Characterizing Traumatic Brain Injury and Its Association with Losing Stable Housing in a Community-based Sample

OBJECTIVE

Traumatic brain injury (TBI) is increasingly recognized as a common and impactful health determinant in homeless and precariously housed populations. We sought to describe the history of TBI in a precariously housed sample and evaluate how TBI was associated with the initial loss and lifetime duration of homelessness and precarious housing.

METHOD

We characterized the prevalence, mechanisms, and sex difference of lifetime TBI in a precariously housed sample. We also examined the impact of TBI severity and timing on becoming and staying homeless or precariously housed; 285 precariously housed participants completed the Brain Injury Screening Questionnaire in addition to other health assessments.

RESULTS

A history of TBI was reported in 82.1% of the sample, with 64.6% reporting > 1 TBI, and 21.4% reporting a moderate or severe TBI. Assault was the most common mechanism of injury overall, and females reported significantly more traumatic brain injuries due to physical abuse than males (adjusted OR = 1.26, 95% CI = 1.14 to 1.39, P < 0.0001). The first moderate or severe TBI was significantly closer to the first experience of homelessness (b = 2.79, P = 0.003) and precarious housing (b = 2.69, P < 0.0001) than was the first mild TBI. In participants who received their first TBI prior to becoming homeless or precariously housed, traumatic brain injuries more proximal to the initial loss of stable housing were associated with a longer lifetime duration of homelessness (RR = 1.04, 95% CI = 1.02 to 1.06, P < 0.0001) and precarious housing (RR = 1.03, 95% CI = 1.01 to 1.04, P < 0.0001).

CONCLUSIONS

These findings demonstrate the high prevalence of TBI in this vulnerable population, and that aspects of TBI severity and timing are associated with the loss and lifetime duration of stable housing.

Traumatic brain injury in precariously housed persons: Incidence and risks

BACKGROUND

Homeless and precarious housed persons are particularly prone to traumatic brain injuries (TBIs), but existent incidence rates are hampered by poor case acquisition. We rigorously documented TBIs in precariously housed persons transitioning in and out of homelessness.

METHODS

Between December 2016 and May 2018, 326 precariously housed participants enrolled in a longitudinal study in Vancouver, Canada were assessed monthly for TBI occurrences after education on sequelae. Over one participant-year, 2433 TBI screenings were acquired for 326 person-years and variables associated with odds of incident TBI were evaluated.

FINDINGS

One hundred participants acquired 175 TBIs, yielding an observed incidence proportion of 30·7% and event proportion of 53·7%. Of the injured, 61% reported one TBI and 39% reported multiple injuries. Acute intoxication was present for more than half of the TBI events assessed. Additionally, 9·7% of TBI events occurred in the context of a drug overdose. Common injury mechanisms were falls (45·1%), assaults (25·1%), and hitting one's head on an object (13·1%). In this community-based but non-randomly recruited sample, exploratory analyses identified factors associated with odds of an incident TBI over one year of follow-up, including: schizophrenia disorders (odds ratio (OR) = 0·43, 95% confidence interval (CI) 0·19, 0·94), role functioning (OR = 0·69, 95% CI 0·52, 0·91), opioid dependence (OR = 2·17, 95% CI 1·27, 3·72) and those reporting past TBIs (OR = 1·99, 95% CI 1·13, 3·52).

INTERPRETATION

Given the ubiquity of TBIs revealed in this precariously housed sample, we identify an underappreciated and urgent healthcare priority. Several factors modified the odds of incident TBI, which can facilitate investigations into targeted prevention efforts.

FUNDING

Canadian Institutes of Health Research, Natural Sciences and Engineering Research Council of Canada, William and Ada Isabelle Steel Research Fund, Simon Fraser University Vice-President Research Undergraduate Student Research Award and Simon Fraser University Psychology Department Research Grant.

Cognitive Impairment in Marginally Housed Youth: Prevalence and Risk Factors

Objective: Homeless and marginally housed youth are particularly vulnerable members of society, and are known to experience numerous health problems, including psychiatric illness, substance use, and viral infection. Despite the presence of these risk factors for cognitive compromise, there is limited research on the cognitive functioning of homeless and marginally housed youth. The present study examines the degree and pattern of cognitive impairment and associations with key risk factors in a sample of marginally housed young adults.

Method: Participants (N = 101) aged 20–29 years old were recruited from single-room occupancy hotels, and underwent cognitive, psychiatric, neurological, and serological assessments.

Results: Forty percent of participants were identified as mildly cognitively impaired across multiple domains, and 16% were moderately-severely impaired. Deficits in memory and attention were most prevalent, while impairments in inhibitory control/processing speed and cognitive flexibility were also present but tended to be less severe. Developmental and historical factors (premorbid intellectual functioning, neurological soft signs, earlier exposure to and longer duration of homelessness or marginal housing), as well as current health risks (stimulant dependence and hepatitis C exposure), were associated with cognitive impairment.

Conclusions: The strikingly high rate of cognitive impairment in marginally housed young adults represents a major public health concern and is likely to pose a significant barrier to treatment and rehabilitation. These results suggest that the pathway to cognitive impairment involves both developmental vulnerability and modifiable risk factors. This study highlights the need for early interventions that address cognitive impairment and risk factors in marginalized young people.

Efficacy of repeat intravenous dosing of ondansetron in controlling postoperative nausea and vomiting: a randomized, double-blind, placebo-controlled multicenter trial

STUDY OBJECTIVES

To compare repeat intravenous (i.v.) dosing of ondansetron 4 mg with placebo for the treatment of postoperative nausea and vomiting (PONV) in patients for whom prophylactic, preoperative ondansetron 4 mg i.v. was inadequate

DESIGN

Randomized, double-blind, placebo-controlled study.

SETTING

Ten outpatient surgical centers in the United States.

PATIENTS

2,199 male and female ASA physical status I, II, and III patients > or = 12 years old scheduled to undergo outpatient surgical procedures and receive nitrous oxide-based general anesthesia.

INTERVENTIONS

Ondansetron 4 mg i.v. was administered to all patients before induction of general anesthesia. Patients who experienced PONV or requested antiemetic therapy within 2 hours after discontinuation of inhaled anesthesia were randomized (1:1) to either a repeat i.v. ondansetron 4 mg dose or placebo.

MEASUREMENTS AND MAIN RESULTS

Of the 2,199 patients prophylactically treated with ondansetron 4 mg before anesthesia induction, 1,771 (80.5%) did not experience PONV or request antiemetic therapy during the 2 hours following discontinuation of anesthesia. Of the 428 patients who experienced PONV or requested antiemetic therapy during the same period, and were randomized to additional treatment (214 randomized to ondansetron, 214 randomized to placebo), the incidence of complete response (no emesis, no rescue medication, no study withdrawal) was similar for both ondansetron-randomized and placebo-randomized groups for the 2-hour (34% and 43%, respectively, p = 0.074) and 24-hour (28% and 32%, respectively, p = 0.342) postrandomization study periods. Repeat ondansetron dosing was not more effective than placebo in controlling either postoperative emesis or the severity/duration of postoperative nausea. The administration of an additional dose of ondansetron 4 mg postoperatively did not result in an increased incidence of adverse effects.

CONCLUSIONS

In patients for whom preoperative prophylaxis with ondansetron 4 mg i.v. is not successful, a repeat dose of ondansetron 4 mg i.v. in the postanesthesia care unit does not appear to offer additional control of PONV.

Transcutaneous measurement of carbon dioxide tension during long-distance transport of neonates receiving mechanical ventilation

OBJECTIVE

To determine the efficacy of transcutaneous carbon dioxide tension measurement during high-risk neonatal transport.

STUDY DESIGN

This was a prospective, randomized comparative study. Infants transported from hospitals more than 30 miles away from our center and who required respiratory intervention were enrolled. Alternating transports used a transcutaneous CO2/O2 monitor. Ventilation parameters and end transport blood gas values served as primary endpoints for the study.

RESULTS

Infants with transcutaneous carbon dioxide tension monitoring were more likely to have decreased ventilator peak pressures during transport than neonates not monitored (-1.5 cm H2O vs + 0.6 cm H2O; p = 0.04). Monitored neonates were more likely to arrive at the tertiary center with a more normal pH and a CO2 tension between 35 and 45 mm Hg (4.7 to 6.0 kPa) than nonmonitored infants (p = 0.03 and p = 0.01, respectively). The stabilization times before transport were not significantly prolonged by the use of the transcutaneous monitor.

CONCLUSIONS

Transcutaneous monitoring of CO2 tension improves short-term respiratory outcome in neonates receiving mechanical ventilation during transport.

Targeted perinatal drug screening in a rural population

The objectives of this study was to evaluate the efficacy of a risk factor-based drug screening program in a rural perinatal population with a low prevalence of substance abuse. The study was done at a university-based children's hospital in central Missouri. A risk factor-based meconium and infant urine drug screening program was compared to a universal meconium screening program in a newborn population over a 3 month period. Eighteen percent of the 462 deliveries met criteria for drug testing. Of those tested, 11/85 (12.9%) tested positive for marijuana (n = 8) or cocaine (n = 3), representing a detection rate of 2.4% of the total population. This compares well to the 2.6% detected in the universal testing protocol. In three patients, meconium analysis detected marijuana exposure, while urine analysis revealed no detectable drug. Risk factor-based meconium drug screening can identify most infants exposed to illicit drugs in rural perinatal populations with low baseline substance abuse rates. Meconium sampling is more likely than urine sampling to identify exposed infants.

In vitro binding of iron with the cation-exchange resin sodium polystyrene sulfonate

STUDY OBJECTIVE

To investigate the ability of the cation exchange resin sodium polystyrene sulfonate to bind iron from ferrous sulfate solutions, along with the effects of pH on binding.

METHODS

We performed a series of in vitro experiments in which various concentrations of iron and sodium polystyrene sulfonate were combined and free ferrous iron was measured with the use of a colorimetric assay.

RESULTS

Sodium polystyrene sulfonate bound iron from ferrous sulfate solutions at pH 2 and pH 7. Slightly less binding of free ferrous iron was demonstrated in experiments performed at pH 7 than in those performed at pH 2. At pH 2, 98% of iron was bound, at pH 7, 95% of iron was bound.

CONCLUSION

Sodium polystyrene sulfonate may be a useful therapy in acute iron poisoning once safety and efficacy are determined with the use of in vivo models.

Applause-induced ulnar artery thrombosis: a case report

A case is described involving ulnar artery thrombosis attributed to vigorous applause. This is a previously unrecognized cause of ulnar artery thrombosis.

Cocaine detection in neonatal gastric aspirate samples

We prospectively analyzed the feasibility and sensitivity of gastric fluid detection of cocaine compared with standard meconium analysis. Cocaine was detected in nearly half (45.5%) of gastric aspirate samples tested from infants in whom meconium was positive for cocaine. The time to sample acquisition was substantially shorter for gastric aspirate sampling versus meconium analysis. The possible ramifications of the presence of cocaine in amniotic fluid are discussed.

Hypoplastic left heart syndrome with male pseudohermaphroditism and bicornuate uterus bicollis

A 39-week-old phenotypically female infant was born with hypoplastic left heart syndrome and expired on the third day of life. An autopsy revealed the patient to also have male pseudohermaphroditism and uterus bicornis bicollis. The association of hypoplastic left heart syndrome and male pseudohermaphroditism has been reported in only two previous patients.

The effect of three different ranitidine dosage regimens on reducing gastric acidity and volume in ambulatory surgical patients

STUDY OBJECTIVE

To evaluate three different preoperative oral dosing regimens of ranitidine in ambulatory patients who had significant risk of aspiration pneumonitis (gastric pH < or = 2.5 or volume > or = 25 ml at intubation or extubation).

DESIGN

Double-blind, placebo-controlled, randomized trial.

SETTING

St. Francis Hospital of Buffalo, New York.

PATIENTS

Two hundred seventy-one ambulatory patients about to undergo a surgical procedure under general anesthesia, of whom 241 (89%) completed the trial and were considered evaluable.

INTERVENTIONS

Patients were randomly assigned to receive one of four regimens administered orally before surgery: placebo at bedtime the night before and in the morning on the day of surgery; ranitidine 150 mg at bedtime and in the morning; ranitidine 150 mg at bedtime and placebo in the morning; or ranitidine 300 mg at bedtime and placebo in the morning.

MEASUREMENTS AND MAIN RESULTS

Patients who received ranitidine 150 mg twice/day, ranitidine 150 mg at bedtime, or ranitidine 300 mg at bedtime had a significantly (p < 0.05) lower frequency of a gastric pH 2.5 or below at intubation or extubation than those taking placebo twice/day (3%, 45%, and 31%, respectively, vs 86%). In addition, gastric volume at intubation or extubation was 25 ml or above in significantly fewer patients receiving ranitidine 150 mg at bedtime than placebo (37% vs 13%, p < 0.05). Overall, the number of patients with risk factors for aspiration pneumonitis was significantly lower with ranitidine 150 mg twice/day (20%), ranitidine 150 mg at bedtime (48%), and ranitidine 300 mg at bedtime (35%) than placebo (86%) (p < 0.001), and significantly lower with ranitidine 150 mg twice/day than ranitidine 150 mg at bedtime (p < 0.05).

CONCLUSIONS

Ranitidine 150 mg twice/day preoperatively reduced to the greatest degree the percentage of patients who developed significant risk factors for aspiration pneumonitis after surgery under general anesthesia.

Mixed venous oxygenation in critically ill neonates

OBJECTIVE

To describe the typical ranges for central venous oxygen saturation and PO2 in a group of critically ill neonates and the relationship of these measurements to measurements of arterial oxygenation and indicators of oxygen supply and demand.

DESIGN

Survey.

SETTING

Newborn intensive care unit (ICU) in a children's hospital.

PATIENTS

Eighteen newborn infants (1 to 3 days old) who required mechanical ventilation for respiratory diseases, but who were hemodynamically stable and in acid-base balance.

INTERVENTIONS

Umbilical artery and right atrial catheterization were performed, allowing simultaneous blood gas sampling.

MEASUREMENTS AND MAIN RESULTS

Simultaneous umbilical arterial and right atrial blood gas measurements were analyzed (n = 100). Mean mixed venous oxygen saturation was 83.3% and mixed venous oxygen tension 37.8 torr (5.1 kPa). The mixed venous oxygen saturation correlated well with the arterial-venous oxygen content difference (C[a-v]O2) and fractional oxygen extraction, r = -.77 (r2 = .59) and -.85 (r2 = .72), respectively (p < .0005). Poor correlation was found between the mixed venous oxygen saturation and arterial oxygen saturation values. Two cases are presented in which measurements of mixed venous oxygenation led to recognition of apparent tissue hypoxia earlier than did measurements of arterial oxygenation.

CONCLUSIONS

We conclude that measurement of central venous oxygenation in ill neonates may reflect more accurately the oxygen supply and demand status of the neonate than measurement of arterial oxygenation alone.

Decreased incidence of intracranial hemorrhage using cephalic jugular venous drainage during neonatal extracorporeal membrane oxygenation

Intracranial hemorrhage (ICH) remains one of the more common serious complications of extracorporeal membrane oxygenation (ECMO) in neonates. In 1990 this center began routine use of cephalic jugular venous drainage during neonatal ECMO to augment blood return to the ECMO pump and potentially decrease the incidence of ICH by decreasing cerebral venous pressure. Thirty-four ECMO cases utilizing cephalic jugular venous drainage were compared with the previous 34 ECMO cases. The incidence of ICH decreased from 35% (12/34) to 6% (2/34) when neonates without cephalic jugular venous drainage are compared with those being subject to this technique (P < .01). No differences were found between the two groups in gestational age, birth weight, duration of ECMO, survival, platelet counts, activated clotting times, or incidence of other bleeding complications. Cephalic jugular venous drainage during neonatal ECMO appears to be safe and may decrease the incidence of ICH.

Echocardiographically guided balloon atrial septostomy during extracorporeal membrane oxygenation (ECMO)

Use of extracorporeal membrane oxygenation (ECMO) in infants with congenital heart disease is becoming more frequent. We present the first reported use of balloon atrial septostomy during ECMO support and describe possible complications of such procedures unique to ECMO therapy.

Penile agenesis associated with urethral and bilateral renal agenesis

Penile agenesis is a rare anomaly, with an estimated incidence of 1 in 30 million. Most cases are compatible with life but require early surgical intervention. This case is unusual in that there was an associated agenesis of the kidneys and urethra leading to fatal oligohydramnios sequence with pulmonary hypoplasia.

Mean platelet volume during coagulase-negative staphylococcal sepsis in neonates

Coagulase-negative staphylococci are the most common cause of late-onset septicemia in neonates in intensive care nurseries. Clinical and laboratory diagnosis of infection with coagulase-negative staphylococci can be difficult. The authors reviewed serial mean platelet volumes of 18 infants in whom coagulase-negative staphylococci sepsis developed and found a significant increase in the mean platelet volume at the time of diagnosis and a return to baseline after resolution of the infection. The increase in mean platelet volume occurred although thrombocytopenia developed in only two of the infants and no difference was found in the mean platelet counts before and at the time of diagnosis of the infection. This finding may be a useful adjunct to the current laboratory tests used to diagnose coagulase-negative staphylococci sepsis in neonates.

Cephalic jugular venous blood gas measurement during neonatal venoarterial extracorporeal membrane oxygenation

Cannulation of the cephalic portion of the right internal jugular vein during extracorporeal membrane oxygenation (ECMO) allows for increased venous return flow to the circuit. This procedure also allows access to venous drainage from the brain. We reviewed data from simultaneous blood gases obtained from the cephalic jugular vein and the mixed venous return in 5 neonates during venoarterial ECMO. Cephalic venous pO 2 values were significantly lower than mixed venous pO 2 values (P less than .001). The values for pH and pCO 2 did not vary between the sites. Our experience with 34 infants using cephalic jugular drainage is reviewed. Since the institution of right jugular venous drainage, the intracranial hemorrhage rate in neonates undergoing ECMO at our center has decreased from 34% to 6% (p less than .01).

Bilirubin encephalopathy in a term infant after planned home delivery

A term infant was delivered at home by his father after a pregnancy which involved no organized medical care. By the third day of life the infant developed fever, poor feeding and severe jaundice. The infant was found to have a serum indirect bilirubin of 49 mg/dl secondary to isoimmune hemolytic anemia due to anti-c antibody. The infant survived but suffers from clinical manifestations of kernicterus.

Arterial red cell indices in preterm and term infants at birth

Baseline arterial red cell indices were determined at birth in 105 infants of various gestational ages. These arterial samples were obtained through an umbilical artery catheter or radial artery puncture from a selected group of patients who were evaluated for respiratory distress or possible infection. The red cell distribution width, a quantitative measure of heterogeneity of red cells in the peripheral blood, was consistently elevated, revealing a physiologic state of anisocytosis in the newborn. This new information has provided a useful baseline reference for normal red cell indices from arterial blood in neonates in the first 24 hours of life.

Trisomy 16p in a liveborn infant and review of trisomy 16p

We report on an infant boy with duplication of part of 16p and partial deficiency of 9p: 46,XY, -9, + der(9)t(9;16)(p24;p13.1)mat. The child has the typical phenotype of dup(16p) even though the extra piece of 16p is small (16p13.1----pter). Manifestations include severe developmental delay, rounded face, sparse hair, ear anomalies, hypertelorism, cleft soft palate, a thin vermilion border of the upper lip, and left renal dysgenesis. We review 16p duplications.

Olfactory neuroblastoma

Fifteen patients with olfactory neuroblastoma were treated during the 17-year period of 1969 to 1986. Data was analyzed with respect to age at presentation, sex, presenting signs and symptoms, stage, and results of treatment. Age ranged from 4 to 67 years with the median age being 27 years. Median follow-up was 8 years. Local control was achieved in nine of nine patients or 100% with successful surgical resection, i.e., minimal residual disease, followed by postoperative radiation therapy (45 to 65 Gy) was employed. There were no distant failures when the primary site was controlled. Regional lymph node metastases were infrequent: only 13% (two of 15 patients) presented with positive nodes. Three of four patients treated initially with surgery alone had a local recurrence, two of which were successfully salvaged by combined therapy. There were four patients treated with radiation therapy alone: three had persistent disease after radiation therapy, and one patient was controlled with 65 Gy. Olfactory neuroblastoma has a propensity to recur locally when treated with surgery alone. The authors' experience suggests excellent local control can be achieved with surgery immediately followed by radiation therapy. Thus the authors recommend planned combined treatment for all resectable lesions.

Erythrocyte pyruvate kinase deficiency. A case of severe congenital hemolytic anemia

Although it occurs rarely, erythrocyte pyruvate kinase deficiency is a cause of neonatal jaundice and anemia across many ethnic and geographic groups. In this report of a Missouri case, an infant with this condition was also found to have Pelger-Huet leukocyte anomaly.

Mesencephalic trigeminal sensory neurons of cat: axon pathways and structure of mechanoreceptive endings in periodontal ligament

We injected 3H-proline into cat brainstem in order to label the entire mesencephalic trigeminal nucleus (Mes-V) for autoradiographic analysis of the size and pathways of Mes-V sensory axons and for microscopic study of Mes-V receptor structure in dental tissue. Labeled sensory axons were found in the trigeminal motor and sensory tracts and roots; approximately equal numbers of axons were found in both roots. The sensory root and all three divisions of the trigeminal nerve contained larger Mes-V axons than the motor root. Labeled Mes-V axons were found at the ganglion in the dorsomedial (infratrochlear) branch of the ophthalmic nerve but not in the ventrolateral branch. The mean diameter of Mes-V axons in periodontal ligament was 4.0 +/- 1.9 micron compared to 7.3 +/- 2.1 micron in maxillary and mandibular nerve, suggesting axonal arborization prior to innervation of ligament. Mes-V receptors in dental tissue were confined to ipsilateral periodontal ligament close to the root apex, with greater innervation on the posterior side. Receptor incidence was moderate for most teeth; however, maxillary first and second incisors and maxillary and mandibular canines had focal areas with remarkably dense innervation. No labeled axons were found in pulp of any ipsilateral teeth, and none was found in any contralateral dental tissue. EM-autoradiography demonstrated that Mes-V axons form unencapsulated Ruffini-like mechanoreceptors in periodontal ligament. The preterminal axons were small and myelinated. Neighboring bundles of unmyelinated axons and rare encapsulated endings were not labeled. The labeled mechanoreceptors branched to varying degrees among the ligament fibers; they contained numerous mitochondria and glycogen particles, as well as some vesicles and rare multivesicular bodies. They were surrounded by special Schwann cells that formed one or several layers around the ending. The endings were exposed to the basal lamina at numerous sites and occasionally extended fingers beyond the lamellar Schwann cells to contact ligament collagen.

Intracranial potentials correlated with an event-related potential, P300, in the cat

Intracranial recordings of long-latency, event-related potentials were obtained from paralyzed, artificially respirated cats. A modified oddball paradigm was employed in which cats were presented with a randomized series of two tones, a 'frequent' 4 kHz stimulus and a 'rare' 1 kHz stimulus. A tail shock was administered 700 ms after onset of the rare tone. Under these circumstances the stimulus elicited a positive component at the vertex similar to the human P300. Intracranial potentials associated with the rare tone usually manifested components of greater amplitude than did potentials associated with the frequent tone. A positive component occurring in latency between 200 and 350 ms only accompanied the presentation of the rare stimulus. The P300 component, which was positive at the dura, appeared as a negative component within a few millimeters of the surface over a wide area of the marginal and suprasylvian gyri. Changing the probability of the rare stimulus resulted in a reduction in the amplitudes of both the intracranial negative component and the P300 recorded at the skull. Components of large amplitude associated with the rare stimulus were obtained from the region of the hippocampus. These components reversed polarity, sometimes more than once, as the electrode was advanced. Substantial latency differences were often observed between the P300 recorded at the skull and P300-like intracranial components associated with the rare stimulus. These results suggest that the cortices of the marginal and suprasylvian gyri and the hippocampal region contribute to the generation of the cat P300.

Postnatal functional development of the dorsal and posteroventral cochlear nuclei of the cat

The postnatal development of firing patterns and response areas was determined for single neurons in the dorsal (DCN) and posteroventral ( PVCN ) cochlear nuclei of the kitten. Extracellular, single-unit responses to pure-tone stimulation were recorded in ketamine and sodium pentobarbital anesthetized kittens between the ages of 5 and 52 days. Within the first two weeks of postnatal life threshold is high, first-spike latency is long, and maximal discharge rate is low as compared to older kittens and adult cats. Prior to the end of the second postnatal week the tone-evoked temporal discharge patterns that characterize neurons of the DCN and PVCN in the adult cat are routinely recorded. These patterns, which appear within the first 50 ms of tonal stimulation, include the so-called " primarylike ," "chopper," " pauser ," "buildup," and "onset" types and their variants. In animals younger than about 10-12 days of age, the driven activity that occurs later than about 50 ms after stimulus onset often is not sustained, but breaks up during the stimulus into bursts that are separated by intervals of about 100-150 ms. Also within the first two weeks of postnatal life, many of the response-area properties of DCN and PVCN neurons are similar to those recorded in adult cats. The excitation and inhibition found within the so-called type II/III, type IV, and type V response areas of the adult occur in this early postnatal period. We conclude that many of the cellular mechanisms that underlie the temporal firing patterns and the organization of the response areas of DCN and PVCN neurons are active in the growing, differentiating cochlear nuclei and that the emergence of these mechanisms does not depend on afferent activity generated in the cochlear and auditory nerve by the animal's acoustic environment. Furthermore, if temporal firing patterns and response-area profiles remain relatively constant over the life span of the animal, then so must the spatial and temporal relationships of the inputs that produce and maintain them as these neurons, and the circuits of which they are a part, grow in size and complexity.

Projections from dental structures to the brain stem trigeminal complex as shown by transganglionic transport of horseradish peroxidase

Horseradish peroxidase (HRP) was implanted in one maxillary canine of cats and the transganglionic transport to the brain stem studied and mapped. HRP-positive fibers and terminal granules are distributed ipsilaterally to each subdivision of the trigeminal complex but are heaviest in the main sensory nucleus, adjacent pars oralis and pars interpolaris near obex with somewhat less in the rest of pars oralis and least in pars caudalis. The distribution indicates a wider central representation than previous anatomical reports and corresponds well with certain physiological studies.

A vertical stereotaxic approach to auditory cortex in the unanesthetized monkey

A procedure is described for chronic single-unit recording from monkey auditory cortex. The cortex is approached in a vertical stereotaxic plane and subsequent histology is performed on tissue sections made in the same plane. The procedure maximizes the probability of locating and identifying auditory cortical areas during the chronic unit recording sessions and of identifying individual electrode tracks in subsequent histologic examination. Average stereotaxic coordinates for the center of area A1 are A-P +5, M-L 17.5 and D-V +20, but variation of +/-5 mm can occur across subjects. The superior temporal plane is sloped at an angle of about 30 degrees in the A-P dimension but is relatively flat in the M-L dimension. Microelectrode penetrations made with this procedure were found, on the average, to terminate within 0.7 mm of the intended site. Procedures for improving this accuracy and for identifying closely-spaced penetrations are discussed.

Response plasticity of neurons in auditory cortex of the rhesus monkey

Auditory-evoked responses in single neurons from rhesus monkey auditory cortex were measured under four relatively well defined behavioral and physiological conditions: (1) monkey awake and performing a simple auditory reaction time task; (2) monkey awake but not performing a task (Stage A); (3) monkey in a drowsy or Stage 1 sleep state (State B); and (4) monkey anesthetized with a short-acting nonbarbiturate anesthetic. For most units studied the response evoked by the auditory stimulus was greater in the performance condition than in the nonperformance condition. Similarly, evoked activity was usually greater in State A than in State B. Finally, evoked responses under anesthesia were usually weaker than those obtained in the unanesthetized animal. Some exceptions were noted in each case. Differences in response patterns and in rate versus intensity functions of neurons were also found to be associated with the behavioral and physiological state of the preparation. No significant changes in unit spontaneous activity associated with changes in behavioral or physiological condition were observed.