ABSTRACT
Neural circuit function is shaped both by the cell types that comprise the circuit and the connections between those cell types 1 . Neural cell types have previously been defined by morphology 2, 3 , electrophysiology 4, 5 , transcriptomic expression 6-8 , connectivity 9-13 , or even a combination of such modalities 14-16 . More recently, the Patch-seq technique has enabled the characterization of morphology (M), electrophysiology (E), and transcriptomic (T) properties from individual cells 17-20 . Using this technique, these properties were integrated to define 28, inhibitory multimodal, MET-types in mouse primary visual cortex 21 . It is unknown how these MET-types connect within the broader cortical circuitry however. Here we show that we can predict the MET-type identity of inhibitory cells within a large-scale electron microscopy (EM) dataset and these MET-types have distinct ultrastructural features and synapse connectivity patterns. We found that EM Martinotti cells, a well defined morphological cell type 22, 23 known to be Somatostatin positive (Sst+) 24, 25 , were successfully predicted to belong to Sst+ MET-types. Each identified MET-type had distinct axon myelination patterns and synapsed onto specific excitatory targets. Our results demonstrate that morphological features can be used to link cell type identities across imaging modalities, which enables further comparison of connectivity in relation to transcriptomic or electrophysiological properties. Furthermore, our results show that MET-types have distinct connectivity patterns, supporting the use of MET-types and connectivity to meaningfully define cell types.
ABSTRACT
This study was designed to determine whether respiratory stimuli can influence the mammalian circadian timing system. Three-hour pulses of hypoxia (inspired O(2) concentration = 8%) or hypercapnia (inspired CO(2) concentration = 11%) were presented for 7 days at mid-subjective day (circadian time 6-9) under constant darkness. Hypoxic and hypercapnic pulses caused cumulative phase delays of 46. 4 +/- 6.9 and 25.9 +/- 12.3 min, respectively. Distance run per day was significantly reduced on hypoxic and hypercapnic pulse days, compared with nonpulsed days. Phase shifts were correlated with the reduction in daily running activity (multiple r(2) = 0.521, P = 0.036), metabolic depression (multiple r(2) = 0.772, P < 0.001), and reduction in body temperature (multiple r(2) = 0.539, P = 0.027), but not lung ventilation (multiple r(2) = 0.306, P = 0.414) during pulses. We conclude that hypoxia and hypercapnia can influence the phase and quantity of activity in free-running hamsters.
Subject(s)
Circadian Rhythm , Hypercapnia/physiopathology , Hypoxia/physiopathology , Animals , Body Temperature , Cricetinae , Mesocricetus , Motor ActivityABSTRACT
Mechanisms underlying the circadian rhythm in lung ventilation were investigated. Ten healthy male subjects were studied for 36 h using a constant routine protocol to minimize potentially confounding variables. Laboratory light, humidity, and temperature remained constant, subjects did not sleep, and their meals and activities were held to a strict schedule. Respiratory chemoreflex responses were measured every 3 h using an iso-oxic rebreathing technique incorporating prior hyperventilation. Subjects exhibited circadian rhythms in oral temperature and respiratory chemoreflex responses, but not in metabolic rate. Basal ventilation [i.e., at subthreshold end-tidal carbon dioxide partial pressure (PET(CO(2)))] did not vary with time of day, but the ventilatory response to suprathreshold PET(CO(2)) exhibited a rhythm amplitude of approximately 25%, mediated mainly by circadian variations in the CO(2) threshold for tidal volume. We conclude that the circadian rhythm in lung ventilation is not a simple consequence of circadian variations in arousal state and metabolic rate. By raising the chemoreflex threshold, the circadian timing system may increase the propensity for respiratory instability at night.
