Block of an insect central nervous system GABA receptor by cyclodiene and cyclohexane insecticides

The effects of a cyclodiene (endrin) and a cyclohexane (lindane) insecticide have been tested on gamma-aminobutyric acid (GABA) receptors in the central nervous system of the cockroach (Periplaneta americana), by using electrophysiological methods and an in vitro functional receptor assay. In electrophysiological experiments on an identified motor neuron (Df), endrin blocked the GABA response with a 50% inhibition concentration of 5.0 x 10(-7) M in a non-competitive manner. The actions of endrin were irreversible under the experimental conditions adopted. Increasing the intracellular chloride concentration reduced the effectiveness of endrin, whereas a change in the potassium concentration failed to influence the block by endrin of GABA responses. Lindane exhibited similar actions to endrin on insect GABA receptors, but was approximately an order of magnitude less effective. In a microsac preparation from cockroach nerve cords, endrin, at a concentration of 1.0 x 10(-5) M, completely blocked GABA-stimulated 36Cl- uptake, whereas the same concentration of lindane was less potent, only blocking about 40% of uptake under similar conditions. Neither insecticide had any effect on L-glutamate-activated chloride channels. The results demonstrate that endrin and lindane block functional insect neuronal GABA receptors.     

Proctolin potentiates synaptic transmission in the central nervous system of an insect

1. Bursts of spike activity in the ventral nerve cord of the cockroach were elicited by mechanically stimulating the cercal organs. 2. In the presence of micromolar proctolin, the peak frequency and the duration of a burst were slowly but significantly increased. 3. In contrast, carbachol produced an immediate enhancement of spontaneous activity, but a potentiation of bursts was not seen. 4. It is proposed that proctolin functions as a neuromodulator in the terminal abdominal ganglion of the cockroach.     

Enzyme effects on the connective tissues of an insect central nervous system

The effect of various enzymes on the two connective tissue matrices of the cockroach central nervous system were investigated. Removal of the neural lamella, using collagenase, allows some of the cells which form the perineurium to pull out of this cell layer but the perineurial bracelet cells maintain an intact blood-brain barrier. Incubation of the nerve cord with hyaluronidase has little or no effect on the neural lamella and allows the selective removal of the matrix from the glial lacunar system. Partial removal of this matrix appears to have little effect on the ability of the axons to conduct action potentials at high frequencies. In addition to this difference in susceptibility of the neural lamella and lacunar matrices to different enzymes, there appears to be a difference between the lacunar matrix of the connectives and of the ganglia, the latter being more resistant to enzyme attack. There is no such difference in the neural lamella covering the ganglia and connectives.     

Degeneration and regeneration in the insect central nervous system. I

Summary After cutting a neck connective of Schistocerca gregaria, only 2% of the axons on each side of the lesion degenerate. The remainder show reactive changes, which last for approximately one week at 28° C. There is no morphological change in either of the pro/mesothoracic connectives after injury to the neck connective. Phagocytes invade the stumps, but attack only degenerating cells, and are absent by Day 7.Regeneration from the connective stumps begins a week after injury; a functional link may be formed by Day 10, but by Day 23 the new connective cannot function adequately for the locust's survival, if the undamaged connective is then cut.The chief morphological changes in the reactive axoplasm are increases in the number of mitochondria, neurotubules, vesicles and vacuoles. These changes appear to be a local response, and not to be influenced by the neuron cell bodies. Some glial cytoplasm (presumably enucleated), degenerates rapidly after injury, and replacement begins by Day 5. Tracheoles, never seen in normal connectives appear in the reactive connective from Days 3–8, this is interpreted as a migration from the ganglion in response to oxygen deficiency in the connective.The results are discussed in relationship to previous work.This work was supported by a Study and Serve grant from the British Government, and a grant from the Worshipful Company of Goldsmiths.I wish to acknowledge the help and advice given to me by Dr. C. H. F. Rowell.     

c-Fos-related antigens in the central nervous system of an insect, Acheta domesticus

Fos-related antigens (Fra) were detected in the nuclei of neurones in young adult Acheta domesticus female crickets by immunohistochemical analysis, using an antibody that recognizes the amino-acid sequence 127-152 of c-Fos protein. Specificity of Fra immunoreactivity was confirmed by Western blot analysis of nuclear extracts from neural tissues. A major immunoreactive doublet with an apparent molecular mass of 52,000/54,000 Da was detected in nuclear extracts. Immunostaining of the 52,000/54,000 Da doublet showed variations in intensity during the first 5 days following the imaginal molt. Staining was more intense between day 2 and day 4 when ecdysteroid titers were high. Expression of Fra was low in allatectomized (i.e., deprived of juvenile hormone and ecdysteroids) and ovariectomized (i.e., deprived of ecdysteroids) females as compared to control females. These results show the involvement of hormone-regulated process in expression of Fra. The effect of nociceptive stimulation on Fra expression was tested. Twenty minutes after removal of the ovipositor, a supplementary band with an apparent molecular mass of 70,000 Da appeared in the nuclear extracts, then decreased and disappeared totally after 45 min. Several other Fos-related antigens with different temporal patterns of expression were also detected.     

The electrophysiological actions of neurotensin in the central nervous system

The endogenous neuropeptide, neurotensin (NT) alters the firing frequencies of certain neurons in the central nervous system (CNS). This is one of the findings that support the hypothesis that NT is a neurotransmitter substance. The direct application of NT on CNS neurons causes predominantly excitatory effects. These effects occur in a dose-related fashion via a calcium-dependent postsynaptic mechanism. The C-terminal hexapeptide fragment, NT 8-13 exerts similar electrophysiological effects to NT, while the N-terminal octapeptide fragment, NT 1-8 is devoid of such activity. NT produces a significant increase in the firing rates of individual neurons in the substantia nigra (SN), ventral tegmental area (VTA), medial prefrontal cortex (MPF), hypothalamus, and periaqueductal grey (PAG). This excitation occurs with a rapid onset and is readily reversible after cessation of NT application. In contrast, NT has no effect or weak inhibitory effects on the firing rates of neurons in the locus coeruleus (LC) and cerebellum. These electrophysiological actions of NT appear to be unique and not shared by other neurotransmitter and neuropeptide receptor antagonists and agonists that have been studied via direct co-application. NT attenuates dopamine (DA)-induced inhibition associated with direct application onto neurons in the SN and VTA both in vivo and in vitro. Intracellular recordings suggest that direct application of higher concentrations of NT appears to produce 'depolarization block' on individual neurons in the SN, VTA, MPF, and hypothalamus. The electrophysiological consequences of NT application not only show similarities to clinically efficacious antipsychotic medications, but also demonstrate the ability of NT to modulate the activity of dopamine (DA) neurons at the cellular level via specific NT binding sites. These findings further underscore the possibility that NT may play a pre-eminent role in the pathogenesis of, and psychopharmacological management of neurological and psychiatric disorders purportedly related to perturbation of CNS DA systems including schizophrenia.     

Immunocytochemical localization of sodium channels in an insect central nervous system using a site-directed antibody

Antibodies to channel proteins and specific peptide sequences have been previously used to localize voltage-activated sodium channels in the rat brain. Here we describe the first localization of sodium channels in an insect nervous system using a site-directed antibody. The mesothoracic ganglion of the cockroach was stained with an antibody to the highly conserved SP19 sequence. Antibody labelling was visualized by light microscopy using the avidin/biotin method on was sections, and transmission electron microscopy of immunogold-labelled thin sections. Central ganglia of insects contain clearly separated regions of cell bodies, synaptic neuropil, axon tracts, and nerves. Antibody staining by light microscopy was limited to neurons, and was intense in axons throughout the ganglion and nerves. Staining was also strong in the cytoplasm, but not the nuclei, of many neuronal cell bodies. Neuropil regions were relatively lightly labelled. These findings can be correlated with the known electrophysiology of the ganglion. Electron microscopy detected sodium channels in areas surrounding axons, probably including axon membranes and enveloping glial cell membranes. Axonal mitochondria were also heavily labelled, suggesting a sodium channel transport function for these organelles. © 1993 John Wiley & Sons, Inc.     

The neurotoxic actions of quinolinic acid in the central nervous system

Excitotoxins such as kainic acid, ibotenic acid, and quinolinic acid are a group of molecules structurally related to glutamate or aspartate. They are capable of exciting neurons and producing axon sparing neuronal degeneration. Quinolinic acid (QUIN), an endogenous metabolite of the amino acid, tryptophan, has been detected in brain and its concentration increases with age. The content of QUIN in the brain and the activity of the enzymes involved in its synthesis and metabolism show a regional distribution. The neuroexcitatory action of QUIN is antagonized by magnesium (Mg2+) and the aminophosphonates, proposed N-methyl-D-aspartate (NMDA) receptor antagonists, suggesting that QUIN acts at the Mg2+ -sensitive NMDA receptor. Like its excitatory effects, QUIN's neurotoxic actions in the striatum are antagonized by the aminophosphonates. This suggests that QUIN neurotoxicity involves the NMDA receptor and (or) another receptor sensitive to the aminophosphonates. The neuroexcitatory and neurotoxic effects of QUIN are antagonized by kynurenic acid (KYN), another metabolite of tryptophan. QUIN toxicity is dependent on excitatory amino acid afferents and shows a regional variation in the brain. Local injection of QUIN into the nucleus basalis magnocellularis (NBM) results in a dose-dependent reduction in cortical cholinergic markers including the evoked release of acetylcholine. A significant reduction in cortical cholinergic function is maintained over a 3-month period. Coinjection of an equimolar ratio of QUIN and KYN into the NBM results in complete protection against QUIN-induced neurodegeneration and decreases in cortical cholinergic markers. In contrast, focal injections of QUIN into the frontoparietal cortex do not alter cortical cholinergic function.(ABSTRACT TRUNCATED AT 250 WORDS)     

The origins of cell diversity in the insect central nervous system

There are thousands of unique neurons and many types of glia in the insect central nervous system. How is this cell diversity generated? Neurogenesis begins with the delamination and enlargement of individual cells of the ventral ectoderm to form a stereotyped array of neuroblasts. Every neuroblast divides asymmetrically to generate a chain of approximately 10 smaller progeny, each of which produces a pair of neurons. Ablation, transplantation and in vitro culture experiments illuminate the role of cell interactions and cell lineage during neurogenesis, and genetic approaches in Drosophila are beginning to provide insight into the molecular mechanisms controlling these events.     

Possible involvement of GABA in the central actions of benzodiazepines.

The effects of several benzodiazepines on a variety of nervous activities known or presumed to depend on GABA are presented and compared with those of agents that deplete or increase the level of endogenous GABA: antagonism of various convulsant agents in mice, enhancement of presynaptic inhibition in the spinal cord and the cuneate nucleus of cats, decrease of the spontaneous firing rate of cerebellar Purkinje cells in cats and rats, antagonism of bicuculine-induced depression of the strio-nigral-evoked potential in the cat, potentiation of haloperidol-induced catalepsy in rats, GABA-mimetic actions on drug-induced PGO-waves in cats and on eserine-induced circling in guinea pigs. Diazepam slightly increased the GABA level in the cat spinal cord and in the total brain of mice and rats; this increase does not seem to be due to an increase of GABA synthesis. It is concluded that benzodiazepines probably enhance presynaptic inhibition at all levels of the neuraxis and that this effect requires not only the presence of GABA but is also dependent on an activity of GABA-ergic neurons. Benzodiazepines also appear to enhance postsynaptic inhibition where this is mediated by GABA. Many actions of benzodiazepines can be tentatively explained by a stimulus-bound enhancement of GABA effects.     

The effects of an anti-mitotic drug,bleomycin, on glial repair in an insect central nervous system

Summary The DNA-binding drug, bleomycin, has a profound effect on neural repair following selective glial disruption by ethidium bromide. The contribution of the granule-containing cells (which normally appear in the early stages of repair) is greatly reduced, the restoration of the blood-brain barrier is delayed and the ultrastructural organization of the reorganising perineurium is dramatically changed. The aberrant perineurial structure and function observed in the presence of bleomycin are postulated to result from the effects of the drug on haemocytes which, together with endogenous reactive cells, contribute to the normal process of glial repair.     

NMDA受体与中枢神经系统发育

中枢神经系统兴奋性氨基酸离子型受体－ＮＭＤＡ受体,是由ＮＭＤＡＲ１和ＮＭＤＡＲ２两个亚单位共同构成的受体通道复合体。ＮＭＤＡ受本激活后可引起神经元细胞对Ｎａ＾＋,Ｋ＾＋和Ｃａ＾２＋通透性增强,产生兴奋性突触后电位,在中枢神经发育的过程中,ＮＭＤＡ受体通过不同亚型的选择性表达,改变自身的结构和功能,进而影响ＮＭＤＡ受体介导的Ｃａ＾２＋内流,调节神经元内Ｃａ＾２＋依赖的第二信使系统,最终实现对中枢神经     

Adenosine receptors in the central nervous system: relationship to the central actions of methylxanthines

Adenosine has a significant role in many functions of the central nervous system. Behaviorally, adenosine and adenosine analogs have marked depressant effects. Electrophysiologically, adenosine reduces spontaneous neuronal activity and inhibits transsynaptic potentials $\text{via}$ interaction with extracellular receptors. Biochemically, adenosine inhibits adenylate cyclase $\text{via}$ a “high” affinity receptor, and activates adenylate cyclase $\text{via}$ a “low” affinity receptor. These receptors, called “A₁” and “A₂” respectively, show differing profiles for activation by adenosine analogs. Radioactive N⁶-cyclohexyladenosine binds selectively to the “high” affinity receptor. One major class of antagonists is known at adenosine receptors: the alkylxanthines, including caffeine and theophylline. Radioactive 1,3-diethyl-8-phenylxanthine, a particularly potent antagonist, appears to bind to both low and high affinity adenosine receptors. Behavioral, electrophysiological, and biochemical effects of alkylxanthines are consistent with the hypothesis that the central stimulatory actions of caffeine and theophylline are due in large part to antagonism of central adenosine receptors.     

Ionic events following GABA receptor activation in an identified insect motor neuron

The ionic events underlying gamma-aminobutyric acid (GABA) receptor activation on the cell body of a cockroach identified motor neuron were investigated by using current-clamp and voltage-clamp techniques. The reversal potential for GABA-induced hyperpolarization was -77.0 +/- 2.4 mV (mean +/- s.e.m.; n = 22). The reversal potential for GABA was highly sensitive to changes in external chloride, only weakly affected by changes in external potassium, and independent of changes in either sodium or calcium ion concentration. Intracellular ion-sensitive microelectrodes confirmed that an influx of chloride ions mediated the GABA response. Intracellular injection of acetate, citrate, sulphate, fluoride or ammonium caused no change in the reversal potential for GABA. Intracellular injection of chloride, bromide, chlorate, bromate, or methyl sulphate shifted the reversal potential for GABA to values more positive than resting membrane potential. Evidence for chloride accumulating and for extrusion mechanisms was examined by using putative inhibitors. However, internal application of ammonium ions, and external application of 4-acetamido-4'-isothiocyanatostilbene-2,2'-disulphonic acid (SITS), 4,4'-diisothiocyanatostilbene-2,2'-disulphonic acid (DIDS), acetazolamide, furosemide, ammonium, zinc and copper ions, were all without effect on the reversal potential for GABA.     

Glutamate receptor binding to cat central nervous system membranes

L-[3H]Glutamate exhibited specific binding to fresh membranes of cat CNS under physiological conditions of pH and temperature. This binding occurred in the absence of sodium ions. Kinetic analysis of the data for cerebellum suggested the presence of two distinct binding sites: a high-affinity process (Kd = 0.33 microM) with a capacity of 15 pmol/mg protein and a low-affinity process (Kd = 1.8 microM) which had a capacity of 65 pmol/mg protein. Several structural analogues of glutamic acid were able to appreciably inhibit the binding of [3H]glutamate. The distribution of glutamate binding between 12 regions of the CNS was measured. The amygdaloid complex exhibited the highest binding followed by hippocampus > hypothalamus identical to visual cortex identical to thalamus identical to caudate nucleus > olfactory bulb identical to tectum identical to cerebellum > dorsal pons identical to medulla > cervical spinal cord. These findings are consistent with the binding of [3H]glutamate being to its receptor.     

Temperature dependence of temporal resolution in an insect nervous system

The vast majority of animals are poikilotherms, and thus face the problem that the temperature of their nervous systems rather smoothly follows the temperature changes imposed by their environment. Since basic properties of nerve cells, e.g., the time constants of ion channels, strongly depend on temperature, a temperature shift likely affects the processing of the temporal structure of sensory stimuli. This can be critical in acoustic communication systems in which time patterns of signals are decisive for recognition by the receiver. We investigated the temperature dependence of the responses of locust auditory receptors and interneurons by varying the temperature of the experimental animals during intracellular recordings. The resolution of fast amplitude modulations of acoustic signals was determined in a gap detection paradigm. In auditory receptors and local (second order) interneurons, temporal resolution was improved at higher temperatures. This gain could be attributed to a higher precision of spike timing. In a third-order neuron, a rise in temperature affected the interactions of inhibition and excitation in a complex manner, also resulting in a better resolution of gaps in the millisecond range.