The Limited Utility of Multiunit Data in Differentiating Neuronal Population Activity

To date, single neuron recordings remain the gold standard for monitoring the activity of neuronal populations. Since obtaining single neuron recordings is not always possible, high frequency or ‘multiunit activity’ (MUA) is often used as a surrogate. Although MUA recordings allow one to monitor the activity of a large number of neurons, they do not allow identification of specific neuronal subtypes, the knowledge of which is often critical for understanding electrophysiological processes. Here, we explored whether prior knowledge of the single unit waveform of specific neuron types is sufficient to permit the use of MUA to monitor and distinguish differential activity of individual neuron types. We used an experimental and modeling approach to determine if components of the MUA can monitor medium spiny neurons (MSNs) and fast-spiking interneurons (FSIs) in the mouse dorsal striatum. We demonstrate that when well-isolated spikes are recorded, the MUA at frequencies greater than 100Hz is correlated with single unit spiking, highly dependent on the waveform of each neuron type, and accurately reflects the timing and spectral signature of each neuron. However, in the absence of well-isolated spikes (the norm in most MUA recordings), the MUA did not typically contain sufficient information to permit accurate prediction of the respective population activity of MSNs and FSIs. Thus, even under ideal conditions for the MUA to reliably predict the moment-to-moment activity of specific local neuronal ensembles, knowledge of the spike waveform of the underlying neuronal populations is necessary, but not sufficient.     

Basic proline-rich proteins from human parotid saliva: complete covalent structures of proteins IB-1 and IB-6

The complete amino acid sequences of two basic proline-rich proteins, IB-1 and IB-6, from human parotid saliva have been determined. Fragments for sequence analysis were obtained by enzymatic digestions. The proteins have molecular weights of 9571 (IB-1) and 11,530 (IB-6) and contain 34 and 39 mol % proline, respectively. IB-1 and IB-6 contain an identical sequence of 54 residues except for an alanine in position 52 of IB-6, where IB-1 has proline. An unusually high number of repeated sequences occurs in both molecules. IB-1 has a blocked amino-terminal residue, pyroglutamic acid, and also contains one phosphoserine residue in position 8. The relationship of these proteins to the basic proline-rich protein IB-9 [Kauffman, D., Wong, R., Bennick, A., & Keller, P. (1982) Biochemistry 21, 6558-6562] and to other salivary proline-rich proteins is discussed.     

Hemorrhagic Shock—Influence of Hyperbaric Oxygen on Metabolic Parameters

Oxygen therapy at atmospheric and increased pressure was used in the treatment of experimental hemorrhagic shock. Arterial gases, pH, lactate and pyruvate were determined and compared. Survival was carefully followed and complete pathological evaluation was carried out. The results showed no difference between control animals and those in the hyperbaric oxygen therapy group. It was concluded that hyperbaric oxygen therapy post facto did not influence the metabolic or survival data in this experiment.