Effects of starvation and sucrose feeding on corpora allata of last instar larvae of Manduca sexta: in vitro activity, size, and cell number

Abstract Larvae of the tobacco hornworm moth Manduca sexta starved for the first 3 days of the last (fifth) stadium undergo a supernumerary moult. If they are provided with sucrose during the starvation period, they develop into normal pupae although pupation is delayed. The activities of the corpora allata (CA) from normal, starved, and sucrose fed larvae were followed through the fifth stadium with a radiochemical assay for Juvenile Hormone (JH) biosynthesis. An attempt was made to correlate CA-activity with CA cell number, size, and protein content.
In CA of normally fed larvae the rate of JH synthesis declined to undetectable levels by day 4 which was also the time of exposure of the dorsal vessel. In CA of starved larvae, the rate of JH synthesis at first decreased but began to increase on day 3 and reached a peak value by day 7 , at which time head capsule slippage occurred. In CA of sucrose fed larvae, the rate of biosynthesis declined as in normal larvae but the decline was extended over a longer period. Exposure of the dorsal vessel was delayed in the same manner and occurred on days 7–9. The major JH in all cases was JH-II.
The CA comprise c. 150 cells in the early fifth stadium, and this number remained constant during the fifth stadium in all three feeding regimens. In normal larvae, CA size and protein content increased several-fold during the stadium whereas in starved and sucrose-fed larvae they increased slowly and in agreement with the altered timing of developmental events. In none of the groups was the CA activity pattern correlated with morphometric changes of the CA. The rates of JH biosynthesis were not closely correlated with published JH titre curves. The in vivo mechanisms for regulation of JH production remain to be elucidated.     

Morphometric and electrophysiologic research on the parafascicular complex of the thalamus in early ontogeny in the rabbit

Electrophysiological, morphometric and behavioural studies have been made on the role of parafascicular complex in regulation of nociceptive sensitivity in 45 rabbits from the 1st to the 16th day of their postnatal life. The evoked potential to nociceptive stimulation was recorded already in 1-day animals. Analysis of amplitude-temporal parameters of the EPs in acute experiments revealed a sharp increase in their positive phase at the 7-8th day of life. As it was shown in the behavioural experiments, that is just the period of maximum generalized reaction to nociceptive stimulation. It was found that to this age, the surface of neurones in the complex significantly increases, their density remaining still high. The data obtained are discussed in relation to factors which account for ontogenetic changes in electrophysiological correlates of neuronal responses in the parafascicular complex to peripheral nociceptive stimulation.     

A decrease in the content of immunoreactive alpha- and gamma-endorphins in the blood and the suppression of their hypersecretion under the influence of dexamethasone in emotional stress in monkeys

Daily administration of 12 mg of dexamethasone to monkeys during 10 days resulted in decrease of the levels of alpha- and gamma-endorphins and cortisol 7 days after the first injection. The titers of these peptides in plasma of monkeys. exposed to two hours of immobilization stress were elevated twice above basal levels. The maximum elevation took place 6 hours after the beginning of immobilization. This effect wasn't detected in monkeys, which received 12 mg of dexamethasone during 10 days.     

Inhibition of RNA Synthesis and the Relationship between Nucleolar and Mitotic Cycles in Zea mays Root Meristems

The relationship between nucleolar and mitotic cycles has beendetermined after treatment of root apices of Zea mays with ethidiumbromide. In the meristematic regions of the stele the two cyclesare not much displaced in relation to each other except fora delay in the onset of the disorganization phase. A few nucleolipersist into metaphase and a few nuclei undergo an amitoticdivision. In the cap initials the drug greatly delays the onsetof disorganization of the nucleolus, which normally occurs beforeprophase in this region. It also delays the completion of reorganizationso that fully organized nucleoli are no longer available duringthe last half of telophase. In the quiescent centre the onsetof disorganization and the end of reorganization of the nucleoliare also delayed in relation to mitosis. There is no evidencefor a delay in the onset of reorganization in any region ofthe meristem. Some cells form multiple micronucleoli and this aberrant behaviouroccurs more often in the cap initials than elsewhere as doesamitotic division.