Effects of haloperidol and phentolamine on the crustacean cardiac ganglion.

Haloperidol (a dopamine D2 blocker in vertebrates) and phentolamine (an alpha-adrenergic blocker) alter the pattern of bursting by the isolated cardiac ganglion of the lobster when perfused at concentrations of 10(-6)-10(-5) mol/l. Both drugs decrease the frequency of bursting and increase burst duration. They are most effective in slowing the ganglion when applied selectively to the anterior ganglionic trunk, the same region of the ganglion where dopamine (DA) and 5-hydroxytryptamine (5HT) are most effective in speeding up bursting. When exogenous monoamine transmitters are applied in the presence of 3x10(-6) mol/l haloperidol, the effect of 5HT, but not of DA, is significantly reduced. At the same concentration, phentolamine does not suppress the actions of DA, 5HT or noradrenaline (NA). Both haloperidol and phentolamine significantly alter the properties of endogenous burst-organizing potentials (driver potentials) generated by motorneurons in the ganglion. It is possible that the effects of these drugs on bursting reflect alteration of endogenous electrical properties of the constituent neurons, rather than receptor antagonism.

Monoamine pharmacology of the lobster cardiac ganglion.

Monoamine agonists and antagonists were applied to the lobster cardiac ganglion in an attempt to clarify the different actions of 5-hydroxytryptamine (5HT) and dopamine (DA) on this rhythmic pattern generator. Experiments were designed to determine whether the similar responses to 5HT and DA applied to the anterior region of the ganglion could be separated by pharmacological approaches, and whether the different responses to 5HT applied to the anterior and posterior regions of the ganglion could be attributed to mediation by different receptors. A small number of the 5HT agonists which were tested mimic the effects of 5HT, in that they increase the frequency of bursting and decrease burst duration when applied to the whole ganglion, but decrease burst frequency and increase burst duration when applied only to the posterior half. Other 5HT agonists decrease frequency and prolong bursts when applied to the whole ganglion. Of the DA agonists tested, none acts as DA itself does. Rather, they mimic the effects of 5HT applied to the posterior ganglion, by slowing bursting and prolonging bursts. The actions of agonists do not correspond in any clear way to the receptor specificities as defined in vertebrates. Most antagonists tested do not show similar specificities to their effects in vertebrates. In particular, most of the DA antagonists tested are more effective in blocking exogenous 5HT than DA. One monoamine agonist directly alters the properties of endogenous burst-organizing potentials (driver potentials) in the motorneurons of the ganglion.

Heterogeneity of motoneuron driver potential properties along the anterior-posterior axis of the lobster cardiac ganglion.

Endogenous long-duration burst-organizing potentials (driver potentials, DPs) generated by neurons in the lobster cardiac ganglion play a critical role in the ability of the system to generate rhythmic bursts of nerve impulses. The DPs are normally terminated by a voltage-dependent potassium current, but when this is suppressed by tetraethylammonium ion (TEA), the five motoneurons in the system show heterogeneity in properties. Perfusion with TEA increases DP amplitude in all cells in a similar fashion, but it increases DP duration disproportionately in the most anterior motoneurons. Substitution of barium ions for calcium also prolongs DPs in all of the motoneurons, but the effect of this treatment is not different along the anterior-posterior axis of the ganglion. The results suggest that the different behavior of the neurons reflects a difference in either the extent of calcium inactivation of the calcium current responsible for the DP, or in the kinetics or magnitude of a calcium-activated potassium conductance which contributes to membrane repolarization. In contrast to previously reported results, reduction in extracellular sodium ion concentration decreases driver potential amplitude and/or duration. This effect is not differentially expressed in different motorneurons.

Serotonin modulation of the release of sequestered [3H]serotonin from nerve terminals in an insect neurohemal organ in vitro.

Exogenous tritiated serotonin ([3H]5-HT) is taken up by and released from serotonin-containing fibers within abdominal nerves of Rhodnius prolixus during in vitro incubations. Sequestered [3H]5-HT behaves as expected of an endogenous neurosecretory product in this system. Release is Ca2+-dependent during both K+-induced and physiologically induced secretory episodes. The kinetics of the release of sequestered label parallels the kinetics of release of endogenous neurohormones. Preloaded preparations which are washed with unlabeled 5-HT release label in two fashions; 5-HT itself induces a release of label and, at lower concentrations, 5-HT facilitates the release of label induced by high K+ washes. Facilitatory effects appear to be mediated through receptors within the neurohemal organ (NHO).

The identification and localization of a catecholamine in the motor neurons of the lobster cardiac ganglion.

The cardiac ganglion from Homarus americanus was investigated for the purpose of providing biochemical and histochemical information as to the identity of the neurotransmitter(s) utilized by this system. Three techniques were employed in this study: (1) the glyoxylic acid histofluorescence staining technique (GA), which showed fluorescence characteristic of catecholamines localized in the five motor neurons; (2) high-voltage electrophoresis (HVE) in one dimension followed by ascending chromatography in the second dimension, which indicated incorporation of label from tritiated tyrosine into norepinephrine (NE) and small amounts of dopamine (DA); (3) high-pressure liquid chromatography with electrochemical detection (HPLC/EC), which indicated the presence of endogenous norepinephrine.

Changes in hormone activity of single neurosecretory cell bodies during a physiological secretion cycle.

Single neurosecretory cell bodies were dissected from the ventral ganglionic mass of Rhodnius prolixus, lysed in distilled water, and bioassayed for diuretic hormone (DH) activity on isolated malpighian tubules. DH was found in a least 10 somata within the ganglion; electron micrographs of isolated cells show a large population of elementary neurosecretory granules. Quantitative measures of hormone activity were made by bioassaying somata from unfed 5th instar larvae, and at the following times after feeding; 1 h, 4 h (near the end of DH-mediated diuresis), 1 day, 5 days, 10 days, 17 days and 21 days (just after the moult to adult). DH activity in cell bodies drops significantly within 1 h after feeding, and remains low long after hormone secretion ceases. Restocking of the soma with active hormone occurs during the period 10-21 days after feeding.

Neurohemal organ extracts effect the ventilation oscillator in crustaceans.

Extracts of the pericardial organs of crabs injected into intact animals cause an increase in the frequency of scaphognathite beating. The active factor is not dopamine of 5-hydroxytryptamine, which are present in pericardial organs; it is probably a peptide. The factor may represent a hormonal mechanism of coordinating heart rate and ventilation.