Tyrosine hydroxylase immunostaining in the central complex of dicondylian insects

Abstract

Dopamine acts as a neurohormone and neurotransmitter in the insect nervous system and controls a variety of physiological processes. Dopaminergic neurons also innervate the central complex (CX), a multisensory center of the insect brain involved in sky compass navigation, goal‐directed locomotion and sleep control. To infer a possible influence of evolutionary history and lifestyle on the neurochemical architecture of the CX, we have studied the distribution of neurons immunoreactive to tyrosine hydroxylase (TH), the rate‐limiting enzyme in dopamine biosynthesis. Analysis of representatives from 12 insect orders ranging from firebrats to flies revealed high conservation of immunolabeled neurons. One type of TH‐immunoreactive neuron was found in all species studied. The neurons have somata in the pars intercerebralis, arborizations in the lateral accessory lobes, and axonal ramifications in the central body and noduli. In all pterygote species, a second type of tangential neuron of the upper division of the central body was TH‐immunoreactive. The neurons have cell bodies near the calyces and arborizations in the superior protocerebrum. Both types of neuron showed species‐specific variations in cell number and in the innervated areas outside and inside the CX. Additional neurons were found in only two taxa: one type of columnar neuron showed TH immunostaining in the water strider Gerris lacustris, but not in other Heteroptera, and a tritocerebral neuron innervating the protocerebral bridge was immunolabeled in Diptera. The data show largely taxon‐specific variations of a common ground pattern of putatively dopaminergic neurons that may be commonly involved in state‐dependent modulation of CX function.

A three‐dimensional atlas of the honeybee central complex, associated neuropils and peptidergic layers of the central body

“…Most notably layer CBU‐Ib can be readily identified due to its unusual patchy staining pattern (Figures 9 and 11). Such a pattern has been previously reported in Acetylcholinesterase staining (Kreissl & Bicker, 1989), immunolabeling of dopamine (Schäfer & Rehder, 1989), and tyrosine hydroxylase (Timm et al., 2021). Tyrosine hydroxylase staining labels the three main layers of the CBU (I, II, III), but does not allow to distinguish the sublayers (a, b).…”

“…Tyrosine hydroxylase staining labels the three main layers of the CBU (I, II, III), but does not allow to distinguish the sublayers (a, b). In the CBL, tyrosine hydroxylase‐ir is mostly found in a dorsal layer probably corresponding to CBL‐I (Timm et al., 2021). A similar threefold layering of the CBL as reported here seems to emerge from immunolabeling of the tyramine receptor AmTAR1, which labels the CBL layers I and IIb (Timm et al., 2021).…”

3D‐atlas of the brain of the cockroach Rhyparobia maderae

“…The CBU lies ventrally from the PB and has a kidney‐shaped form typical for a hemimetabolic insect (Figures 7a and 7a′). Immunolabeling with antisera against tyrosine hydroxylase (Timm et al., 2021), SIFamide (Arendt et al., 2016), GABA (Homberg et al., 2018), orcokinin (Hofer et al., 2005), and myoinhibitory peptide (Schulze et al., 2012) revealed at least three horizontal layers and nine vertical segments in the CBU, while these subcompartments could not be clearly distinguished with anti‐synapsin. The CBL adjoins ventrally and shows a highly peculiar internal organization.…”

“…In the locust, the ALI is highly connected with the CBU (Heinze & Homberg, 2008; Vitzthum et al., 1996). In the cockroach the ALI is particularly large, partly organized as a chain of glomerular condensations ( P. americana ; Eckert et al., 1999) and densely innervated by dopamine‐immunoreactive fibers (Hamanaka et al., 2016; Timm et al., 2021).…”

“…The CBU lies ventrally from the PB and has a kidney-shaped form typical for a hemimetabolic insect (Figures 7a and 7a′). Immunolabeling with antisera against tyro- sine hydroxylase (Timm et al, 2021), SIFamide (Arendt et al, 2016), GABA (Homberg et al, 2018), orcokinin (Hofer et al, 2005), and myoinhibitory peptide (Schulze et al, 2012) framing the eight cones (Figure 7a′). Both, cones and teeth are innervated by tangential neurons that connect the CBL with the BU through the IT (Homberg et al, 2018) and are strongly GABA-immunoreactive (Figure 7d).…”