Tissue polypeptide antigen (TPA) is related to the non-epidermal keratins 8, 18 and 19 typical of simple and non-squamous epithelia: re-evaluation of a human tumor marker

Because of the broad clinical interest which tissue polypeptide antigen (TPA) has attracted as a tumor marker, human cell lines and human tissues have been analyzed for TPA expression using immunofluorescence microscopy. Epithelial cell lines including HeLa, MCF-7, and A-431 are recognized by TPA antibodies whereas human lines of non-epithelial origin are not. The positive staining patterns coincide with keratin-type intermediate filaments of the cytoskeleton. On tissue sections a subset of epithelial cells including uterine epithelium, bile duct cells in liver and tumor cells in breast carcinoma are strongly positive; cells of the squamous epithelia of skin and tongue as well as cells of non-epithelial origin are negative. In immunoblots of human epidermis, human tongue mucosa, human hair follicles, Detroit 562 cells, HeLa cells, MCF-7 and RT-4 cells, only keratins 8, 18 and 19 show TPA antigenicity. Conversely a TPA preparation is recognized by various antibodies known to react with keratins, including alpha-IFA, KG 8.13.2 and two antibodies which recognize keratins 18 (CK2) and 19, respectively. Our results thus relate TPA to human keratins 8, 18 and 19 which are known cytoskeletal components in both normal and malignant epithelial cells of simple and non-squamous origin. We speculate that the elevated levels of circulating TPA antigenicity present in the sera of patients with carcinoma, which are often used to monitor tumor progression, correspond to soluble proteolytic fragments originating from this particular keratin subgroup.

Interaction of fluorescently-labeled contractile proteins with the cytoskeleton in cell models

To determine if a living cell is necessary for the incorporation of actin, alpha-actinin, and tropomyosin into the cytoskeleton, we have exposed cell models to fluorescently labeled contractile proteins. In this in vitro system, lissamine rhodamine-labeled actin bound to attachment plaques, ruffles, cleavage furrows and stress fibers, and the binding could not be blocked by prior exposure to unlabeled actin. Fluorescently labeled alpha-actinin also bound to ruffles, attachment plaques, cleavage furrows, and stress fibers. The periodicity of fluorescent alpha-actinin along stress fibers was wider in gerbil fibroma cells than it was in PtK2 cells. The fluorescent alpha-actinin binding in cell models could not be blocked by the prior addition of unlabeled alpha-actinin suggesting that alpha-actinin was binding to itself. While there was only slight binding of fluorescent tropomyosin to the cytoskeleton of interphase cells, there was stronger binding in furrow regions of models of dividing cells. The binding of fluorescently labeled tropomyosin could be blocked by prior exposure of the cell models to unlabeled tropomyosin. If unlabeled actin was permitted to polymerize in the stress fibers in cell models, fluorescently labeled tropomyosin stained the fibers. In contrast to the labeled contractile proteins, fluorescently labeled ovalbumin and BSA did not stain any elements of the cytoskeleton. Our results are discussed in terms of the structure and assembly of stress fibers and cleavage furrows.

Detection of various forms of brain myelin basic protein in vertebrates by electroimmunoblotting

An electroimmunoblot technique was used to detect various forms of myelin basic protein (MBP) in brain homogenates of 14 vertebrate species. Three antibodies were used to probe the immunoblots: a monoclonal anti-human MPB reacting with an antigenic determinant located at amino acid residues 131 to 136; a polyclonal anti-human MBP and a polyclonal anti-chicken MBP. Because no processing of the tissue is required prior to electrophoresis, in vitro artifacts are minimized. The 18.5 K form of MBP was present in all species except the shark. A 21.5 K MBP was observed in ovine, bovine, pig, rabbit, mouse, rat, monkey, but not in human, guinea pig, shark, toad and marsupial brains. A variant with a molecular weight between 17 K and 18 K was found in mouse, rat, bovine, human, monkey, pig, and chicken brains, and was the sole component in the shark brain. Marsupial brains had five or six forms of MBP between 14.5 K and 18.5 K.

Changes in the thermal characteristics of hypothalamic neurons during sleep and wakefulness

The characteristics of the mammalian thermoregulatory system are dependent upon arousal state. During NREM sleep thermoregulatory mechanisms are intact but body temperature is regulated at a lower level than during wakefulness. In REM sleep thermoregulatory effector mechanisms are inhibited and thermal homeostasis is severely disrupted. Thermosensitivity of neurons in the preoptic/anterior hypothalamus (POAH) was determined for behaving kangaroo rats (Dipodomys deserti) during electrophysiologically defined wakefulness, NREM sleep and REM sleep to elucidate possible neural mechanisms for previous findings of state-dependent changes in thermoregulation. Thirty cells were tested during at least two arousal states. During wakefulness, 70% of the recorded cells were sensitive to changes in local temperature, with the number of warm-sensitive (W) cells outnumbering cold-sensitive (C) cells by 1.6:1. In NREM sleep, 43% of the cells were thermally sensitive, with the ratio of W:C remaining the same as in wakefulness. In REM sleep only two cells were thermosensitive (both W). The decrease in neuronal thermosensitivity of POAH cells during REM sleep parallels findings of inhibition of thermoregulatory effector responses during REM, although further work is necessary to determine the source and nature of the inhibition.

Distribution of DNA insertion element IS5 in natural isolates of Escherichia coli

DNA from Escherichia coli strains in a reference collection of 72 recent natural isolates (ECOR strains) and 25 natural isolates from the "pre-antibiotic" period 1930-1940 (Murray strains) were studied to determine the genomic abundance of insertion element IS5 and the size of genomic restriction fragments carrying sequences homologous to IS5. Among the ECOR strains, nearly two-thirds lack DNA sequences that hybridize with IS5, and one-half of the remainder have only one copy. Among strains in which IS5 is present, extensive variation in the size of IS5-bearing restriction fragments occurs, in many cases allowing distinction among strains that are judged to be nearly identical in genotype because of the identical electrophoretic mobility of the enzyme coded by each of 11 chromosomal loci. Among the Murray strains in which IS5 is present, the average number of elements per strain is larger, but not markedly so, than among recent isolates. Comparison between duplicate strains in the Murray collection suggests that the rate of accumulation of IS5 elements in prolonged storage in stab tubes corresponds to an apparent probability of transposition of approximately 0.008 +/- 0.002 per IS5 element per year. Because of the extensive genetic variation among strains, insertion elements such as IS5 would seem to be convenient genetic markers with which to detect recent common ancestry among strains.

Phosphoproteins are components of mitotic microtubule organizing centers

Protein phosphorylation has been suggested as an important control mechanism for the events leading toward the initiation and completion of mitosis. Using a monoclonal antibody recognizing a class of phosphoproteins abundant in mitotic cells, we demonstrated the localization of a subset of these phosphoproteins to several discrete mitotic structures. Patchy immunofluorescence was present in the interphase nuclei, but a significant increase in nuclear immunofluorescence was apparent at prophase. Subsequent mitotic stages demonstrated that immunoreactive material was particularly apparent at microtubule organizing centers, namely, centrosomes, kinetochores, and midbodies. Intense centrosomal localization occurred at the prophase-prometaphase transition and persisted until the reformation of the nuclear membrane in early G1. The cytoplasm of mitotic cells also contained immunoreactive material in sharp contrast to interphase cells that exhibited no cytoplasmic fluorescent staining. Much of the diffuse immunofluorescent cytoplasmic material was removed by a brief lysis of the cells with 0.15% Triton X-100 prior to fixation. The localization of the remaining immunoreactive material after detergent lysis to mitotic microtubule organizing centers suggests that they contain phosphoprotein structural components important, perhaps, in the mitotic phase-interphase transition.

Osmium ferricyanide fixation improves microfilament preservation and membrane visualization in a variety of animal cell types

Using a fixation formula which includes adding potassium ferricyanide (K3Fe(CN)6) to the osmium step and an en bloc aqueous uranyl acetate step before dehydration we have looked at cells from mammals, birds, amphibia, algae, and higher plants and we have collaborated in fixing cells of teleost fish. In every cell type except the algae and higher plants the final EM image was improved by the OsFeCN-uranium method. The most common improvement was an increase in the membrane contrast but more significantly, some cells show improved preservation of microfilaments. We conclude that the OsFeCN adds contrast to all classes of membrane and does not destroy microfilaments to the extent that osmium alone does. Adding uranyl acetate to the cells may protect delicate filamentous structures from collapse during dehydration and embedding. We have preliminary evidence in PtK1 cells that addition of tannic acid after OsFeCN may function in a similar manner. This method is recommended for any animal cell type where improved visualization of membranes and filaments is required.

Neural responses elicited by stimuli associated with masking of low-frequency, monaural tonal signals by noise

The responses of low-frequency, primary-like neurons of the ventral cochlear nucleus were measured as a function of signal-to-noise ratio for gated tonal signals and noise maskers that were varied in bandwidth and duration. For a given signal-to-noise ratio, each of the maskers is known to produce the same amount of masking in psychophysical experiments. The neural discharge rates measured in the present experiment were different, however, for each of the maskers for each signal-to-noise ratio. In contrast, all three maskers produced the same orderly relationship between signal-to-noise ratio and the degree of neural synchrony to the signals. It is concluded that information concerning the presence and relative strength of a low-frequency tonal signal in a background of masking noise is carried by the nervous system as the degree to which responses are synchronized to the phase of the signal.

Laser-induced multiphoton processes in living cells

It is shown that specific light-induced subcellular alterations, usually referred to as phase "paling," result from multiphoton absorption processes. For green light (532 nm), four photons are required to induce paling in chromosomes and nucleoli; a two-photon process is observed for UV light (266 nm).

A rat monoclonal antibody reacting specifically with the tyrosylated form of alpha-tubulin. II. Effects on cell movement, organization of microtubules, and intermediate filaments, and arrangement of Golgi elements

A rat monoclonal antibody against yeast alpha-tubulin (clone YL 1/2; Kilmartin, J. V., B. Wright, and C. Milstein, 1982, J. Cell Biol., 93:576-582) that reacts specifically with the tyrosylated form of alpha-tubulin and readily binds to tubulin in microtubules when injected into cultured cells (see Wehland, J., M. C. Willingham, and I. V. Sandoval, 1983, J. Cell Biol., 97:1467-1475) was used to study microtubule organization and function in living cells. Depending on the concentration of YL 1/2 that was injected the following striking effects were observed: (a) When injected at a low concentration (2 mg IgG/ml in the injection solution), where microtubules were decorated without changing their distribution, intracellular movement of cell organelles (saltatory movement) and cell translocation were not affected. Intermediate concentrations (6 mg IgG/ml) that induced bundling but no perinuclear aggregation of microtubules abolished saltatory movement and cell translocation, and high concentrations (greater than 12 mg IgG/ml) that induced perinuclear aggregation of microtubules showed the same effect. (b) YL 1/2, when injected at intermediate and high concentrations, arrested cells in mitosis. Such cells showed no normal spindle structures. (c) Injection of an intermediate concentration of YL 1/2 that stopped saltatory movement caused little or no aggregation of intermediate filaments and no dispersion of the Golgi complex. After injection of high concentrations, resulting in perinuclear aggregation of microtubules, intermediate filaments formed perinuclear bundles and the Golgi complex became dispersed analogous to results obtained after treatment of cells with colcemid. (d) When rhodamine-conjugated YL 1/2 was injected at concentrations that stopped saltatory movement and arrested cells in mitosis, microtubule structures could be visualized and followed for several hours in living cells by video image intensification microscopy. They showed little or no change in distribution and organization during observation, even though these microtubule structures appeared not to be stabilized by injected YL 1/2 since they were readily depolymerized by colcemid or cold treatment and repolymerized upon drug removal or rewarming to 37 degrees C, respectively. These results are discussed in terms of the participation of microtubules in cellular activities such as cell movement and cytoplasmic organization and in terms of the specificity of YL 1/2 for the tyrosylated form of alpha-tubulin.

90Sr and 137Cs in soil and biota of fallout areas in southern Nevada and Utah

Measurements of 90Sr and 137Cs in soil, vegetation and small mammals were made periodically at sites in southern Nevada and Utah that were contaminated by radioactive fallout from nuclear detonations at the Nevada Test Site (NTS) as well as from global sources. Results from a survey in 1980 indicate that both of these fallout-derived radionuclides have remained primarily within the top 5-cm layer of undisturbed soil in these arid land areas. Trace amounts of 90Sr and 137Cs were measured in soil and biota samples. The 90Sr concentrations in jackrabbit and rodent bone samples in 1980 varied within the range of 2-8 pCi/g ash (equivalent to 0.4-1.6 pCi/g wet bone or 5-20 pCi/g Ca). The 137Cs concentrations in muscle-tissue samples were generally less than 1.5 pCi/g ash (less than 0.045 pCi/g wet muscle). Comparisons of data obtained periodically since the early 1950s show that measured concentrations of 90Sr in bone tissues have been highly variable in trace amounts, and that the concentration attenuation appears to be following radioactive decay of this radionuclide.

Enhanced survival and decreased mutation frequency after photoreactivation of UV damage in rat kangaroo cells

The effect of pyrimidine dimers on cytotoxicity, DNA repair and mutagenesis was studied in cells, derived from the rat kangaroo, which possess photoreactivating capabilities. A significant enhancement in colony-forming ability was achieved after UV irradiation in exponentially growing cells if photoreactivating light treatment followed the UV irradiation. If photoreactivation treatment was delayed 24 h after UV irradiation, no significant increase in survival was observed. Assays of pyrimidine dimers, unscheduled DNA synthesis, and survival in contact-inhibited cells all confirmed a minor role of dark excision repair and a major role of photoreactivation. Photoreactivation decreased the frequency of mutations to 6-thioguanine resistance to a greater extent than the alteration seen in survival. Approximately 1.6 times the dose must be given to get equal killing in photoreactivated cells, whereas 4 times the dose must be given to obtain equal mutation frequencies in light-treated cells. This suggests that the removal of dimers is more effective in mutant reduction than enhancement of survival.

Photoelectron microscopy and immunofluorescence microscopy of cytoskeletal elements in the same cells

Pt K2 rat kangaroo epithelial cells and Rat-1 fibroblasts were grown on conductive glass discs, fixed, and permeabilized, and the cytoskeletal elements actin, keratin, and vimentin were visualized by indirect immunofluorescence. After the fluorescence microscopy, the cells were postfixed and dehydrated for photoelectron microscopy. The contrast in these photoelectron micrographs is primarily topographical in origin, and the presence of fluorescent dyes at low density does not contribute significantly to the material contrast. By comparison with fluorescence micrographs obtained on the same individual cells, actin-containing stress fibers, keratin filaments, and vimentin filaments were identified in the photoelectron micrographs. The apparent volume occupied by the cytoskeletal network in the cells as judged from the photoelectron micrographs is much less than it appears to be from the fluorescence micrographs because the higher resolution of photoelectron microscopy shows the fibers closer to their true dimensions. Photoelectron microscopy is a surface technique, and the images highlight the exposed cytoskeletal structures and suppress those extending along the substrate below the nuclei. The results reported here show marked improvement in image quality of photoelectron micrographs and that this technique has the potential of contributing to higher resolution studies of cytoskeletal structures.

Localization of nucleolar phosphoproteins B23 and C23 during mitosis

Nucleolar phosphoproteins B23 and C23 were simultaneously localized in unsynchronized male rat-kangaroo PtK2 cells during mitosis using a mouse monoclonal antibody against protein B23 and a rabbit antibody against protein C23. The distribution of proteins B23 and C23 during mitosis was compared with the distribution of the silver staining protein. During interphase, proteins B23 and C23 were both localized to the nucleolus. As the nucleolus disappeared in prophase, the distribution of protein B23 became nucleoplasmic, whereas most of protein C23 remained associated with the disappearing nucleolus. Throughout metaphase and anaphase protein B23 was found associated with the chromosomes, whereas protein C23 seemed to disappear. When the nucleolus reformed during telophase, protein C23 appeared first in 'prenucleolar bodies' and then in the nucleolus, whereas protein B23 did not appear in the nucleolus until late telophase or early G1 phase. Silver staining during mitosis closely paralleled the distribution of protein C23, supporting previous conclusions that protein C23 is a silver staining nucleolus organizer region (NOR) protein [19, 20].

In vitro cellular effects of hematoporphyrin derivative

Several in vitro cell systems were exposed to hematoporphyrin derivative (HPD): established lines of rat kangaroo epithelial kidney; normal mouse embryonic fibroblasts; and differentiated neonatal rat myocardial cells. The uptake of HPD (25 to 100 micrograms/ml) by individual cells occurred rapidly over a 2-hr period and leveled off by 24 hr. HPD was excreted from cells by 48 hr after exposure. However, a low level of HPD (above background) was maintained in cells for up to 4 days following cessation of exposure. Intracellular binding of HPD was to mitochondria as demonstrated by fluorescence microscopy. HPD was also shown to have a growth-inhibiting effect on rat kangaroo cells without added light. The growth effects on mouse cells were less marked.

Evidence for a relationship between longevity of mammalian species and life spans of normal fibroblasts in vitro and erythrocytes in vivo

The replicative life spans of mammalian fibroblasts in vitro were studied in a number of cell cultures representing eight species. Emphasis was placed on determining the population doubling level at which phase III (a period of decrease in the rate of proliferation) and chromosomal alterations occur. All the cell cultures studied went through a growth crisis, a period of apparent growth cessation lasting for at least 2 weeks. In most cultures, the crisis represented the end of their replicative capacities, but in some cultures cell proliferation was resumed after the crisis. A predominantly diploid chromosome constitution (more than 75%) was demonstrated prior to the growth crisis. In cultures in which cell proliferation was resumed after the crisis, a nondiploid constitution prevailed in all cases except the rat (with 90% or more diploid cells all the time). The growth crisis occurred at population doubling levels that were characteristic for the species and was shown to be related to the species' maximal life span by a strict power law, being proportional to the square root of the maximal life span. Based on data in the literature, the same relationship was also valid for the lifespans of circulating mammalian erythrocytes in vivo. These results may indicate the prevalence of a common functional basis regulating the life span of fibroblasts and erythrocytes and thus operating in replicative as well as postmitotic cells in vitro and in vivo.

Actin rearrangement in living cells revealed by microinjection of a fluorescent phalloidin derivative

A fluorescent derivative of phalloidin with a high affinity for F-actin was microinjected into tissue culture cells and its intracellular reorganization was followed by TV image intensification and video recording. When the F-actin stabilizing drug is used at concentrations, which do not inhibit cellular movement, rearrangement of fluorescently labelled microfilament bundles can be followed directly. We discuss the possibility that active ruffles are governed by structural rules different from those applying to stress fibers and raise the possibility that actin may be released from microfilaments in a form different from G-actin.

Differential staining of actin in metaphase spindles with 7-nitrobenz-2-oxa-1,3-diazole-phallacidin and fluorescent DNase: is actin involved in chromosomal movement?

The distribution and polymerization state of actin in metaphase rat kangaroo cells was studied by fluorescence microscopy. Formaldehyde-fixed, acetone-extracted cells were labeled with either of two types of actin probes. The first, 7-nitrobenz-2-oxa-1,3-diazole-phallacidin, has high affinity for F actin and does not bind monomeric G actin. The second was a conjugate of DNase I labeled with either tetramethylrhodamine or fluorescein. DNase binds with high affinity to G actin and with lesser affinity to F actin. The polymerization state of actin was deduced by comparing the fluorescence distribution of the phallacidin derivative with that of the fluorescent DNase. The results indicate that the pole-to-chromosome region of the metaphase spindle contains G actin but little if any conventional F actin. F actin is found concentrated in a diffuse distribution outside the spindle region in metaphase cells and returns to the interzone area between the chromosomes by early telophase. These results exclude spindle models for chromosomal movement that require more than about five F actin filaments per chromosome, support the hypothesis that F actin is involved in force generation for cell cleavage, and are not inconsistent with the possibility that actin outside the spindle may be involved in chromosomal movement.

Antibodies against merokeratin from sheep wool decorate cytokeratin filaments in non-keratinizing epithelial cells

Merokeratin is an easily soluble proteolytic derivative of mature alpha-keratin. Guinea pig antibodies have been raised to merokeratin prepared from sheep wool. These antibodies decorate in immunofluorescence microscopy arrays of bundles of intermediate sized filaments present in established epithelial cell lines growing in culture. Thus, the highly helical soluble proteolytic fragments of mature alpha-keratin contains antigenic determinants shared by the cytokeratins present in non-epidermal cells, and antibodies to these keratin fragments can be used for the demonstration of at least some cytokeratin-containing structures in other cells and tissues.

Dissolution of cytoplasmic actin bundles and the induction of nuclear actin bundles by dimethyl sulfoxide

Within 30 minutes of exposure to medium containing 10% dimethyl sulfoxide, PtK2 cells begin to round up and lose their cytoplasmic actin bundles. At the same time, bundles of actin filaments appear in the nuclei of the cells. One to 2 hours after the dimethyl sulfoxide is removed from the medium, the cells revert to their flattened shape, losing the nuclear actin bundles and regaining the cytoplasmic bundles.

The 500 Hz frequency-following potential in kangaroo rat: an evaluation with noise masking

This study on kangaroo rat has shown that the volume-conducted 500 Hz FFP can be recorded at stimulus levels which are near behavioral threshold. The response is a complex, double-peaked wave form, indicating that multiple brain stem sources are involved in its generation. The FFP wave form changes in a complex manner with intensity. Recordings of the FFP in the presence of broadband noise demonstrate that the response is neural in origin at suprathreshold stimulus levels. The various configurations of the FFP in the presence of noise, high-pass or broadband, are dependent upon the level of the tone, the level of the noise, and the frequency at which the noise high-pass is set. High-pass masking experiments near threshold levels have demonstrated that the FFP is initiated at a restricted region of the apical cochlea. From all of the results, we conclude that the FFP at moderate and low levels (55--65 dB SPL) is generated primarily by neurons with best frequencies below 1.5--2.0 kHz. The onset component of the FFP is similarly affected by noise, indicating that it too is low frequency in origin.

Laser microirradiation of kinetochores in mitotic PtK2 cells: chromatid separation and micronucleus formation

Irradiation of the kinetochore region of PtK2 chromosomes by laser light of 532 nm was used to study the function of the kinetochore region in chromosome movement and to create an artificial micronuclei in cells. When the sister kinetochores of a chromosome were irradiated at prometaphase, the affected chromosome detached from the spindle and exhibited no further directed movements for the duration of mitosis. The chromatids of the chromosome remained attached to one another until anaphase, at which point they separated. No poleward movement of the chromatids was observed, and at telophase they passively moved to one of the daughter cells and were enclosed in a micronucleus. The daughter cell containing the micronucleus was then isolated by micromanipulation and followed through subsequent mitoses. At the next mitosis, two chromosomes, each with two chromatids, condensed in the micronucleus. These chromosomes did not attach to the spindle and showed chromatid separation, but no poleward movements at anaphase. They were again enclosed in micronuclei at telophase. The third generation mitosis was similar to the second. Occasionally, both the irradiation-produced and naturally occurring micronuclei exhibited no chromosome condensation at mitosis. Feulgen-stained monolayers of PtK2 cells with naturally occurring micronuclei showed that some micronuclei stain positive for DNA and others do not. This finding raises questions about the fate of chromosomes in a micronucleus.

Influence of hypothalamic and ambient temperatures on sleep in kangaroo rats

Unanesthetized, unrestrained kangaroo rats (Dipodomys) were studied to examine the changes in the frequency and duration of sleep states caused by long-term manipulations of hypothalamic temperature (Thy) at a thermoneutral (30 degrees C) and a low (20 degrees C) ambient temperature (Ta). A cold stimulus present in either the hypothalamus or the skin decreased both the total sleep time (TST) and the ratio of paradoxical sleep (PS) to TST. At a low Ta, TST, but not the PS-to-TST ratio, was increased by raising Thy, indicating that a cold peripheral stimulus could differentially inhibit PS. At a thermoneutral Ta, cooling Thy decreased both TST and the PS/TST. Changes in the amount of PS were due largely to changes in the frequency, but not the duration, of individual episodes of PS, suggesting that the transition to PS is partially dependent on the thermoregulatory conditions existing during slow-wave sleep (SWS). These results are consistent with the recent findings that the thermoregulatory system is functional during SWS but is inhibited or inactivated during PS.

Response characteristics of cochlear nucleus neurons to vowel sounds

Most studies in auditory neurophysiology have utilized tonal stimuli to determine the coding properties of neurons in the cochlear nuclei. In this investigation of the kangaroo rat, cochlear nuclei, neuronal responses to vowel sounds, as well as tones, were studied. The vowel sounds, each about 40 msec in duration were: see article. Five were linked together to form a 200 msec stimulus and various combinations of five vowel sounds provided us with 18 different stimuli. The results show that neurons in the cochlear nuclei are remarkably sensitive and selective to vowel sounds. Furthermore, the responses of these neurons to pure tones do not provide a complete basis to predict the types of responses to the vowel sounds. More significant is the finding that the neural discharge rate and pattern of discharge to a particular vowel may depend on where the vowel appears in the stimulus and what other vowel precedes it. This vowel positional effect is not the same for every neuron. We have called this phenomenon a neural "set".

Central nervous regulation of body temperature during sleep

The relationship between hypothalamic temperature and metabolic heat production was measured during wakefulness, slow-wave sleep, and paradoxical sleep in unrestrained kangaroo rats (Dipodomys). Hypothalamic temperature was manipulated with chronically implanted, water-perfused thermodes while cortical electroencephalogram, electromyogram, metabolic rate, and body movement were continuously recorded. During slow-wave sleep, in comparison to wakefulness, there is a lowered threshold hypothalamic temperature for the metabolic heat production response and a lowered proportionality constant relating rate of metabolic heat production to hypothalamic temperature. During paradoxical sleep no increase in metabolic heat production could be elicited by lowering hypothalamic temperature, which indicates that the thermoregulatory system is inoperative. These results provide a basis for explaining the changes in various body temperatures, metabolic rate, and other thermoregulatory responses during sleep in a variety of mammals.