A structural study of the cerebral ganglionic complex and retrocerebral system in the adult of Chironomus riparius

Abstract

Descriptions are given of the cerebral ganglionic complex and retro cerebral system of neoimaginal Chironomus riparius reared at 20°C. Changes resulting from differences in age, rearing temperature and reproductive state are also presented.

The anatomy of the cerebral ganglia, including the organisation of neuropile masses, of male neoimagines, and the fine structure of the neural sheath, cortical layer and neuropile is described for the first time in an adult chironomid. Two types of perineurial cells and three types of glial cells are distinguished on ultra structural criteria. A classification of five non-neurosecretory neuron types, based upon size, nuclear to cytoplasmic proportions and appearance, is given. Four paired groups of neurosecretory neurons were found in the brain and two paired groups in the suboesophageal ganglion. Five neurosecretory cell types are classified on the basis of their ultrastructural characteristics. The axon pathways of the cerebral neurosecretory cells and the elements of the retrocerebral system, including the paired corpora cardiaca, corpora allata, peritracheal tissues and "glandes post-cerebrales ant erieures", are described. The nervous and endocrine structures of the neoi maginal male are compared to those of the female.

Age related changes occurring within the brain and endocrine system are described in relation to fat body depletion, behavioural activity and appearance of the dorsal longitudinal flight muscles.

The effect that differences in rearing temperature have upon the longevity, size and weight of the adult is presented. The influence of rearing temperature upon the ultrastructure of the brain is described for the first time in an insect.

Evidence suggesting an association between the activity of the cerebral neurosecretory cells and female reproduction is given.

In the light of the results functional roles for several elements within the endocrine system are postulated. The possible significance that the observed structural changes in the nervous system have upon its functioning is discussed.