RESUMEN
This study examined experience effects upon the formation of multiple synaptic contacts among individual dendritic and axonal elements. Axonal boutons and dendritic spines forming contacts with more than one process were assessed within layer IV of the visual cortex in adult rats following 60 days of housing in standard laboratory cages (IC) or in complex environments (EC). Multiple synaptic boutons (MSBs) that formed synaptic contacts with both a dendritic spine and a dendritic shaft were found to be markedly increased in number per neuron in EC rats in comparison to those in IC rats. In contrast, single-synaptic contacts were not increased, indicating that the formation of new single-synaptic boutons is, at most, merely sufficient to replace boutons that may have been recruited into the population of MSBs. This apparent tendency to reutilize presynaptic processes may indicate a constraint upon the formation of neural circuitry and a fundamental form of plastic synaptic change.
Asunto(s)
Sinapsis/fisiología , Corteza Visual/fisiología , Animales , Vivienda para Animales , Masculino , Microscopía Electrónica , Ratas , Sinapsis/ultraestructura , Corteza Visual/ultraestructuraRESUMEN
The stomatogastric ganglion (STG) of the crab, Cancer borealis, contains the neural networks responsible for rhythmic pattern generation of the foregut. Neuron counts indicate that the STG of C. borealis has 25-26 neurons, 4-5 fewer than that found in lobsters. We describe the ultrastructural features of the ganglion by focusing on those that may be involved in storage, release, or range of action of peptide modulators, including a lacunar system and multiple types of intercellular junctions. In the neuropil, we identify five synaptic profile classes that contain the invertebrate presynaptic apparatus (dense bars, small clear vesicles), two of which also contain dense core (modulator-containing) vesicles. These latter two are comprised of multiple immunocytochemical classes that are not easily distinguished by structural criteria. In addition, we find neurohemal-like profiles that contain primarily dense core vesicles. Our finding that multiple profile types in the STG possess modulator-containing vesicles coincides with immunocytochemical results better than do previous ultrastructural studies that report only one such profile type. We show that a single modulatory input, stomatogastric nerve axon 1, makes only classical synapses and not neurohemal-like profiles, although some modulators are found in both these profile types. These data provide the groundwork for understanding the architecture of modulatory input-target interactions and suggest ways that the specificity of modulatory effects within a complex neuropil may be attained.
Asunto(s)
Braquiuros/fisiología , Ganglios de Invertebrados/ultraestructura , Neuronas/ultraestructura , Animales , Axones/fisiología , Axones/ultraestructura , Recuento de Células , Espacio Extracelular/metabolismo , Ganglios de Invertebrados/citología , Uniones Comunicantes/fisiología , Uniones Comunicantes/ultraestructura , Taninos Hidrolizables , Inmunohistoquímica , Lantano/metabolismo , Masculino , Microscopía Electrónica , Neuroglía/ultraestructura , Neuronas/fisiología , Oligopéptidos/metabolismo , Adhesión en Plástico , Sinapsis/fisiología , Sinapsis/ultraestructura , Ácido gamma-Aminobutírico/metabolismoRESUMEN
Small invertebrate nervous systems allow one to ask a series of questions concerning the functional roles of cotransmitters. This review outlines some of the implications of cotransmission for target selectivity in complex neuropils. We suggest the possibility that a unique constellation of cotransmitters in individual identified modulatory neurons allows a specificity of action even when peptides may act over an extended distance, and when individual modulatory substances may be released from several modulatory neurons.
Asunto(s)
Invertebrados/fisiología , Fenómenos Fisiológicos del Sistema Nervioso , Transmisión Sináptica/fisiología , Animales , Neurotransmisores/fisiología , Distribución TisularRESUMEN
To assess the capacity for experience to induce rapid alterations in the dendritic fields of cortical neurons, male Long-Evans hooded rats aged 30-31 days were housed in either a complex environment (EC) or an individual cage (IC) for 4 days. The basilar dendrites of layer III pyramidal cells in area 17 of visual cortex were measured in Golgi-stained sections. EC rats exhibited significant increases in total dendritic length and total number of branches. This finding demonstrates that the structural modifications previously reported after 30 days in the complex environment are well underway after only 4 days.