Nonanesthetized Condition Research Articles

Genetically-targeted Recordings from Respiratory Chemoreceptor Neurons in the Retrotrapezoid Nucleus of Freely Behaving Mice by Fiber Photometry

Central respiratory chemoreceptors regulate breathing homeostasis in relation to arterial pH/PCO2. Neurons located in the retrotrapezoid nucleus (RTN) are considered to function as central respiratory chemoreceptors and/or to be part of the neural network that drives the central chemoreflex. RTN neurons are sensitive to changes in pH in vitro under synaptic blockade and in anesthetized preparations with artificial ventilation. However, there is limited information about their activity in vivo in non-anesthetized conditions. Recent studies have shown that Nmb-expressing neurons in the RTN have acid-sensitive properties and are necessary for the respiratory response to CO2. In this study, we hypothesized that RTN- Nmb neurons are activated during hypercapnia in freely behaving condition. To test this hypothesis, we measured the dynamic activity of RTN neurons using a genetically encoded calcium indicator (GCaMP7s) via fiber photometry in non-anesthetized mice. Expression of GCaMP7s was genetically targeted to RTN neurons by microinjection of a Cre-dependent viral vector (AAV1-Syn-Flex-jGCAMP7s) in transgenic Nmb-Cre mice. One month later, the animals were placed in a plethysmography chamber to simultaneously record breathing and GCaMP7s fluorescence from RTN- Nmb neurons in freely behaving conditions. During hypercapnia, RTN neurons were markedly activated, and the effect size was graded to FICO2 (DF/F0 from baseline: 1.9 ± 1.0 % at 0.03, 8.0 ± 4.0% at 0.06 and 12.0 ± 5.0% at 0.09, n=6), and significantly different for each level of CO2 (RM One-way ANOVA, p=0.0012). Importantly, the increase in RTN neuron activity correlates with changes in the FICO2 (p<0.0001, R2=0.97) and respiratory frequency (p<0.0001, R2=0.85). This study shows that RTN neurons are potently activated by hypercapnia in freely behaving conditions, and the response of RTN neurons to CO2 aligns with changes in breathing. These results are consistent with the concept that RTN neurons monitor arterial PCO2/pH and are essential for the hypercapnic ventilatory response. This study was supported by National Institutes of Health (HL148004 ) to Stephen BG Abbott. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

9 Randel Lecture: In Vivo investigation of pregnancy Physiology

Abstract Pregnancy in any mammal requires the integration of three distinct compartments; the maternal, placental and fetal compartments. Compromised function of any of the three compartments can result in suboptimal pregnancy outcomes, including increased morbidity and mortality at delivery, reduced livestock production efficiency and adult-onset of metabolically-related disease in humans. To accurately understand the progression of both normal and compromised pregnancies, therefore, requires the simultaneous assessment of all three compartments, which for most species is not technically feasible. Consequently, over the past 60 yr the pregnant sheep has been used extensively for in vivo investigation of pregnancy physiology. The ability to place indwelling catheters, within both maternal and fetal vessels, allows the simultaneous steady-state assessment of uterine and umbilical blood flows, hormone secretion, and nutrient uptake and utilization of nutrients by each of the three compartments, under non-stressed and non-anesthetized conditions. This has provided unrivalled insight into the physiology of pregnancy, and the realization that the placenta is a highly metabolic tissue, utilizing the majority of oxygen and glucose taken up by the uterus. However, the deficit in studying pregnant sheep is the lack of genetic models, readily available in rodents, that could help define specific gene function during pregnancy. Consequently, we developed in vivo lentiviral-mediated RNA interference (RNAi) methods to specifically alter the abundance of specific gene transcripts/proteins within the placenta, beginning at 9 d of gestation (dGA). Our lentiviral-mediated approach limits the RNAi to the trophectoderm derivatives of the placenta. Initially we used this approach to determine the importance of PRR15 and LIN28 during the establishment of pregnancies, but turned our efforts towards combining in vivo RNAi with steady-state physiological assessments during late gestation to examine the function of genes involved in placental nutrient transport (SLC2A3) and placenta derived hormones (CSH). By creating a placental deficiency in SLC2A3, not only was the fetus smaller and hypoglycemic at mid-gestation, but by interfering with placental glucose uptake, maternal hormone concentrations were also impacted, yet near-term, a distinctly different phenotype was present. For the placental hormone CSH (a.k.a. placental lactogen), CSH RNAi not only impacts placental and fetal growth, but also reductions in uterine blood flow, nutrient fluxes to the fetus, and produces an altered hormonal environment. Combining these methodological approaches provides new and often unexpected insights into the physiological integration of the maternal, placental and fetal compartments. Supported by NIH-NICHD grants HD093701 and HD094952.

In vivo investigation of ruminant placenta function and physiology-a review.

The placenta facilitates the transport of nutrients to the fetus, removal of waste products from the fetus, immune protection of the fetus and functions as an endocrine organ, thereby determining the environment for fetal growth and development. Additionally, the placenta is a highly metabolic organ in itself, utilizing a majority of the oxygen and glucose derived from maternal circulation. Consequently, optimal placental function is required for the offspring to reach its genetic potential in utero. Among ruminants, pregnant sheep have been used extensively for investigating pregnancy physiology, in part due to the ability to place indwelling catheters within both maternal and fetal vessels, allowing for steady-state investigation of blood flow, nutrient uptakes and utilization, and hormone secretion, under non-stressed and non-anesthetized conditions. This methodology has been applied to both normal and compromised pregnancies. As such, our understanding of the in vivo physiology of pregnancy in sheep is unrivalled by any other species. However, until recently, a significant deficit existed in determining the specific function or significance of individual genes expressed by the placenta in ruminants. To that end, we developed and have been using in vivo RNA interference (RNAi) within the sheep placenta to examine the function and relative importance of genes involved in conceptus development (PRR15 and LIN28), placental nutrient transport (SLC2A1 and SLC2A3), and placenta-derived hormones (CSH). A lentiviral vector is used to generate virus that is stably integrated into the infected cell's genome, thereby expressing a short-hairpin RNA (shRNA), that when processed within the cell, combines with the RNA Induced Silencing Complex (RISC) resulting in specific mRNA degradation or translational blockage. To accomplish in vivo RNAi, day 9 hatched and fully expanded blastocysts are infected with the lentivirus for 4 to 5h, and then surgically transferred to synchronized recipient uteri. Only the trophectoderm cells are infected by the replication deficient virus, leaving the inner cell mass unaltered, and we often obtain ~70% pregnancy rates following transfer of a single blastocyst. In vivo RNAi coupled with steady-state study of blood flow and nutrient uptake, transfer and utilization can now provide new insight into the physiological consequences of modifying the translation of specific genes expressed within the ruminant placenta.

Non-invasive measurement of pulse waves in the soles of rats using an RGB camera

In this paper, we propose a non-invasive method for measuring pulse waves corresponding to heart rate (HR) by capturing the color change on the soles of rats’ feet using a high-speed RGB camera. Remote photoplethysmography (rPPG) with a camera has been used as a non-invasive biometric method. However, the rPPG method has been challenging to apply to rats with body hair. We applied the rPPG method using a high frame rate to the sole where the skin was directly visible and successfully and accurately detected pulse waves under non-invasive, non-restraint, and non-anesthetized conditions.

264 Using in vivo RNA Interference to Investigate Ruminant Placental Function

Abstract Pregnant sheep have been used extensively for investigating pregnancy physiology, providing valuable information about the progression of ruminant pregnancy. The ability to place indwelling catheters, within both maternal and fetal vessels, allows for steady-state investigation of blood flow, nutrient uptakes and utilization, and hormone secretion, under non-stressed and non-anesthetized conditions. As such, our understanding of the in vivo physiology of pregnancy in sheep is unrivalled by any other species. However, until recently, a significant deficit existed in determining the specific function or significance of individual genes expressed by the placenta in livestock. To that end, we developed and have been using in vivo RNA interference (RNAi) within the sheep placenta to examine the function and relative importance of genes involved in conceptus development (PRR15 and LIN28), placental nutrient transport (SLC2A1 and SLC2A3), and placenta derived hormones (CSH). The lentiviral vector LL3.7 is used to generate virus that is stably integrated into the infected cell’s genome, thereby expressing a short-hairpin RNA (shRNA), that when processed within the cell, combines with the RNA Induced Silencing Complex (RISC) resulting in specific mRNA degradation or translational blockage. To accomplish in vivo RNAi, day 9 hatched and fully expanded blastocysts are infected with the lentivirus for 4–5 hours, and then surgically transferred to synchronized recipient uteri. Only the trophectoderm cells are infected by the replication deficient virus, leaving the inner cell mass unaltered, and we typically obtain 70–80% pregnancy rates following transfer of a single blastocyst. Data will be presented from two projects. One is focused on generating a deficiency in placental glucose transporters at mid-gestation, and the other on the impact of CSH RNAi during late gestation, demonstrating the utility of this experimental approach for examining gene function within the placenta of livestock. Supported by NIH-NICHD grants HD093701 and HD094952.

Use of topical nasal anesthesia during flexible endoscopic evaluation of swallowing in dysphagic patients.

This study aimed to determine the effect of topical lidocaine on Penetration-Aspiration Scale (PAS) scores and patient comfort and tolerance of flexible endoscopic evaluation of swallowing (FEES) examinations in dysphagic patients. Adults with dysphagia referred for swallowing evaluation were recruited to participate in consecutive nonanesthetized and then anesthetized FEES examinations. Under endoscopic visualization, participants consumed 6 swallows consisting of graduated volumes of milk, pudding, and cracker in each condition and recorded their discomfort and tolerance in the 2 conditions. Penetration-Aspiration Scale scores were assigned in blinded fashion for each swallow. Twenty-five adults participated in the study. Although there was no statistically significant effect of anesthesia on PAS scores (P=.065), the odds of a higher PAS score were 33% higher during anesthetized swallows. The anesthetized condition yielded significantly less discomfort and pain during the examination, significantly less pain and discomfort during insertion and removal of the endoscope, and significantly greater overall tolerance than the nonanesthetized condition. The use of topical lidocaine during FEES may impair swallowing ability in patients with dysphagia, but this result does not achieve statistical significance. Topical nasal anesthesia significantly reduces subjective pain and discomfort and improves tolerance during FEES.

An implantable CMOS device for blood-flow imaging during experiments on freely moving rats

An observation technique for animal brain activity under freely moving conditions is important to understand brain functions because brain activity under an anesthetized condition is different from that under a nonanesthetized condition. We have developed an ultrasmall CMOS imaging device for brain activity observation under freely moving conditions. This device is composed of a CMOS image sensor chip and nine LEDs for illumination. It weighs only 0.02 g and its small size enables experiments to be performed without restricting animal movement. This feature is advantageous for brain imaging, particularly in freely moving situations. In this study, we have demonstrated blood-flow imaging using the device for the stable observation of brain activity over a long period. The blood flow can be observed without staining the brain during optical imaging. We have successfully estimated the blood-flow velocity under freely moving conditions.

The Effects of topical anesthetic on swallowing during nasoendoscopy

To assess the effects of a typical otolaryngologic dose of 1 mL of 4% lidocaine on penetration aspiration scale scores and participant discomfort during flexible endoscopic evaluation of swallowing. A prospective pilot study. Twenty healthy participants consumed 12 swallows consisting of graduated volumes of milk, water, pudding, and cracker in anesthetized and nonanesthetized conditions. Each participant was randomly selected to begin with the anesthetized or nonanesthetized condition. Each participant returned within 7 days to repeat the study in the other condition. Digital recordings of their evaluations were scored via the penetration-aspiration scale in a blinded fashion. Participants recorded their discomfort and tolerance of each flexible endoscopic evaluation of swallowing. The anesthetized condition yielded significantly worse swallowing function (P = .001) than the nonanesthetized condition. The nonanesthetized condition yielded greater discomfort and pain during the procedure (P = .006, .018), greater pain during insertion and removal of the endoscope (P = .002, .003) and less overall tolerance (P = .016) than the anesthetized condition. A typical otolaryngologic anesthetic dose of 1 mL of 4% lidocaine during flexible endoscopic evaluation of swallowing predisposed healthy young adults to higher penetration aspiration scale scores (less safe swallowing) than the nonanesthetized condition; however, the anesthetic reduced discomfort and provided better overall tolerance. Future studies need to evaluate the effects of lower doses of lidocaine (0.2 and 0.5 mL) on swallowing function and comfort.

Parallel fiber and climbing fiber responses in rat cerebellar cortical neurons in vivo

Over the last few years we have seen a rapidly increasing interest in the functions of the inhibitory interneurons of the cerebellar cortex. However, we still have very limited knowledge about their physiological properties in vivo. The present study provides the first description of their spontaneous firing properties and their responses to synaptic inputs under non-anesthetized conditions in the decerebrated rat in vivo. We describe the spike responses of molecular layer interneurons (MLI) in the hemispheric crus1/crus2 region and compare them with those of Purkinje cells (PCs) and Golgi cells (GCs), both with respect to spontaneous activity and responses evoked by direct electrical stimulation of parallel fibers (PFs) and climbing fibers (CFs). In agreement with previous findings in the cat, we found that the CF responses in the interneurons consisted of relatively long lasting excitatory modulations of the spike firing. In contrast, activation of PFs induced rapid but short-lasting excitatory spike responses in all types of neurons. We also explored PF input plasticity in the short-term (10 min) using combinations of PF and CF stimulation. With regard to in vivo recordings from cerebellar cortical neurons in the rat, the data presented here provide the first demonstration that PF input to PC can be potentiated using PF burst stimulation and they suggest that PF burst stimulation combined with CF input may lead to potentiation of PF inputs in MLIs. We conclude that the basic responsive properties of the cerebellar cortical neurons in the rat in vivo are similar to those observed in the cat and also that it is likely that similar mechanisms of PF input plasticity apply.

Cardiovascular effects produced by activation of GABA receptors in the rostral ventrolateral medulla of conscious rats

The rostral ventrolateral medulla (RVLM) has been proposed as a region playing a major role in the tonic and reflex control of sympathetic vasomotor activity and blood pressure. Pharmacological activation of GABA A receptors with muscimol in the RVLM of anesthetized rats results in a large fall in mean arterial pressure (MAP), heart rate (HR) and sympathetic activity. In this study we evaluated the effects of activation of GABA receptors in the RVLM of conscious, freely moving rats. Bilateral microinjections of muscimol into the RVLM of conscious rats produced a large fall in MAP (−38±4 mm Hg, n=7) when compared with saline injections (NaCl 0.9%, 7±1 mm Hg, n=4). The decrease in MAP evoked by muscimol was accompanied by a significant increase in HR (muscimol 69±13 bpm vs. vehicle −33±12 bpm, P<0.05), an effect that was completely abolished by beta1 adrenergic receptor blockade. Conversely, bilateral microinjections of GABA B agonist, baclofen, evoked a pressor response, but in this case, the increase was not significantly different from that evoked by vehicle injections. These results 1) indicate that GABA A receptors have a powerful influence on the resting activity of RVLM neurons in conscious rats; 2) indicate that a compensatory sympathetic-mediated tachycardia is present after inhibition of RVLM neurons in conscious rats; 3) confirm and extend previous findings showing that RVLM neurons are critical for blood pressure maintenance even in normal non-anesthetized conditions.

Sensory and Motor Effects of Etomidate Anesthesia

The effects of anesthesia with etomidate on the cellular mechanisms of sensory processing and sensorimotor coordination have been studied in the active electric sense of the mormyrid fish Gnathonemus petersii. Like many anesthetics, etomidate is known to potentiate GABA(A) receptors, but little is known about the effects on sensory processing at the systems level. A better understanding is necessary for experimental studies of sensory processing, in particular regarding possible effects on the dynamic structure of excitatory and inhibitory receptive fields and to improve the knowledge of the mechanisms of anesthesia in general. Etomidate slowed the electromotor discharge rhythm, probably because of feedback inhibition at the premotor level, but did not alter the structure of the electromotor command. Sensory translation through primary afferents projecting to the cerebellum-like electrosensory lobe (ELL) was not changed. However, central interneurons and projection neurons were hyperpolarized under etomidate, and their spiking activity was reduced. Although the spatial extent and the center/surround organization of sensory receptive fields were not changed, initial excitatory responses were followed by prolonged inhibition. Corollary discharge input to ELL was maintained, and the temporal sequence of excitatory and inhibitory components of this descending signal remained intact. Later inhibitory corollary discharge responses were prolonged by several hundred milliseconds. The result was that excitatory reafferent sensory input was conserved with enhanced precision of timing, whereas background activity was greatly reduced. Anti-Hebbian synaptic plasticity evoked by association of sensory and corollary discharge input was still present under anesthesia, and differences compared with the nonanesthetized condition are discussed.

Two α1-Adrenergic Receptor Subtypes Regulating the Vasopressor Response Have Differential Roles in Blood Pressure Regulation

To study the functional role of individual alpha1-adrenergic (AR) subtypes in blood pressure (BP) regulation, we used mice lacking the alpha1B-AR and/or alpha1D-AR with the same genetic background and further studied their hemodynamic and vasoconstrictive responses. Both the alpha1D-AR knockout and alpha1B-/alpha1D-AR double knockout mice, but not the alpha1B-AR knockout mice, had significantly (p < 0.05) lower levels of basal systolic and mean arterial BP than wild-type mice in nonanesthetized condition, and they showed no significant change in heart rate or in cardiac function, as assessed by echocardiogram. All mutants showed a significantly (p < 0.05) reduced catecholamine-induced pressor and vasoconstriction responses. It is noteworthy that the infusion of norepinephrine did not elicit any pressor response at all in alpha1B-/alpha1D-AR double knockout mice. In an attempt to further examine alpha1-AR subtype, which is involved in the genesis or maintenance of hypertension, BP after salt loading was monitored by tail-cuff readings and confirmed at the endpoint by direct intra-arterial recording. After salt loading, alpha1B-AR knockout mice developed a comparable level of hypertension to wild-type mice, whereas mice lacking alpha1D-AR had significantly (p < 0.05) attenuated BP and lower levels of circulating catecholamines. Our data indicated that alpha1B- and alpha1D-AR subtypes participate cooperatively in BP regulation; however, the deletion of the functional alpha1D-AR, not alpha1B-AR, leads to an antihypertensive effect. The study shows differential contributions of alpha1B- and alpha1D-ARs in BP regulation.

Noninvasive Method to Measure Airway Obstruction in Nonanesthetized Allergen-Sensitized and Challenged Mice

Background: Conventional methods used to measure bronchoconstriction are invasive, technically demanding and time consuming. Objectives: Our purpose was to evaluate a noninvasive method, by barometric whole-body plethysmography (WBP), to evaluate bronchoconstriction and bronchial hyperreactivity in mice induced by ovalbumin (OA) inhalation challenge in comparison with an invasive method. Enhanced pause (P_enh) was used as an index of airway obstruction. Methods: Eight mice were sensitized by OA (group I) and then challenged with OA. Twenty-four hours later, pulmonary function testing (PFT) was measured by WBP at baseline and after a methacholine (MCh) inhalation challenge. Eight weight-matched normal mice served as controls (group II). Four hours after PFT in a nonanesthetized condition, all animals were anesthetized and paralyzed. Baseline PFT was performed by the maximal forced expiratory maneuver (MFEM), and then the animals were given varying doses of acetylcholine (ACh; 25, 50, 75, 100 µg/kg) injected through the jugular vein. Five seconds after ACh injections, pulmonary functions were examined, including MFEM, peak airway pressure and total lung compliance. After completing PFT, bronchoalveolar lavage (BAL) was performed, the animals were sacrificed, and the lungs were examined histologically. Results: Group I had increased P_enh in response to MCh in the nonanesthetized condition and decreased flow in the anesthetized condition, characterized by greater decreases in MFEM flow rates MFEF 50% and MFEF 25% than the control group. The peak flows, MFEF 75%, MFEF 50% and MFEF 25%, for group I were lower than those for group II at doses of ACh higher than 25 µg/kg. There were concentration-dependent increases in P_enh in response to aerosolized MCh in both groups, but the P_enh in response to aerosolized MCh was significantly enhanced in group I when compared with controls. The doses of MCh required for 100% increases in P_enh were significantly reduced for sensitized and challenged mice. There was a positive correlation between provocative doses PD200 P_enh MCh, PD20 MFEF 50% ACh and PD20 MFEF 25% ACh. There was a negative correlation between the PD200 P_enh MCh and the percentage of eosinophils in BAL fluid. There was an increased total cell count and an increased percentage and absolute number of eosinophils and lymphocytes in the BAL fluid of sensitized animals. OA-sensitized mice also had a severe inflammatory reaction of airway and lung tissue, characterized by congestion, edema and inflammatory cell infiltration and desquamation of bronchial epithelial cells. Conclusion: The noninvasive method of WBP can be used to evaluate airway obstruction and hyperreactivity induced in mice by allergen challenge.

Stimulated changes in localized cerebral energy consumption under anesthesia.

Focal changes in the cerebral metabolic rate of glucose utilization (CMRglc) are small (10-40%) during sensory activation in awake humans, as well as in awake rodents and primates (20-50%). They are significantly larger (50-250%) in sensory activation studies of anesthetized rats and cats. Our data, in agreement with literature values, show that in the resting anesthetized state values of CMRglc are lower than in the resting nonanesthetized state whereas the final state values, reached upon activation, are similar for the anesthetized and nonanesthetized animals. The lower resting anesthetized state values of CMRglc explain why the increments upon activation from anesthesia are larger than when starting from the nonanesthetized conditions. Recent 13C NMR measurements in our laboratory have established a quantitative relationship between the energetics of glucose oxidation, CMRglc (oxidative), and the flux of the glutamate/gamma-aminobutyric acid/glutamine neurotransmitter cycle, Vcycle. In both the resting awake value of CMRglc(oxidative), and its increment upon stimulation, a large majority (approximately 80%) of the brain energy consumption is devoted to Vcycle. In the differencing methods of functional imaging, it is assumed that the incremental change in the measured signal represents the modular activity that supports the functional response. However, the same amount of activity must be present during the response to stimulation, irrespective of the initial basal state of the cortex. Thus, whereas the incremental signals of DeltaCMRglc can localize neurotransmitter activity, the magnitude of such activity during the response is represented by the total localized CMRglc, not the increment.

Nonshivering thermogenesis during acute cold exposure in adult and aged C57BL/6J mice.

In C57BL/6J adult and aged mice, housed at room temperature (22.5 +/- 1 degrees C), we measured O2 consumption and CO2 production and calculated metabolic heat production under conditions of anesthesia and myorelaxation during acute cold stimulation when body temperature was lowered 7.5 degrees C below control level. An independent group of mice was subjected to a three hour partial physical restraint at 6 degrees C and concentration of uncoupling protein (thermogenin) was measured in interscapular brown adipose tissue mitochondria at different times after cold exposure. Heat production under anesthesia and myorelaxation was about 57-66% lower than in nonanesthetized conditions, but increased significantly during cold stimulation in both age groups. Under anesthesia and myorelaxation before and during cold stimulation aged mice produced about 20% more heat than adult mice. Because in these experiments all sources of facultative thermogenesis, except nonshivering, were suppressed by anesthesia and myorelaxation, and because brown adipose tissue is the major source of nonshivering thermoproduction, we concluded that aged mice housed at room temperature have an increased thermogenesis in brown adipose tissue. This conclusion was also supported by the finding that the concentration of uncoupling protein measured in the mitochondria of brown adipose tissue after single cold exposure was significantly higher in aged than in adult mice. Therefore, we propose that the lower, cold-induced, heat production typically observed in nonanesthetized aged mice may reflect reduced thermogenic capacity of skeletal muscles. While aged mice have less brown adipose tissue than adult animals, the remaining brown adipose tissue may compensate by increasing the concentration of uncoupling protein.

Inhalation of platelet-activating factor increases respiratory resistance in rats: determination by means of an astograph under nonanesthetized conditions.

Intratracheal administration of platelet-activating factor (PAF) to dogs, baboons, and humans has been shown to induce hyperreactivity of the airways and contraction of the smooth muscle. However, it has not yet been reported whether intratracheal administration of PAF to rats induces hyperreactivity. In the present study, the authors estimated the respiratory resistance of rats during intratracheal administration of PAF in order to evaluate the reactivity of the airways to PAF. In both the nonsensitized group and the sensitized group of rats, intratracheal administration of PAF induced an increase in respiratory resistance. The results obtained clarify that responsiveness to PAF exists in the airways of rats.

ネコ４０Ｈｚ反応 無麻酔時と各種麻酔剤との比較

ネコ４０Ｈｚ反応 無麻酔時と各種麻酔剤との比較

The Influence of TMJ and Central Incisor Sensory Impairment on Bite Force Discrimination

AbstractIn this study the authors temporarily altered sensation around the upper and lower front teeth as well as within the temporomandibular joints of 12 subjects. The purpose of the study was to determine the effect of such impairment by comparing bite force discrimination scores obtained under these experimental conditions with scores obtained under a normal non-anesthetized condition. A specially designed strain gauge scale was constructed for the measurement of incisor bite force. The subjects' abilities to discriminate differences in their biting forces were assessed under the following four experimental conditions: 1. Normal (no anesthetization).2. Regional block to the upper and lower anterior teeth.3. Bilateral regional block of the TMJs.4. A combination regional block of the anterior teeth and the TMJs. Bite force discrimination was found to be significantly impaired (P<.05) only in the two conditions in which the teeth were anesthetized. These findings suggest that the periodontal ligament (PD...

Pathways mediating metrazol induced irradiation of visual impulses An experimental study in the cat

Studies of the irradiation pathways for photic-Metrazol induced impulses have been made in the cat. 1. 1. It has been confirmed that Metrazol increases the amplitude of the evoked potentials to photic stimulation in the visual cortex. 2. 2. Two pathways for the irradiation of responses to the frontal lobe have been established and isolated anatomically: one is transcortical and one is subcortical. There is evidence to suggest the existence of a third pathway (cortico-subcortico-cortical). 3. 3. The subcortical pathway demonstrated after ablation of the visual areas has been identified with the “unspecific” reticulothalamic pathway for the visual modality (Magoun et coll., Dell et coll.) because identical regions in the brain stem appear to be involved. The latency of frontal irradiation responses elicited along this sub-cortical pathway has been found to be more than 40 msec. (42–50 msec.), i.e., “long latency” irradiation. The underlying mechanisms was sensitive to the experimental procedure itself and ceased to function if the experiment was prolonged. 4. 4. It has been confirmed that frontal irradiation potentials in the intact preparation have a latency of 21–38 msec. from the light flash (“short latency irradiation”). 5. 5. The transcortical pathway was demonstrated after the removal of mesencephalic and diencephalic structures (except the lateral geniculate body and its immediate surroundings). Frontal irradiation responses mediated via this pathway had a latency of the same order as in the intact preparation (21–38 msec., “short latency irradiation”). This type of irradiation was unaffected by the experimental procedure. 6. 6. From the timing of visual events in the central nervous system in non-anesthetized conditions preparations without Metrazol (Ingvar and Hunter 1955a), as well as in preparations with Metrazol, it is concluded that the primary ascending visual pathways and the visual cortical projection areas play a leading role during irradiation in the intact brain. 7. 7. Transcallosal connections may transmit irradiation potentials between the hemispheres. 8. 8. At the Metrazol concentrations used, no evidence has been found of an extraneuronal irradiation of visual impulses. 9. 9. At a certain Metrazol concentration when light flashes of frequencies of 2.5-4 flashes per sec. are used for stimulation, the irradiation responses will either attenuate and disappear or become driven into a 3/sec. spike and wave pattern which usually leads to a seizure. Inherent cortical factors have been considered responsible for bringing about the attenuation. 10. 10. It has been confirmed that 3 per second spike and wave activity may occur in a self-sustained form during photo-Metrazol activation. 11. 11. Transcortical irradiation is blocked by the anticonvulsant Tridione. This finding does not exclude an action of the drug upon subcortical structures.