Immunocytochemical mapping and quantification of expression of a putative type 1 serotonin receptor in the crayfish nervous system

Abstract

Serotonin is an important neurotransmitter that is involved in modulation of sensory, motor, and higher functions in many species. In the crayfish, which has been developed as a model for nervous system function for over a century, serotonin modulates several identified circuits. Although the cellular and circuit effects of serotonin have been extensively studied, little is known about the receptors that mediate these signals. Physiological data indicate that identified crustacean cells and circuits are modulated via several different serotonin receptors. We describe the detailed immunocytochemical localization of the crustacean type 1 serotonin receptor, 5-HT1crust, throughout the crayfish nerve cord and on abdominal superficial flexor muscles. 5-HT1crust is widely distributed in somata, including those of several identified neurons, and neuropil, suggesting both synaptic and neurohormonal roles. Individual animals show very different levels of 5-HT1crust immunoreactivity (5-HT(1crust)ir) ranging from preparations with hundreds of labeled cells per ganglion to some containing only a handful of 5-HT(1crust)ir cells in the entire nerve cord. The interanimal variability in 5-HT(1crust)ir is great, but individual nerve cords show a consistent level of labeling between ganglia. Quantitative RT-PCR shows that 5-HT1crust mRNA levels between animals are also variable but do not directly correlate with 5-HT(1crust)ir levels. Although there is no correlation of 5-HT1crust expression with gender, social status, molting or feeding, dominant animals show significantly greater variability than subordinates. Functional analysis of 5-HT1crust in combination with this immunocytochemical map will aid further understanding of this receptor's role in the actions of serotonin on identified circuits and cells.

Neural Circuit Reconfiguration by Social Status

“…For example, 5-HT has been shown to enhance the synaptic response of the LG command neuron for escape in dominants and inhibit it in subordinates (Yeh et al, 1996(Yeh et al, , 1997. These results indicated that a change in status creates a persistent change in distant parts of the nervous system by mechanisms that may include changes in the type or balance of 5-HT receptors expressed in target cells (Spitzer et al, 2005(Spitzer et al, , 2008.…”

“…Indeed, as in crayfish (Yeh et al, 1996;Cattaert et al, 2010), the status-dependent changes in Mauthner excitability have been linked to status-dependent changes in serotonergic modulation (Whitaker et al, 2011). Other proximate mechanisms may result from the kinds of status-related differences in the nervous system already observed in many animals, including transmitter or neuromodulator concentration (Gutzler et al, 2010), receptor populations (Spitzer et al, 2005;Burmeister et al, 2007), changes in neuronal size and shape (White et al, 2002), neurogenesis (Kozorovitskiy and Gould, 2004;Song et al, 2007), and gross brain morphology (Holmes et al, 2007;O'Donnell et al, 2007).…”

“…These behavioral differences result from changes in the nervous system induced by social experience. Social status affects neurogenesis in rodents (Kozorovitskiy and Gould, 2004) and crayfish (Song et al, 2007), neuronal size in fish (White et al, 2002), brain morphology in wasps (O'Donnell et al, 2007) and naked mole rats (Holmes et al, 2007), and cell receptor populations in crayfish (Spitzer et al, 2005) and fish (Burmeister et al, 2007). Social status also affects the serotonergic neuromodulation of synaptic responses in both crayfish (Yeh et al, 1996(Yeh et al, , 1997 and fish (Whitaker et al, 2011), and the excitability of neural circuits that produce different behaviors (Krasne et al, 1997;Herberholz et al, 2001;Neumeister et al, 2010).…”

Spatial segregation of excitatory and inhibitory effects of 5-HT on crayfish motoneurons

“…Immunocytochemical staining has shown this receptor on efferent axons of the fifth thoracic ganglion (Spitzer et al 2005) near the terminals of 5-HT neurons that innervate the Dep MNs (Fig. 2).…”

“…Two 5-HT receptors have been identified in crayfish nervous system, and one of those, 5-HT 1␣ , may be present in the initial segments of the Dep MNs and the LG command neuron (Spitzer et al 2005). Immunocytochemical staining has shown this receptor on efferent axons of the fifth thoracic ganglion (Spitzer et al 2005) near the terminals of 5-HT neurons that innervate the Dep MNs (Fig.…”