Hyperglycemic and osmotic effects of dopamine and recombinant hormone CHH-B1 in the Pacific white shrimp Litopenaeus vannamei

The effects of dopamine (DA) on crustacean hyperglycemic hormone (CHH) release and osmoregulation were investigated in the white shrimp Litopenaeus vannamei. Application of 2 μg of the recombinant CHH-B1_His hormone or 2?×?10^?6 mol L^?1 of DA to intact shrimp caused an increase in the hemolymph glucose levels 1 h post-injection, suggesting that DA might stimulate hyperglycemia through CHH release from the sinus glands. This assumption was supported by similar experiments using bilaterally eyestalk-ablated shrimp. Additionally, rCHH-B1_His restored the osmoregulatory capacity (OC) of shrimp under hyperosmotic conditions to basal values 2 h post-injection, whereas DA led to an OC decrease in shrimp at all sampling times. These neuroendocrine factors may be involved in the control of metabolism and osmoregulation in L. vannamei and could be important for its adaptation to different environmental conditions.     

Branchial carbonic anhydrase activity and ninhydrin positive substances in the Pacific white shrimp, Litopenaeus vannamei, acclimated to low and high salinities

The Pacific white shrimp, Litopenaeus vannamei, acclimated to 30 ppt salinity, was transferred to either low (15 and 5 ppt), or high (45 ppt) salinity for 7 days. Hemolymph osmolality, branchial carbonic anhydrase activity, and total ninhydrin-positive substances (TNPS) in abdominal muscle were then measured for each condition. Hemolymph osmotic concentration was regulated slightly below ambient water osmolality in shrimp acclimated to 30 ppt. At 15 and 5 ppt, shrimp were strong hyper-osmotic regulators, maintaining hemolymph osmolality between 200 and 400 mOsm above ambient. Shrimp acclimated to 30 ppt and transferred to 45 ppt salinity were strong hypo-osmotic and hypo-ionic regulators, maintaining hemolymph osmolality over 400 mOsm below ambient. Branchial carbonic anhydrase (CA) activity was low (approximately 100 micromol CO(2) mg protein(-1) min(-1)) and uniform across all 8 gills in shrimp acclimated to 30 ppt, but CA activity increased in all gills after exposure to both low and high salinities. Anterior gills had the largest increases in CA activity, and levels of increase were approximately the same for low and high salinity exposure. Branchial CA induction appears to be functionally important in both hyper- and hypo-osmotic regulations of hemolymph osmotic concentrations. Abdominal muscle TNPS made up between 19 and 38% of the total intracellular osmotic concentration in shrimp acclimated to 5, 15, and 30 ppt. TNPS levels did not change across this salinity range, over which hemolymph osmotic concentrations were tightly regulated. At 45 ppt, hemolymph osmolality increased, and muscle TNPS also increased, presumably to counteract intracellular water loss and restore cell volume. L. vannamei appears to employ mechanisms of both extracellular osmoregulation and intracellular volume regulation as the basis of its euryhalinity.     

Short Communication

Anaerobic metabolism and oxygen carrying-capacity of white shrimp ( Penaeus vannamei ) exposed to short term (three days) and long term (two weeks) moderate hypoxia (2-2.6 mg/L) was investigated. Glucose and lactate levels in hemolymph increased under both hypoxic conditions, indicating an activation of anaerobic pathways during the two-weeks exposure period. In muscle, no differences of glucose and lactate levels were observed between the control group and the exposed groups. In animals exposed to hypoxia for two weeks, hemocyanin and copper in hemolymph were higher than in animals under normoxic conditions or exposed for three days. These results indicate that an increase in oxygen carrying-capacity in shrimp is evident only after a sustained condition of hypoxia. Copper levels in the hepatopancreas decreased in both hypoxic conditions, suggesting a mobilization of copper stores for hemocyanin synthesis. These results indicate that penaeid shrimp can tolerate moderate hypoxic conditions by physiological adaptations, such as anaerobic metabolism and increased oxygen carrying-capacity. These adaptations require an adequate dietary supply of proteins and copper for hemocyanin synthesis and of carbohydrates for anaerobic metabolism.     

Short Communication

Anaerobic metabolism and oxygen carrying-capacity of white shrimp (Penaeus vannamei) exposed to short term (three days) and long term (two weeks) moderate hypoxia (2-2.6 mg/L) was investigated. Glucose and lactate levels in hemolymph increased under both hypoxic conditions, indicating an activation of anaerobic pathways during the two-weeks exposure period. In muscle, no differences of glucose and lactate levels were observed between the control group and the exposed groups. In animals exposed to hypoxia for two weeks, hemocyanin and copper in hemolymph were higher than in animals under normoxic conditions or exposed for three days. These results indicate that an increase in oxygen carrying-capacity in shrimp is evident only after a sustained condition of hypoxia. Copper levels in the hepatopancreas decreased in both hypoxic conditions, suggesting a mobilization of copper stores for hemocyanin synthesis. These results indicate that penaeid shrimp can tolerate moderate hypoxic conditions by physiological adaptations, such as anaerobic metabolism and increased oxygen carrying-capacity. These adaptations require an adequate dietary supply of proteins and copper for hemocyanin synthesis and of carbohydrates for anaerobic metabolism.     

Effects of dopamine on the immunity of white shrimp Litopenaeus vannamei

The total haemocyte count (THC), phenoloxidase activity, respiratory burst, superoxide dismutase (SOD) activity, phagocytic activity and clearance efficiency in response to pathogen Vibrio alginolyticus were measured when the white shrimp Litopenaeus vannamei (20.0+/-1.5 g) were injected individually with dopamine at 10(-8), 10(-7) and 10(-6)mol shrimp(-1), respectively. For the shrimp that received dopamine at 10(-7) and 10(-6)mol shrimp(-1), the THC decreased by 25% and 39%, phenoloxidase activity decreased by 15% and 32%, respiratory burst decreased by 21% and 36%, and SOD activity decreased by 50% and 63%, respectively, after 4 h. The phagocytic activity and clearance efficiency of shrimp that received dopamine at either dose decreased significantly after 2 h. The THC, phenoloxidase activity, respiratory burst, SOD activity, phagocytic activity and clearance efficiency returned to normal values after 16, 8, 8, 24, 16 and 4 h, respectively, for the shrimp that received dopamine at either dose. In another experiment, L. vannamei which had received dopamine at 10(-8), 10(-7) and 10(-6)mol shrimp(-1) were challenged after 1 h by injection with V. alginolyticus at 1.0x10(5) colony-forming units (cfu) shrimp-1 and then placed in seawater of 20 per thousand. The cumulative mortality of shrimp that received dopamine at either dose was significantly higher than that of shrimp that received saline after 8 h, and of shrimp that received saline at the termination of the experiment (48 h after the challenge). It is therefore concluded that dopamine administration at 10(-6)mol shrimp-1 or less causes immune modulation of L. vannamei.     

Hemolymph osmolality and cation concentrations in Litopenaeus vannamei during exposure to artificial sea salt or a mixed-ion solution: relationship to potassium flux

Interest in culturing the Pacific white shrimp Litopenaeus vannamei in low-salinity and brackish-well waters has led to questions about the ability of this species to osmo- and ionoregulate in environments containing low concentrations of ions and in environments with ionic ratios that differ from those found in sea water. After seven days, hemolymph osmolality and potassium, sodium and calcium values were all significantly affected by salinity (as artificial sea salt) with values decreasing with decreasing salinity. These decreases were small, however, relative to decreases in salinity, indicating iono- and osmoregulation with adjustment for gradients. The hemolymph osmolality and sodium and calcium concentrations in shrimp exposed to either 2 g/L artificial sea salt or 2 g/L mixed-ion solution (a mixture of sodium, potassium, calcium, and magnesium chlorides that approximate the concentrations and ratios of these cations found in 2 g/L dilute seawater) did not differ significantly. However, hemolymph potassium levels were significantly lower in shrimp held in the mixed-ion environment. Potassium influx rates were similar in shrimp held in either artificial sea salt or mixed ions. The results of this study indicate that salinity affects hemolymph-cation concentrations and osmolality. Further, differential potassium-influx rates do not appear to be the basis for low hemolymph potassium levels observed in shrimp held in mixed-ion environments.     

Expression and applications of recombinant crustacean hyperglycemic hormone from eyestalks of white shrimp (Litopenaeus vannamei) against bacterial infection

Crustacean hyperglycemic hormone (CHH) has many functions to regulate carbohydrate metabolism, ecdysis and reproduction including ion transport in crustaceans. The cDNA encoding CHH peptides containing 369 bp open reading frame encoding 122 amino acids was cloned from eyestalk of white shrimp (Litopenaeus vannamei) and was produced by a bacterial expression system. The biological activity of recombinant L. vannamei crustacean hyperglycemic hormone (rLV-CHH) was tested. The hemolymph glucose level of shrimp increased two-fold at 1h after the rLV-CHH injection and then returned to normal after 3h. In addition to the effect of rLV-CHH administration (25 μg/shrimp) on immunological responses of white shrimp against pathogenic bacteria, Vibrio harveyi was studied. Results showed that the blood parameters of shrimp injected with rLV-CHH; the THC, PO activity, serum protein level and clearance ability to V. harveyi, were also higher than those of Neg-protein and PBS-injected shrimp. The survival of shrimp injected with rLV-CHH was significantly higher (66.0%) than shrimp that injected with Neg-protein (33.3%) and PBS (28.9%) after 14 days. It is possible that the administration of rLV-CHH in L. vannamei exhibited a higher immune response related to resistance against V. harveyi infection.     

Affinity proteomic approach for identification of an IgA-like protein in Litopenaeus vannamei and study on its agglutination characterization

An unknown protein reacted with anti-human IgA, namely, IgA-like protein, has been reported in shrimp, but information regarding its identification is not available. In the present study, an affinity proteomic strategy was applied to identify the IgA-like protein of shrimp Litopenaeus vannamei. The protein of 75 kDa was isolated and confirmed by affinity chromatography and Western blotting with goat anti-human IgA, respectively, and then identified as hemocyanin, a member of IgSF, by mass spectrometry. Moreover, our results showed that human IgA and L. vannamei hemocyanin could separately react with goat anti-human IgA or rabbit anti-shrimp affinity hemocyanin (a-hemocyanin). Further evidences indicated that the recombinant protein of the Ig-like conserved domain could react with anti-human IgA. Interestingly, our results indicated that L. vannamei hemocyanin could aggregate with eight species of shrimp pathogenic bacteria and four types of animal erythrocytes directly. These results indicate that L. vannamei hemocyanin, an IgA-like protein, has dual function of reaction with anti-human IgA as an antigen and of activity binding to bacteria and animal erythrocytes as an agglutinin, suggesting its characteristic role as an IgSF molecule. In addition, our approach suggests that affinity proteomics based on heterogeneous antibody can speed up the identification of Fossman antigens.     

Thee effect of 5-HTP on the reproductive timer in the male cricket

The post-copulatory sexually refractory stage in the male cricket Gryllus bimaculatus consists of the two substages: the first refractory stage (RS1, time-variable) between copulation and spermatophore preparation, and the second refractory stage (RS2, time-constant) between spermatophore preparation and the recommencement of courtship. To understand the mechanism of the timer for RS2, subcuticular or intraganglionic injection of biogenic amines (10(-2) mol l(-1)) was performed immediately after spermatophore preparation. RS2 was shortened by octopamine, 5-HT, 5-HTP and NA-5-HT. Among these, 5-HTP was most potent. It shortened RS2 to maximally about 38% of the control. The shortening effect continued for 4.5 h after subcuticular injection even when the hemolymph was washed out with saline at 1 hour after injection. Simultaneous injection of 5-HTP with the inhibitor (NSD-1015) of 5-HT synthesis enzyme nullified the effect of 5-HTP, indicating that the shortening effect was caused by 5-HT synthesized from extrinsic 5-HTP. Injection of the inhibitor (CHX) of protein synthesis had no effect of on RS2. These results suggest that the reproductive timer in the TAG may be controlled by 5-HT or a second messenger mediated by 5-HT.     

Monoamine Synthesis and Concentration in Neonatal Rat Brain During Hypercapnia and Recovery

One-day-old rats were exposed to a gas mixture of 15% CO2-21% O2-64% N2 for a 30-min period. Monoamine synthesis in whole brain was measured during, and at various intervals after, hypercapnia by estimating the accumulation of dihydroxyphenylalanine (DOPA) and 5-hydroxytryptophan (5-HTP) after inhibition of aromatic L-amino-acid decarboxylase with NSD 1015. Endogenous concentrations of tyrosine, dopamine (DA), noradrenaline (NA), tryptophan, 5-hydroxytryptamine (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) were measured at the same intervals. Exposure to CO2 induced an increased synthesis of catecholamines and 5-HT. Further, an increase in DA concentration was seen during hypercapnia, while NA and 5-HT were unchanged. After the CO2 exposure the increased in vivo synthesis rates of catecholamines and 5-HT were rapidly normalized, as was the endogenous DA concentration. A slight increase in 5-HT and 5-HIAA concentrations was seen immediately after CO2 exposure. These results indicate that in neonatal animals, hypercapnia induces changes in central monoamine neurons, primarily an increased synthesis. These alterations may be relevant to some physiological changes seen during CO2 exposure, such as the alteration in central respiratory performance.     

Swimming ability and physiological response to swimming fatigue in whiteleg shrimp, Litopenaeus vannamei

Some penaeids are active swimmers, undertaking migrations of hundreds of nautical miles. At present, however, very little is known of swimming ability in penaeid shrimps. The aim of the present study is to investigate swimming endurance of whiteleg shrimp, Litopenaeus vannamei, against one of five flow velocities (5.41, 6.78, 8.21, 10.11, and 11.47 cm s(-1)) for up to 9000 s at 20 degrees C in a swimming channel. Body mass, hemolymph total protein concentration, and hemolymph glucose level were measured before swimming and immediately following swimming to evaluate physiological effect of swimming in L. vannamei. No shrimp swam the full 9000 s at any of the velocities tested. The swimming endurance decreased as swimming speed was increased. The relationship between swimming endurance (t, in s) and swimming speed (v, in cm s(-1)) can be described by the Curve Estimation: v.t0.38 = 159.64 (R2 = 0.94). The swimming ability index (SAI), defined as SAI = integral 0-9000 vdt x 10(-4) (cm) was found to be 7.28 cm for the shrimp tested. Swimming to fatigue leads to severe loss of body mass, hemolymph total protein concentration, and hemolymph glucose level in L. vannamei (P < 0.05). Furthermore, these decreases and swimming speed showed significantly polynomial relationships (P < 0.05). The results suggest that the power model fits well to the observed endurance estimates and the SAI is a good index to quantitatively describe the overall swimming ability of L. vannamei. Furthermore, hemolymph total protein concentration may be used as a rapid and reliable indicator to assess the penaeid shrimps' swimming speed and hence swimming ability.     

Hemolymph analysis and evaluation of newly formulated media for culture of shrimp cells (Penaeus stylirostris)

Summary Creation of a shirmp cell line has been an elusive goal. This failure may be due to the composition of the cell culture medium, which may be inadequate to support primary cultured cells. Shrimp hemolymph should contain the nutritional components needed to support cell growth and division. We report here the comprehensive biochemical analysis of hemolymph from the blue shrimp,Penaeus stylirostris (Litopenaeus stylirostris) (see Holthuis, L. B. Shrimps, and prawns of the world, in: FAO species catalog. Vol. 1. Rome: Food and Agriculture Organization of the United Nations; 1980), for free amino acids (FAAs), carbohydrates, electrolytes, metals, pH, and osmolality. Levels of hemolymph components were compared to 2×L-15 with 20% fetal bovine serum, a commonly used culture medium for crustacean cells. The FAAs, taurine and proline, and the metals, strontium and zinc, were significantly higher in hemolymph than in the 2×L-15 medium. In contrast, other FAAs were up to 50 times higher in the 2×L-15 medium than in the hemolymph. To mimic more closely the hemolymph composition, we created two new media based on either the 0.2×L-15 or the M199 medium. We compared the microscopic appearance of cells cultured in these media and evaluated deoxyribonucleic acid (DNA) and protein synthesis by³H-thymidine uptake and³⁵S-methionine uptake assays. The ovary cells ofP. stylirostris cultured in either of the new media formed monolayers, while the cells cultured in 2×L-15 medium did not. Despite these differences, there was no evidence of sustained DNA or protein synthesis with any of the media. Future studies to establish a shrimp cell line should focus on analysis of the cell cycle and on overcoming the molecular blocks to cell division.     

Monoamine Neurotransmitter Metabolism and Locomotor Activity During Chemical Hypoxia

The effects of hypoxia on metabolism of 5-hydroxytryptamine (5-HT or serotonin) and 3,4-dihydroxyphenylethylamine (DA or dopamine) were compared with those on open-field activity in male CD-1 mice. Chemical hypoxia was induced with NaNO2. Hypoxia did not alter striatal concentrations of DA, 5HT, Trp, Tyr, 5-hydroxyindoleacetic acid, or homovanillic acid. However, NaNO2 (75 mg/kg) reduced the rates of conversion of [3H]Tyr to [3H]DA (-41%) and [3H]Trp to [3H]5-HT (-39%). Hypoxia also reduced dihydroxyphenylacetic acid (DOPAC) levels (-27%) and DOPAC/DA ratios (-20%). Open-field behavior, as measured in an automated activity monitor, decreased in a dose-dependent fashion with 75-150 mg/kg of NaNO2 (-35 to -90%). Comparison with previous studies suggests that the syntheses of dopamine, serotonin, and the amino acids are equally vulnerable to hypoxic insults but may be less sensitive than the synthesis of acetylcholine.     

Anticonvulsant action of hippocampal dopamine and serotonin is independently mediated by D and 5-HT receptors

The present microdialysis study evaluated the anticonvulsant activity of extracellular hippocampal dopamine (DA) and serotonin (5-HT) with concomitant assessment of the possible mutual interactions between these monoamines. The anticonvulsant effects of intrahippocampally applied DA and 5-HT concentrations were evaluated against pilocarpine-induced seizures in conscious rats. DA or 5-HT perfusions protected the rats from limbic seizures as long as extracellular DA or 5-HT concentrations ranged, respectively, between 70-400% and 80-350% increases compared with the baseline levels. Co-perfusion with the selective D(2) blocker remoxipride or the selective 5-HT(1A) blocker WAY-100635 clearly abolished all anticonvulsant effects. These anticonvulsant effects were mediated independently since no mutual 5-HT and DA interactions were observed as long as extracellular DA and 5-HT levels remained within these protective ranges. Simultaneous D(2) and 5-HT(1A) receptor blockade significantly aggravated pilocarpine-induced seizures. High extracellular DA (> 1000% increases) or 5-HT (> 900% increases) concentrations also worsened seizure outcome. The latter proconvulsive effects were associated with significant increases in extracellular glutamate (Glu) and mutual increases in extracellular monoamines. Our results suggest that, within a certain concentration range, DA and 5-HT contribute independently to the prevention of hippocampal epileptogenesis via, respectively, D(2) and 5-HT(1A) receptor activation.     

Noradrenaline modulates the immunity of white shrimp Litopenaeus vannamei

The total haemocyte count (THC), phenoloxidase activity, respiratory burst, superoxide dismutase (SOD) activity, phagocytic activity and clearance efficiency in response to pathogen Vibrio alginolyticus were measured when the white shrimp Litopenaeus vannamei (18.4 +/- 1.2 g) were injected individually with noradrenaline at 10(-8), 10(-7) and 10(-6) mol shrimp(-1). For the shrimp that received noradrenaline at 10(-8), 10(-7) and 10(-6) mol shrimp(-1), the THC decreased by 15%, 21% and 32%, phenoloxidase activity decreased by 15%, 31% and 31%, respiratory burst decreased by 13%, 21% and 32%, and SOD activity decreased by 46%, 56% and 55%, respectively, after 2 h. The phagocytic activity and clearance efficiency of shrimp that received noradrenaline at either dose decreased significantly after 2 h. The THC, phenoloxidase activity, respiratory burst, SOD activity, phagocytic activity and clearance efficiency returned to normal values after 4, 4, 8, 24, 16 and 8 h, respectively, in the shrimp that received noradrenaline at either dose. In another experiment, L. vannamei which had received noradrenaline at 10(-8), 10(-7) and 10(-6) mol shrimp(-1) were challenged after 1h by injection with V. alginolyticus at 1.0 x 10(5) colony-forming units (cfu)shrimp(-1) and then placed in seawater of 20 per thousand. The cumulative mortality of shrimp that received noradrenaline at either dose was significantly higher than that of shrimp that received saline after 4 h, and at the termination of the experiment (48 h after the challenge). It is therefore concluded that noradrenaline administration at 10(-6) mol shrimp(-1) or less causes immune modulation of L. vannamei.     

The role of biogenic amines in the control of blood glucose level in the decapod crustacean,Carcinus maenas L.

1. Administration of biogenic amines into intact Carcinus maenas induces dose- and timedependent elevation of hemolymph glucose level.2. Removal of the neurosecretory centre containing the crustacean hyperglycemic hormone (CHH) by ablation of the eyestalks did not induce hypoglycemia.3. Injection of dopamine (DA) into eyestalkless crabs showed no hyperglycemic effect, while serotonin (5-HT), epinephrine (E), norepinephrine (NE), and octopamine (OA) elevated glucose levels.4. The dopaminergic effect was significantly reduced by administration of trifluoperazine (TFP).5. 5-HT and OA were found to be strong elevators of glucose levels, while the other biogenic amines had moderate effects only.6. The results indicate, that DA exerts its hyperglycemic effect by stimulating the release of CHH from the eyestalk neurosecretory centre. Elevation of hemolymph glucose level by 5-HT, OA, E, and NE, occurs independently of CHH.     

Serotonin influences locomotion in the nudibranch mollusc Melibe leonina

Serotonin (5-HT) influences locomotion in many animals, from flatworms to mammals. This study examined the effects of 5-HT on locomotion in the nudibranch mollusc Melibe leonina (Gould, 1852). M. leonina exhibits two modes of locomotion, crawling and swimming. Animals were bath-immersed in a range of concentrations of 5-HT or injected with various 5-HT solutions into the hemolymph and then monitored for locomotor activity. In contrast to other gastropods studied, M. leonina showed no significant effect of 5-HT on the distance crawled or the speed of crawling. However, the highest concentration (10(-3) mol l(-1) for bath immersion and 10(-5) mol l(-1) for injection) significantly increased the time spent swimming and the swimming speed. The 5-HT receptor antagonist methysergide inhibited the influence of 5-HT on the overall amount of swimming but not on swimming speed. These results suggest that 5-HT influences locomotion at the behavioral level in M. leonina. In conjunction with previous studies on the neural basis of locomotion in M. leonina, these results also suggest that this species is an excellent model system for investigating the 5-HT modulation of locomotion.     

SNPs of hemocyanin C-terminal fragment in shrimp Litopenaeus vannamei

In this study, we identified a variable region in the C-terminus of hemocyanin from the shrimp Litopenaeus vannamei (2288-2503bp, HcSC) by sequence alignments. A total of 13 SNPs were identified by PCR-SSCP and HcSC clone sequencing. The SSCP patterns of HcSC could be modulated in Vibro parahaemolyticus-treated shrimps. A novel SSCP band with four SNP sites was identified in V. parahaemolyticus-resistant shrimps. More importantly, three of these four SNPs introduced variations in amino acid sequence and possibly secondary structure of the HcSC polypeptide and resulted in a higher agglutinative activity against seven pathogenic bacteria. These results suggest that the C-terminus of shrimp L. vannamei hemocyanin possesses SNPs, which may be related to shrimp resistance to different pathogens.     

Activation of 5-HT(1A) but not 5-HT(1B) receptors attenuates an increase in extracellular dopamine derived from exogenously administered L-DOPA in the striatum with nigrostriatal denervation

In order to determine whether L-DOPA-derived extracellular dopamine (DA) in the striatum with dopaminergic denervation is affected by activation of serotonin autoreceptors (5-HT(1A) and 5-HT(1B) receptors), we applied in vivo brain microdialysis technique to 6-hydroxydopamine-lesioned rats and examined the effects of the selective 5-HT(1A) receptor agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) and the selective 5-HT(1B) receptor agonist CGS-12066 A on L-DOPA-derived extracellular DA levels. Single L-DOPA injection (50 mg/kg i.p.) caused a rapid increase and a following decrease of extracellular DA, with a peak value at 100 min after L-DOPA injection. Pretreatment with both 0.3 mg/kg and 1 mg/kg 8-OH-DPAT (i.p.) significantly attenuated an increase in L-DOPA-derived extracellular DA and the times of peak DA levels were prolonged to 150 min and 225 min after L-DOPA injection, respectively. These 8-OH-DPAT-induced changes in L-DOPA-derived extracellular DA were antagonized by further pretreatment with WAY-100635, a selective 5-HT(1A) antagonist. In contrast, intrastriatal perfusion with the 5-HT(1B) agonist CGS-12066 A (10 nM and 100 nM) did not induce any changes in L-DOPA-derived extracellular DA. Thus, stimulation of 5-HT(1A) but not 5-HT(1B) receptors attenuated an increase in extracellular DA derived from exogenous L-DOPA. These results support the hypothesis that serotonergic neurons are primarily responsible for the storage and release of DA derived from exogenous L-DOPA in the absence of dopaminergic neurons.