Neurons projecting from the brain to the corpora allata in orthopteroid insects: anatomy and physiology

Abstract

Retrograde and orthograde labeling of neurons projecting to the corpus allatum was performed in locust, grasshopper, cricket, and cockroach species in order to identify brain neurons that may be involved in the regulation of juvenile hormone production. In the acridid grasshopper Gomphocerus rufus L., and the locusts Locusta migratoria (R.&F.) and Schistocerca gregaria Forskal, the corpora allata are innervated by two morphologically distinguishable types of brain neurons. One group of 9-13 neurons (depending on species) with somata in the pars lateralis extend axons via the nervus corporis cardiaci 2 and nervus corporis allati 1 to the ipsilateral corpus allatum, whereas two cells in each pars lateralis have bilateral projections and innervate both glands. No direct connection between the pars intercerebralis and corpus allatum has been found. In contrast, neurons with paired axons innervating both glands are not present in Periplaneta americana (L.) and Gryllus bimaculatus de Geer. Instead, two cells in each pars lateralis project only to the gland contralateral to their somata. Electrophysiological experiments on acridid grasshoppers have confirmed the existence of a direct conduction pathway between the two glands via the paired axons of four cells that have been identified by neuroanatomy. These cells are not spontaneously active under experimental conditions. Ongoing discharges in the left and right nerves are unrelated, suggesting that the corpora allata receive independent neuronal inputs from the brain.

Anatomy and functions of brain neurosecretory cells in diptera

“…Electrophysiological properties of the NSCs have been studied in many species in other orders of insects (e.g., Carrow et al, 1984;Ichikawa, 1991;Moore and Loher, 1988;Virant-Doberlet et al, 1994). In flies, however, to date electrical activities of the MNCs have been recorded only in Sarcophaga bullata.…”

Nervous control of juvenile hormone biosynthesis in Locusta migratoria.

“…Sci. USA 91 (1994) (20). Furthermore, since the four neurons innervating both CA were not spontaneously active under the experimental conditions, the inhibition removed by nerve transection originated from neurons in the ipsilateral PL.…”

“…JH3 production was measured at room temperature using a RCA (7,8) Initially, the Ringer's solution in the chamber was replaced with this medium for a 30-min preincubation. Subsequently, the medium was exchanged at 1-h intervals for, in most cases, 9 h. To measure the amount of labeled JH produced, each sample was mixed with 100 ,ul of ethanol containing 20 ,ug of nonradioactive JH3 and applied directly to analytical silica plates (Merck; silica gel 60 F245; 0.2 mm). Lipophilic substances were concentrated to a line 3 cm above the application area by using ether, the gel of the application area was removed, and the plate was developed in n-hexane/ether ( (28,29), and great asymmetry between left and right CA activity of an individual locust occurs (30,31).…”

“…A recent study of the CA-innervation pattern in locusts indicates a possible neuroanatomical substrate for antagonistic control mechanisms of the CA, since two morphologically different types of brain neurons with somata in the PL innervate the CA (20). Two cells in each PL extend axons bilaterally and innervate both CA, while 13 cells in each PL project to the ipsilateral gland only (Fig.…”

Reproduction-Related Sound Production of Grasshoppers Regulated by Internal State and Actual Sensory Environment

“…Protocerebral neurons that innervate the corpora allata via the nervi corporis allati I have been identified in the pars intercerebralis and pars lateralis regions of various insects (Moore and Loher, 1988; Virant-Doberlet et al, 1994; Vullings et al, 1999). Whether these neurons activate or inhibit JH production seems to be different among species as are the chemical signals (summarized as allatotropins and allatostatins) that mediate this regulation (Tobe and Stay, 1980; Kataoka et al, 1989; Horseman et al, 1994; Bräunig et al, 1996; Gilbert et al, 2000; Weaver and Audsley, 2009).…”