The localization and rate of disappearance of a synaptic vesicle antigen following denervation

Association of axonally transported heparan sulfate with isolated synaptic plasma membrane

Studies on isolated synaptic plasma membranes (SPM) have detected little if any heparan sulfate or other glycosaminoglycans (GAGs), while more recent studies employing proteoglycan antibodies have localized heparan sulfate proteoglycan in presynaptic plasma membrane of intact tissue. To further address the issue of proteoglycans in synaptic plasma membrane, we have investigated the possible presence of axonally transported GAGs in SPM isolated from the goldfish optic tectum. SPMs isolated from tecta following rapid axonal transport of 35SO4 labeled molecules down the optic nerve, showed specific radioactivity approximately two-fold higher than the starting homogenate. Treatment of the transport labeled SPM with the enzyme heparitinase liberated 21% of the radioactivity, indicating the presence of a significant fraction of transported label in heparan sulfate. In a separate series of experiments a GAG fraction was isolated from transport labeled SPM and was found to consist of heparan sulfate containing 28% of transported radioactivity. Chondroitin (4 or 6) sulfate, which undergoes axonal transport in the goldfish optic system, was not found associated with SPM. Taken together the results support immunological evidence for the presence of heparan sulfate proteoglycans in presynaptic plasma membrane.

Development of the electromotor system in Torpedo marmorata: cationic staining of the electric organ

The electric organs of embryonic Torpedo marmorata have been reacted with three cationic stains to evaluate the appearance and distribution of anionic sites. Ruthenium red, alcian blue and lysozyme were used at different pHs and found to react in a time-related manner to anionic components within the interelectrocyte space. The basal lamina covering the ventral electrocyte surface possesses the greatest number of anionic sites whereas growth cone, presynaptic terminal and glial membranes displayed almost no staining. Since this lamina serves as the exclusive substrate for ingrowing neurites during synaptogenesis, the results are consistent with the idea that charge distribution on the membrane surface may provide a necessary cue for neurite motility, extension and eventual synaptogenesis.

An immunohistochemical study of synaptogenesis in the electric organ of Torpedo marmorata by use of antisera to vesicular and presynaptic plasma membrane components

Synaptogenesis has been studied in the electric organ of embryonic Torpedo marmorata by use of two antisera directed against components of synaptic vesicles (anti-SV) and presynaptic plasma membranes (ap-anti-TSM), respectively. The anti-SV serum was previously shown to recognize a proteoglycan specific for synaptic vesicles. The ap-anti-TSM serum was raised to plasma membranes of synaptosomes derived from the electromotor nerve terminals and affinity-purified on electric-organ gangliosides. The vesicular antigen was first detectable at the 81-mm stage of development, which is 1-2 weeks earlier than the formation of morphologically mature presynaptic terminals, but is coincident with a rise in choline acetyltransferase levels and the ability of the electric organ to generate discharges. The gangliosidic antigen recognized by the ap-anti-TSM was first detectable on the ventral electrocyte surface at the 93-mm stage of development. This indicates that specific carbohydrate epitopes, not present on the growth cones, are expressed during maturation of the nerve terminal. The nerve terminal components recognized by these sera arose pari passu with neurite coverage of the ventral surface of the electrocyte, reaching a maximum in the adult. In contrast, postsynaptic aggregates of acetylcholine receptor, rendered visible with rhodamine-labeled alpha-bungarotoxin, arose previous to the presynaptic antigens, reaching a maximum surface density at 110 mm and then declining in the adult.

Presence of vasoactive intestinal polypeptide-like immunoreactivity in the cholinergic electromotor system of Torpedo marmorata

Vasoactive intestinal polypeptide (VIP)-like immunoreactivity was detected in the cholinergic electro-motor system of Torpedo marmorata using a combination of immunohistochemical assays, radioimmunoassay, and HPLC. The immunohistochemical assays revealed that the distribution of VIP-like immunoreactivity in the electric lobes, electromotor nerves, and electric organ is comparable to that of the stable cholinergic synaptic vesicle marker vesicle-specific proteoglycan. Ligation of the electromotor nerves caused a marked accumulation of VIP-like immunoreactivity in the lobes (180%) and the proximal portions of the electromotor nerves (130%) and a decrease in the electric organ (-50%), when measured by radioimmunoassay using synthetic VIP (porcine sequence) as the standard. VIP-like immunoreactivity in extracts of electric lobes electromotor nerves, and electric organ was eluted from a semipreparative reverse-phase HPLC column as a single peak with a retention time similar to that of porcine VIP. Rechromatography at higher resolution on an analytical column indicated diversity between the molecular forms of VIP-like immunoreactivity extracted from electric lobe and electric organ, suggesting the possibility of posttranslational processing.