Nervous System Of Cockroach Research Articles

Dopamine 1-like receptor in the brain holds key to zombie cockroach transformation

It's a grizzly scene; a female jewel wasp (Ampulex compressa) wrestles an American cockroach (Periplaneta americana) to the ground. But what follows is a masterclass in neurosurgery. Following a precise sting aimed at the first bundle of nerves in the body, immobilising the cockroach's front legs, the wasp then deals its coup de grâce through the neck, aiming a second sting directly into a region of the brain known as the central complex, transforming the cockroach into a zombie-incubator for her egg. ‘Biochemical analysis of the venom shows the presence of [the neurotransmitter] dopamine’, says Frederic Libersat from Ben Gurion University of the Negev, Israel, adding that the neurotransmitter is entirely responsible for the initial stage of the transformation, when the cockroach begins to groom obsessively. However, it wasn't clear which of the two possible dopamine receptors (D1-like receptor or D2-like receptor) in the cockroach brain could be mediating the neurotransmitter's gruesome effect. So, Stefania Nordio (Ben Gurion University of the Negev) and Libersat set about bamboozling the cockroach's nervous system with drugs to identify which receptors are responsible for the deadly transformation that robs the insects of free will.‘These experiments require some technical skill and lots of practice’, says Libersat, who chose a series of drugs that selectively activate or disable the dopamine receptors in the cockroach's brain, to identify which receptors are targeted by the wasp's mind-bending venom. Injecting a drug that specifically activates the D1-like receptor into the central complex, Nordio and Libersat watched the insects as they ceased ambling around the arena and settled down to grooming, as if they'd been stung. However, the cockroaches that were injected with a drug that activates the D2-like receptor did not behave as if they had been stung and continued wandering around. The D1 receptor is the key receptor that controls the cockroaches’ urge to settle down and groom.The duo then injected cockroaches with a drug that blocks both dopamine receptors and waited a few hours before releasing jewel wasps in with the cockroaches to see if the drugs could prevent the wasps’ venom cocktail from disabling the cockroaches. Sure enough, the cockroaches were protected from the wasps’ stings, continuing to stroll around the arena even after being stung 6 h after the drug was applied. In addition, selectively blocking the D2 receptor with a drug, leaving the D1 receptor responsive, left the cockroaches vulnerable to the wasps’ stings, while the cockroaches treated to prevent the D1 receptor from responding to the toxic venom continued moving around the arena unaffected, providing more evidence that the D1 receptor is essential for initiating the transformation.Finally, the team tested the protective powers of the dopamine receptor blocking drugs to find out whether the dopamine receptors are targeted by wasp venom later in the cockroach's zombie transformation. Treating the cockroaches with a drug before letting the wasps loose, the team kept an eye on the stung insects for 2 days to find out whether they lost the ability to flee. Initially the cockroaches were unable to make a run for it. However, a day after being stung, when most cockroaches can no longer walk independently, the cockroaches that had been pre-treated with the drug had regained their free will and could make a dash for it; the wasp venom was targeting both dopamine receptors to rob the zombies of the ability to walk independently.So, jewel wasp venom specifically targets the D1 receptors in the cockroach brain to trigger the first stage of the zombie transformation, while both receptors rob the cockroach of the ability to walk unaided as the mind-altering venom takes hold.

Cloning and Expression of Cockroach α7 Nicotinic Acetylcholine Receptor Subunit.

Understanding insect nicotinic acetylcholine receptor (nAChR) subtypes is of major interest because they are the main target of several insecticides. In this study, we have cloned a cockroach Pameα7 subunit that encodes a 518 amino acid protein with futures typical of nAChR subunit, and sequence homology to α7 subunit. Pameα7 is differently expressed in the cockroach nervous system, in particular in the antennal lobes, optical lobes and the mushroom bodies where specific expression was found in the non-compact Kenyon cells. In addition, we found that cockroach Pameα7 subunits expressed in Xenopus laevis oocytes can assemble to form homomeric receptors. Electrophysiological recordings using the two-electrode voltage clamp method demonstrated that nicotine induced an Imax current of −92 ± 27 nA at 1 mM. Despite that currents are low with the endogenous ligand, ACh, this study provides information on the first expression of cockroach α7 homomeric receptor.

Depressing activity of Jaburetox, a natural insecticide-derived from Jack Bean Urease, at cockroach nervous system

Depressing activity of Jaburetox, a natural insecticide-derived from Jack Bean Urease, at cockroach nervous system

Exposure to 50Hz electromagnetic field changes the efficiency of the scorpion alpha toxin.

BackgroundExtremely low-frequency (50 Hz) electromagnetic field (ELF-EMF) is produced by electric power transmission lines and electronic devices of everyday use. Some phenomena are proposed as “first effects” of ELF-EMF: the discrete changes in the membrane potential and the increase of the calcium channel activity as well as the intracellular concentration of Ca2+. Interaction of the scorpion alpha toxin with the sodium channel depends on the orientation of the charges and may be perturbed by changes in the membrane polarization. The toxin induces overexcitability in the nervous system and an increase in the neurotransmitters released with different consequences, mainly the paralysis of muscles. We assumed that the exposure to ELF-EMF 0.7 mT will change the effects of the insect selective scorpion alpha toxin (recombinant LqhαIT from Leiurus quinquestriatus hebraeus) at the level of the cercal nerve function, the synaptic transmission and on the level of entire insect organism. Taking into account the compensatory mechanisms in organisms, we tested in addition ten times higher ELF-EMF on whole insects.MethodsExperiments were performed in vivo on cockroaches (Periplaneta americana) and in vitro – on isolated cockroach abdominal nerve cord with cerci. In biotests, the effects of LqhαIT (10−8 M) were estimated on the basis of the insect ability to turn back from dorsal to ventral side. Three groups were compared: the control one and the two exposed to ELF-EMF – 0.7 and 7 mT. Bioelectrical activity of the cercal nerve and of the connective nerve that leaves the terminal abdominal ganglion was recorded using extracellular electrodes. LqhαIT (5 × 10−8 M) induced modifications of neuronal activity that were observed in the control cockroach preparations and in the ones exposed to ELF-EMF (0.7 mT). The exposure to ELF-EMF was carried out using coils with a size appropriate to the examined objects.ResultsThe exposure to ELF-EMF (0.7 mT) modified the effects of LqhαIT (5 × 10−8 M) on activity of the cercal nerve and of the connective nerve. We observed a decrease of the toxin effect on the cercal nerve activity, but the toxic effect of LqhαIT on the connective nerve was increased. Biotests showed that toxicity of LqhαIT (10−8 M) on cockroaches was reduced by the exposure to ELF-EMF (0.7 and 7 mT).ConclusionsThe exposure to 50 Hz ELF-EMF modified the mode of action of the anti-insect scorpion alpha toxin LqhαIT at cellular level of the cockroach nervous system and in biotests. Toxin appeared as a usefull tool in distinguishing between the primary and the secondary effects of ELF-EMF.

Neural Circuit Recording from an Intact Cockroach Nervous System

The cockroach ventral nerve cord preparation is a tractable system for neuroethology experiments, neural network modeling, and testing the physiological effects of insecticides. This article describes the scope of cockroach sensory modalities that can be used to assay how an insect nervous system responds to environmental perturbations. Emphasis here is on the escape behavior mediated by cerci to giant fiber transmission in Periplaneta americana. This in situ preparation requires only moderate dissecting skill and electrophysiological expertise to generate reproducible recordings of neuronal activity. Peptides or other chemical reagents can then be applied directly to the nervous system in solution with the physiological saline. Insecticides could also be administered prior to dissection and the escape circuit can serve as a proxy for the excitable state of the central nervous system. In this context the assays described herein would also be useful to researchers interested in limb regeneration and the evolution of nervous system development for which P. americana is an established model organism.

Neural Circuit Recording from an Intact Cockroach Nervous System

The cockroach ventral nerve cord preparation is a tractable system for neuroethology experiments, neural network modeling, and testing the physiological effects of insecticides. This article describes the scope of cockroach sensory modalities that can be used to assay how an insect nervous system responds to environmental perturbations. Emphasis here is on the escape behavior mediated by cerci to giant fiber transmission in Periplaneta americana. This in situ preparation requires only moderate dissecting skill and electrophysiological expertise to generate reproducible recordings of neuronal activity. Peptides or other chemical reagents can then be applied directly to the nervous system in solution with the physiological saline. Insecticides could also be administered prior to dissection and the escape circuit can serve as a proxy for the excitable state of the central nervous system. In this context the assays described herein would also be useful to researchers interested in limb regeneration and the evolution of nervous system development for which P. americana is an established model organism.

Alterations in acetylcholinesterase and electrical activity in the nervous system of cockroach exposed to the neem derivative, azadirachtin

Botanical insecticides are relatively safe and biodegradable, and are readily available sources of bioinsecticides. In recent years, the neem derivative, azadirachtin, has been examined as an alternative to synthetic insecticides because of its broad-spectrum insecticidal action. Because many of the natural products and synthetic compounds used in the control of insect pests are known to exhibit electrophysiological effects, in this paper we focused our studies on the alterations in the activity of the enzyme acetylcholinesterase (AChE) and electrical activity in the nervous system of the cockroach, Periplaneta americana, exposed to azadirachtin. Exposure to azadirachtin produced an excitatory effect on spontaneous electrical activity as well as cercal sensory-mediated giant-fiber responses in the cockroach. Topical exposure to sublethal doses of azadirachtin did not result in any significant alterations in the AChE activity in different regions of the nervous system. We suggest that azadirachtin exerts excitatory action on the electrical activity in the nervous system of cockroach by interfering with the ion channels in the nerve membrane, the probable target of several insecticides.

Imidacloprid actions on insect neuronal acetylcholine receptors

The neonicotinoid insecticide Imidacloprid acts at three pharmacologically distinct acetylcholine receptor (AChR) subtypes in the cockroach (Periplaneta americana) nervous system, but is ineffective on muscarinic receptors. Imidacloprid (3-100µmoll-1) induced dose-dependent depolarizations at cockroach cercal afferent/giant interneurone synapses. These responses were insensitive to 20µmoll-1 atropine but were completely blocked by the nicotinic antagonist mecamylamine (50µmoll-1). Similarly, Imidacloprid-induced depolarizations of cultured cockroach dorsal unpaired median (DUM) neurones dissociated from the same (terminal abdominal) ganglion were also completely blocked by 100µmoll-1 mecamylamine. However, two components of the response could be distinguished on the basis of their differential sensitivities to 0.1µmoll-1-bungarotoxin (-BTX), which selectively blocks AChRs with 'mixed' nicotinic/muscarinic pharmacology in this preparation. This indicates that Imidacloprid affects both AChRs sensitive to -BTX and -BTX-insensitive nicotinic acetylcholine receptors (nAChRs). Thus, in the cockroach, Imidacloprid activates -BTX-sensitive synaptic nAChRs in giant interneurones, -BTX-insensitive extrasynaptic nAChRs in DUM neurones, and a recently characterized DUM neurone 'mixed' AChR that is sensitive to both nicotinic and muscarinic ligands. Imidacloprid does not act on muscarinic acetylcholine receptors (mAChRs) present on DUM neurone cell bodies and at the cercal afferent/giant interneurone synapses. This study shows that Imidacloprid can act on pharmacologically diverse nAChR subtypes.

Novel tachykinin-related peptides in the cockroach nervous system and intestine. Structure, distribution, and actions.

Novel tachykinin-related peptides in the cockroach nervous system and intestine. Structure, distribution, and actions.

Dihydrooxadiazines: Octopaminergic system as a potential site of insecticidal action

Dihydrooxadiazines are structural analogs of octopamine and were compared with octopamine for their ability to compete with [ 3 H]dihydroergocryptine ([ 3 H]DHE) for binding sites on DHE-sensitive receptors, to stimulate adenylate cyclase activity in nervous system homogenates of Periplaneta americana L., and to modulate the action of the peptide proctolin on the oviducal muscles of Locusta migratoria L. [ 3 H]DHE binding was inhibited by low concentrations (μM range) of octopamine, phentolamine, N-demethylchlordimeform (DCDM) and several dihydrooxadiazines. The tested dihydrooxadiazines acted as aminergic agonists in stimulating cyclic AMP production in cockroach nervous system homogenates and did not show additive effects with octopamine, whereas additivity was observed with 5-hydroxytryptamine. The relative potency of octopaminergic antagonists, including mianserin, cyproheptadine, phentolamine, and gramine, to block octopamine-mediated elevation of cyclic AMP production was similar to the rank-order potency of the same antagonists to inhibit dihydrooxadiazine-mediated elevation of cyclic AMP production. Octopamine, 2-(4-bromophenyl)-5,6-dihydro-4H-1,3,4-oxadiazine (4-Br-PDHO), and 8-Br-cyclic AMP caused increased phosphorylation of proteins that are phosphorylated by exogenously added cyclic AMP-dependent protein kinase. These results indicate that the dihydrooxadiazine-induced rise in cyclic AMP levels in homogenates of the cockroach nervous system results directly in activation of an endogenous cyclic AMP-dependent protein kinase. 4-Br-PDHO behaved similarly to octopamine in modulating the action of proctolin-induced contractions in locust oviducal muscles. These observations suggest that dihydrooxadiazines act as octopamine agonists and have an octopaminergic action in modulating the action of proctolin. Thus, it is proposed that dihydrooxadiazines exert at least part of their insecticidal and miticidal actions through interaction with the octopaminergic system.

Dihydrooxadiazines: Octopaminergic system as a potential site of insecticidal action

Dihydrooxadiazines are structural analogs of octopamine and were compared with octopamine for their ability to compete with [3H]dihydroergocryptine ([3H]DHE) for binding sites on DHE-sensitive receptors, to stimulate adenylate cyclase activity in nervous system homogenates of Periplaneta americana L., and to modulate the action of the peptide proctolin on the oviducal muscles of Locusta migratoria L. [3H]DHE binding was inhibited by low concentrations (μM range) of octopamine, phentolamine, N-demethylchlordimeform (DCDM) and several dihydrooxadiazines. The tested dihydrooxadiazines acted as aminergic agonists in stimulating cyclic AMP production in cockroach nervous system homogenates and did not show additive effects with octopamine, whereas additivity was observed with 5-hydroxytryptamine. The relative potency of octopaminergic antagonists, including mianserin, cyproheptadine, phentolamine, and gramine, to block octopamine-mediated elevation of cyclic AMP production was similar to the rank-order potency of the same antagonists to inhibit dihydrooxadiazine-mediated elevation of cyclic AMP production. Octopamine, 2-(4-bromophenyl)-5,6-dihydro-4H-1,3,4-oxadiazine (4-Br-PDHO), and 8-Br-cyclic AMP caused increased phosphorylation of proteins that are phosphorylated by exogenously added cyclic AMP-dependent protein kinase. These results indicate that the dihydrooxadiazine-induced rise in cyclic AMP levels in homogenates of the cockroach nervous system results directly in activation of an endogenous cyclic AMP-dependent protein kinase. 4-Br-PDHO behaved similarly to octopamine in modulating the action of proctolin-induced contractions in locust oviducal muscles. These observations suggest that dihydrooxadiazines act as octopamine agonists and have an octopaminergic action in modulating the action of proctolin. Thus, it is proposed that dihydrooxadiazines exert at least part of their insecticidal and miticidal actions through interaction with the octopaminergic system.

Actions of nitromethylenes on an α-Bungarotoxin-sensitive neuronal nicotinic acetylcholine receptor

Nine nitromethylene analogues were tested for their actions on insect neuronal nicotinic acetylcholine receptors (nAChRs). Microelectrode recordings were used to study the actions of nitromethylenes on the cell body of an identified cockroach ( Periplaneta americana) motor neurone, the fast coxal depressor ( D f ) in the metathoracic ganglion. Six nitromethylenes showed potent nAChR agonist actions; others were without nAChR agonist actions. Five nitromethylenes competitively displaced bound [ 125I]-α-bungarotoxin from cockroach nervous system membranes. The rank orders of potency for the compounds determined by their depolarizing actions and their ability to displace [ 125I]-α-bungarotoxin binding were similar. These findings, together with toxicity data obtained on the insects, Nephotettix cinciteps and Nilaparvata lugens, support the hypothesis that insect nAChRs are molecular targets of nitromethylene insecticides. Structure-activity relationships of the nitromethylenes suggest that optimal activity at neuronal nAChRs requires the presence of an electron-withdrawing component in the region of the aryl substituent and an electron-donating component at the 3′ position of the imidazolidine ring.

Monoclonal antibody immunohistochemistry in the American cockroach identifies a novel neuropeptidergic system similar to, but distinct from this insect's (FM)RFamide-like system

A monoclonal antibody to peptidergic neurons in the neuroendocrine system of the Colorado potato beetle immunohistochemically labels neuropeptide-like substances throughout the cephalic neurosecretory system of the American cockroach, Periplaneta americana. The dictyopteran antigen shows a histological distribution similar to that of the neuropeptide-like material which we have described earlier using (FM)RFamide specific antibodies. It was conclusively demonstrated, particularly by means of a convenient double labelling procedure, that the (FM)RFamide- and the coleopteran neuropeptide-like antigens are not localized in the same neuronal structures, although both neurochemicals are in close vicinity to one another. The relative abundance of the immunoreactive products in neurons throughout the cockroach nervous system and retrocerebral complex, in addition to its apparently homologous distribution in species of different insect orders, suggests an important role of this material in insect neuro(endocrine)-physiology.

Characterization of phenylalkylamine binding sites in insect (Periplaneta americana) nervous system and skeletal muscle membranes

AbstractThis study has identified specific, stereoselective phenylalkylamine (PAA, (±)‐ [3H]verapamil) binding sites of low‐affinity and high‐density in cockroach (Periplaneta americana) nervous system and skeletal muscle membranes. Scatchard transformation of equilibrium binding data revealed a single population of binding sites in both tissues with dissociation constants (Kd) of 273 nM and 377 nM and binding capacities (Bmax) of 23 pmol·mg protein−1 and 37pmol·mg protein−1 for cockroach nervous tissue and skeletal muscle membranes, respectively. The PAA binding site in cockroach nervous tissue membranes was found to be dihydropyridine (DHP)‐insensitive, whereas the corresponding site in cockroach skeletal muscle membranes was DHP‐sensitive. This property of a DHP‐sensitive PAA receptor distinguishes the binding sites identified in cockroach skeletal muscle from those in cockroach nervous tissue and indicates that pharmacologically distinct putative Ca2+ channel subtypes are present in insect nerve and muscle. © 1993 Wiley‐Liss, Inc.

Pharmacologically distinct calcium channels are present in insect nervous system and skeletal muscle

Radiotracer flux methods have demonstrated the presence of dihydropyridine(DHP)-insensitive and DHP-sensitive components of phenylalkylamine(PAA)-sensitive 45Ca 2+ uptake in cockroach ( Periplaneta americana) nervous system and skeletal muscle membranes respectively. When microsac and proteoliposome preparations were incubated with 10 μM (±)-verapamil, control uptake (i.e. K +-stimulated 45Ca 2+ uptake measured in the absence of drugs, taken as 100%) was reduced by ∼ 80–90% in all preparations. However, when these preparations were incubated with 10μM (±)-nitrendipine, almost complete block of 45Ca 2+ uptake by cockroach skeletal muscle proteoliposomes was observed, but (±)-nitrendipine at the same concentration failed to inhibit > 50% of control uptake by either microsacs or proteoliposomes prepared from nervous tissue. These findings suggest that tissue-specific Ca 2+ channels with distinct pharmacological properties are present in cockroach nerve and muscle. PAA- and DHP-sensitivity are well-documented pharmacological characteristics of vertebrate L-type Ca 2+ channels, so the results of the present study indicate that Ca 2+ channels with L-type properties are present in insect skeletal muscle. By contrast, the identification of PAA-sensitive/DHP-insensitive components of 45Ca 2+ uptake in cockroach nervous system preparations suggests that this tissue contains Ca 2+ channels that are pharmacologically distinct from vertebrate L-type Ca 2+ channels.

Accessibility of the insect nervous system to a neurotoxic polypeptide

AbstractThe binding and accessibility of an insect selective neurotoxic polypeptide derived from scorpion venom (AaIT, Mr = 8 kDa) to the cockroach nervous system was studied by the aid of binding assays and light microscopy autoradiography resulting in the following information: The toxin possesses high paralytic potency to the cockroach (ED50= 4 ng per 100 mg of body weight) and high binding capacity (13.8 ± 1.8 pmol per mg protein) to its nervous system. When incubated with dissected and anatomically desheathed central nervous tissue the radioiodinated toxin ([125I]AaIT) revealed an obvious high affinity binding specificity. In contrast, the skeletal muscles of the cockroach were completely devoid of specific binding sites of the [125I]AaIT. The latter observation provides additional support for the sodium channel selectivity of the AaIT toxin. Autoradiography of [125I]AaIT injected into the body cavity in doses inducing a fast paralysis revealed that the central and most parts of the peripheral nervous system are impermeable to the toxin. In the above injection assays the toxin was shown to bind to the terminal branches of motor nerves at their close proximity to the skeletal muscles. Computerized image analysis of the autoradiographical data followed by electron microscopy of the neuromuscular junctions suggest an accessibility of the terminal axonal membranes to the toxin. The above data, supported by previous electrophysiological studies, led to the conclusion that the peripheral terminal outbranchings of the motor nerves serve as the main sites of accessibility to paralytic polypeptide neurotoxins.

Octopamine Uptake and Metabolism in the Insect Nervous System

Several insect tissues were examined for their ability to take up octopamine in the presence and absence of sodium ions. The cockroach Malpighian tubules, ovary, and ventral nerve cord showed the highest level of sodium-dependent uptake. The adult firefly lantern exhibited substantial sodium-independent uptake. Some of these tissues were also examined for their ability to metabolize octopamine by N-acetylation. Measurable N-acetyltransferase activity was present in the cockroach ventral nerve cord, tobacco hornworm CNS, and firefly light organ. N-Acetylation is proposed to be the major metabolic pathway for octopamine in the cockroach (Periplaneta americana) nervous system. Several classes of compounds, including octopamine receptor agonists, tricyclic antidepressants, amphetamines, chloroethylbenzylamines, and some experimental insecticides, were tested for their ability to inhibit octopamine uptake and metabolism. The sodium-insensitive component of uptake was not inhibited by most compounds tested, but the sodium-sensitive component was strongly inhibited by xylamine, N-ethyl-N-chloroethyl-o-bromobenzylamine, and their aziridinium ions (60-100%). These compounds also effectively inhibited N-acetyl-transferase (IC50 values at or below 1 microM). Other good inhibitors of N-acetyltransferase included desipramine, synephrine, and an experimental insecticide, CGA 132427. Formamidine pesticides had limited effect on both processes, and neither action seems likely to be involved in their octopaminergic actions in vivo. Cocaine was unique in stimulating N-acetyltransferase activity. When inhibition of sodium-sensitive uptake is compared with inhibition of N-acetyltransferase in the cockroach ventral nerve cord, two groups of inhibitors are discernible. Type 1 compounds inhibit uptake without an effect on N-acetyltransferase, whereas type 2 compounds inhibit both processes. These results suggest a functional linkage between the uptake and acetylation of octopamine.

Insect nervous system [3H]saxitoxin binding sites: characterization and target size

Saxitoxin (STX) has proved useful in the isolation and characterization of vertebrate and invertebrate voltage-operated sodium channels. Membrane extracts from the nervous system of the cockroach Periplaneta americana contain a saturable component of specific [(3)H]STX binding. Scatchard analysis yields a K(D) of 0.84 nM, similar to that (3.0 nM) determined in electrophysiological studies on axons in the same tissue (Sattelle et al., 1979). The maximum number of binding sites, B(max) (8.25 pmol/mg protein), was higher than previously observed. The specific binding component was blocked by STX and tetrodotoxin (TTX), but not by scorpion (Leiurus quinquestriatus) venom, aconitine, veratridine, sea anemone toxin and deltamethrin, which act at different sites on the channel molecule. Unlabelled STX samples prepared from different sources (Mytilus, Saxidomus and Gonyaulax) were all effective as inhibitors of [(3)H]STX binding. Radiation inactivation was employed to determine the molecular target size of the [(3)H]STX binding molecule in membranes prepared from the cockroach nervous system. By this means M(r) = 171,400 +/- 25,000 was estimated for the insect sodium channel.

The potency of gamma-1,2,3,4,5,6-hexachlorocyclohexane (lindane)

The potency of gama-1,2,3,4,5,6-hexachlorocyclohexane (lindane) as a convulsant was examined in rats by infusion into a tail vein of the unrestrained animal using a lipid emulsion as vehicle and a dose rate of 200 μg/min. The concentration of drug in brain rose linearly up to a convulsant level, the rate of rise increasing with relative organ mass. The decline from a convulsant level was biphasic with half times of, respectively, 30 min and 3 days. Convulsant concentrations (CC) in brain were within the range obtained with other modes of administration and exhibited normal distribution but there was a moderate influence of sex, the ovarian cycle, and age on the individual response. The minimally effective and the mean convulsant doses recorded in the survey were, respectively, 1.5 and 2.4 mg/kg and, thus, of the same order as doses reportedly convulsant in the American cockroach as well as, under certain circumstances, in man. In the neonate, the mean CC in brain was 2.5 as against 4.5 μg/g wet weight in the adult. An argument is put forward to support the contention that this difference might be largely accounted for by the maturational increase in the lipid content of the brain. The argument uses an approximation to the mean CC in brain water which is 70 nmol/l in both the young suckling and the adult and corresponds to concentrations in which the drug reportedly effects neuroexcitation in the cockroach nervous system or binds to the ionophore of GABA-A receptors in rat brain membranes. The findings call for convulsive states in children after dermal application of lindane to be considered in terms of individual factors favouring rapid absorption as well as in terms of individual supersensitivity of the nervous system.

Monoclonal antibodies to the cockroach nervous system.

In the cockroach nervous system individual motor neurons may be identified with respect to their position in the thoracic ganglia and to the muscles they innervate. When their axons are cut they have the ability to regrow such that when regeneration is completed they have specifically reinnervated their normal target muscles. This suggests the existence of a specific intercellular recognition process between motor neurons and muscles, and that neurons innervating different muscles are biochemically distinct from one another. The goal of this study was to use hybridoma techniques to obtain monoclonal antibodies that bind to some motor neurons and not others. Mice were injected with whole nerve cord and hybridoma supernatants were screened immunohistochemically on sections of ganglion and leg muscle. The monoclonal antibodies were categorized according to four types of specificity: tissue, regional, cell-type, and neuron-subset specificities. Antibodies expressing neuron-subset specificity were obtained very rarely. The probability of their occurrence could be increased by treating the mice with immunosuppressant drugs after initial administration of immunogen or by fixing the immunogen with paraformaldehyde in a manner similar to that of the tissue sections used in the screening process. Two of the neuron-subset specific monoclonal antibodies (MAbs) are of particular interest with respect to the goals of this study. They bind to axon terminals in the muscles of some neurons and not others. They do not bind to neuronal cell bodies in the ganglion, which makes identification of the neurons difficult. However, from the known innervation pattern of the coxal depressor muscles it appears that one of these MAbs selectively binds to axon terminals from either the inhibitory motor neurons or the dorsal unpaired median cells. Other antibodies of interest bind selectively to the synapse-rich neuropile in the ganglia or to peripheral parts of the nervous system like the nerve roots.