Exceptions to Cajal's neuron theory: communicating synapses.

Ultrastructural images of some neurons and their synaptic connections, belonging to the nucleus of the periaqueductal grey substance in the domestic cat mesencephalon, are shown. The finding that some axosomatic synapses showed an open communication between the pre- and postsynaptic portion attracted our attention. In this way a continuity is made between the presynaptic bouton of one neuron (axon) and the postsynaptic portion of the other (neuronal soma). Synapses having these interneuronal communications could be denominated communicating synapses. Accepting Cajal's neuron theory and his law of neuronal independence, it is very difficult to interpret these images. We wonder if this type of communicating synapses could be the exception that proves the rule of the neuron independence.

High-energy adhering junctional complexes or with mitochondrial coupling.

A variety of adhering junction is found in the ependyma of the domestic cat with a coupling of mitochondria. These are symmetrically situated (in mirror form) at both sides of the intercellular cleft, which always maintain the same separating distance, thereby leaving a limiting cellular space of a constant amplitude. The hypothesis is put forward that the energy (ATP), provided by the mitochondria over adhering junctional complexes, would produce separate fields of force which would position in a lengthwise direction the molecules which give rise to the anchoring filaments. The mitochondrial energy provided and the electrostatic forces generated would produce an adhering, intercellular junction which is functionally very strong and which could be called: high-energy adhering junctional complexes or with mitochondrial coupling.

Extracellular osmiophilic oval bodies in the vagal and facial lobes of Carassius auratus (Teleostei-Cyprinidae).

During the study of ultrathins sections of the vagal lobes and the facial lobe of Carassius auratus (Teleostei Cyprinidae), by electron microscopy, extracellular oval or discoidal, very osmiophilic structures were found in the neuropil of the lobes. The structures measured approximately 73 nm long 58 nm wide, and 29 nm thick and were located within the extracellular spaces surrounding some glial and neural processes; they were closely apposed to the external membrane of these cells, sometimes forming a pavement like pattern. These structures, as far as we know, have not been previously described and their function is unknown.

Ultrastructural basis of the coordination of ciliary movement. Contractile function of the interconnecting cross-striated roots in ependymal epithelium.

A hypothesis for contraction was suggested (molecular basis of the transmission of ciliary coordination) by means of the slipping and interdigitation of the microfilaments of one period with those of the adjacent periods, occurring at the level of the periodic band. The amplitude of the period is greater in the relaxed than in the contracted state, while the reverse is true with the periodic band amplitude. The microfilament length is constant, probably varying with the species. This hypothesis of the slipping and interdigitation of the microfilaments would be the basis of the ciliary coordination from cilium to cilium and from cell to cell, because of the anchoring of the bunches in the peribasal complexes and in the adherent connection complexes, respectively.