CHEMICAL STIMULUS DETERMINANTS OF CAT GENICULATE GANGLION CHEMORESPONSIVE GROUP II UNIT DISCHARGE

Geniculate ganglion chemoresponsive group II units were studiedin anesthetized cats. A wide variety of chemical substanceswere applied to the surface of the tongue to test for theirstimulating effectiveness. Distilled water extracts of animaltissues (beef, cod, eggs, etc.) proved to be strong stimuli.A survey of a variety of chemical subtances disclosed that themost effective excitatory stimuli were certain amino acids (L-proline,L-cysteine, L-lysine, L-histidine, etc.), di- and triphosphatenucleosides and certain other substances (usually containingnitrogen). In testing compounds related to proline and histidineit was discovered that the heterocyclic ring components pyrrolidineand imidazole were as stimulatory as the parent amino acids.To further specify the properties of excitatory stimuli manysimple heterocyclic compounds were tested. Optimum heterocyclicstimuli were four to six member nonaromatic (except for imidazole),nitrogen compounds. Neural discharge to nitrogen heterocycleswas related to two structural and chemical factors: (1) a stericfactor (in particular, ring size); and (2) the relative basicityof the compounds as indicated by pKa values. ^* This research was financed in part by USPHS Research GrantNINDS-11220 and NSF Research Grants GB-4l446X, GB-39868.     

Optimal water-use efficiency in a California shrub

Abstract. The stomatal behaviour of a California chaparral shrub was compared with that predicted by a model of optimal water-use efficiency (Cowan & Farquhar, 1977). The daily courses of stomatal conductance, evaporation, and assimilation were calculated as was the derivative of evaporation with respect to assimilation (∂ E /∂ A ). The derivative ∂ E /∂ A was not constant, and the measured courses of conductance were not optimal, but daily courses of evaporation and assimilation were usually very close to what would have been predicted had ∂ E /∂ A been constant. This discrepancy arises because evaporation and assimilation are sometimes so severely constrained by the microenvironment that stomatal conductance has almost no effect on them.     

Anopheles culicifacies: effects of age on the male reproductive system and mating ability of virgin adult mosquitoes

Abstract. Under controlled laboratory conditions of 28–30^oC and 16:8 L:D photoperiod, an attempt was made to develop an age-grading technique for Anopheles culicifacies males. Mating activity was maximal when females were 5–12 days old and males were 5–7 days old. The numbers of total and mature spermatocysts declined significantly with age, and the proportion of the testes occupied by the sperm reservoir increased as virgin males grew older. Mating resulted in the loss of spermatozoa and accessory gland substance from the reproductive system. Loss of mating ability of older virgin males seemed to be age-related, because the reproductive system contained ample supplies of accessory gland substance and spermatozoa. Morphological changes of the reproductive system, due to mating and age, were used to infer the age and reproductive history of unknown males in a laboratory evaluation.     

Observations on thermoregulation in the western slender glass lizard, Ophisaurus attenuatus attenuatus (Sauria: Anguidae)

Based upon thermocouple implantation, thermal preferenda and voluntary maxima for the head and body were studied in three individuals of Ophisaurus attenuatus attenuatus collected in Texas. Calculated grouped data for the head and body mean preferred temperature were 31.2°C (range 29.O° -34.7°C) and 31.8°C (range 30.3° -34.5°C) respectively. Gaping or panting were found to be absent in the O. a. attenuatus examined in this study.     

Extracellular Matrix Augments Mechanical Properties of Pseudopodia in the Carnivorous Foraminiferan Astrammina rara: Role in Prey Capture

The seemingly delicate, strand-like pseudopodia of Astrammina rara , a carnivorous benthic foraminiferan, adhere to and withstand the rigorous movements of meiofaunal prey. Previous electron microscopic studies identified two novel structures that might account for the unusual tensile properties of these pseudopodia: 1) an extensive, coiled microtubule cytoskeleton and 2) a fibrous extracellular matrix vesting the pseudopodial surface. In the present study, we found that pseudopodial networks microsurgically removed from A. rara's cell body captured Artemia metanauplii as efficiently as intact organisms, and therefore used them to test the role of microtubules and extracellular matrix components in augmenting pseudopodial strength. Agents that specifically disassemble micro-tubules (1 mM colchicine or 20 μM nocodazole) or generally disrupt pseudopodial integrity (heat, 10 mM formaldehyde, 1 mg/ml saponin) failed to inhibit prey capture. All of these treatments left the extracellular matrix intact as revealed by immunofluorescence and scanning electron microscopy. The elastic and tensile properties of the extracellular matrix, isolated by solubilization of pseudopodial cytonhsm using the nonionic detergent Triton X-100, were similar to those of intact pseudopodial networks when assayed with calibrated microneedles or a flexible rubber substrate. These observations indicate that A. rara uses a fibrous extracellular matrix to augment cytoplasmic tensile properties.