Neurotransmitter-Mediated Changes in the Electrophysiological Properties of Pituicytes

Intracellular recordings were obtained from pituicytes in the neural lobe of the isolated rat pituitary. Like other glia, pituicytes lacked action potentials in response to depolarizing current injection, but they tended to have more positive resting membrane potentials and higher input resistances than astrocytes in other preparations. Dye-coupling typical of astrocytes was also demonstrated amongst pituicytes, and their morphologies were similar to those of pituicytes stained for glial fibrillary acidic protein. Action potentials, anode-break spikes or barium spikes were not observed in pituicytes, even under conditions that maximized the elicitation of Ca²⁺-dependent responses. This suggests that pituicytes either have no or a very low density of Ca²⁺ channels or Ca²⁺ currents that are too small to generate action potentials. Dynorphin A (1–13), a kappa-opioid agonist, produced long-lasting increases in pituicyte input resistance with no significant changes in resting membrane potential. Dynorphin's action was concentration-dependent and was blocked by the opioid antagonist naloxone. This is consistent with previous reports demonstrating kappa-opioid receptors on pituicytes in the neurohypophysis. The β-adrenergic agonist isoproterenol (100 μM) reversed the increases in pituicyte input resistance produced by opioid application, with no significant changes in resting membrane potential. The fact that pituicytes responded to neurotransmitters suggests a functional link between pituicytes and neurosecretory nerve fibres.     

Creating empowering meaning: an interactive process of promoting health with chronically ill older Canadians

Many health promotion approaches afford education about disease prevention and enhancement of one's health status. But strategies for enabling older people with chronic illness to better mobilize their resources for everyday living still require development. This practical action research study explored the experiences of 13 purposefully selected older persons who participated in a health promotion intervention premised on the adult education theory of perspective transformation. Findings illuminate health promotion through a holistic interactive process in which professional and chronically ill older person together evolved a caring relationship and enhanced conscious awareness of life and health experiences. Five health-promoting strategies were identified: building trust and meaning; connecting; caring; mutual knowing; and mutual creating. Researchers suggest several important directions to refine professional practice approaches and health care delivery systems in order to promote the health of older persons with chronic conditions.     

Prevention of arginine-vasopressin-induced motor disturbances by a potent vasopressor antagonist

The antivasopressor analog d(CH2)5Tyr(Me) arginine-vasopressin completely blocked the convulsive-like behavior and other severe motor disturbances which are normally observed following a second central arginine-vasopressin injection. This vasopressor antagonist appears to be selective for arginine-vasopressin-induced motor disturbances, in that the convulsive and motor effects of pentylenetetrazol and somatostatin were not altered significantly by pretreatment with the central antagonist. Results suggest that arginine-vasopressin-induced motor disturbances are mediated via central receptors. The classic antidiuretic (V2) type of arginine-vasopressin receptor does not appear to be involved, since the agonist 1-desamino-8-D-arginine-vasopressin did not elicit convulsive-like behavior or other severe motor disturbances 2 days following a first ('priming') injection of arginine-vasopressin.     

Release of benzalkonium chloride from a heparin-bonded umbilical catheter with resultant factitious hypernatremia and hyperkalemia

Elevated serum sodium and potassium levels were recently observed when sampled through a heparin-bonded umbilical catheter and measured with certain ion-selective electrodes. The cationic surfactant, benzalkonium chloride (BZC), is known to falsely elevate those cations in serum. Inasmuch as most heparin-bonded umbilical catheters use BZC during the bonding process, an in vitro study was performed to estimate the quantity of BZC released and the duration of sodium and potassium elevations during pooled sera infusion. Three heparin-bonded umbilical catheters and 3 silastic umbilical catheters were first flushed with 0.3 mL of normal saline and then perfused with pooled sera (sodium, 142 mEq/L; potassium, 4.6 mEq/L) at 2.5 microL/h. Effluent samples were collected from 0 to 8 hours and analyzed by ion-selective electrodes. Elevated serum sodium concentrations from 160 to greater than or equal to 250 mEq/L and potassium concentrations from 6.0 to greater than or equal to 9.6 mEq/L were observed. The BZC concentration in the catheter effluent was measured by mass spectrometry, with peak values of 10 micrograms/mL detected by this method. When varying concentrations of BZC (1 to 100 micrograms/mL) were added directly to pooled serum, a dose-dependent increase in serum sodium was observed. These data demonstrate that BZC released from heparin-bonded umbilical catheters elevates serum electrolyte values measured with some ion-selective electrodes. The observed increase in sodium and potassium concentrations may lead to clinical errors in management. Benzalkonium chloride is associated with myriad of linical symptomatology. Whether this amount of BZC is toxic in the small premature neonate is presently unknown.     

Estimation of red cell flow microvessels: consequences of the Baker-Wayland spatial averaging model

The dual sensor cross-correlation method of H. Wayland and P.C. Johnson [1967), J. Appl. Physiol. 22, 333-337) has become a standard technique for determining the velocity of red blood cells (RBCs) in glass tubes and blood vessels. M. Baker and H. Wayland [1974), Microvasc. Res. 7, 131-143) found that under a variety of conditions the ratio of dual sensor velocity at the centerline of a glass tube to the blood velocity averaged over the lumen was close to 1.6. They provided an explanation of this factor based on spatial averaging of RBC velocity vertically through the tube as well as laterally across the face of the sensor. Their spatial averaging model could also account for the apparent blunting of RBC velocity profiles determined with the dual sensor technique. We used Baker and Wayland's spatial averaging model to calculate how the above velocity ratio depends on sensor size. A nonlinear relation between the velocity ratio and sensor size was found such that the velocity ratio varied from 1.6 to 1.33 as the ratio of sensor width to vessel or tube diameter was varied from 0 to 1. These results also hold for vessels or tubes of elliptic cross section. Some investigators have found that the velocity of red cells near the walls of blood vessels can be a substantial fraction of centerline velocity which suggests that RBC velocity distributions can be blunter than a Poiseuille distribution. We repeated the above calculation for blunted parabolic profiles and we found that the velocity ratio ranged from 1 for plug flow to 1.6 for Poiseuille flow. These calculations show that reliable estimates of RBC flow from dual sensor centerline velocity measurements require one to take into account the relative size of the sensor and blood vessel diameter as well as the bluntness of the RBC velocity distribution.     

Neuropeptide Y action in the rat hippocampal slice: site and mechanism of presynaptic inhibition

Neuropeptide Y (NPY), the most abundant peptide in mammalian CNS, has been shown to inhibit excitatory neurotransmission presynaptically at the stratum radiatum-CA1 synapse in the in vitro rat hippocampal slice. We examined the site and mechanism of this inhibition in a series of in vitro intra- and extracellular recordings in areas CA1 and CA3, the source of much of the excitatory synaptic input to the CA1 neurons. NPY's inhibitory action at the stratum radiatum-CA1 synapse was unaffected by high concentrations of the antagonists bicuculline, theophylline, or atropine, suggesting that it does not act by stimulating the release of the known presynaptic inhibitory transmitters GABA, adenosine, or ACh, respectively. Bath application of 10(-6) NPY, a concentration that strongly inhibited the stratum radiatum-CA1 synapse had no effect on CA3 neuron resting potential, input resistance or action potential amplitude, threshold, or duration. NPY also does not alter the amplitude or duration of the prolonged CA3 action potentials evoked in the presence of TTX, tetraethyl-ammonium, and elevated external Ca2+ or those evoked in the presence of TTX and Ba2+ ions. NPY therefore does not alter the passive or active properties of the somata of the presynaptic CA3 neurons. Neither the afferent fiber volley of the Schaffer collaterals in stratum radiatum of area CA1 nor the excitability of the CA3 terminals in CA1 was affected by NPY application. However, application of the transient K+ current blocker, 4-aminopyridine (4-AP) at concentrations of 10 and 50 microM, completely abolished the action of 10(-6) M NPY on the stratum radiatum-CA1 excitatory synaptic potentials. This action of 4-AP could be reversed by reducing extracellular Ca2+ concentrations from a control level of 1.5 to 0.7 mM (in 10 microM 4-AP) and to 0.5 mM (in 50 microM 4-AP). The evidence suggests that NPY inhibits excitatory synaptic transmission at the Schaffer collateral-CA1 synapse by acting directly at the terminal to reduce a Ca2+ influx.     

Inguinal hernia repair in infants less than six months of age.

Previous studies reviewing the morbidity and mortality of infant inguinal hernia surgery have all been done in university hospital settings. From our community-based tertiary hospital, 100 consecutive cases on infants less than six months of age, undergoing inguinal hernia repair, were reviewed. No infants were excluded. Sixty-eight were full term and 32 were premature. A number of different variables were analyzed and none appeared to affect outcome. Infants were followed for three to five years. There were no true complications in any infant in this series, although six infants developed wound erythema that resolved spontaneously. Parents were given a questionnaire to subjectively evaluate the infant before and after surgery with 78% showing improvement.     

Spectral characteristics of speech at the ear: implications for amplification in children.

This study examined the long- and short-term spectral characteristics of speech simultaneously recorded at the ear and at a reference microphone position (30 cm at 0 degrees azimuth). Twenty adults and 26 children (2-4 years of age) with normal hearing were asked to produce 9 short sentences in a quiet environment. Long-term average speech spectra (LTASS) were calculated for the concatenated sentences, and short-term spectra were calculated for selected phonemes within the sentences (/m/, /n/, /s/, [see text], /f/, /a/, /u/, and /i/). Relative to the reference microphone position, the LTASS at the ear showed higher amplitudes for frequencies below 1 kHz and lower amplitudes for frequencies above 2 kHz for both groups. At both microphone positions, the short-term spectra of the children's phonemes revealed reduced amplitudes for /s/ and [see text] and for vowel energy above 2 kHz relative to the adults' phonemes. The results of this study suggest that, for listeners with hearing loss (a) the talker's own voice through a hearing instrument would contain lower overall energy at frequencies above 2 kHz relative to speech originating in front of the talker, (b) a child's own speech would contain even lower energy above 2 kHz because of adult-child differences in overall amplitude, and (c) frequency regions important to normal speech development (e.g., high-frequency energy in the phonemes /s/ and [see text]) may not be amplified sufficiently by many hearing instruments.     

Effect of aging on wound healing: current concepts.

The population is aging, and advanced age is commonly identified as a risk factor for delayed wound healing. Therefore, it is important for WOC nurses to be knowledgeable about how aging affects the wound healing and repair process, and strategies they can use to promote healing in the elderly population. Impaired wound healing in the aged is due partly to comorbidities common among the elderly, but evidence also suggests that inherent differences in cellular structure and function may impair tissue repair and regeneration as well. This article will address the effect of aging on wound healing, with a particular focus on processes of cellular senescence and related factors hypothesized to result in slowed or impaired wound healing in the elderly.