Presynaptic Regions Research Articles

Effect of prednisolone on motor end-plate fine structure: a morphometric study in hamsters.

The fine structure of quadriceps motor end-plates in hamsters was analyzed quantitatively one, two, four, seven, and thirty-two weeks following intraperitoneal injections of prednisolone. Except for transient increases in postsynaptic length and membrane profile concentration after prednisolone administration at dosages of 4 mgper kilogram of body weight for one week and 2 mg per kilogram for four weeks, mean values for various measurable profiles in the presynaptic and postsynaptic regions showed no significant differences between control and treated animals.

Voltage sensitive calcium channels in the presynaptic terminals of a decrementally conducting photoreceptor.

1. Intracellular recordings were made from the presynaptic regions of the photoreceptors of the median ocellus of the giant barnacle, Balanus nubilus.2. Millivolt changes in membrane potential near the dark resting level in the terminals elicit post-synaptic activity and consequently must be sufficient to modulate transmitter release from these endings.3. In normal saline the terminal voltage usually changes in a graded manner to increasing intensities of illumination of the cell. When the terminal region is superfused with saline containing TEA, 3-AP or high concentrations of K, an all-or-none action potential can be elicited consistently by light or injected current.4. The peak value of this action potential depends on the Ca concentration in the saline. The action potential can be generated if Sr or Ba ions replace Ca, but is reduced or blocked if Mg, Co, or Mn ions are added to the saline. It is virtually unaffected by TTX or replacement of Na with TMA ions in the saline. These results suggest that Ca carries most or all of the inward current during the action potential.5. The action potential is followed by a large undershoot which can last several seconds. The amplitude and duration of the action potential and the duration of the undershoot all grow in increasing concentrations of TEA up to 400 mM, the highest concentration tested. The threshold for the action potential decreases as the concentration of TEA is increased to 10 mM; increasing the concentration further has no effect on the threshold. These observations suggest that TEA blocks a voltage-sensitive potassium conductance at low concentrations but has less effect on the current responsible for the undershoot.6. Electrophysiological and pharmacological evidence suggests that the Ca channels are concentrated in the presynaptic terminals of this photoreceptor.

A functional model of sialo-glyco-macromolecules in synaptic transmission and memory formation

A concept is presented of the molecular involvement of sialo-glyco-macromolecules in the processes of synaptic transmission and memory formation. The main point of the concept is the assumption that by complexation between lipid-bound negative charged sialic acid and Ca 2+ -ions the synaptic membrane is “closed”, while dissociation of these complexes will cause an “opening” of presynaptic regions. The synaptic zones of contact are assumed to become functionable during ontogenesis, only after the incorporation of sialyl residues into the carbohydrate coat of neuronal membrane. Additional accretion of sialo-glyco-macromolecules at the contact zones, could be the molecular basis for a facilitation of defined neural pathways, which might be the morphological correlate of an engram. Published experimental data are used as evidence for the validity of this concept.

Motor innervation of the supercontracting longitudinal ventro-lateral muscles of the blowfly larva

The gross motor innervation of the abdominal longitudinal ventro-lateral muscles of the larva of Calliphora erythrocephala is described. Two of these muscles, 6A and 7A, are innervated by the same two multiterminally-ending axons, and thus comprise a single motor unit. No difference is found between the axon diameters in the main nerve trunks, but there is a difference where the axons run over the muscle surface. Only the dorsal, inner, surface of the muscle is innervated. Electro-physiological results show two sizes of EPSP: the large fast EPSP presumably corresponds to the thicker axon and the small slow one to the thinner axon. Preliminary work indicates that it is not possible to distinguish between the two axons with electron microscopy; the presynaptic regions possess both ‘classical’ synaptic and ‘neurosecretory’ type vesicles, and have no glial cell covering.