Neurons In CA1 Region Research Articles

Protective effect of stobadine, a pyridoindole antioxidant, in hypoxia-reoxygenation injury of ganglionic and hippocampal neurotransmission.

Hypoxia (HYP) followed by reoxygenation (REOX) occurs frequently in the pathophysiology of the CNS. Free oxygen radicals (FOR) may participate in cerebral injury under such circumstances. Pharmacological control of the generation and/or subsequent effects of FOR by new effective compounds might contribute to the treatment of disorders such as stroke and cerebral trauma. Effects of stobadine, a pyridoindole antioxidant that is able to interact with some FOR, were analyzed on synaptic transmission in rat superior cervical ganglia and hippocampal slices during HYP-REOX procedure in vitro. The amplitude of compound action potential in the ganglion evoked by supramaximal electrical stimulation of preganglionic nerve was reduced to approximately 20% of the control value during HYP (90 min). The action potential did not recover during REOX (60 min). Stobadine (10 mM) applied before, during, and after HYP, did not change the HYP-induced inhibition; however, a significant recovery of transmission (to 78.5% +/- 8.3) occurred during REOX. A similar effect was observed in the presence of the antioxidant Trolox (0.2 mM), a derivative of alpha-tocopherol. Stobadine, in concentrations of > 30 microM inhibited ganglionic transmission in a concentration-dependent manner. HYP lasting more than 2-3 min fully depressed field action potentials evoked in hippocampal CA1 region neurons by supramaximal electrical stimulation of Schäffer collaterals. If HYP exceeded 8 min, transmission did not recover during REOX. Stobadine (10 microM) applied during HYP significantly enhanced the probability of transmission recovery in the REOX period. Some preparations recovered following HYP lasting as long as 13-15 min. On applying the compound before, during, and after HYP that lasted for 8 min, the transmission recovery was 72.6% +/- 21.8 of the control value, compared to only 16.1% +/- 12.7 in the untreated preparations. In concentrations ranging from 0.3-1.73 mM, stobadine inhibited hippocampal transmission. Stobadine proved to be an effective agent in the protection of synaptic transmission against HYP-REOX-induced injury in both neuronal preparations studied in vitro. This effect might be linked to the antioxidant and free radical scavenging effects of stobadine.

Block of induction and maintenance of calcium-induced LTP by inhibition of protein kinase C in postsynaptic neuron in hippocampal CA1 region

Calcium-induced LTP (Ca-LTP) refers to the long-lasting potentiation of synaptic transmission in hippocampal synapses that can be induced by a transient (7–10 min) and small increase (from 2 mM to 4 mM) in extracellular calcium concentration. In this paper the effects of protein kinase C (PKC) inhibitors, polymyxin B (PMB) and PKC(19–31), given intracellularly to the postsynaptic neuron in the CA1 region, on the induction and maintenance of Ca-LTP were studied and compared with those found in a similar study earlier made in this laboratory on tetanic stimulation-induced LTP (TS-LTP) [18]. When the intracellular delivery of the inhibitor(s) was made to begin 30 min before the exposure to increased [Ca 2+] 0, the development of Ca-LTP was completely blocked, leaving only a brief enhancement of EPSPs directly attributable to the brief increase in [Ca 2+] 0. When the intracellular delivery of either PKC(19–31) alone or PMB + PKC(19–31) was made to begin after the full establishment of Ca-LTP, it soon made the maintained potentiation begin to decline, the EPSP amplitude gradually returning to the control value before the exposure to increased calcium. Thus postsynaptic PKC inhibition blocks both the induction and the maintenance of Ca-LTP, just as it has been shown to do to TS-LTP. But quantitative differences exist: both the induction and the maintenance of Ca-LTP appeared to be more susceptible to block by postsynaptic PKC inhibition than those of TS-LTP.

Inhibition of GABA and glycine responses by glutamate in rat hippocampal neurons

Currents elicited by activation of GABA A, glycine (GLY) and glutamate (GLU) receptors (R) in pyramidal neurons of CA1 region from thin slices of rat hippocampus were studied using the tight-seal whole-cell recording techniques. GLU (100 mM) induced a long-lasting depression of GABA- and GLY-activated currents ( I GABAandI GLY) when using standard saline in conjunction with depolarization. The long-lasting depression was not observed: (1) in neurons held at −70 mV during GLU application; (2) in neurons depolarized by current injection but not exposed to GLU; (3) when GLU/depolarization protocol was performed in Ca 2+-free medium; or (4) by using recording patch-pipettes filled with a medium that tightly controlled cytosolic Ca 2+ transients. Sphingosine (10 mM), staurosporine (1 mM) and the specific inhibitor of protein kinase C (PKC(19–36) (200 mM in the patch-pipette solution), blocked the long-lasting depression of I GABA·I GABA was depressed even when the treatment with GLU was performed before patch-clamping the neuron. We conclude that the sustained I GABAandI GLY depression is mediated by cytosolic events triggered by the activation of GLUR.

Persistent degenerative state of non-pyramidal neurons in the ca1 region of the gerbil hippocampus following transient forebrain ischemia

Morphological changes in the neurons of the gerbil hippocampus following 5 min of forebrain ischemia were examined using light and electron microscopy. Although non-pyramidal neurons in the CA1 region of the hippocampus survived through the full length of the observation period, up to six weeks after ischemia, they consistently demonstrated degenerative changes distinct from those of the well-known “delayed neuronal death” of CA1 pyramidal cells. When examined with the light microscope, CA1 non-pyramidal neurons were found to be shrunken and their nuclei and cytoplasm were hyperchromatic between seven days and six weeks after ischemia. When examined with the electron microscope, postischemic non-pyramidal neurons were found to have markedly electron-dense profiles; their cytoplasm contained numerous free ribosomes and heterogeneous smaller granular substances, the latter also filling the nuclei. However, there was no loss of ribosomes from the rough endoplasmic reticulum, and mitochondrial cristae were preserved, suggesting that these neurons were viable. CA1 non-pyramidal neurons were studied immunohistochemically using three types of monoclonal antibodies, one each against parvalbumin, a nonphosphorylated epitope on the 168,000 mol. wt and 200,000 mol. wt subunits of neurofilament proteins, and microtubule-associated protein 2. CA1 nonpyramidal neurons lost immunoreactivity to these neuron-specific substances six weeks after ischemia, suggesting that these degenerating cells lacked certain types of normal neuronal activity. We conclude that non-pyramidal neurons in the hippocampal CA1 region survive transient ischemia but undergo degenerative changes following complete loss of CA1 pyramidal cells. These changes may be due to depletion of presumptive target-derived trophic factors within the non-pyramidal neurons.

Kainic acid induces long-lasting depolarizations in hippocampal neurons only when applied to stratum lucidum.

The actions of alpha-kainic acid (KA) were reexamined in thin sections of the hippocampus and the cerebellum of the guinea pig in view of various discrepancies between our previous findings and reports from other laboratories. Brief pulses of KA ejected in st. lucidum in the CA3 region induced short- and long-lasting depolarizations in neurons nearby, whereas those ejected in st. radiatum or st. oriens induced only short-lasting responses. Neurons in CA1 region and Purkinje cells in the cerebellum generated only short-lasting depolarizations in response to KA pulses ejected in their dendritic fields. The short-lasting KA responses in CA1 region were sensitive to gamma-D-glutamylglycine and pentobarbital. The slow KA responses were suppressed by kynurenic acid. They were not accompanied by increases in extracellular potassium concentration. These results suggest that the mossy fiber-innervated portions of the surface membrane of CA3 neurons have a type of KA receptor different from those ubiquitously distributed in central neurons.

Stratum lacunosum-moleculare interneurons of hippocampal CA1 region. I. Intracellular response characteristics, synaptic responses, and morphology

Stable intracellular recordings were obtained from nonpyramidal cells (interneurons) in stratum lacunosum-moleculare (L-M) of the CA1 region of guinea pig hippocampal slices. The intracellular response characteristics of these interneurons were distinctly different from responses of pyramidal cells and of other interneurons (basket cells and oriens-alveus interneurons). L-M interneurons had a high resting membrane potential (-58 mV), a high input resistance (64 M omega), and a large amplitude (60 mV), relatively long duration (2 msec) action potential. A large afterhyperpolarization (11 mV, 34 msec) followed a single action potential. Most L-M interneurons did not display any spontaneous firing. Lucifer yellow (LY)-filled L-M interneurons showed nonpyramidal morphology. Cells were generally fusiform or multipolar, with aspinous, beaded dendritic processes ramifying in stratum lacunosum-moleculare, radiatum, and (sometimes) oriens. The varicose axon originated from a primary dendrite, projected along stratum lacunosum-moleculare, branched profusely in stratum radiatum, and coursed toward and into stratum pyramidale and occasionally into oriens. Processes of cells with somata in the L-M region of CA1 were not restricted to the CA1 region. The dendritic and axonal processes of some L-M interneurons were seen ascending in stratum lacunosum-moleculare, crossing the hippocampal fissure, and coursing in stratum moleculare of the dentate gyrus. Excitatory and inhibitory postsynaptic potentials (EPSPs and IPSPs) were evoked in L-M interneurons from stimulation of major hippocampal afferents. EPSPs were most effectively elicited by stimulation of fiber pathways in transverse slices, whereas IPSPs were predominantly evoked when major pathways were stimulated in longitudinal slices. We have identified a population of interneurons with intracellular response characteristics and morphology distinctly different from previously described pyramidal and nonpyramidal neurons of CA1 region. The possible role of these interneurons in hippocampal circuitry is discussed.