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Biomedical subjects

R B McCall

Publications and source records attributed to R B McCall.

At least 91 records · Page 5Linked to original sources
PubMed1977

Spinal interneurons in the baroreceptor reflex arc.

The zona intermedia of the cat thoracic spinal cord was explored with metal microelectrodes in an attempt to locate interneurons within the pathway that mediates the spinal component of baroreceptor-induced sympathoinhibition. Twenty-nine neurons whose discharges were interrupted during occlusion of the common carotid arteries were found in the vicinity of the intermediomedial nucleus (IMM). The spontaneous discharges of 10 of these units were correlated in time with the R wave of the ECG. The pattern of R-wave locking of spinal unitary discharge was similar to that for some neurons in the nucleus of the tractus solitarius (NTS; primary site of baroreceptor fiber termination). In addition, spinal units, whose discharges were interrupted during carotid artery occlusion, were activated by stimulation of depressor sites in NTS. These observations suggest that bulbospinal fibers of the baroreceptor reflex arc terminate on and excite interneurons in the vicinity of IMM. It is postulated that these neurons directly inhibit components of sympathoexcitatory pathways located in the intermediolateral spinal nucleus. Furthermore, it was demonstrated that the inhibitory interneurons receive auxiliary input from sympathetic afferents in the inferior cardiac nerve.

Action Potentials↗
PubMed1977

Imitation of live and televised models by children one to three years of age.

The results of these studies indicated that children younger than 1 year possess the cognitive capability of translating a perception of a novel action into their own behavior. However, the likelihood of imitation varied as a function of the nature of the target behavior. For example, actions requiring direct social commerce with the examiner were imitated less frequently than simple motor behaviors with objects, and reproducing gestures was more common than vocalizations. Moreover, imitation seemed to depend upon the child's level of mental development--the imitation of coordinated sequences, which requires the child to associate two external events, lagged behind the imitation of single-unit behaviors. There was no evidence for individual traits of general imitativeness, at least not until symbolic relations were involved. Live models were imitated more than TV models but only prior to age 3. While children under 2 years of age were not facile at imitating sequences of behaviors or delaying performance at short time after modeling, older toddlers readily and accurately imitated televised sequences even after a 24-hour delay. Whereas socially extroverted and fearless children imitated live models more than shy children, TV imitation was not related to temperament, home TV viewing habits, or parental education. Finally, the experience of being imitated may facilitate the social cognition of influencing another person.

Age Factors↗
PubMed1977

The interfering effect of distracting stimuli on the infant's memory.

Infants 3 1/2 months of age were assessed for the possible role of the dissimilarity of the distracting stimulus to the originally learned standard in a modified familiarization-distraction-test paradigm. When data for all subjects were analyzed, there was no evidence that the distraction had any interfering effect at all on the memory for the original standard. However, specialized analyses suggested that interference varied with the likelihood that subjects actually encoded the distracting stimuli might govern the probability or extent that an infant encodes the distracting stimulus rather than affecting the interference process directly.

Attention↗
PubMed1976

Differential effect of baroreceptor reflexes and clonidine on frequency components of sympathetic discharge.

The effects of the baroreceptor reflexes and clonidine on the 3 and 10 Hz components of spontaneously occurring renal sympathetic nervous discharge (SND) were studied in the cat. The proportion of 3 : 10 Hz SND was assessed by selective filtering and integration of activity in the 2-4 Hz and 9-11 Hz frequency bands. Baroreceptor denervation increased activity in both frequency bands while significantly lowering the 3 : 10 Hz ratio. Baroreceptor reflex activation (i.v. phenylephrine) decreased activity in both frequency bands while significantly increasing the 3 : 10 ratio. Clonidine (4-20 mug/kg, i.v.) affected the 3 : 10 Hz ratio of SND in a manner similar to baroreceptor reflex activation. These results indicate that the 3 and 10 Hz components of SND, both of which have been previously shown to be inherent to the central vasomotor system, are differentially affected by the baroreceptor reflexes and clonidine. It is concluded that it is possible to characterize certain cardiovascular states with respect to the 3 : 10 Hz ratio of SND.

Animals↗
PubMed1976

Identification and discharge patterns of spinal sympathetic interneurons.

Sympathetic interneurons, in the vicinity of the intermediolateral cell column of the cat thoracic spinal cord, were identified by determining whether the probability of spontaneously occurring unitary discharge was correlated in time with the R wave of the ECG. Fifteen units which could not be antidromically activated by stimulation of the cervical sympathetic nerve exhivited a positive post-R wave relationship. The discharge patterns of these cells were distinctly different from those of antidromically identified preganglionic neurons. The interneurons discharged spontaneously in bursts with short interspike intervals (less than 20 ms). Preganglionic neurons rarely discharged more than once during a cardiac cycle. Single shocks applied to medullary pressor sites evoked a train of spikes in the interneurons. Preganglionic units usually discharged only once to medullary pressor stimulation. Electrial activation of medullospinal inhibitory tracts suppressed the discharges of both interneurons and preganclionic units. This observation indicates that spinal inhibition is exerted at an interneuronal level within sympathoexictatory pathways. No evidence was found for the existence of inhibitory interneurons in the intermediolateral cell column. This study demonstrated that the post-R wave time interval histogram in combination with a test for antidromic activation can be used to differentiate between spinal sympathetic internuerons and preganglionic cells.

Animals↗
PubMed1970

Intelligence quotient pattern over age: comparisons among siblings and parent-child pairs.

Comparisons between sibling and parent-child pairs with unrelated control pairs matched for year of birth and parental education were made to determine the relative heritability of the general level of intelligence quotient as opposed to that of the sequential pattern of IQ change over age (3 to 12 years). There was greater similarity among related siblings relative to matched controls for general level than for pattern of IQ over age. Relationships between the IQ's of children and that of their parents as children were not consistent across age.

Age Factors↗