Choline acetyltransferase‐like immunoreactivity in a physiologically distinct subtype of olfactory nonspiking local interneurons in the cockroach (periplaneta americana)

Abstract

Behavioral and physiological studies have shown that local interneurons are pivotal for processing odor information in the insect antennal lobe. They mediate inhibitory and excitatory interactions between the glomerular pathways and ultimately shape the tuning profile of projection neurons. To identify putative cholinergic local interneurons in the antennal lobe of Periplaneta americana, an antibody raised against the biosynthetic enzyme choline acetyltransferase (ChAT) was applied to individual morphologically and electrophysiologically characterized local interneurons. In nonspiking type IIa1 local interneurons, which were classified in this study, we found ChAT-like immunoreactivity suggesting that they are most likely excitatory. This is a well-defined population of neurons that generates Ca(2+) -driven spikelets upon depolarization and stimulation with odorants, but not Na(+) -driven action potentials, because they lack voltage-activated transient Na(+) currents. The nonspiking type IIa2 and type IIb local interneurons, in which Ca(2+) -driven spikelets were absent, had no ChAT-like immunoreactivity. The GABA-like immunoreactive, spiking type I local interneurons had no ChAT-like immunoreactivity. In addition, we showed that uniglomerular projection neurons with cell bodies located in the ventral portion of the ventrolateral somata group and projections along the inner antennocerebral tract exhibited ChAT-like immunoreactivity. Assigning potential transmitters and neuromodulators to distinct morphological and electrophysiological types of antennal lobe neurons is an important prerequisite for a detailed understanding of odor information processing in insects.

Complete identification of four giant interneurons supplying mushroom body calyces in the cockroach Periplaneta americana

“…To label putative GABAergic neurons in the brain of P. americana , we used a commercially available polyclonal antibody (Table , Cat# A2052, RRID: AB_477652, Sigma‐Aldrich) that was raised against a GABA‐bovine serum albumin (BSA) conjugate in rabbits. The resulting staining pattern was identical to that obtained in previous immunocytochemical studies in the protocerebrum (Yamazaki et al, ) and in the antennal lobe of P. americana (Distler, ; Fusca et al, ). According to the manufacturer's data sheet, the antibody showed positive binding with GABA and GABA‐KLH in a dot blot assay, and negative binding with BSA.…”

Rapid and Slow Chemical Synaptic Interactions of Cholinergic Projection Neurons and GABAergic Local Interneurons in the Insect Antennal Lobe

“…Accordingly, we observed no hyperpolarization of the postsynaptic type I LN when the presynaptic uPN was hyperpolarized. In agreement with previous immunohistochemical and physiological studies, which suggested that uPNs are mostly cholinergic (Waldrop and Hildebrand, 1989;Homberg et al, 1995;Bicker, 1999;Homberg, 2002;Wilson et al, 2004;Fusca et al, 2013;Liu and Wilson, 2013), the excitatory synaptic transmission between uPNs and type I LNs could be reversibly blocked by the nicotinic acetylcholine receptor blocker mecamylamine (Fig. 2).…”

“…The study was conducted in the AL of the cockroach Periplaneta americana. In P. americana the physiology of the central olfactory neurons (Ernst and Boeckh, 1983;Lemon and Getz, 1997, 1998Strausfeld and Li, 1999;Husch et al, 2009a,b;Pippow et al, 2009) and the circuitry of the olfactory system have been analyzed in great detail down to the biochemical, structural, and ultrastructural level (Distler, 1989(Distler, , 1990Malun, 1991a,b;Malun et al, 1993;Distler and Boeckh, 1997a,b;Distler et al, 1998;Neupert et al, 2012;Fusca et al 2013). …”

Neonicotinoids Interfere with Specific Components of Navigation in Honeybees

“…Within the brain cholinergic synaptic transmission is suggested to occur from axons of the olfactory receptor neurons onto local interneurons and projection neurons within the antennal lobes (in addition some of the local interneurons are cholinergic), from antennal lobe projection neurons onto mushroom body Kenyon cells and onto neurons of the lateral horn, between ocellar second-order neurons and their postsynaptic neurons. In addition, the insect central brain, optic lobes and the thoracic ganglia contain cholinergic neurons (e. g., Manduca sexta : [21], Schistocerca gregaria : [22], Periplaneta americana : [23], Drosophila melanogaster : [24], [25], [26], [27], Apis mellifera : [28]). Given this wide-spread central nervous distribution, it is not surprising that sublethal neonicotinoid doses compromise behavior and cognitive abilities also in honeybees including memory formation and retrieval [29], [30], social interactions, navigation and communication [11], [12] [31].…”