Electrical activity of caudal neurosecretory neurons in seawater and freshwater-adapted Platichthys flesus, in vivo

Abstract

SUMMARY This study examined the electrical firing activity of neuroendocrine Dahlgren cells in the caudal neurosecretory system (CNSS) of the euryhaline flounder in vivo. Intracellular recordings revealed generally similar activity patterns and membrane properties to those previously reported in vitro. To investigate the potential role of the CNSS in osmoregulatory adaptation, extracellular, multiunit, recordings compared the activity patterns of Dahlgren cells in fully seawater- and freshwater-adapted fish. The proportion of cells showing bursting (as opposed to phasic or tonic) activity was greater in seawater-than in freshwater-adapted fish, as was the Correlation Index, a measure of the degree of correlation between firing activities of cells recorded simultaneously from the same preparation. Acute transfer of fish from seawater to freshwater gill perfusion led to recruitment of previously silent Dahlgren cells and a reduction in Correlation Index;freshwater to seawater transfer increased the Correlation Index. Severing the spinal cord anterior to the CNSS led to an increase in overall Dahlgren cell activity. Electrical stimulation of branchial nerve branches providing input to the brainstem, or tactile (pinch) stimulation of lips or fins, led to a reduction in CNSS activity lasting up to 500 s, indicating the presence of descending modulatory pathways from the brain. These results are consistent with a role for CNSS neuropeptides, urotensins, in supporting survival in a hypertonic, seawater, environment.

Gene expression and hormone secretion profile of urotensin I associated with osmotic challenge in caudal neurosecretory system of the euryhaline flounder, Platichthys flesus

“…In our study, expression level of L-type Ca 2+ channel is lower in FW-adapted flounder CNSS than in SW-adapted flounder CNSS in both season. In consistent with our results, electrophysiological experiments have shown that bursting activity in Dahlgren cells is less robust in FW-adapted compared to SW-adapted fish (Ashworth et al, 2005;Brierley et al, 2003) and this is due, at least in part, to a reduction in Ca 2+ channel-dependent ADP and Ca-activated K + channels-dependent DAP (Brierley et al, 2003). In this study, we also examined L-type Ca 2+ channels or Ca-activated K + channels gene expression in fish transferred from SW to FW and reverse transfer.…”

Precise and Fuzzy Coding by Olfactory Sensory Neurons

“…We then used CED Spike2 (version 5.17) software to assign spikes to a number of separate classes (OSNs). We have previously used this approach to reliably identify the activity of neuroendocrine cells in the spinal cord of fish in which characteristic patterned activity of neurons as seen in Spike2 analysis of extracellular multiunit recordings was mirrored by intracellular recordings of the activity of individual neurons (Brierley et al, 2003;Ashworth et al, 2005). Spike2 identifies neuronal events on the basis of amplitude and waveform (Fig.…”

Heads or tails? Stressor-specific expression of corticotropin-releasing factor and urotensin I in the preoptic area and caudal neurosecretory system of rainbow trout

“…Therefore, the increase in CNSS CRF-related peptide mRNA levels in response to hyperammonemia and hypoxia are unlikely to result from the stimulation of osmoreceptorsensitive regulatory pathways. Instead, since electrical stimulation of branchial nerve branches can affect Dahlgren cell activity (Ashworth et al 2005), we raise the possibility that the afferent fibers from the gill chemoreceptors involved in mediating hypoxic reflexes also synapse onto descending pathways that reach the CNSS. In contrast, if ammonia neurotoxicity in fish results from a local synaptic excess of glutamate as proposed by Walsh et al (2007), then the stimulatory effects of hyperammonemia on the CRF-and UI-expressing cells of the CNSS are more likely to be of local rather than extrinsic origin.…”

“…Indeed, the results from electrophysiological and pharmacological studies suggest that the Dahlgren cells are subject to a complex balance of excitatory and inhibitory input of both extrinsic and intrinsic origin (see for review). To date, however, only one type of stressor, osmotic disturbances, has been shown to activate descending pathways that modulate Dahlgren cell activity (Ashworth et al 2005). While hyperammonemia and hypoxia may elicit small ionic disturbances (Thomas et al 1986, Knoph & Thorud 1996, the changes in CNSS CRF and UI expression in response to these stressors differ markedly from those elicited by seawater transfer .…”