Effects of a centipede venom fraction on insect nervous system, a native Xenopus oocyte receptor and on an expressed Drosophila muscarinic receptor.

Centipede venoms are complex protein mixtures; very few is known about their pharmacological actions. Application of a Scolopendra sp. venom fraction (SC1) on the cockroach giant axon induced an increase in the leak current correlated with a decrease in the membrane resistance, suggesting the presence in SC1 of components opening non-specific pores in the axonal membrane. On a cockroach central cholinergic synapse, microinjection of SC1 induced a small transient depolarization of the postsynaptic membrane, followed by a slow stable depolarization and a drastic decrease in the evoked subthreshold excitatory postsynaptic potential amplitude. A pretreatment of the ganglion with atropine or scopolamine reduced the amplitude of the SC1-induced depolarizing wave, suggesting a possible cholinergic muscarinic target. On control Xenopus oocytes, SC1 induced an inward oscillatory Ca2(+)-dependent Cl- current mediated through the activation of native lysophosphatidic acid receptors (LPAr). Indeed, pretreatment of oocytes with 1 microM N-palmitoyl-tyrosine phosphoric acid, a selective competitive antagonist of LPAr, decreased responses to SC1 by 70%. Application of SC1 to oocytes expressing a cloned Drosophila muscarinic receptor (Dml) induced a biphasic response comprising: (1) a large fast Cl- current that was abolished by pretreatment with atropine and scopolamine and (2) a slow and small oscillating Cl- current corresponding to the response observed in control oocytes. These observations confirm the presence of muscarinic agonists in SCI and reveal their direct action on an insect muscarinic receptor subtype homologous to mammalian M1-M3 receptors.

Significance of cranial circulation for the brain homeothermia in rabbits. I. The brain-arterial blood temperature gradient.

The hypothalamic-arterial blood temperature gradient (THpr-TAC difference) was studied on 10 freely moving rabbits at ambient temperatures between 0 and 42 degrees Celsius. In cold environment, below 10 degrees Celsius the THpt-TAC gradient varied considerably, but some distinct correlations were found between vasomotor responses of the nasal mucosa and fluctuations of brain temperature, as well as between vasomotor responses of the ear pinnas and changes of the arterial blood temperature. Vasodilatation of the nasal mucosa or the ear pinna caused respectively a drop in brain temperature or in arterial blood temperature. Opposite changes were induced by vasoconstriction in those areas. Variations in THpt-TAC gradient resulted from oppositely directed vasomotor responses in the nasal mucosa and in the ear pinnas. At high ambient temperatures above 35 degrees Celsius thermal panting was accompanied by selective brain cooling with respect to the arterial blood. Blocking the heat loss from the nasal mucosa caused an increase of the THpt-TAC difference, and under these conditions brain temperature was determined solely by arterial blood temperature. The assumed mechanism of the selective brain cooling in rabbits is the exchange of heat through the neurocranial bottom, between the ventral brain and the spacious splanchnocranial venous lakes supplied with blood from the nasal mucosa.

Significance of cranial circulation for the brain homeothermia in rabbits. II. The role of the cranial venous lakes in the defence against hyperthermia.

Chronic experiments were conducted on five freely moving rabbits at ambient temperatures of 0-42 degrees Celsius. The influence of nasal mucosal thermal changes on the venous blood temperature inside the pterygoid plexus and on the temperatures at three intracerebral sites were investigated against the background of the carotid arterial blood temperature shifts. A correlation was found between: (i) the fluctuations in the nasal mucosal temperature reflecting its vasomotor responses, (ii) temperature shifts of the pterygoid plexus venous blood, and (iii) of the ventral brain. Mucosal vasodilatation caused parallel drops in both the plexal blood and brain temperatures. However, mucosal vasoconstriction was accompanied by increases in temperatures at those sites. Intracranial thermal shifts were independent of the arterial blood temperature changes. During motor activity in normothermia nasal mucosal vasoconstriction was present, and in that case brain temperatures exceeded arterial blood temperature. During rest, mucosal vasodilatation appeared and brain base cooled below the arterial blood temperature. During panting in dry heat, the brain base was cooler than the arterial blood by as much as 0.5 degree Celsius. The intensity of the selective brain cooling was directly proportional to deep body temperature. The blockade of the respiratory evaporation in heat elicited an increase of the plexal venous blood as well as brain temperatures above the arterial blood temperature. We conclude that the venous blood outflowing from the nasal mucosa exerts a cooling influence on the brain through the pterygoid plexus.

Effect of K+ accumulation removal and high extracellular osmolarity on K+ current in insect axonal membrane.

The effect of a removal of K+ accumulation on K+ current in insect axonal membrane was observed. Experiments were performed on isolated giant axon of a cockroach using double oil gap technique. K+ accumulation was reduced by: (1) an outward water flow induced by non-electrolytes (urea, glucose) added to extracellular saline and (2) by an increase of non-specific permeability of axonal glial layer obtained after the application of DMSO. The conclusions are: (1) osmolar effect depends on the type of molecule used for osmotic shock, (2) increase of outward K+ current in conditions of high extraaxonal osmotic pressure is attributed to the decrease of K+ accumulation and outward water flow, (3) removal of K+ accumulation doesn't affect the kinetics and the time course of K+ current, (4) experiments confirmed the presence of an inactivating component in the axonal outward K+ current, (5) DMSO must be used cautiously as a solvent in electrophysiological experiments.

Ambient thermal conditions and thermoregulatory mechanisms in fever in rabbits.

At ambient temperatures 10 degrees C, 20 degrees C, 30 degrees C, and 40 degrees C the influence of heat dissipation on the thermoregulatory mechanisms in rabbits with fever was investigated. Temperature of the brain (TBr-accuracy +/- 0.05 degree C) temperature of the nasal mucosa (TN) and temperature of the ear pinna (TAU-accuracy +/- 0.5 degree C) were measured in freely moving rabbits. Changes of conditions of heat dissipation were produced by: preventing heat dissipation by convection and radiation by putting ear-pads on the ear pinnae, high humidity of air for blocking of heat loss through evaporation, and facilitation of heat dissipation through shearing of the fur. The changes of the ambient thermal conditions as well as of the ability of heat dissipation were followed by changes in the dynamics of functions of the remaining (effective) thermoregulatory mechanisms in the rabbits. Thus despite changed thermal conditions of the environment, the TBr of the rabbits with fever was stabilized at a similar level.

A method for analysis of thermosensitivity in the insect CNS.

A set for analysis of temperature effects on the CNS activity in insects is described. Thermostimulation can be applied to the whole body or to only some regions of CNS. An amplitude and rate interval analyzer (in cooperation with a microcomputer) makes it possible to do an analysis of the correlation between temperature and the neuronal firing rate. As an example of the use of this set an experiment on American cockroach Periplaneta americana was described. Thermosensitivity of the prothoracic ganglion was presented.

A simple method for recording body temperature in insects.

Application of thermocouples for measuring body temperature of insects is described in experiments on American cockroach (Periplaneta americana). The temperature of the head, mesothorax and abdomen was measured at rest and during flight. The overall accuracy of the measuring system was +/- 0.1 degrees C.

Arylsulphatase A and acid phosphatase activities in plasma and leucocytes during LPS fever in the ox (Bos taurus).

Intravenous injection of E. coli LPS (0.5 micrograms/kg) produced the biphasic elevation of rectal temperature (TR) in conscious oxen. The fever was accompanied by a significant increase of the arylsulphatase A (AsA) activities in plasma and in mononuclear leucocytes. In polymorphonuclear cells a substantial decrease of the AsA activity after 1 hr fever was observed. After 3.5 hr of fever the polymorphonuclear activity of AsA restored to normal found before LPS administration. In contrast with AsA, the pyrogenic dose of LPS caused negligible changes of the acid phosphatase (AcP) activities in the sampled materials. Daily-repeated injections of pyrogen into the same oxen attenuated magnitudes of fever as well as AsA responses in plasma and granulocytes. Heat-induced hyperthermia provoked only minute changes of the AsA and AcP.

[Modification of bioelectric functions in the nervous system as a result of neurotoxin action]. / Modyfikacja czynnosci bioelektrycznej osrodkowego ukladu nerwowego owada w wyniku dzialania neurotoksyn.

Natural neurotoxins are promising molecules in the actual search for the development of alternative pest management since chemical insecticides pose unacceptable risks to the environment and to health. The aim of the article is to describe the application of two electrophysiological methods (double-oil-gap technique used on cockroach isolated giant axon and microelectrode technique used on cockroach neurosecretory DUM cells in situ) to study neurotoxin effects on insect nervous system function.