Norman T. Davis

Serotonin-immunoreactive visceral nerves and neurohemal system in the cockroach Periplaneta americana (L.)

SummaryBy use of the indirect immunofluorescent technique applied to whole mounts of tissues and organs of the American cockroach, Periplaneta americana, serotonin-like reactivity has been demonstrated in an extensive meshwork of fibers on the surface of nerves of the subesophageal ganglion and the tritocerebrum. This meshwork appears to serve the neurohemal release of serotonin. In addition, several of these nerves contain two or more centrally located axons that appear to be serotonergic. The corpora cardica show immunoreactivity but do not appear to be a principal release site for serotonin. The nerves and ganglia of the stomadeal nervous system show immunoreactivity for serotonin and provide serotonin-positive innervation to the salivary glands and the visceral muscles of the stomodeum and midgut. The heart, hindgut, Malpighian tubules, fat body, and skeletal muscles all appear to lack serotonin immunoreactivity.

Improved Methods for Cobalt Filling and Silver Intensification of Insect Motor Neurons

A Parafilm disk floating on saline and bearing a drop of cobalt solution in which the nerve stump is bathed provides a convenient and versatile method for in vitro or in vivo filling of neurons for cobalt sulfide staining. Silicone grease around the edge of the disk provides an effective seal around the nerve as it passes between the two solutions. Using a modified developer, silver intensification of cobalt sulfide stained neurons may be done in the light at room temperature, and the time of optimum intensification may be observed under a dissecting microscope.

Studies of the reproductive physiology of Cimicidae (Hemiptera)—I. Fecundation and egg maturation

Abstract Observations were made under controlled conditions to determine the time required for the spermatozoa to reach various points in their migration. Special organs at the base of the ovarioles serve to hold the sperm until eggs are ready for fertilization. In virgin and mated females egg maturation is similar up to an early stage of yolk deposition, at which time eggs of the virgin females are resorbed. Ligation and implantation experiments indicate that the corpus allatum is essential for egg maturation. Its secretion does not become effective until at least 10 hr after feeding and is required for egg maturation to continue. Virgin females may be induced to produce eggs by corpora allata implants. Implants from males and virgin females as well as mated females are effective. External application of farnesol has an effect on egg maturation similar to corpus allatum implantation.

Studies of the reproductive physiology of Cimicidae (Hemiptera)—II. Artificial insemination and the function of the seminal fluid

Abstract Cimex lectularius L. was artificially inseminated by injecting sperm and seminal fluid into the spermalege. The fecundity of females inseminated in this way is about the same as normally inseminated females. Insemination may be made directly into the haemocoele but the resulting mortality is high. Seminal fluid is essential in insemination; without it spermatozoa do not migrate. Spermatozoa in seminal fluid in vitro become active and aggregate into dense masses from which the tails extend and move actively. The waves originate at the end of the tail and move towards the head. In vitro activity of the sperm resembles that observed in vivo . Spermatozoa can be activated in 0·07 M sodium citrate containing seminal fluid. Seminal fluid of various other cimicids can activate the sperm of C. lectularius . Artificial insemination may be done using activated sperm masses washed free of seminal fluid. The principal function of the spermalege is probably to hold the semen until activation occurs. Once activated the sperm pass through the haemocoele as a mass. Injection of activated sperm masses into the haemocoele is usually harmless and results in fecundation. Injection of unactivated sperm into the haemocoele often results in the death of the female and no eggs are produced. Eggs do not mature unless spermatozoa reach the upper part of the reproductive tract; this region is probably the source of the stimulus activating the corpus allatum.

Serial homologies of the motor neurons of the dorsal intersegmental muscles of the cockroach, Periplaneta americana (L.)

The types and locations of serially homologous motor neurons of the dorsal muscles in the cockroach Periplaneta americana remain rather constant regardless of the various adaptations of their muscles or the fusion of ganglia. However, the size and number of neurons do vary according to the development of the muscles they innervate. Neurons in four distinctive locations, two ipsisegmental and two antesegmental, innervate the dorsal longitudinal (DL) muscles in most segments. One of the ipsisegmental neurons (DLC) is common to all of the DL muscles of a segment and probably has a modulatory function. The dorsal oblique (DO) muscles of most segments have neurons in two antesegmental positions. One of these, an antesegmental, contralateral neuron, innervates both DO and DL muscles in each segment and is also probably modulatory. One neuron (DOC) of the prothoracic ganglion is the principal exception to the constancy of these serially homologous neurons. This neuron appears to be homologous to the DLC neurons of other segments but innervates the DO rather than the DL muscles.

Sperm activation and migration in bed bugs

Abstract The causes of sperm immotility in the seminal vesicles appear to be the lack of O 2 and the absence of carbohydrate substrates but not the hydrogen ion concentration or crowding. The process of activation of sperm results not only in sperm motility but in their aggregation to form masses. The motionless sperm can be activated in the absence of the seminal fluid by a variety of metal chelating agents such as EDTA, histidine, and dithizone. There is evidence for the presence of divalent cations in an easily dissociable form in the sperm. The findings suggest a possible mechanism of sperm activation, viz. the removal of divalent cations from an ‘energy reserve-divalent cation complex’ and the release of the substrates to initiate sperm activity. The seminal fluid, it is suggested, may exert a similar effect during sperm activation. Artificial insemination with chemically activated sperm reveals that such sperm fail to migrate. The cohesive and adhesive properties of sperm aid in the aggregation and migration of sperm mass in the hemocoel. An O 2 -gradient appears to be responsible for the directed migration of the sperm mass in the haemocoel. An activity-gradient in the sperm mass, corresponding to an O 2 -gradient, is apparent in in vitro experiments. Thiourea, an inhibitor of the actomyosin system, affects not only sperm motility but inhibits aggregation of sperm. The sperm mass placed in a droplet of haemolymph in vitro shows peripheral motility. Active sperm separate from such a preparation and remain motile for 24 hr. The possible significance of this in vitro finding is discussed in relation to the in vivo disaggregation of sperm.

Studies of the reproductive physiology of Cimicidae (Hemiptera)—III. The seminal stimulus

Abstract The presence of spermatozoa in the tissue of the upper reproductive tract of the female results in the release from the corpus allatum of the hormone controlling egg maturation. A ligature applied behind the head 2 hr after mating prevents egg maturation. Surgical removal of the conceptacula seminis of mated females usually results in inactivation of the corpus allatum. Females mated after removal of the conceptaculum can produce eggs. Injection of blood or the conceptacula of mated females into virgins does not result in the activation of the corpus allatum. Severance of the ventral nerve cord within 3 hr after mating prevents activation of the corpus allatum. Evidence that activation can be blocked by cutting the abdominal nerves is inconclusive.