Ventral medullary surface responses to hypoxic and hyperoxic transient ventilatory challenges in the cat

Exploring the brain with sleep-related injuries, and fixing it

The focus of my research efforts rests with determining dysfunctional neural systems underlying disorders of sleep, and identifying interventions to overcome those disorders. Aberrant central and physiological control during sleep exerts serious consequences, including disruptions in breathing, motor control, blood pressure, mood, and cognition, and plays a major role in sudden infant death syndrome, congenital central hypoventilation, and sudden unexpected death in epilepsy, among other concerns. The disruptions can be traced to brain structural injury, leading to inappropriate outcomes. Identification of failing systems arose from the assessment of single neuron discharge in intact, freely moving and state-changing human and animal preparations within multiple systems, including serotonergic action and motor control sites. Optical imaging of chemosensitive, blood pressure and other breathing regulatory areas, especially during development, were useful to show integration of regional cellular action in modifying neural output. Identification of damaged neural sites in control and afflicted humans through structural and functional magnetic resonance imaging procedures helped to identify the sources of injury, and the nature of interactions between brain sites that compromise physiological systems and lead to failure. Interventions to overcome flawed regulatory processes were developed, and incorporate noninvasive neuromodulatory means to recruit ancient reflexes or provide peripheral sensory stimulation to assist breathing drive to overcome apnea, reduce the frequency of seizures, and support blood pressure in conditions where a failure to perfuse can lead to death.

State influences on ventral medullary surface and physiological responses to sodium cyanide challenges

Intravenous sodium cyanide (NaCN) administration lowers ventral medullary surface (VMS) activity in anesthetized cats. Sleep states modify spontaneous and blood pressure-evoked VMS activity and may alter VMS responses to chemoreceptor input. We studied VMS activation during peripheral chemoreceptor stimulation by intravenous NaCN using optical procedures in six cats instrumented for recording sleep physiology during sham saline and control site trials. Images of scattered 660-nm light were collected at 50 frames/s with an optical device after 80-100 microg total bolus intravenous NaCN delivery during waking and sleep states. Cyanide elicited an initial ventilatory decline, followed by large inspiratory efforts and an increase in respiratory rate, except in rapid eye movement sleep, in which an initial breathing increase occurred. NaCN evoked a pronounced decrease in VMS activity in all states; control sites and sham injections showed little effect. The activity decline was faster in rapid eye movement sleep, and the activity nadir occurred later in waking. Sleep states alter the time course but not the extent of decline in VMS activity.

A 6-month, double-blind, placebo-controlled trial of eptastigmine in Alzheimer's disease

OBJECTIVES

To evaluate the efficacy and safety of eptastigmine as a treatment for patients with mild-to-moderate Alzheimer's disease (AD).

PATIENTS AND METHODS

The study was designed as a randomized, double-blind, placebo-controlled, parallel-group study. It was performed in 26 Italian and American geriatric and neurological centers. The study group comprised 349 outpatients with a diagnosis of probable AD according to the criteria of the National Institute of Neurological and Communicative Disorders and Stroke and the AD and Related Disorders Association. Patients were assigned to one of the three study groups: placebo (n = 119), eptastigmine 10 mg t.i.d. (n = 115) or eptastigmine 12 mg t.i.d. (n = 115) for 25 weeks. The AD Assessment Cognitive Subscale (ADAS-Cog) and the Clinical Dementia Rating Scale-Sum of the Boxes (CDR-SB) were the primary outcome measures for efficacy.

RESULTS

The two doses of eptastigmine produced similar results and are presented together. Percentages of patients completing double-blind treatment were 82 and 87% in the placebo and eptastigmine groups, respectively. At the end of treatment, the intent to-treat analysis on 342 patients showed a statistically significant effect of eptastigmine compared to placebo on both ADAS-Cog (p = 0.047) and CDR-SB (p = 0.010). Patients on eptastigmine performed significantly better than placebo-treated patients also on the Mini-Mental State Examination (p < 0.001). The drug was well tolerated with 5% of patients withdrawing due to adverse events versus 3% on placebo. Adverse events were recorded in 46% of the patients on placebo compared to 52% of the patients taking eptastigmine. Cholinergic side effects (nausea, vomiting, diarrhea and abdominal pain) were reported with similar frequency in the eptastigmine and placebo-treated patients.

CONCLUSION

Eptastigmine doses up to 12 mg t.i.d. for 25 weeks are well tolerated. The drug positively affects cognitive performance and global function of patients with mild-to-moderate AD.

Physiological and ventral medullary surface activity during hypovolemia

The objective was to determine ventral medullary surface responses to blood loss sufficient to induce shock. We examined changes in scattered light from rostral and intermediate areas of the ventral medullary surface in four intact, drug-free cats during acute hypovolemia. Scattered light images, collected during 660 and 560 nm illumination to measure cellular activity and hemodynamic aspects, respectively, were digitized at 50 frames/s during baseline, and during withdrawal of 20-30% blood volume. Hypovolemia elicited a profound hypotension and eventual bradycardia. In all cats, a modest increase in ventral medullary surface reflectance (activity decline) accompanied initial blood loss; as hypovolemia continued, and blood pressure declined, reflectance switched to a decline (activity increase), with the lowest reflectance occurring at maximal blood loss. Hypovolemia elicited multiple transient physiologic behaviors, including tachycardia, tachypnea, intermittent isolated and sustained bursts of enhanced inspiratory efforts, and extensor activation of the somatic musculature. The phasic physiological behaviors during hypovolemia were accompanied by partial recovery of medullary surface reflectance and blood pressure towards baseline values; however, reflectance continued to decrease as blood pressure progressively fell after these recovery efforts. Patterns of reflectance were not uniform over areas examined; isolated regions of enhanced or diminished reflectance appeared upon the overall images. Optical signals indicating hemodynamic changes followed the neural activity patterns, but not precisely. Regions within the ventral surface are responsive to hypovolemia, and to transient behaviors associated with momentary restoration of blood pressure; these ventral surface areas may assume essential roles in the systemic response to hypovolemic-induced shock.

Two-year treatment of Alzheimer's disease with eptastigmine. The Eptastigmine Study Group

The effectiveness of long-term treatment of Alzheimer's disease with cholinesterase inhibitors is a matter of controversy. We evaluated the effects of prolonged treatment with eptastigmine in 176 patients with mild to moderate Alzheimer's disease participating in the open-label extension phase of a 25-week double-blind, placebo-controlled trial of eptastigmine. The effects of eptastigmine on cognition and daily functioning were evaluated with the cognitive portion of the Alzheimer's Disease Assessment Scale (ADAS-Cog) and the Instrumental Activities of Daily Living (IADL) scale, respectively. Safety was monitored by physical examination, laboratory tests, vital functions and electrocardiogram measurements and by the assessment of adverse events. One hundred and fifty-three patients (87%) completed 1 year of treatment, 77 patients (44%) 18 months and 33 patients (19%) 2 years of treatment. Patients treated for 2 years showed an improvement of mean ADAS-Cog scores compared to baseline for 31 weeks and mean IADL scores remained close to baseline for 25 weeks. Cognitive and functional scores then worsened as expected in this progressive disease. After 2 years, patients deteriorated compared to baseline by 13.4 points on the ADAS-Cog and 6.1 points on IADL. Historical untreated controls with identical disease severity are expected to have an annual worsening of approximately 10.9 points on ADAS-Cog and 4.9 points on IADL. Thus patients treated with eptastigmine for 2 years had a benefit of 8.5 points on ADAS-Cog and 3.8 points on IADL. These benefits translate to about 9 months difference between eptastigmine-treated patients and untreated historical patients. The drug was generally well tolerated with 14 patients (7.9%) withdrawing due to adverse events. Adverse events, not necessarily drug-related, were recorded in 66 patients (37.5%) and were transient and generally mild in severity. This study indicates that prolonged treatment with eptastigmine is safe and produced a clinically long-term benefit in patients with Alzheimer's disease.

Ventral medullary neuronal responses to peripheral chemoreceptor stimulation

Recent findings suggest that carotid chemoreceptor input into the ventral medullary surface intermediate area during hypoxia is inhibitory (Gozal et al., (1994) Neurosci. Lett. 178, 73-76. However, systemic hypoxia is a complex stimulus, and effects of carotid chemoreceptor stimulation per se on intermediate ventral medullary surface neuronal activity are difficult to isolate. Therefore, we studied neural activation of the intermediate ventral medullary surface during peripheral chemoreceptor stimulation by intravenous sodium cyanide using optical procedures in seven pentobarbital-anesthetized cats. Control recordings were also acquired in the suprasylvian cortex of three cats. Images of reflected 660 nm light were collected at l/s with a charge-coupled device camera, triggered by the cardiac R wave, after 0.0, 0.5, 2, 5, 10, 20 and 40 micrograms/kg i.v. sodium cyanide administration before and following carotid sinus denervation. Sodium cyanide doses > 5 micrograms/kg significantly increased ventilation, an effect which was eliminated following carotid sinus denervation. A pronounced, dose-dependent activity decrease within the intermediate ventral medullary surface occurred within seconds of sodium cyanide administration, with subsequent return to baseline. Carotid sinus denervation eliminated rapid-onset neural responses to all sodium cyanide doses. However, at the 40 micrograms/kg dose, a smaller, slower onset (25 s), activity decrease occurred both pre- and postdenervation. In the neocortex, the sodium cyanide-induced fast responses were absent. Intravenous cyanide, acting via a carotid sinus nerve pathway, results in a dose-dependent decrease in neural activity within the intermediate ventral medullary surface of cats. High-dose sodium cyanide also appears to decrease intermediate ventral medullary surface neural activity directly.