Uptake of the neurotransmitter histamine into the eyes of larvae of the barnacle (Balanus amphitrite)

Nitric oxide synthase (NOS) in the cyprid of Amphibalanus amphitrite (Cirripedia, Crustacea)

The Amphibalanus amphitrite barnacle is a sessile marine crustacean and a major constituent of benthic as well as intertidal communities. A. amphitrite is also an important component of biofouling on artificial substrates. The role of nitric oxide (NO) was recently observed in the settlement of this species. In this work, we used immunohistochemical and histoenzymatic methods to investigate, for the first time, the presence and distribution of NO synthetic enzymes (NOS) in the competent-for-settlement cyprid of A. amphitrite. NOS-like immunoreactivity was observed in various regions of the cyprid: gut mucosa, mantel epithelium, thoracic muscle, and abductor muscles. Intense immunoreactivity was also present in the cement gland and oil cells, while widespread immunoreactivity was observed in the compound eye. NADPH-diaphorase method was used to provide further data and understand NOS-distribution. The results show that NOS is likely to be present in structures - such as muscles and cement gland - which are key for settlement.

The functional organisation of glia in the adult brain of Drosophila and other insects

This review annotates and categorises the glia of adult Drosophila and other model insects and analyses the developmental origins of these in the Drosophila optic lobe. The functions of glia in the adult vary depending upon their sub-type and location in the brain. The task of annotating glia is essentially complete only for the glia of the fly's lamina, which comprise: two types of surface glia-the pseudocartridge and fenestrated glia; two types of cortex glia-the distal and proximal satellite glia; and two types of neuropile glia-the epithelial and marginal glia. We advocate that the term subretinal glia, as used to refer to both pseudocartridge and fenestrated glia, be abandoned. Other neuropiles contain similar glial subtypes, but other than the antennal lobes these have not been described in detail. Surface glia form the blood brain barrier, regulating the flow of substances into and out of the nervous system, both for the brain as a whole and the optic neuropiles in particular. Cortex glia provide a second level of barrier, wrapping axon fascicles and isolating neuronal cell bodies both from neighbouring brain regions and from their underlying neuropiles. Neuropile glia can be generated in the adult and a subtype, ensheathing glia, are responsible for cleaning up cellular debris during Wallerian degeneration. Both the neuropile ensheathing and astrocyte-like glia may be involved in clearing neurotransmitters from the extracellular space, thus modifying the levels of histamine, glutamate and possibly dopamine at the synapse to ultimately affect behaviour.

The GABAergic-like system in the cyprid of Balanus amphitrite (=Amphibalanus amphitrite) (Cirripedia, Crustacea)

In the present study, biochemical and immunochemical methods were used to investigate the presence and distribution of GABA, glutamate decarboxylase (GAD), GABA(B)R1 and GABA(A) gamma2 subunit receptors and the vesicular GABA transporter (vGAT) in the cyprid of Balanus amphitrite (=Amphibalanus amphitrite). GAD(65/67) immunoreactive neuron cell bodies and nerve fibers were detected in the central nervous system. Paired GAD(65/67) immunoreactive nerves running from the posterior ganglion to the body and limb muscles were detected. Thin GABA-immunoreactive nerve terminals were present on striated muscular fibers and in the antennules. Furthermore, GABA, GAD(65/67), GABA(B)R1 and GABA(A)gamma2 subunit receptors and vGAT were observed in the lateral compound eyes, and GABA(A)gamma2 subunit receptor immunoreactivity was seen in the naupliar eye. These results suggest a neurotransmitter/neuromodulatory role for GABA in thoracic muscle contraction and regulatory functions in compound eyes and antennules of B. amphitrite cyprids.

Presence and distribution of FMRFamide-like immunoreactivity in the cyprid of the barnacle Balanus amphitrite (Cirripedia, Crustacea)

The presence and distribution of FMRFamide-like peptides (FLPs) in the cyprid larvae of the barnacle Balanus amphitrite were investigated using immunohistochemical methods. Barnacles are considered to be one of the most important constituents of animal fouling communities, and the cyprid stage is specialized for settlement and metamorphosis in to the sessile adult condition. FLPs immunoreactive (IR) neuronal cell bodies were detected in both the central and the peripheral nervous system. One bilateral group of neurons somata was immunodetected in the brain, and IR nerve fibers were observed in the neuropil area and optic lobes. Intense immunostaining was also observed in the frontal filament complex: frontal filament tracts leaving the optic lobes and projecting towards the compound eyes, swollen nerve endings in the frontal filament vesicles, and thin nerve endings in the external frontal filament. Thin IR nerve fibers were also present in the cement glands. Two pairs of neuronal cell bodies were immunodetected in the posterior ganglion; some of their axons appear to project to the cirri. FLPs IR neuronal cell bodies were also localized in the wall of the dilated midgut and in the narrow hindgut; their processes surround the gut wall and allow gut neurons to synapse with one another. Our data demonstrated the presence of FLPs IR substances in the barnacle cyprid. We hypothesize that these peptides act as integrators in the central nervous system, perform neuromuscular functions for thoracic limbs, trigger intestinal movements and, at the level of the frontal filament, play a neurosecretory role.

Evidence for the presence of histamine uptake into the synaptosomes of rat brain

Histamine has many physiological roles in the brain and periphery. Neuronal histamine is metabolized almost exclusively by histamine N-methyltransferase. Although several neurotransmitter systems such as dopamine and 5-hydroxytryptamine have their specific reuptake system in their neurons and glial cells, a specific histamine reuptake system into the corresponding nerve terminals or glial cells has not yet been clearly elucidated. We characterized the uptake of histamine into the P2 fractions of rat brain homogenized in 0.32 mol/l sucrose using in vitro uptake techniques. [3H]histamine uptake increased with the increment of added protein amount and elapsed time. [3H]histamine uptake was also temperature-dependent. The uptake of [3H]histamine into the P2 fractions occurs by two saturable processes, a high-affinity and a low-affinity, characterized by K(m) values of 0.16 and 1.2 micromol/l, respectively. Na(+), Cl(-) and HCO(3)(-) ions were essential for the uptake of histamine in P2 fractions. [3H]histamine uptake was inhibited in the presence of several tricyclic antidepressants. In accordance with this, the endogenous release of histamine from brain slices evoked by 100 mmol/l K(+) was augmented in the presence of 20 micromol/l imipramine. These results further support the existence of a specific histamine uptake system in the brain, although the precise molecular entities have not been identified until now.

Hepoxilins and trioxilins in barnacles: an analysis of their potential roles in egg hatching and larval settlement

The barnacle life cycle has two key stages at which eicosanoids are believed to be involved in cellular communication pathways, namely the hatching of nauplii and the settlement of cypris larvae. Barnacle egg-hatching activity has previously been reported to reside in a variety of eicosanoids, including 8-hydroxyeicosapentaenoic acid and a number of tri-hydroxylated polyunsaturated fatty acid derivatives, the trioxilins. The production of the eicosapentaenoic acid metabolite trioxilin A4 (8,11,12-trihydroxy-5,9,14,17-eicosatetraenoic acid) by the barnacles Balanus amphitrite and Elminius modestus was confirmed using a combination of high-performance liquid chromatography and gas chromatography, both linked to mass spectrometry. In addition, both species also generated trioxilin A3 (8,11,12-trihydroxy-5,9,14-eicosatrienoic acid; an arachidonic acid-derived product), 8,11,12-trihydroxy-9,14,17-eicosatrienoic acid (a omega3 analogue of trioxilin A3; derived from omega3 arachidonic acid) and 10,13,14-trihydroxy-4,7,11,16,19-docosapentaenoic acid (a docosahexaenoic acid-derived product). In contrast to earlier reports, trioxilin A3 had no E. modestus egg-hatching activity at any of the concentrations tested (10(-9)-10(-6) mol l(-1)). The unstable epoxide precursor hepoxilin A3, however, caused significant levels of hatching at 10(-6) mol l(-1). Furthermore, the stable hepoxilin B3 analogue PBT-3 stimulated hatching at 10(-7) mol l(-1). Neither trioxilin A3, hepoxilin A3 or PBT-3 at 0.25-30 micromol l(-1) served as settlement cues for B. amphitrite cypris larvae.