Yumiko Ishizawa

Presence of nicotinic acetylcholine receptors in cat carotid body afferent system.

With immunocytochemical techniques using a monoclonal antibody for alpha7 subunits of neuronal nicotinic acetylcholine receptors, we have found these subunits to be exclusively expressed in nerve fibers in the carotid body. Double-immunostaining showed that alpha7 subunit-positive nerve endings enveloped tyrosine hydroxylase-positive glomus cells. Some carotid sinus nerve fibers and tyrosine hydroxylase-positive petrosal ganglion neurons also expressed alpha7 subunits. These data support a role for acetylcholine in carotid body neurotransmission.

Intrathecal morphine dose-response data for pain relief after cholecystectomy

We studied the effect of low-dose intrathecal morphine (0.00–0.20 mg) on pain relief and the incidence of side effects after cholecystectomy in 139 patients divided into eight groups according to intrathecal morphine dose: groups 1 (0.00 mg), 2 (0.04 mg), 3 (0.06 mg), 4 (0.08 mg), 5 (0.10 mg), 6 (0.12 mg), 7 (0.15 mg), and 8 (0.20 mg). Preservative-free morphine hydrochloride mixed in hyperbaric tetracaine solution was administered at the time of induction of spinal anesthesia just before surgery. Pain relief was significantly greater for the first 24 h in groups 3, 4, 5, 6, 7, and 8 than in group 1. The incidence of respiratory depression was significantly greater in groups 7 and 8 than in the other groups in the first 48 h. Vomiting occurred significantly more often in group 1 than in groups 2, 3, 4, and 5. Intraoperative cholangiography and the postoperative clinical course indicated no increase in tone of the sphincter of Oddi in any patient. We conclude that 0.06–0.12-mg intrathecal morphine is the best dose range for pain relief after cholecystectomy without respiratory depression and with the lowest incidence of vomiting or pruritus, or both.

Non-gabaergic effects of midazolam, diazepam and flumazenil on voltage-dependent ion currents in Ng108-15 cells

NON-γ-AMINOBUTYRIC acid (GABA)-mediated effects of benzodiazepines (BZs) have not been widely investigated. However, there is significant evidence in the literature to suggest that several experimental and clinical observations are inconsistent with the commonly accepted GABAergic mechanisms of action for these drugs. The purpose of the present study was to explore electrophysiological effects of midazolam, diazepam and a specific BZ antagonist, flumazenil, using patch-clamp techniques in NG108-15 cells which do not express the GABAA receptor. Midazolam and diazepam decreased Na+, K+ and Ca2+ currents in a dose-related manner. Ca2+ currents were reduced more significantly by diazepam than by midazolam. Flumazenil showed no effects on voltage-dependent ion currents. GABA by itself showed neither effects on the membrane potential nor these ion currents. Midazolam and diazepam, but not flumazenil, exhibited effects on voltage-dependent ion currents in cultured neurons.

Minimal Effective Dose of Intrathecal Morphine for Pain Relief Following Transabdominal Hysterectomy

Intrathecal morphine is useful for relief of various types of pain. Postoperative pain relief is one of the most common indications (1). The dose range suggested for postoperative pain relief has ranged from 0.1 to 20 mg morphine (2-6), with the resulting pain relief lasting as much as 24 hours (7-10). Intrathecal morphine is also, however, accompanied by complications such as nausea, vomiting, urinary retention, pruritus, and delayed respiratory depression (1 1-15), the latter potentially life threatening (16). As side effects cannot be predicted (17) and because respiratory depression may be delayed by as much as 20 hours, careful observation for side effects is required (5,18,19). As a result, intrathecal morphine may not be as widely used as it deserves to be for postoperative pain relief because of lack of data on doseresponse relationships for intrathecal morphine, in which responses included both delayed respiratory depression as well as potentially less lethal side effects. In this study, we prospectively investigated the effects of low doses of intrathecal morphine, 0.10 mg as the maximum, on pain relief after transabdominal hysterectomy. We report the minimum effective intrathecal morphine dose defined as that amount of morphine that provides relief of postoperative pain with the least incidence of side effects.

Mechanisms of anesthetic actions and the brain

The neural mechanisms behind anesthetic-induced behavioral changes such as loss of consciousness, amnesia, and analgesia, are insufficiently understood, though general anesthesia has been of tremendous importance for the development of medicine. In this review, I summarize what is currently known about general anesthetic actions at different organizational levels and discuss current and future research, using systems neuroscience approaches such as functional neuroimaging and quantitative electrophysiology to understand anesthesia actions at the integrated brain level.

Localization of nicotinic acetylcholine receptors in cat carotid body and petrosal ganglion

How the carotid body converts hypoxic stimuli into neural activity remains largely unknown. Several neurotransmitters, which have been demonstrated in type I cells in the carotid body, are still candidates for primary neurotransmitter(s) of chemotransduction.

Selective activation of G-protein coupled receptors by volatile anesthetics

Ion channels and ionotropic neurotransmitter receptors have long been investigated as the principle targets of inhaled volatile anesthetics (VAs), but emerging evidence suggests that G-protein coupled receptors (GPCRs) might also directly interact with VAs. To survey the extent of interaction between VAs and diverse GPCRs, we have turned to the 1000+ member family of olfactory receptors (ORs), taking advantage of their unique expression pattern of a single OR per neuron. Through optical imaging and electrophysiological recordings, we show that different VAs trigger the normal transduction cascade in distinct subsets of cells in a dose-dependant manner. Together with evidence of antagonism by odorants, this selective activation strongly implicates a direct action of VAs upon particular olfactory receptors. The finding that VAs stimulate nearly 8% of olfactory GPCRs suggests that probing related Class A GPCRs may reveal a pool of VA targets whose altered signaling contributes to anesthetic effects.

Acetylcholine Sensitivity of Cat Petrosal Ganglion Neurons

We investigated if neuronal nicotinic acetylcholine receptors (nAChRs) are localized in chemoreceptor afferent neurons in the cat petrosal ganglion (PG) and if acetylcholine (ACh) excites chemoreceptor afferent neurons. Immunocytochemistry revealed that a majority of PG neurons expressed alpha 4 and/or alpha 7 subunits of neuronal nAChRs, and a part of them were tyrosine hydroxylase positive. Excitability of cultured PG neurons was studied with patch clamp techniques (whole cell configuration). ACh and nicotine evoked both inward and outward currents. The inward current was partially blocked by removal of extracellular calcium and by antagonists for alpha 4 beta 2 (dihydro-beta-erythroidine) or alpha 7 nAChRs (methyllycaconitine). Outward current was blocked by 4-aminopyridine (4-AP) and sometimes by atropine. ACh-induced membrane potential changes were well correlated with ACh-induced currents. Depolarization and hyperpolarization occurred in response to ACh. Occasionally depolarization was followed by a train of action potentials. The results suggest that heterogeneous neuronal nAChRs are widely distributed in both chemoreceptor and other PG neurons. In some neurons nAChRs may be functionally coupled with outward K+ channels. Further studies are required to determine whether chemoreceptor neurons have a distinct distribution pattern of nAChRs and K+ channels.

Release of Acetylcholine from Cultured Cat and Pig Glomus Cells

It is generally accepted that neurotransmitters play an essential role in the carotid body chemotransduction. Although roles of each transmitter are in debate, substantial evidence suggests that in cats acetylcholine (ACh) is involved in an excitatory step in the carotid body chemotransduction. The presence of choline acetyl transferase, an ACh-synthesizing enzyme, in glomus cells of cats has been known (Wang et al, 1989). Cholinergic receptors are localized on glomus cells (Dinger et al, 1985, 1986; Chen et al, 1981) and possibly on the carotid sinus nerve (Fitzgerald & Shirahata, 1990). Exogenously applied ACh provokes a fast and clear increase in carotid sinus nerve chemoreceptor discharge (Eyzaguirre et al, 1983; Fidone et al, 1990). Further, perfusion of the carotid body with cholinergic blockers inhibits hypoxia-mediated elevation in chemoreceptor neural activity (Fitzgerald & Shirahata, 1994). However, little is known about the release of ACh from glomus cells. This study was designed to obtain basic information as to the release pattern of ACh from cultured glomus cells.

Dynamics of Propofol-Induced Loss of Consciousness Across Primate Neocortex

The precise neural mechanisms underlying transitions between consciousness and anesthetic-induced unconsciousness remain unclear. Here, we studied intracortical neuronal dynamics leading to propofol-induced unconsciousness by recording single-neuron activity and local field potentials directly in the functionally interconnecting somatosensory (S1) and frontal ventral premotor (PMv) network during a gradual behavioral transition from full alertness to loss of consciousness (LOC) and on through a deeper anesthetic level. Macaque monkeys were trained for a behavioral task designed to determine the trial-by-trial alertness and neuronal response to tactile and auditory stimulation. We show that disruption of coherent beta oscillations between S1 and PMv preceded, but did not coincide with, the LOC. LOC appeared to correspond to pronounced but brief gamma-/high-beta-band oscillations (lasting ∼3 min) in PMv, followed by a gamma peak in S1. We also demonstrate that the slow oscillations appeared after LOC in S1 and then in PMv after a delay, together suggesting that neuronal dynamics are very different across S1 versus PMv during LOC. Finally, neurons in both S1 and PMv transition from responding to bimodal (tactile and auditory) stimulation before LOC to only tactile modality during unconsciousness, consistent with an inhibition of multisensory integration in this network. Our results show that propofol-induced LOC is accompanied by spatiotemporally distinct oscillatory neuronal dynamics across the somatosensory and premotor network and suggest that a transitional state from wakefulness to unconsciousness is not a continuous process, but rather a series of discrete neural changes. SIGNIFICANCE STATEMENT How information is processed by the brain during awake and anesthetized states and, crucially, during the transition is not clearly understood. We demonstrate that neuronal dynamics are very different within an interconnecting cortical network (primary somatosensory and frontal premotor area) during the loss of consciousness (LOC) induced by propofol in nonhuman primates. Coherent beta oscillations between these regions are disrupted before LOC. Pronounced but brief gamma-band oscillations appear to correspond to LOC. In addition, neurons in both of these cortices transition from responding to both tactile and auditory stimulation before LOC to only tactile modality during unconsciousness. We demonstrate that propofol-induced LOC is accompanied by spatiotemporally distinctive neuronal dynamics in this network with concurrent changes in multisensory processing.