Grace Hagiwara

Melanopsin as a sleep modulator: circadian gating of the direct effects of light on sleep and altered sleep homeostasis in Opn4(-/-) mice.

Analyses in mice deficient for the blue-light-sensitive photopigment melanopsin show that direct effects of light on behavior and EEG depend on the time of day. The data further suggest an unexpected role for melanopsin in sleep homeostasis.

Mechanosensory integration in the crayfish abdominal nervous system: Structural and physiological differences between interneurons with single and multiple spike initiating sites

SummaryCobalt backfills were used to demonstrate a population of approximately 50 paired interneurons in the 6th abdominal ganglion of the crayfish,Procambarusclarkii. Intracellular recordings from somata were used to study the response properties of individual interneurons, which were subsequently injected with Lucifer yellow. This report deals with 22 identified mechanosensory interneurons, which were each studied 2 to 20 times. (The total number of cells studied was 177). All but two of the interneurons could be assigned to one of two homogeneous classes, based on their receptive field sizes and four other consistent features: amplitude of soma spikes, duration of afterdischarge, presence of postsynaptic inhibition, and structure of the neuropilar processes. Unisegmental interneurons (Type I) (n=9) had excitatory receptive fields restricted to one segment, small soma spikes, little afterdischarge, and received extensive postsynaptic inhibition from contralateral and occasionally anterior sensory fields. All of these interneurons had a large diameter neuropilar segment (integrating segment) that was separated from the main axon by a constricted region. Multisegmental interneurons (Type II) (n=11) had excitatory receptive fields of at least six hemisegments (one half of the abdomen), large (sometimes overshooting) soma spikes, prolonged afterdischarge, and little evidence of postsynaptic inhibition. These interneurons lacked any expanded region of the dendritic tree that could be called an integrating segment. Anomalous interneurons (n=2) had multisegmental receptive fields, but in all other respects they resembled unisegmental interneurons, although their soma spikes were somewhat larger in amplitude.We hypothesize that the fundamental difference between the two main kinds of interneurons is that Type II interneurons have multiple spike initiating sites distributed throughout their dendritic trees, with any site being capable of initiating a spike that propagates to the main axon, while Type I interneurons have a single spike initiating site. The properties of anomalous interneurons are consistent with them having a single spike initiating site in each of several ganglia.

Local interneurons in the terminal abdominal ganglion of the crayfish

Summary1.On the basis of comparisons between total cell counts and cell counts of cobalt backfills of all roots and connectives leaving the ganglion, we estimate that 38–50% of the approximately 650 neurons in the last abdominal ganglion of the crayfish are local interneurons.2.The soma size distributions for all of the neurons and for projecting neurons were compared. The comparison indicates that most local neurons are small. All neurons larger than 40 μm (n = 121) have axons that leave the ganglion, while 77 % of neurons smaller than 21 μm (n = 140) are local interneurons (Figs. 1,2).3.We have recorded and filled with Lucifer yellow 63 local interneurons from which 15 unambiguously different types could be recognized. Five criteria were used in our initial classification. In addition to structure, we noted if each local interneuron was spiking or nonspiking, and, in our most complete experiments, if it was capable of affecting motor activity or projecting interneuron activity when depolarized. We also tried to determine its optimal sensory modality and receptive field.4.Of the 15 interneuron types we encountered, 5 types (represented by 11 fills) were unilateral, nonspiking, premotor interneurons in the uropod motor circuits (Figs. 3–6).5.Two types of local premotor interneurons were bilateral and spiking. One excited exopodite motor neurons on one side only. Our evidence suggests that the cells had a nonspiking input region on one side and a spiking output region on the other (Figs. 7–9).6.Six other types of interneuron were encountered for which we have no evidence of motor effects. All of these neurons had bilateral but asymmetric processes, and were spiking on the putative output side. Some of these neurons appear to be part of sensory processing circuits on the basis of clear modality, distinct receptive field, and short-latency response to sensory input (Figs. 10–12).7.Two nonspiking, bilateral interneurons were found (Fig. 13). These cells had very large processes which permitted them to be penetrated repeatedly and studied in detail. Although nonspiking, these neurons had separate input and output sides. They are involved in lateral inhibition within the sensory circuits (Reichert et al., submitted).8.Our results indicate considerable heterogeneity in the properties and functions of local interneurons. Three basic modes of operation were found: (i) five types of interneurons functioned without spikes and may have diffuse input and output; (ii) eight types of bilateral interneurons had properties suggestive of nonspiking input and spiking output sides; and (iii) two bilateral neurons were nonspiking but had distinct input and output sides.

Crayfish escape behavior: Neurobehavioral analysis of phasic extension reveals dual systems for motor control

Summary1.Electromyograms (EMGs) from phasic abdominal muscles of unrestrained and variously restrained crayfish were used to study the involvement of sensory information in phasic abdominal extension during escape behavior.2.Lateral giant neuron impulses (escape commands), elicited either with natural stimuli or via direct shocks, caused a flexion which was followed at short and near-constant latency by extension (Figs. 1 and 2).3.Extension produced as above was termed ‘postgiant’ extension and had the following properties: it was labile (Figs. 3 and 4), it was eliminated when flexion was prevented, and it was reduced or eliminated if flexion was hampered (Fig. 5 and Table 1).4.The above observations, which suggest sensory involvement in post-giant extension, are complemented by the observation that phasic extensor activity could be evoked without prior flexion by rapid water displacements over the abdomen or by taps to the abdomen (Fig. 7).5.In addition to post-giant extension the extensors were active during many kinds of non-giant tailflips. During swimming, non-giant extensionpreceded flexion at short and constant latency (Fig. 9) and persisted after flexor root section (Fig. 10) or during restraint. Non-giant extension was not labile (Fig. 11), and it depended on the integrity of the rostral nervous system.6.Animals frequently initiate escape with a giantmediated tailflip followed by non-giant swimming. When this occurred our most common observation was consistent with the interpretation that both postgiant and non-giant extension occurred between the first two flexions (Figs. 13 and 14).7.We interpret our results to mean that extension occurs as a chained reflex following giant-mediated flexion, with subsequent control of the extensors passing to a central pattern generator.

Hyposecretion of |[beta]|-Adrenergically Induced Sweating in Cystic Fibrosis Heterozygotes

ABSTRACT.: In order to determine if expression of the eystic fibrosis gene can be detected in heterozygotes, we determined sweat responses induced by local stimulation with cholinergic and β-adrenergic agents for 20 heterozygotes, 19 age- and sex-matched controls, and five subjects with cystic fibrosis. Active sweat glands were counted and sweat droplets were collected in constant bore capillaries and measured optically. Kach subject was tested two to six times. The central finding was that the sweat response of carriers was significantly lower than controls to β-adrenergic stimulation (P= 0.0013, two-tailed r test; P < 0.02, Mann-Whitney U). while cystic fibrosis homozygotes did not sweat at all. In contrast, the cholinergic sweat responses did not differ between carriers and controls. For both groups the correlation between cholinergic and (1- adrenergic sweating was positive, but a linear regression of β-adrenergic sweat responses as a function of cholinergic sweat responses yielded slopes that were significantly different for the two groups. The ratio of β-adrenergic to cholinergic sweating was plotted for each subject; the mean ratio of the carriers was approximately half of the mean for the controls (P = 0.0002 using r test or P<0.002 using the Mann-Whitney U). Our results confirm previous studies and provide new evidence that carriers have, on average, a β-adrenergically stimulated secretory response that is significantly reduced relative to the control response.

Patch-clamp study of cultured human sweat duct cells: amiloride-blockable Na+ channel

The reabsorptive duct of the eccrine sweat gland has a large transepithelial conductance consisting mainly of a high conductance to Cl− and a smaller, amiloride-blockable Na+ conductance (Bijman and Frömter 1986; Quinton 1985). Cells have been cultured from sweat ducts and their properties previously studied in Ussing chambers (Pedersen 1988) and with microelectrodes (Jones et al. 1988). We have now studied the ion channels present in excised, inside-out patches of human cultured sweat duct cells, and find a marked predominance of linear, 16 pS, amiloride-blockable, low selectivity, Na+ channels. Such channels were seen in 54/92 (59%) of the patches, with up to 7 channels recorded in a single patch.Other channel types were seen at much lower densities. The prevalence of an amiloride-blockable Na+ channel in cultured duct cells clearly distinguishes these cells from cultured sweat gland secretory cells, which lack such a channel.

Glycogen content in the cerebral cortex increases with sleep loss in C57BL/6J mice.

We hypothesized that a function of sleep is to replenish brain glycogen stores that become depleted while awake. We have previously tested this hypothesis in three inbred strains of mice by measuring brain glycogen after a 6h sleep deprivation (SD). Unexpectedly, glycogen content in the cerebral cortex did not decrease with SD in two of the strains and was even found to increase in mice of the C57BL/6J (B6) strain. Manipulations that initially induce glycogenolysis can also induce subsequent glycogen synthesis thereby elevating glycogen content beyond baseline. It is thus possible that in B6 mice, cortical glycogen content decreased early during SD and became elevated later in SD. In the present study, we therefore measured changes in brain glycogen over the course of a 6 h SD and during recovery sleep in B6 mice. We found no evidence of a decrease at any time during the SD, instead, cortical glycogen content monotonically increased with time-spent-awake and, when sleep was allowed, started to revert to control levels. Such a time-course is opposite to the one predicted by our initial hypothesis. These results demonstrate that glycogen synthesis can be achieved during prolonged wakefulness to the extent that it outweighs glycogenolysis. Maintaining this energy store seems thus not to be functionally related to sleep in this strain.

Cystic fibrosis, the CFTR, and rectifying Cl- channels.

The human genetic disease cystic fibrosis is caused by a single defective gene on chromosome 7 that codes for a 1480 amino acid protein called the cystic fibrosis transmembrane conductance regulator (CFTR). The defect causes a profound reduction of Cl- permeability in several tissues, which in turn impairs salt absorption and fluid secretion. A 25-80 pS, rectifying Cl- channel has been targeted as the exclusive or primary channel affected in CF. However, we have found no evidence for significant activation or spontaneous activity of this channel in cell-attached patches of normal lymphoblasts or dog tracheal cells. However, in dog tracheal cells, we find lower conductance, linear Cl- channels that are spontaneously active in unstimulated cells and may show increased activity in stimulated cells. Attempts to correlate the expression of mRNA for the CFTR protein in various types of cells with the presence of the rectifying Cl- channel show a lack of correlation: i.e., depolarization-activated rectifying Cl- channesl have been found in excised, inside-out patches from all cell types that we have examined to date, but the CFTR mRNA has so far only been detected in a subset of epithelial cells.