Circadian pacemaker coupling by multi-peptidergic neurons in the cockroach Leucophaea maderae

Abstract

Lesion and transplantation studies in the cockroach, Leucophaea maderae, have located its bilaterally symmetric circadian pacemakers necessary for driving circadian locomotor activity rhythms to the accessory medulla of the optic lobes. The accessory medulla comprises a network of peptidergic neurons, including pigment-dispersing factor (PDF)-expressing presumptive circadian pacemaker cells. At least three of the PDF-expressing neurons directly connect the two accessory medullae, apparently as a circadian coupling pathway. Here, the PDF-expressing circadian coupling pathways were examined for peptide colocalization by tracer experiments and double-label immunohistochemistry with antisera against PDF, FMRFamide, and Asn13-orcokinin. A fourth group of contralaterally projecting medulla neurons was identified, additional to the three known groups. Group one of the contralaterally projecting medulla neurons contained up to four PDF-expressing cells. Of these, three medium-sized PDF-immunoreactive neurons coexpressed FMRFamide and Asn13-orcokinin immunoreactivity. However, the contralaterally projecting largest PDF neuron showed no further peptide colocalization, as was also the case for the other large PDF-expressing medulla cells, allowing the easy identification of this cell group. Although two-thirds of all PDF-expressing medulla neurons coexpressed FMRFamide and orcokinin immunoreactivity in their somata, colocalization of PDF and FMRFamide immunoreactivity was observed in only a few termination sites. Colocalization of PDF and orcokinin immunoreactivity was never observed in any of the terminals or optic commissures. We suggest that circadian pacemaker cells employ axonal peptide sorting to phase-control physiological processes at specific times of the day.

Myoinhibitory peptides in the brain of the cockroach Leucophaea maderae and colocalization with pigment‐dispersing factor in circadian pacemaker cells

“…However, colocalization of PDF-and FMRFamide-, and orcokinin immunoreactivity, respectively, has not been observed in the AOC. Thus, it was proposed that circadian pacemaker cells employ axonal peptide sorting, a differential release of neuromodulating peptide cocktails, to couple both pacemakers (Soehler et al, 2011). Consistently, in this study no colocalized MIP/PDF immunostaining was observed in the AOC ( Fig.…”

“…The less dense internodular region and shell of the AMe are suggested to serve as output as well as input regions. The internodular neuropil receives inputs from the contralateral eye, in addition to nonphotic input such as coupling signals from the contralateral AMe (Petri et al, 1995;Stengl, 1996, 2003b;Homberg et al, 2003;Reischig et al, 2004;Soehler et al, 2011). Here we report particularly dense MIP immunostaining in the noduli, but also in the internodular neuropil and shell of the AMe.…”

“…Triple-label studies revealed that at least four PDF-ir VNes are among the MC I cells which appear to directly connect both AMae via the POC and AOC with two specific branching patterns in the optic lobe (Reischig and Stengl, 2002;Reischig et al, 2004;Soehler et al, 2011). These four neurons include the largest aPDFMe, which projects via the POC and AOC, and three medium-sized aPDFMes, which project via the AOC and contain colocalized PDF-/orcokinin-and PDF-/FMRFamide-related peptides.…”

“…Backfills from the contralateral optic stalk and from the contralateral AMe identified neurons in several medulla cell groups (MC I-IV) and seven commissures that directly connect both optic lobes (Reischig and Stengl, 2002;Reischig et al, 2004;Soehler et al, 2011). The Figure 11.…”

“…The arborizations of the small aPDFMes appear to be restricted to the AMe and possibly also branch in other neuropils of the ipsilateral optic lobe (Reischig and Stengl, 2003b). One large and three medium-sized aPDFMes directly connect both accessory medullae (AMae; Reischig and Stengl, 2002;Reischig et al, 2004;Soehler et al, 2011). The medium-sized aPDFMes project through the anterior optic commissure (AOC), whereas the largest anterior PDF-ir neuron (aPDFMe) sends processes both via the AOC and the posterior optic commissure (POC).…”