Synaptic dimorphism in Onychophoran cephalic ganglia

The taxonomic location of the Onychophora has been controversial because of their phenotypic and genotypic characteristics, related to both annelids and arthropods. We analyzed the ultrastructure of the neurons and their synapses in the cephalic ganglion of a poorly known invertebrate, the velvet worm Peripatus sedgwicki, from the mountainous region of El Valle, Mérida, Venezuela. Cephalic ganglia were dissected, fixed and processed for transmission electron microscopy. The animal has a high degree of neurobiological development, as evidenced by the presence of asymmetric (excitatory) and symmetric (inhibitory) synapses, as well as the existence of glial cell processes in a wide neuropile zone. The postsynaptic terminals were seen to contain subsynaptic cisterns formed by membranes of smooth endoplasmic reticulum beneath the postsynaptic density, whereas the presynaptic terminal showed numerous electron transparent synaptic vesicles. From the neurophylogenetic perspectives, the ultrastructural characteristics of the central nervous tissue of the Onychophora show important evolutionary acquirements, such as the presence of both excitatory and inhibitory synapses, indicating functional synaptic transmission, and the appearance of mature glial cells.

Synaptic dimorphism in Onychophoran cephalic ganglia.

The taxonomic location of the Onychophora has been controversial because of their phenotypic and genotypic characteristics, related to both annelids and arthropods. We analyzed the ultrastructure of the neurons and their synapses in the cephalic ganglion of a poorly known invertebrate, the velvet worm Peripatus sedgwicki, from the mountainous region of El Valle, Mérida, Venezuela. Cephalic ganglia were dissected, fixed and processed for transmission electron microscopy. The animal has a high degree of neurobiological development, as evidenced by the presence of asymmetric (excitatory) and symmetric (inhibitory) synapses, as well as the existence of glial cell processes in a wide neuropile zone. The postsynaptic terminals were seen to contain subsynaptic cisterns formed by membranes of smooth endoplasmic reticulum beneath the postsynaptic density, whereas the presynaptic terminal showed numerous electron transparent synaptic vesicles. From the neurophylogenetic perspectives, the ultrastructural characteristics of the central nervous tissue of the Onychophora show important evolutionary acquirements, such as the presence of both excitatory and inhibitory synapses, indicating functional synaptic transmission, and the appearance of mature glial cells.

Levels of amino acid neurotransmitters during mouse olfactory bulb neurogenesis and in histotypic olfactory bulb cultures.

The developmental changes in the levels of amino acid neurotransmitters were analyzed by high pressure liquid chromatography during mouse olfactory bulb neurogenesis, from embryonic day (E)13 until the young adult age, between postnatal days (P)30 and P40. During the embryonic period, high levels of glutamate, aspartate and GABA were observed, with the values of GABA about 2-fold higher than those of glutamate and aspartate. At P0, the production of these neurotransmitters experienced birth stress as shown by a significant 2-fold reduction in their levels. During the first two postnatal weeks, a progressive increase in the glutamate content was detected diminishing slightly in the adult stage. The aspartate concentrations showed a maximal value at P3 and then decreased gradually until the second postnatal week; in the young adult age, its concentration was comparable with that of glutamate. The postnatal GABA contents increased progressively from birth to maturity, showing maximal levels at P3, P11 and in the adult. Throughout the studied developmental period, the concentration of glycine remained relatively low. With regard to taurine, very low concentrations were detected during the prenatal period but after birth, the taurine content gradually increased with age, and in the adult animal, its concentration was comparable with those of GABA and glutamate. Our data demonstrate the predominance of GABA and glutamate during olfactory bulb synaptogenesis, however, in the adult animal, both glutamate and aspartate exert the same influence in the excitatory synaptic transmission; in the adult inhibitory synaptic transmission, taurine appears to play an important neuromodulatory or neurotransmitter role as that of GABA. To determine the intrinsic neurotransmitter production, primary histotypic olfactory bulb cultures were prepared from mice at P10. The comparative analysis of in vitro neurotransmitter contents with those in in situ adult animal showed higher levels of endogenously produced glutamate, glycine and GABA in the olfactory bulb than the extrinsic ones coming from olfactory nerve axons and higher olfactory brain centers. On the other hand, most of aspartate and taurine neurotransmitters apparently come from extrinsically located neurons.

Intradermal implants of histotypic adrenal gland rotary cultures.

The implantation of histotypic adrenal gland cultures is described in the present study. The cultures were prepared from mice at birth and were rotary incubated for 10 days. When the cells reached phenotypic maturation, they were implanted in the dermal bed of the auricular pavilion of young adult mice. This location was ideal for implantation because transillumination enabled daily inspection of the progress of implant survival. Twenty days after implantation, the implants and associated tissues were removed to study the degree of maturation and the viability of the implants. Some cultures showed a moderate percentage of steroidal cells, while others demonstrated a high predominance of the chromaffin cells. All the implanted cultures successfully survived a postoperative period of 20 days. Both adrenergic and noradrenergic cells reached their maximum grade of cytological differentiation and neither inflammatory reactions nor adverse immunological effects were observed. On the contrary, the implants were profusely vascularized by the host tissue, particularly in those implants with a higher content of chromaffin cells.