Peter Bräunig

The morphology of suboesophageal ganglion cells innervating the nervus corporis cardiaci III of the locust

SummaryThe nervus corporis cardiaci III (NCC III) of the locust Locust migratoria was investigated with intracellular and extracellular cobalt staining techniques in order to elucidate the morphology of neurons within the suboesophageal ganglion, which send axons into this nerve. Six neurons have many features in common with the ‘dorsal, unpaired, median (DUM)’ neurons of thoracic and abdominal ganglia. Three other cells have cell bodies contralateral to their axons (contralateral neuron 1–3; CN 1–3). Two of these neurons (CN2 and CN3) appear to degenerate after imaginal ecdysis. CN3 innervates pharyngeal dilator muscles via its anterior axon in the NCC III, and a neck muscle via an additional posterior axon within the intersegmental nerve between the suboesophageal and prothoracic ganglia. A large cell with a ventral posterior cell body is located close to the sagittal plane of the ganglion (ventral, posterior, median neuron; VPMN). Staining of the NCC III towards the periphery reveals that the branching pattern of this nerve is extremely variable. It innervates the retrocerebral glandular complex, the antennal heart and pharyngeal dilator muscles, and has a connection to the frontal ganglion.

The peripheral branching pattern of identified dorsal unpaired median (DUM) neurones of the locust

Abstract. Identified dorsal unpaired median (DUM) neurones of the locust Locusta migratoria were stained intracellularly with large amounts of cobalt to reveal their extensive peripheral branching patterns. Two neurones of the suboesophageal ganglion were studied as well as several neurones of thoracic ganglia. The peripheral branching pattern of all these neurones is described completely. As expected, the prevalent target organs of all DUM neurones are skeletal muscles. In addition several, but not all DUM neurones studied here form neurohaemal release sites on the surface of peripheral nerves and thus represent potential sources for octopamine acting as a neurohormone.

Identification of a single prothoracic ‘dorsal unpaired median’ (DUM) neuron supplying locust mouthpart nerves

SummaryThe peripheral nerves of the suboesophageal ganglion of the locust,Locusta migratoria have been investigated with respect to their innervation by dorsal unpaired median (DUM) neurons. The DUM neuron supply of the suboesophageal periphery was found to be strikingly sparse: No segmental DUM neurons could be found in all three mouthpart segments. While in the mandibular segment DUM neuron innervation appears to be missing entirely, both the maxillary and the labial peripheral nerves are supplied by a single, intersegmentally projecting prothoracic DUM neuron.

Actions and interactions of proprioceptors of the locust hind leg coxo-trochanteral joint

Summary1.The coxo-trochanteral joint of the locust hindleg is supplied with five mechanoreceptive sense organs: A hairplate (HP) and a row of hairs (RH), two strand receptors (SR1, SR2) and a muscle receptor organ (MRO) (BrÄunig 1982). We report here an investigation of these mechanoreceptors with regard to their afferent responses to static and dynamic mechanical stimulation.2.The only receptor suited for continuous measurement of joint position is the HP: its units are active over the entire range of possible joint positions and their number increases in proportion to the degree of joint levation (Fig. 3). The RH complements the HP as an additional sensor for extreme levation (Fig. 4).3.Both SR are sensitive to the dynamic phase of joint depressions. Units of the multicellular SR1 respond over the entire range of joint movements, the single unit of SR2 is tuned to the lower half of that range (Fig. 5).4.The sensory cell of the MRO is activated when the organ is stretched during depression of the joint (Fig. 6). Increasing slack of the organ during levation is compensated by activation of its receptor muscle. The MRO motor neuron is progressively excited with increasing joint levation, mainly by HP and RH (Figs. 6, 7, 8).5.During stimulation of internal mechanoreceptors (SR1, SR2, and the sensory cell of the MRO) and during spontaneous motor activity the MRO motor neuron is co-activated with levator motor neurons (Figs. 9, 10). This mechanism may help to compensate for slack before the reflexes from HP and RH set in (see 4.).6.The motor neuron of the MRO receptor muscle is not only activated by sense organs of the coxo-trochanteral joint, but also by proprioceptors of neighboring joints (Fig. 11).7.Since all coxo-trochanteral joint receptors exert reflexes on motor neurons of power muscles and the efferent unit of the MRO, manipulation and extirpation of any one receptor must result in direct effects on the motor output of the metathoracic ganglion, but also additional indirect effects due to altered operation of the MRO.

MORPHOLOGY OF LOCUST NEUROSECRETORY CELLS PROJECTING INTO THE NERVUS CORPORIS ALLATI II OF THE SUBOESOPHAGEAL GANGLION

The morphology of neurosecretory cells that project from the suboesophageal ganglion into the retrocerebral complex via the Nervus corporis allati II (NCA II) was studied in the migratory locust, Locusta migratoria, using backfilling techniques and intracellular staining. There are two populations of cells located ventrally in the ganglion: an anterior group of four larger cells, and a posterior group of up to 22 smaller cells. Apart from cell body size and position, members of both cell groups have almost all features in common. They show long‐lasting soma spikes with large amplitudes typical for arthropod neurosecretory cells. Their dendritic arborisations are found in the same regions of the neuropile. Both types project into the corpora cardiaca and an additional putative neurohaemal region associated with posterior pharyngeal dilator muscles. The axons of the cells bypass the corpora allata, but frequently form putative release sites on the surface of nerve branches in the vicinity of these glands. Finally, using double‐labelling techniques, both anterior and posterior cells are shown to be identical with immunoreactive suboesophageal ganglion cells detected in previous studies using antisera directed against either bovine pancreatic polypeptide (BPP) or locustamyotropin II (Lom‐MT‐II).

Activity pattern of suboesophageal ganglion cells innervating the salivary glands of the locust Locusta migratoria

The salivary gland of the locust, Locusta migratoria, is innervated from the suboesophageal ganglion by two neurones, SN1 and SN2 which innervate the gland via the salivary gland nerve (nerve 7B of the suboesophageal ganglion). In addition, like most other peripheral nerves of the head, this nerve carries on its outer surface axons and neurohaemal terminal ramifications of the so called satellite nervous system, established by a group of neurosecretory cells also located in the suboesophageal ganglion. These superficial collaterals ramify over the nerve from its origin in the head to its terminals within the gland in the thoracic segments.Nerve 7B was recorded chronically in freely moving locusts. Both salivary neurones are active during and shortly before feeding, as defined by continuous rhythmic activity of the mandibular closer muscle (M9). The activity of the salivary neurones, particularly that of SN2, thus resembles that of the satellite neurones as described recently. While SN2 ceases firing at the end of a feeding bout, SN1 continues firing for a short period. Also, SN1 fires short bursts of impulses for a few minutes following the end of a feeding bout. Similar bursts also occur at random intervals during the long-lasting phases between feeding events.

GABA-like immunoreactivity in a common inhibitory neuron of the antennal motor system of crickets

SummaryIn crickets, a deutocerebral motoneuron sends axon collaterals to 6 of the 7 antennal muscles. Previous results indicated that this neuron exerts inhibition on these muscles and thus may be a common inhibitory motoneuron. In our present study, we show by doublelabelling, i.e. retrograde cobalt-filling and GABA-immunocytochemistry, that this neuron is GABA-immunoreactive, thus demonstrating that one common inhibitory motoneuron is part of the antennal motor system of crickets.

The coxo-trochanteral muscle receptor organ of locusts

SummaryThe coxo-trochanteral muscle receptor organ of the hind leg of the locust Locusta migratoria migratorioides (R.&F.) has been investigated by use of scanning and transmission electron microscopy with special emphasis on its distal attachment site. The overall morphology of the receptor muscle, the sensory neuron and its dendrites was found to share many common features with other arthropod sense organs of that type with two important differences: (1) the connective tissue segment (= intercalated tendon) is extremely short compared to that of other muscle receptor organs; (2) the naked dendritic terminals of the non-ciliated, multipolar sensory neuron of the organ contain clusters of microtubules, interconnected by an amorphous matrix, that resemble the tubular bodies of ciliated, epithelial receptor cells.