The dorsal vagal complex of the ferret: anatomical and immunohistochemical studies.

To further the understanding of gastrointestinal function in this species, and in particular to advance our own work concerning central emetic pathways, the cytoarchitecture and the distribution of eight neurochemicals were studied in the ferret dorsal vagal complex (DVC; area postrema, nucleus of the solitary tract [nTS] and dorsal motor nucleus of the vagus). The cytoarchitectural features of this region in the ferret were similar to those seen in other species; however, the ferret possesses a particularly large and distinct subnucleus gelatinosus of the nTS. Dense calcitonin gene-related peptide-immunoreactivity was found in the gelatinous, interstitial and commissural subnuclei of the nTS, with lesser amounts in other regions of the DVC. Enkephalin-immunoreactivity of varying densities was found throughout the DVC. Moderate to dense galanin-immunoreactivity was observed throughout the DVC, with the exception of the subnucleus gelatinosus of the nTS, from which it was virtually absent. Dense neuropeptide Y-immunoreactivity was observed in the subnucleus gelatinosus and interstitial subnucleus, with moderate staining in other regions of the DVC. Neurotensin immunoreactivity was very sparse or absent. Immunoreactivity for serotonin was sparsely distributed throughout the DVC. Moderate somatostatin-immunoreactivity was observed over a large portion of the DVC, but was virtually absent from the gelatinosus and interstitial subnuclei. Substance P immunoreactivity was observed throughout the DVC and was particularly dense in the dorsal/dorsolateral subnucleus and the dorsal aspects of the medial and commissural subnuclei. In terms of its cytoarchitecture the DVC of the ferret is more similar to the cat than the rat, especially with regard to the area postrema and the subnucleus gelatinosus of the nTS. The distribution of neuroactive substances was largely similar to other species; however, differences were present particularly in patterns of immunoreactivity for enkephalin, serotonin, neuropeptide Y and somatostatin.

Relationship between Myers-Briggs Type Indicator and Gregorc Style Delineator.

The relationship between the Myers-briggs Type Indicator and Gregorc Style Delineator, and achievement was examined by administering these instruments to 259 first-year nursing students enrolled in an introductory human anatomy and physiology course. A principal component factor analysis using a varimax rotation of the scores from the two psychometric instruments, achievement examinations and an over-all grade point average indicated that each learning style from the Gregorc Style Delineator corresponds to certain traits on the Myers-Briggs Type Indicator. An individual who had a preference for the learning style of Concrete Sequential tended to have the traits of sensing and judging on the Myers-Briggs Type Indicator, while an individual who used the learning style of Concrete Random tended to have the traits of intuition and perceiving on the Myers-Briggs Type Indicator. One who had a preference for the learning style of Abstract Sequential tended to use the trait of thinking while another who used the learning style of Abstract Random tended to have the trait of feeling. The factor analysis also indicates no relationship of any scores of the traits on the Myers-Briggs Type Indicator or learning styles of the Gregorc Style Delineator with the examination scores achieved in the human anatomy and physiology course or to the students' over-all grade point average. However, factor analysis indicates that the Myers-Briggs Type Indicator traits of Judging vs Perceiving collapsed into the Sensing vs Intuition scale, and that the Gregorc Style Delineator consists of two bipolar scales that are different from those proposed by Gregorc.

Relationship between Myers-Briggs psychological traits and use of course objectives in anatomy and physiology.

The results from the Myers-Briggs Type Indicator (MBTI), which identified preferred psychological traits for 131 nursing students, were compared to their usage levels of course objectives in an undergraduate course in anatomy and physiology. The three usage levels (user, occasional user, and nonuser) were also compared to exam scores in the course, overall grade point averages (GPA) in first-year nursing, and the various psychological traits measured by the MBTI. A multivariate analysis of variance (MANOVA) indicated that users of objectives achieved significantly higher exam scores and maintained a higher GPA than occasional and nonusers. The MANOVA also indicated that users of course objectives preferred a sensing judging modality, whereas nonusers preferred an intuiting perceiving style to guide their studying and learning.

Gregorc learning styles and achievement in anatomy and physiology.

Results from the Gregorc Style Delineator (GSD), administered to 260 undergraduate nursing students, were compared with achievement scores in a human anatomy and physiology course. Factor analysis and VARIMAX rotation demonstrate that there is no relationship between any of the four learning styles allegedly identified by the GSD and achievement in anatomy and physiology. Factor analysis also shows that the GSD measures only a single bipolar scale of sequential vs. random ability rather than two bipolar scales comprising four learning styles, as suggested by Gregorc. These findings question the validity of the GSD and recommend discontinuing its use as an indicator of learning styles.

Myers-Briggs psychological type and achievement in anatomy and physiology.

Results from the Myers-Briggs Type Indicator (MBTI) for 259 nursing students were compared with their achievement on examinations in an undergraduate course in anatomy and physiology. Factor analysis demonstrated that no relationship existed between any of the eight individual personality traits purported to be measured by MBTI (i.e., E, Extrovert; I, Introvert; S, Sensing; N, Intuition; T, Thinking; F, Feeling; J, Judging; P, Perceiving) and examination scores in this course. The analysis also showed that the bipolar scales S vs. N and J vs. P collapsed into a single bipolar scale (S/J vs. N/P). This means that the MBTI is only capable of measuring three bipolar scales of personality traits instead of four scales as currently claimed. Contrary to other findings, results from an analysis of variance revealed no meaningful relationship between course achievement and psychological types.

Trigeminal nuclear complex of the ferret: anatomical and immunohistochemical studies.

In order to establish the ferret as an animal model for studies of trigeminal pain, we describe the cytoarchitecture and neurochemistry of the trigeminal nuclear complex in the ferret and compare them to those of the cat and rat. The complex was divided as previously described, but the ferret differed in the extent of the nuclear boundaries. The neuroanatomical istribution of substance P-, calcitonin gene-related peptide-, galanin-, enkephalin-, serotonin-, somatostatin-, neuropeptide Y-, and neurotensin-immunoreactivity was determined throughout the rostrocaudal extent of the complex. In subnucleus caudalis, substance P-, calcitonin gene-related peptide-, enkephalin-, serotonin-, somatostatin-, neuropeptide Y-, and galanin-immunoreactivity was densest in laminae I and II. In subnucleus interpolaris, immunoreactivity for all the above neurochemicals was most dense along the lateral border and the ventral third of the caudal part of the subnucleus. Enkephalin-immunoreactive cell bodies were present in subnucleus caudalis and interpolaris. In subnucleus oralis, labelling for substance P, calcitonin gene-related peptide, galanin, enkephalin, and serotonin was most prominent in the dorsomedial part of the subnucleus. Somatostatin-immunoreactive cell bodies were distributed throughout the spinal nucleus. Labelling of serotonin, substance P, calcitonin gene-related peptide, galanin, enkephalin, and somatostatin was present in the main sensory nucleus. The motor nucleus contained fibers immunoreactive for substance P, enkephalin, serotonin and neuropeptide Y, and cell bodies immunoreactive for calcitonin gene-related peptide. The majority of neurotensin-immunoreactivity was found at the level of subnucleus caudalis, where it was densest in the trigeminal extension of the lateral cervical nucleus. The distribution of peptides in this species throughout the spinal nucleus is consistent with the notion that all the subnuclei may be involved in the processing of nociceptive inputs.

Effects of ethmoidal nerve stimulation on respiration-related neurones in the dorsal medulla of the cat.

Stimulation of the nasal mucosa produces a number of respiratory reflexes the afferent limb of which is provided by the ethmoidal nerve, a branch of the trigeminal nerve. In the cat this nerve terminates within the trigeminal nucleus. It has no direct projection to brainstem respiratory centres. This study examines the response of respiratory-related neurones in the nucleus of the solitary tract (NTS) to ethmoidal stimulation. It demonstrates that these neurones show both excitatory and inhibitory responses to ethmoidal stimulation. Thus, the NTS appears to be involved in respiratory reflexes initiated by stimulation of the nasal mucosa.

The role of medical instructional resources in a three-year systems-based curriculum.

This article focuses on a unique method of approaching medical education. It outlines the role of a service-based medical instructional resources unit within a three-year curriculum and emphasizes the consolidation of an instructional philosophy in one centralized learning resource center. This dynamic approach incorporates the evolving technological tools of communication and may serve as a model for other educational institutions considering a break from a traditional four-year rigid curriculum to a more flexible, self-paced learning environment.

The inhibitory effect of halothane on the emetic response in the ferret.

Emesis and nausea are often associated with anaesthesia and continue to be a common clinical problem. Past clinical studies have demonstrated that halothane produces a higher incidence of vomiting compared with other anaesthetics, but some investigators have described an antiemetic effect. The purpose of this study was to investigate the effects of various doses of halothane on the emetic response in the decerebrate ferret. Following a control emetic response, a maximum of six increasing cumulative concentrations of halothane were delivered. At the end of each delivery period, the supradiaphragmatic vagal communicating branch, which has been shown to reproducibly elicit vomiting, was electrically stimulated and the emetic response was monitored. An increase in halothane concentration produced a marked depression of tongue, abdominal muscle, and diaphragm EMG activity as well as a decrease in central venous pressure. Licking, a prodromal response comparable to nausea in the human, appeared to be most sensitive. An increase in latency of the emetic response occurred as the concentration of halothane was increased. All phases of the response were observed at concentrations below 0.6 vol% halothane. At 0.6 vol% halothane, 75% of the animals vomited. At higher concentrations, the emetic response was completely abolished. One hour post-halothane, all latencies had returned to near control values. The methods utilized in this study provided a model that was not complicated by a large number of variables usually present in clinical studies. These data demonstrate that halothane exerts an inhibitory, concentration-dependent, and reversible effect on the emetic response in the ferret and provide further support that halothane alone does not possess emetic properties at clinical properties at clinical concentrations.

Characterization of cat nasal afferents and brain stem neurones receiving ethmoidal input.

Stimulation of the nasal mucous membrane can initiate protective reflexes, particularly sneezing and apnea. Very little is known about the receptors in the nasal cavity responsible for initiating these reflexes, which are thought to be mediated by trigeminal rather than olfactory pathways. In the cat, the ethmoidal branch of the ophthalmic division of V carries this afferent information. The objectives of the present study were to determine a set of adequate nasal receptor stimuli capable of initiating these protective reflexes; to characterize the types of information carried in the ethmoidal nerve afferents, by recording from single fibers dissected from the nerve; to determine the conduction velocities of these afferents, by recording from the cell bodies of ethmoidal afferents in the trigeminal ganglion; and to study the second-order neurones in the brain stem on which these afferents make contact. Results of single fiber recording indicated that, in addition to being tactile, approximately half of the neurones studied also responded to noxious chemical stimuli. The conduction velocity of the majority of these afferents were found to be in the A-delta range. Second-order neurones in spinal trigeminal nucleus which had an input from the ethmoidal nerve could be divided into two classifications: (i) low threshold mechanoreceptive (LTM) neurones which received light tactile input and did not respond to noxious chemical or mechanical stimuli applied to the nasal cavity, and (ii) wide dynamic range (WDR) neurones which responded to both noxious and nonnoxious chemical or mechanical stimuli applied to the nasal cavity.

Evidence for the presence of substance P in cat nasal receptor afferents.

The afferents of the nasal receptors responsible for many upper airway protective reflexes are carried in the ethmoidal branch of the ophthalmic division of the trigeminal nerve. Previous electrophysiological studies indicate that a significant number of ethmoidal afferents respond to noxious stimuli applied to the nose. The objective of the present study was to identify ethmoidal nerve cell bodies within the trigeminal ganglion which demonstrated the presence of the neurotransmitter substance P (SP). SP is believed to be involved in the relay of nociceptive information. A double-labelling technique was employed and involved tracing the afferents to their cell bodies using horseradish peroxidase (HRP) and subsequent identification of SP-immunoreactivity within HRP-filled cells using monoclonal antibody immunohistochemistry. SP-immunoreactive cell bodies constituted 43 per cent-50 per cent of the total number of labelled ethmoidal cell bodies within the trigeminal ganglion. Although ethmoidal cell bodies were much smaller than the overall population of trigeminal ganglion cells, the size of SP-immunoreactive ethmoidal cell bodies was not significantly different from that of ethmoidal cell bodies not exhibiting SP-immunoreactivity.

Connections of a vagal communicating branch in the ferret. II. Central projections.

There is increasing interest in the central mechanisms involved in the regulation of gastrointestinal function. The ferret is becoming widely used for research in this area. However, knowledge of the brain stem organization of this species is inadequate. As part of an on-going study designed to provide information regarding the site of termination of abdominal afferents, the central connections of a supradiaphragmatic vagal communicating branch were determined in the ferret through the use of the horseradish peroxidase (HRP) tracing technique. The branch was exposed using a thoracotomy and HRP crystals were applied to the cut ventral end of the branch. Following a 72 hour survival period, the animals were reanesthetized and perfused. The brain stem was removed and processed using the tetramethylbenzidine method. Afferent terminals were found bilaterally in the nucleus of the solitary tract (nTS), area postrema (AP), the dorsal motor nucleus of the vagus (DMV), the external cuneate nucleus (ECN) and the principal subnucleus of the inferior olive (IOP). This is the first study of a brain stem projection of a specific vagal branch in this species, and demonstrates the similarities and differences which exist between the ferret and other species.

Connections of a vagal communicating branch in the ferret. I. Pathways and cell body location.

In contrast to most other species, ferrets possess a single communicating branch connecting the dorsal and ventral vagal trunks immediately rostral to the diaphragm. This branch is being used in physiological studies of gastrointestinal function and emesis. However, the fibre routes which pass through this branch are not known. In this study, the afferent and efferent pathways within this supradiaphragmatic vagal communicating branch of the ferret were studied through the use of the horseradish peroxidase (HRP) tracing technique. The region of the branch was exposed using a thoracotomy and HRP crystals were applied to one of the following: (A) the ventral end of the communicating branch, (B) the dorsal end of the communicating branch, (C) the distal end of the dorsal vagal trunk rostral to the communicating branch or (D) the distal end of the ventral vagal trunk rostral to the communicating branch. Following a 72 hour survival period, the animals were reanaesthetized and perfused. The superior cervical and nodose ganglia and the brain stem were processed using the tetramethylbenzidine method. Following application of HRP to the cut ventral end of the communicating branch, labelled cell bodies were found in the left and right nodose ganglia and in the left dorsal motor nucleus of the vagus. After HRP application to the cut dorsal end of the communicating branch, labelled cells were found in the left and right nodose ganglia. No HRP containing cell bodies were found following HRP application to the cut distal end of either the dorsal or the ventral vagal trunk. These results indicate that several afferent pathways exist within the branch, although only one consistently labelled efferent pathway was found.

Projections of the internal branch of the superior laryngeal nerve of the cat.

The internal branch of the superior laryngeal nerve (iSLN) conveys sensory afferent information from receptors located in the laryngeal mucosa. The objectives of this study were: to determine the specific anatomical location of iSLN cell bodies within the nodose ganglion; to ascertain whether the jugular ganglion might also contain iSLN afferent bodies; to determine whether the iSLN contains sympathetic efferents originating in the cervical sympathetic ganglion; to determine whether the cell bodies of these efferents, if present, are localized within a specific region of this ganglion and to trace the transganglionic projection of iSLN afferents into the brain stem. Horseradish peroxidase was applied to the iSLN in ten adult cats. Following a survival period of 72 hours, the animals were sacrificed and the tissue was processed according to the tetramethylbenzidine method. Reaction product was localized in the rostral end of the nodose ganglion extending into the exiting vagus nerve, in the caudal end of the jugular ganglion and in the posterior portion of the cervical sympathetic ganglion. Transganglionic projections to the nucleus tractus solitarius were localized primarily in the dorsolateral subnucleus with substantial amounts of reaction product also in the intermediate and interstitial subnuclei. Except for a small bilateral projection observed in the commissural subnucleus, no other projections were seen to any other brain stem structures.

Central projections of the ethmoidal nerve of the cat as determined by the horseradish peroxidase tracer technique.

The ethmoidal nerve innervates the nasal mucosa and constitutes the afferent limb of several upper airway protective reflexes. Protective reflexes, such as sneezing, coughing, and apnea, are those reflexes that either expel foreign substances from the respiratory tract or stop them from gaining access to the lungs. The afferents for nasal receptors are thought to be a part of the trigeminal system rather than olfactory in nature. The objective of this study was to localize the cell bodies of these ethmoidal afferents and to trace the central projections of these neurons. Horseradish peroxidase was applied to the ethmoidal nerve in 11 adult cats. Following a survival period of 48-72 hours, the animals were killed and the tissue was processed according to the tetramethylbenzidine method. Reaction product was localized in cell bodies within the trigeminal ganglion, concentrated caudal to the entrance of the ophthalmic trunk of the trigeminal nerve. Transganglionic projections to the spinal trigeminal nucleus were localized primarily in the subnucleus interpolaris and in layers I and II of the subnucleus caudalis. There was also reaction product in cell bodies within the mesencephalic trigeminal nucleus. These results are in keeping with projections of other ophthalmic division receptor afferents, such as the cornea and the supraorbital nerve.

Modification of motor output to compensate for unanticipated load conditions during rapid voluntary movements.

Mechanisms responsible for load compensation during fast voluntary movements were investigated in 20 normal subjects trained to carry out rapid wrist flexions against a standard load. When an unanticipated increase in load occurred, there was a compensatory increase in agonist EMG and decrease in antagonist EMG. Unanticipated decreases in load produced reciprocal changes with a decrease in agonist EMG and an increase in antagonist EMG. The latency of these EMG changes was quite short and compatible with a spinal reflex mechanism rather than a long loop response. The results suggest that mechanisms exist at the spinal level to allow rapid modification of motor programs when unanticipated load conditions are encountered on initiation of movement.

Presynaptic excitability changes induced in the solitary tract endings of laryngeal primary afferents by stimulation of nucleus raphe magnus and locus coeruleus.

To determine if the nucleus raphe magnus (NRM) and locus coeruleus (LC) might exert presynaptic modulatory influences on the endings in the medullary solitary tract nucleus of laryngeal afferents, multi-unit and single unit laryngeal afferent activity was recorded in the nodose ganglion in chloralose-anaesthetized cats. The afferents could be orthodromically activated by superior laryngeal nerve stimulation and antidromically activated from the solitary tract nucleus. An increase in antidromic excitability of laryngeal afferents, which was considered a reflection of primary afferent depolarization, could be induced by either NRM or LC conditioning stimuli and lasted for 300-400 msec. The findings suggest that presynaptic mechanisms may contribute to the suppression of solitary tract neuron or reflex activities induced by NRM or LC stimulation.

Suppressive influences from periaqueductal gray and nucleus raphe magnus on respiration and related reflex activities and on solitary tract neurons, and effect of naloxone.

Possible opiate-related descending influences from the periaqueductal gray matter (PAG) and nucleus raphe magnus (NRM) were tested on the activity of neural systems involved in respiration and related reflex functions in cats. Stimulation of PAG and NRM could powerfully suppress the simple buccopharyngeal reflexes of jaw-opening and tongue-protrusion and the more complex reflexes of coughing and swallowing; respiration in contrast appeared to be only weakly influenced. The reflexly induced responses of 57 single reflex interneurons recorded in the solitary tract nucleus (NST) could also be markedly suppressed by PAG and NRM conditioning stimulation. In contrast, the rhythmic activity of 30 respiratory neurons in NST was not abolished by PAG and NRM stimuli but most did show a decrease in the peak firing frequency of each rhythmic burst. The suppressive effect of PAG and NRM stimulation on the reflexes and NST reflex interneurons could be reduced by the intravenous administration of naloxone. These studies indicate that neuronal functions associated with respiration and respiratory-related activities can be suppressed by descending influences from PAG and NRM that are in part opiate-related. The observations add to the accumulating evidence that the raphe system is implicated in functions other than pain and its control, and they may also be relevant to clinical observations of opiate-induced effects on respiration and the cough reflex.