Dopaminergic Modulation of Neurosecretory Cells in the Crayfish

Abstract

The main aims of this paper are (a) to locate possible dopaminergic neurons in the eyestalk with anti-tyrosine hydroxylase antibodies, (b) to search for the presence of dopamine (DA) in the nervous structures of the eyestalk, (c) to explore its release, and (d) to test the effect of DA on neurosecretory cells in the eyestalk. Experiments were performed in adult crayfishes Procambarus clarkii, in isolated optic peduncle. Immunocytochemistry was made with the antibody against its precursor synthesizing enzyme tyrosine-hydroxylase. The content and release studies of DA were made using high performance liquid chromatography (HPLC). Extracellular and intracellular recordings were conducted with conventional recording techniques. A large number (approximately 2000) of immunopositive somata of different sizes and shapes were identified in various regions of the eyestalk. The majority of somata are of the smallest size (5-25 microm diameter). DA content in the eyestalk was 5.6 +/- 0.1 pmol per structure; the greatest content is in the MT (over 60%). A basal level release of DA was observed. Incubation of eyestalks in solution containing a high K+ concentration increased the DA release (79%). Two effects of DA on the excitability of X-organ neurons were observed; an excitatory effect on neurons of approximately 25 microm somata diameter and another inhibitory effect in the group of approximately 35-microm somata diameter neurons. The excitation occurs with a depolarization and decrement of membrane conductance in the cell soma while the inhibition occurs with a hyperpolarization and increment of membrane conductance in soma. We concluded the following: (1) Dopamine is present in each optic ganglia of the crayfish eyestalk. (2) There is a basal release of DA from the isolated eyestalk. (3) DA release is enhanced threefold by eyestalk incubation in 40 mM [K+] solution. (4) DA selectively excites a population of neurons with low-speed conduction axons, and small somata in the X-organ-sinus gland system, while inhibiting another population characterized by higher axonal conduction speed and large somata. (5) These observations support a role for DA as a neurotransmitter or neuromodulator in the X-organ neurons of the crayfish eyestalk.

Inducing synchronous ovarian maturation in the crayfish,Procambarus clarkii, via eyestalk interventional injection as compared with eyestalk ablation and combined injection of serotonin and domperidone

“…The DA content in the eyestalks of P. clarkii was reported by Alvarez et al (2005) to be 5.6 AE 0.1 pmol (about 1062 AE 18.9 pg) per structure; the highest content was also found in the MT (over 60%). Using electrical stimulation and high concentrations of K + and Ca 2+ , enhanced levels of DA and 5-HT were also detected (Alvarez et al 2005;Rodriguez-Sosa et al 1997). These studies suggested that eyestalks might play an important role in the release of DA and 5-HT to control ovarian development.…”

“…As the XO-SG located in the eyestalk has been postulated to control gonad development in crustaceans, the eyestalk ganglia were also examined to determine the localization and release of 5-HT (Rodriguez-Sosa, Picones, Rosete & ArEChigaY 1997) and DA (Alvarez, Villalobos, Rosete, Sosa & Arechiga 2005). In the eyestalks of P. clarkii, the basal level of 5-HT detected by Rodriguez-Sosa et al (1997) was 95.4 AE 49.3 pg mg À1 wet mass, which was comparable to the value reported by Kulkarni et al (1992) of 102 pg mg À1 wet mass.…”

Distribution and changes of serotonin and dopamine levels in the central nervous system and ovary of the Pacific white shrimp, Litopenaeus vannamei, during ovarian maturation cycle

“…DA-ir has been identified in neurons, fibers, and neuropils of the eyestalks (e.g., MT and the optic tracts of C. sapidus and M. rosenbergii), suggesting a role of DA in the regulation of neurosecretory activity of the eyestalk (Wood and Derby 1996;Tinikul et al 2009b). In the crayfish, P. clarkii, DA has been shown to excite small neurons in the XO-SG, suggesting a direct role of DA in controlling the XO (Alvarez et al 2005). Sarojini et al (1995b) have reported that DA stimulates the release of a putative GIH from the XO in P. clarkii, thereby inhibiting gonadal maturation.…”

“…On the other hand, DA has been shown to inhibit testicular maturation in P. clarkii (Sarojini et al 1995b), and ovarian maturation in M. rosenbergii (Tinikul et al 2009a). Because of the important roles of 5-HT and DA in reproduction and in the control of ovarian maturation, the levels of 5-HT and DA have been determined by high performance liquid chromatography (HPLC) in relation to seasonality and reproductive stages in various regions of the eyestalks and intestinal nerves of P. clarkii (Alvarez et al 2005;Mercier et al 1991), the CNS of Pacifastacus leniusculus (Elofsson et al 1982), and the CNS and ovary of M. rosenbergii (Tinikul et al 2008). These studies have reported that the changes of 5-HT and DA levels occur in opposite directions during various stages of the ovarian cycle in these species.…”

Circadian clocks in crustaceans: identified neuronal and cellular systems

“…and further inputs from areas next to the olfactory-globular tract (OGT), the likely PDH-ir (see below) optic-globular tract (OPT-GT) which is connected to the so-called diamedullary neuropil adjacent to the medulla and lobula (terminology according to (123), apart from other inputs originating in the brain (77). As judged from pharmacological experiments, serotonin (103,180,181), GABA (182), dopamine (183), and several other components (see 178) likely regulate CHH rhythmicity. Furthermore, axonal terminals of brain extraretinal photoreceptors contacting serotonin-ir fibres within the protocerebral bridge of the brain (184,185) may convey circadian information via electron-microscopically proven serotonergic inputs to the XOSG (186).…”