Comparative localization of two serotonin receptors and sensorin in the central nervous system ofAplysia californica

Abstract

Aplysia californica is a powerful model for understanding the cellular and molecular mechanisms underlying modulation of neuronal plasticity and learning. In the central nervous system of Aplysia, serotonin is associated with various behaviors. For example, it induces short-, intermediate-, and long-term synaptic changes in sensory neurons during learning and inhibits the afterdischarge of the bag cells that initiate egg-laying behavior. Little is known about the nature and contribution of serotonin receptors involved in the numerous serotonin-mediated physiological responses in Aplysia. Recently, two G(i)-coupled serotonin receptors (5-HT(ap1) and 5-HT(ap2)) were cloned. We now report that, by using in situ hybridization to express the profile of these receptors, we are able to gain critical insight into their roles in the behavior of Aplysia. We compared their distribution to that of sensorin-A, a peptide specifically found in sensory neurons. We wished to determine their involvement in some simple forms of behavioral modifications. 5-HT(ap1) and 5-HT(ap2) mRNAs are expressed in all ganglia of the Aplysia central nervous system. Stronger signal was observed with the 5-HT(ap2) antisense probe than with the 5-HT(ap1) antisense probe. Notably, mRNA coding for the receptors was found in several identified neurons, in the bag cells, in characterized serotonergic neurons, and in neurons of the mechanosensory clusters that expressed sensorin. We also observed heterogeneity of receptor expression between R2 and LPl1 and among neurons of a single cluster of sensory neurons. These results suggest that 5-HT(ap1) and 5-HT(ap2) receptors may regulate the response to serotonin and/or its release in several neurons.

Inhibition of the Aplysia sensory neuron calcium current with dopamine and serotonin

“…As stated above, the pleural sensory neurons serve as mechanoreceptors with a nociceptive role, and thus inhibition with dopamine [or with 5-HT in the small subset of sensory neurons that express endogenous 5-HT 1Apl(a) ; Barbas et al 2005;Dunn et al 2012] would be expected to have a hypoalgesic or analgesic effect on behavior. Interestingly, modulation of nociception in vertebrates appears to function through a conserved general mechanism, namely a reduction in membrane excitability and reduced transmitter release through reduced calcium influx (Cregg et al 2010).…”

“…Similar inhibition (reduction in membrane excitability and synaptic efficacy) is observed with activation of a known 5-HT receptor, the Aplysia 5-HT 1Apl(a) receptor, that can be exogenously expressed (Angers et al 1998;Dunn et al 2012). The 5-HT 1Apl(a) receptor is only endogenously expressed in a very small subset of pleural sensory neurons (Barbas et al 2005;Nagakura et al 2010;Dunn et al 2012). Therefore, we overexpressed the receptor with an eGFP tag [5-HT 1Apl(a) -eGFP] in cultured sensory neurons with nuclear microinjection of pNEX3 vectors containing the tagged receptor (Nagakura et al 2010).…”

Imatinib Enhances Functional Outcome after Spinal Cord Injury

“…Given that imatinib has been reported to modulate immune cell function and secretion profile, it was surprising to observe that imatinib treatment had no significant impact on plasma concentrations of pro-inflammatory cytokines, IL-β, IL-6, IL-8, and TNF-α, reported to be involved in the orchestration of the inflammatory response [44], [39], [37] at 6 hours post-injury which translates to 5.5 hours after the treatment began. It was also surprising to find that imatinib had no impact on neutrophil infiltration into the injured spinal cord 24 hours after injury.…”

Expression levels of glutamate and serotonin receptor genes in the brain of different behavioural phenotypes of worker honeybee (Apis mellifera)

“…Using both invertebrates and mammals, recent studies have revealed that endogenous 5-HT modulates plasticity processes, including learning and memory (Meneses, 1999;Barbas et al, 2003Barbas et al, , 2005Schmitt et al, 2006). It has been shown that pharmacological manipulation of 5-HT1-7 receptors or 5-HT re-uptake sites might modulate memory consolidation, which is consistent with the emerging notion that 5-HT plays a key role in memory formation (reviewed by Meneses, 2002;Meneses, 2007).…”