Experience-dependent development of dendritic arbors in mouse visual cortex

Despite the importance of dendritic arbors for proper neuronal function, our knowledge of how sensory experience influences these structures during postnatal cortical development is incomplete. We present a large-scale dataset of 849 three-dimensional reconstructions of pyramidal neuron basal arbors collected across early postnatal development in the mouse visual cortex. We found that the basal arbor underwent a 45% increase in total length between postnatal day 7 (P7) and P30. Surprisingly, comparisons of dark-reared and typically-reared mice revealed that only 15% of arbor length could be attributed to visual experience. Furthermore, we characterized the role of the activity-regulated small GTPase Rem2, showing that Rem2 is an experience-dependent negative regulator of dendritic segment number during the visual critical period. These data establish a detailed, quantitative analysis of the basal arbor that has high utility for understanding circuit development and providing a framework for computationalists wishing to generate anatomically accurate neuronal models.

Notes on the ultrastructure of the setae on the fourth antennulary segment of the Balanus amphitrite cyprid (Crustacea: Cirripedia: Thoracica)

This study presents electron microscopy (SEM, TEM) observations on the putative settlement receptors of the fourth antennulary segments. The TEM data from all nine setae are from the outer dendritic segment. Eight of them have morphological characteristics, indicating bimodal sensory properties while one seta (sE) is presumed to be a unimodal mechanoreceptor. We suggest that setae A and B are stimulated by the water flow, seta D is olfactory, seta E detects the topography of the substratum by touch, and the subterminal setae are touch chemoreceptors. No function is suggested for seta C.

Muscarinic Control of Dendritic Excitability and Ca2+Signaling in CA1 Pyramidal Neurons in Rat Hippocampal Slice

The cholinergic system is critically involved in synaptic models of learning and memory by enhancing dendritic [Ca2+]i signals. Diffuse cholinergic innervation suggests subcellular modulation of membrane currents and Ca2+ signals. Here we use ion-selective microelectrodes to study spread of carbachol (CCh) after focal application into brain slice and subcellular muscarinic modulation of synaptic responses in CA1 pyramidal neurons. Proximal application of CCh rapidly blocked the somatic slow afterhyperpolarization (sAHP) following repetitive stimulation. In contrast, the time course of potentiation of the slow tetanic depolarization (STD) during synaptic input was slower and followed the time course of spread of CCh to the dendritic tree. With distal application, augmentation of the somatic STD and of dendritic Ca2+ responses followed spread of CCh to the entire apical dendritic tree, whereas the sAHP was blocked only after spread of CCh to the proximal dendritic segment. In dendritic recordings, CCh blocked a small sAHP, augmented the STD, and rather reduced dendritic action potentials. Augmentation of dendritic Ca2+ signals was highly correlated to augmentation of the STD. The NMDA receptor antagonist dl-2-amino-5-phosphonovaleric acid (APV) blocked ∼55% of the STD in control and during CCh application. In conclusion, muscarinic suppression of the proximal sAHP can augment firing and thereby Ca2+ responses. Dendritic augmentation of the STD by blockade of the sAHP and direct enhancement of N-methyl-d-aspartate (NMDA) receptor–mediated currents potentiates Ca2+ signals even when firing is not affected due to suprathreshold input. In this way, subcellular muscarinic modulation may contribute to parallel information processing and storage by dendritic synapses of CA1 pyramidal neurons.

Fine structure of sensilla on the ovipositor of the tephritid fly Urophora affinis

There are four types of sensilla on the ovipositor blade of Urophora affinis Frauenfeld, one more than was observed on three other species of fruit flies studied by other authors. Three of the types, uniporous gustatory pegs, campaniform organs, and tactile short hairs are common to the four species and generally are in similar positions on the blade. The fourth, uniporous gustatory plates, were noted in U. affinis only. The chemosensilla are innervated by three chemosensory dendrites that terminate below the pore and a mechanosensory dendrite with a tubular body that is attached to a basal cuticular apodeme of the covering cuticle. The dendritic tubular bodies of the campaniform organs and tactile hairs terminate parallel to the surface in a right-angular bend, where they are attached to basal apodemes of the covering cuticle. The chemosensilla and tactile hairs have individual outer and inner sheath cells, but the campaniform organs have individual inner sheath cells only. The part of the ciliary dendritic segment that is encased by the dendritic sheath passes through an epidermal cell, often with several sensilla sharing the same epidermal cell in place of an outer sheath cell. The role of these sensilla during oviposition is discussed.