Local olfactory interneurons provide the basis for neurochemical regionalization of olfactory glomeruli in crustaceans

Abstract

The primary olfactory centers of metazoans as diverse as arthropods and mammals consist of an array of fields of dense synaptic neuropil, the olfactory glomeruli. However, the neurochemical structure of crustacean olfactory glomeruli is largely understudied when compared to the insects. We analyzed the glomerular architecture in selected species of hermit crabs using immunohistochemistry against presynaptic proteins, the neuropeptides orcokinin, RFamide and allatostatin, and the biogenic amine serotonin. Our study reveals an unexpected level of structural complexity, unmatched by what is found in the insect olfactory glomeruli. Peptidergic and aminergic interneurons provide the structural basis for a regionalization of the crustacean glomeruli into longitudinal and concentric compartments. Our data suggest that local olfactory interneurons take a central computational role in modulating the information transfer from olfactory sensory neurons to projection neurons within the glomeruli. Furthermore, we found yet unknown neuronal elements mediating lateral inhibitory interactions across the glomerular array that may play a central role in modulating the transfer of sensory input to the output neurons through presynaptic inhibition. Our study is another step in understanding the function of crustacean olfactory glomeruli as highly complex units of local olfactory processing.

Neurochemical diversity in the central olfactory pathway of the crustacean Parhyale hawaiensis (Amphipoda): evolutionary implications

“…Our study reveals the presence of many different neurochemical substances in the olfactory glomeruli of P. hawaiensis and taken together with information on other representatives of the Peracarida (Table 1), these findings support the suggestion that a high level of neurochemical diversity characterized the local olfactory interneurons already in a malacostracan representative close to the stem line. This claim is supported by evidence from the Hexapoda, which represent the closest relatives or even an in‐group of crustaceans (Lozano‐Fernandez et al., 2016; Misof et al., 2014; Reumont et al., 2012; Schwentner et al., 2017; Wipfler et al., 2019), and which display diverse populations of local olfactory interneurons (Harzsch et al., 2021; Krieger et al., 2015; Schachtner et al., 2005). Detailed information on the immunohistochemical localization of various neuroactive substances are available, for example, for the spiny lobster P. argus (Schmidt, 1997; Wachowiak & Ache, 1997) and the hermit crab C. clypeatus (Harzsch & Hansson, 2008; Polanska et al., 2012; Harzsch et al., 2021).…”

“…We used a polyclonal antiserum raised in rabbit against serotonin coupled to BSA with PFA. Preadsoprtion experiments with 10–25 μg serotonin coupled to BSA per milliliter of diluted antiserum eliminated all specific staining (Harzsch et al., 2021). According to the manufacturer, using the horse radish peroxidase labeling method, 5‐hydroxytryptophan, 5‐hydroxyindole‐3‐acetic acid, and dopamine did not react with the 1:20,000 diluted antiserum.…”

“…We used a polyclonal rabbit Asn 13 ‐orcokinin antiserum, which was raised against glutaraldehyde‐conjugate of bovine thyroglobulin and synthetic orcokinin (Bungart et al., 1994). The antiserum showed almost full reactivity withVal13‐orcokinin (Dircksen et al., 2000) and showed clear staining in C. clypeatus and Pagus berhardus (Harzsch et al., 2021; Polanska et al., 2020). As we did not do any preadsorption experiments ourselves nor an analysis of the genome, we will refer to the labeling in our study as “orcokinin‐like IR.”…”

“…Many different neurotransmitters are present in the local olfactory interneurons of crustaceans. So far, the presence of “classical” neurotransmitters such as acetylcholine (ACh), γ‐aminobutyric acid (GABA), l ‐glutamate, and nitric oxide was shown in crustaceans, as well as the presence of biogenic amines such as serotonin, dopamine, histamine, and octopamine and diverse neuropeptides (summarized in table 1, reviewed in Harzsch et al., 2021; Schachtner et al., 2005). Different neurotransmitters provide the basis for a regionalization of the olfactory glomeruli of decapod crustaceans into cap, subcap, and base along their long axis (Harzsch et al., 2012; Harzsch et al., 2021; Polanska et al., 2020).…”

“…So far, the presence of “classical” neurotransmitters such as acetylcholine (ACh), γ‐aminobutyric acid (GABA), l ‐glutamate, and nitric oxide was shown in crustaceans, as well as the presence of biogenic amines such as serotonin, dopamine, histamine, and octopamine and diverse neuropeptides (summarized in table 1, reviewed in Harzsch et al., 2021; Schachtner et al., 2005). Different neurotransmitters provide the basis for a regionalization of the olfactory glomeruli of decapod crustaceans into cap, subcap, and base along their long axis (Harzsch et al., 2012; Harzsch et al., 2021; Polanska et al., 2020). Notably, the neurochemistry of olfactory glomeruli is best understood in decapod crustaceans such as crayfish, crabs, and lobsters (Table 1), whereas large gaps in our knowledge exist for nondecapod Malacostraca.…”