenger RNA was expressed most strongly and widely, with most areas except the Bergmann glia containing this messenger RNA. GluR4 messenger RNA was also present widely, although the expression level was low. However, we observed many areas which lacked or expressed very little GluR1 messenger RNA, such as some nuclei in the general motor system and auditory system. In addition, some nuclei in the hypothalamus and general somatosensory system lacked or expressed very little GluR3 messenger RNA. These results suggest that in the rat CNS non-N-methyl-D-aspartate receptors varied their composition according to the area where they were expressed, and that the combination pattern might be related to the functional role of neurons.

Changes in synaptosomal glutamate release during postnatal development in the rat hippocampus and cortex

The effectiveness of K+ depolarisation in inducing the release of [3H]L-glutamate from preloaded hippocampal and cortical synaptosomes was examined in rats aged from postnatal day 4 (PND 4) to adult. In the lower age groups studied (PND 4-PND 15), the response to depolarisation was always smaller than that seen in the adult. From PND 15, the sensitivity of the release process increased steadily to a maximum level in the adult. The relatively small amounts of glutamate released in response to K(+)-depolarisation in the younger age groups may be a factor which contributes to the relative insensitivity of neonatal brain to ischaemic damage. Discrete variations in the sensitivity to K+ depolarisation observed in animals aged from PND 4 to PND 15 may be involved in plastic changes in neural activity which are known to occur during this important development period.

Modification of modulatory sites of NMDA receptor in the fetal guinea pig brain during development

Ontogeny of the NMDA receptor and modification of its modulatory sites in the developing fetus brain was determined. MK-801 binding characteristics in the presence of glycine, glutamate, Mg2+ and spermine were determined and used as an index of NMDA receptor modification. Experiments were performed on guinea pig fetuses at 30, 45, 50, 55, and 60 days (term = 63 days) of gestation. The Bmax value increased approximately three-fold from 30 days to 60 days of gestation. The Kd value decreased during the 45-50 day period and then increased toward the end of gestation. The Bmax value reached its maximum level by 55 days of gestation, indicating the presence of a maximum number of NMDA receptors by this age, while the apparent affinity of the receptor showed its peak at 45-50 days of gestation, indicating a potential role for NMDA receptor during the proliferation period of brain development in the guinea pig fetus. The activation of NMDA receptor in the presence of glutamate (10 microM) and glycine (10 microM), as measured by MK-801 binding, was absent at 30 days gestation, with the earliest observation occurring at 35 days gestation. The spermine dependent activation decreased with gestational age. Mg2+ ions increased MK-801 binding in the range of 1-20 microM concentration. Sensitivity to Mg2+ dependent activation increased with the gestational age (from 10 microM Mg2+ at 45 days to 2.5 microM at 55 and 60 days).(ABSTRACT TRUNCATED AT 250 WORDS)

Proconvulsive effects of histamine H1-antagonists on electrically-induced seizure in developing mice

The purpose of this study was to investigate the developmental differences in seizure susceptibility in mice and the roles of the histaminergic neuron system in inhibition of convulsions in development. First, we studied developmental differences in electrically-induced seizures. Since the 14-day-old mice showed a different seizure pattern from that of older mice, we evaluated the seizure susceptibility of mice older than 21 days. The durations of all the convulsive phases were significantly increased in 21- and 30-day-old mice, compared with older mice. Second, pyrilamine (or mepyramine), ketotifen, and d-chlorpheniramine, centrally-acting H1-antagonists, increased the durations of all the convulsive phases in the 21- and 30-day-old mice, but did not increase duration in 42-day-old mice. Terfenadine and astemizole, H1-antagonists that hardly enter the brain, did not affect the durations of all the convulsive phases in 21-, 30- and 42-day-old mice. The proconvulsant effect of centrally-acting H1-antagonists in 21- and 30-day-old mice were considered to be mediated via the central H1-receptors. Thus, the histaminergic neuron system may have an important physiological role in inhibition of seizures in 21- and 30-day-old mice which have higher seizure susceptibility. This would compensate for the immaturity of the other protective neuron systems such as NMDA receptor complexes and GABA receptors. In conclusion, the present findings support the view that the central histaminergic system plays a role in inhibition of convulsions.

The ontogeny of phencyclidine-induced wall climbing and locomotor activity

Wall climbing behavior is an age-specific behavior that is elicited during postnatal Days 7 through 17 by various stimuli that include heat, odors, shock, and the catecholaminergic agonists apomorphine, amphetamine, and clonidine. In a previous study, a significant amount of wall climbing behavior was observed during ataxia and activity testing following phencyclidine (PCP) administration in Day 19 but not Day 40 rat pups. The present study describes the ontogeny of PCP-induced wall climbing behavior and locomotor activity. Frequency and duration of wall climbing bouts and locomotor activity were recorded on Days 5, 12, 19, 26, 33, or 40 following PCP treatment. On Day 12, all doses of PCP induced significant amounts of wall climbing behavior. A similar pattern of results was observed on Day 5 although these effects were not statistically significant. After Day 12, PCP-induced wall climbing behavior declined precipitously. PCP increased locomotor activity at all ages tested with maximum activities observed on Day 19. These results demonstrate that PCP-elicited wall climbing behavior follows an ontogenetic profile similar to that previously reported for other stimuli and that there are robust ontogenetic differences in the locomotor response to PCP.

Density and distribution of excitatory amino acid receptors in the developing human fetal brain: a quantitative autoradiographic study

The binding of [alpha-3H]amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) to quisqualate receptors, [3H]kainate (KA) to KA receptors, and L-[3H]glutamate to N-methyl-D-aspartate (NMDA) receptors was determined by quantitative autoradiography in brains obtained from twelve aborted human fetuses ranging from 16.5 to 26 weeks of gestational age. Among the three receptor subtypes, specific binding to AMPA was the highest, followed by NMDA and KA, respectively, in all age groups. Receptor binding was already apparent by 16.5 weeks in the hippocampus, thalamus, and subthalamic nucleus, rose sharply by 20-21.5 weeks, and subsequently declined to their lowest levels by 24-26 weeks. Anatomically distinct binding patterns for each of the three major excitatory amino acid (EAA) receptor subtypes were well established by 20-21.5 weeks. Within the hippocampus, AMPA was localized primarily in the stratum pyramidale, NMDA in the stratum radiatum, and KA in the molecular layer of the dentate gyrus and in the stratum lucidum of the CA3 region. The cerebral cortex showed dense labeling of AMPA in the outer layers, whereas KA binding was more prominent within the inner layers. The putamen and globus pallidus also showed relatively dense receptor binding in all age groups. The sharp rise in receptor density at 20-21.5 weeks of age suggests involvement of EAA pathways in developmental plasticity, including reorganization of neuronal processes or synapses, during this period of development. Developmental changes in the density and distribution of EAA receptors, as shown in this study, may also provide insight into shifts in the localization of age-dependent selective vulnerability within the developing human fetal brain.