Neil A. Croll

Cytology and Kinetics of microgametogenesis and fertilization in Plasmodium yoelii nigeriensis

The sexual development of the microgametocyte of Plasmodium yoelii nigeriensis may be subdivided into microgametogenesis which includes exflagellation, dispersal of the gametes and fertilization. Under our experimental conditions microgametogenesis takes about 8-15 min at 20 degrees C, the duration of this period being inversely related to temperature. Exflagellation takes less than 1 min, subsequent dispersal of gametes may continue for 40 min. We find that exflagellation is totally inhibited in vitro by temperatures of 30 degrees C and above, and by certain invertebrate tissue culture media. Exflagellation may occur within a persistent host cell plasmalemma, which seriously impedes the escape of the 8 microgametes. Microgametes move by sinusoidal or helical waves which may be rapid (10 waves/s), slow (smaller than 1 wave/s) or they may be immobile. Microgamete activity, which is alternately rapid/slow or slow/immobile, declines linearly with time. Fertilization which takes less than 1 min results from characteristic behavioural changes by the microgamete; vibratory waves are responsible for the penetration of the macrogamete by the microgamete. The microgamete completely enters the macrogamete and therein continues its cyclical activity.

Acclimatization in the Eccritic Thermal Response of Ditylenchus Dipsaci

The eccritic temperature or thermal preferendum of D. dipsaci in a heat gradient has been investigated with respect to acclimatization. By storing D. dipsaci at 10°, 20°, and 30° C for 30 days and then introducing them into a heat gradient it was found that they accumulated at temperatures which corresponded to the storage temperature; acclimatization had therefore occurred. They also showed greatest activity at their storage temperatures.

Activity, ageing and penetration of hookworm larvae

Lipid levels of infective larvae of Ancylostoma tubaeforme are reduced and their behavioural activity declines with age. We have measured behavioural activity using the percentage active, rate of activity, and the percentage of larvae able to penetrate a membrane. Neostigmine bromide, a cholinergic drug, increased larval activity in all tests. Larvae, stored at 4 and 10 °C and in hypertonic saline, were inactive but consumed lipid. When returned to isotonic saline at 26 °C, these larvae were no more active than those at 26 °C throughout. We found no evidence that such inactive larvae had entered a state of quiescence. All our results, and those of other workers, have been used to emphasize that larval ageing is related directly to decreased metabolic rates, and not primarily to lipid levels.

Asymmetry in Nematode Movement Patterns and Its Possible Significance in Orientation

An analysis of previously published and fresh data emphasises the possible significance of movement patterns in orientation and in sampling the environment by nematodes. A comparison is made of the asymmetry of lateral undulation in several nematodes and examples are given from P. redivivus which suggest that such asymmetries may be influenced by temperature and electrical currents. Vertical and horizontal movement patterns in P. redivivus are also related to orientation mechanisms.

Sensory basis of activity in Ancylostoma tubaeforme infective larvae

Upon stimulation, following a period of ambient conditions, infective A. tubaeforme larvae follow a committed characteristic pattern of activity, after being released by short-term mechanical or continuous photic stimulation. For the photic response this is stimulated by an increase in the intensity of stimulation, and for non-dark-adapted larvae a sudden fivefold increase in illumination is required, irrespective of previous stimulation. Acetylcholine chloride, adenosine triphosphate, γ-amino butyric acid, histamine diphosphate, 5-hydroxytryptamine, neostigmine bromide, physostigmine (eserine), potassium hydroxide, succinyl choline chloride and d -tubocurarine chloride have been added to larvae and their subsequent postures and activity recorded. It is concluded that the typical activity pattern of larvae may be altered by the use of drugs which interfere with neuromuscular phenomena, and therefore the activity responses of infective A. tubaeforme are based on sensory and neurosecretory rather than energetic considerations. We thank Mrs Helen Foreman for maintaining the larvae and the Medical Research Council of Great Britain for their generous support.

Sensory basis of activation in nematodes

Abstract Activation in nematodes may be either spontaneous, or in response to exogenous stimulation. The initiation of activity in free-living nematodes, and free-living stages of parasitic nematodes, has been related to their biology. Under uniform conditions Panagrellus redivivus is continuously active, Trichonema spp. infective larvae are inactive, and Ditylenchus dipsaci and preinfective Trichonema spp. are spontaneously active. The results fit the hypothesis that a “quantum of activity” is released in infective Trichonema by environmental changes, and once triggered off, the nematode is apparently “committed” to a period of activity. These observations have been used to construct models showing the relationship between exogenous sensitivity and endogenous pacemakers.

Necator americanus: Activity patterns in the egg and the mechanism of hatching☆

Abstract Necator americanus developed normally in distilled water and in solutions of up to 4% NaCl, hatching however, occurred only in the lower tonicities. Together with other observations, this led to the conclusion that, as with many other nematodes, osmotic changes were critical for emergence. Behavioural movements of the larva within the egg have been described, and it has been suggested that the larva ‘feeds’ within the egg, and this involves head waving and oesophageal pumping into the intestine. Enzymes are thus flushed into the egg, causing membrane changes, an influx of water, and a considerable distention of the egg. The pressure is finally released by the rotary movements of the stoma against the egg membranes, causing a break in the egg through which the larva immediately passes.

The mechanism of orientation in nematodes.

The possible mechanisms of nematode orientation are related to their categories of behaviour, and the presence of orientations which are not taxes is reviewed. The problem of movement and bilateral symmetry is then discussed. Using stimuli at differing pulse rates, the galvanotaxis of Panagrellus redivivus and the phototaxis of Chromadorina viridis are investigated. Finally the results are related to possible mechanisms of orientation.

Ancylostoma tubaeforme: Osmoregulatory ampulla of larvae

Abstract Weinsteins 1952 observations on the osmoregulatory ampulla of Ancylostoma caninum and Nippostrongylus brasiliensis have been reexamined using A. tubaeforme . Weinsteins data have been broadly confirmed, but there are certain differences. Pulsations of the ampulla ceased below 15 C and above 45 C, or when sealed on a slide for 24 hr or in propylene phenoxytol. succinyl choline, or cyanide. The relationship between pulsation rate and osmosity was not linear, as found by Weinstein. It is suggested that larval movement is a necessary part of osmoregulation, and that ampulla contraction is a reflex action occurring when distended. The sheath plays no part in osmoregulation; larvae are unable to regulate in hypertonic conditions; and the ampulla is involved in osmoregulation of preinfective larvae.

Nematode Setae as Mechanoreceptors

The somatic setae of Chromadorina bioculata and Enoplus communis have been examined with the electron microscope. Their structure is in agreement with their function as mechanoreceptors. The cuticular elements of the setae are weakened at their base and they appear to pivot in a cuticular depression. The sensory element is a modified cilium, which takes the form of a typical (9 + n) microtubular organisation at the base of the setae. These cilia connect with nerves which proceed into the lateral cords. The wider possibility of mechanical deformation of the cuticle being transmitted to the setae is discussed.