James A. Holloway

Responses of caudal raphe neurons to peripheral somatic stimulation

Abstract Response characteristics of single neurons in the caudal region of the brain stem raphe were recorded extracellularly in both chloralose-anesthetized and decerebrate cats. Each animal was immobilized with gallamine triethiodide. Natural stimuli included light touch, pressure, hair and joint movements, temperature, noxious pinch, and an 80-db click. Electrical stimuli to hindlimb cutaneous and muscular nerves at 1.5 and 10 times threshold were delivered at a frequency of one per 3 sec. Seventy-four neurons shown histologically to be located in the nucleus raphe pallidus and nucleus raphe magnus responded with increased firing to a variety of the natural stimuli used, excluding joint movement. Deep pressure applied to proximal musculature was particularly effective in evoking a response. Units generally demonstrated large receptor field characterisics. Unlike other units in n. raphe pallidus and n. raphe magnus, the most rostral neurons in n. raphe magnus responded to auditory and noxious stimulation and to extremes in temperature. No somatotopic organization could be discerned. The response to electrical stimulation consisted of an 18- to 35-msec latency burst of impulses followed by a silent period having a mean duration of 215 and 96.8 msec for high and low stimulation intensities, respectively. Similarities between response characteristics of raphe units and reticular formation neurons suggest that they are functionally related.

Spectral mechanisms of the compound eye in the fireflyPhotinus pyralis (Coleoptera: Lampyridae)

SummaryElectroretinograms (ERG) were recorded from dark- and chromatic-adapted compound eyes in the dusk-active firefly,Photinus pyralis ♂, at different wavelengths ranging from 320 to 700 run and over 4.5 log units change in stimulus intensity. ERG waveforms differed in the short (near-UV and violet) and long (yellow) wavelengths (Fig. 1). Waveform differences were quantitated by analysis of rise and fall times as a function of the amplitude of the response. Rise times were found to be relatively constant for all stimulus wavelengths. However, variations in the fall times were detected and followed characteristically different functions for short and long wavelengths (Fig. 2).No significant differences in the slopes of the Vlog-I curves at different stimulus wavelengths were observed (Fig. 3).Spectral sensitivity curves obtained from the ventral sector in dark- and chromatic-adapted conditions revealed peaks in the short (λ max 400 nm: Fig. 4;λ max 430 nm: Fig. 5 A; andλ max 380 nm; Fig. 5B) and long (λ max 570 nm: Figs. 4, 5) wavelengths, suggesting the presence of two spectral mechanisms. The long wavelength (yellow) mechanism was in close tune with the species bioluminescence emission spectrum (Fig. 4B).

Naloxone application to the ventrolateral medulla enhances the respiratory response to inspired carbon dioxide

Previous studies have shown that systemic administration of the opiate antagonist naloxone potentiates the ventilatory response to inspired carbon dioxide. The present study was designed to localize the site of action of naloxone for increasing the respiratory chemosensitivity to inhaled carbon dioxide (CO2) in cats. Naloxone applied topically to the caudal chemosensitive area on the ventral medullary surface (VMS) during hypercapnic breathing produced a 75% greater increase in minute ventilation than hypercapnic breathing alone. Furthermore, hypercapnic breathing produced a 200% increase in neuronal activity of VMS chemosensitive cells; this was further increased 120% by naloxone. It is concluded that naloxone increases the sensitivity of neurons in the caudal respiratory chemosensitive area of cats to hypercapnia, and that endogenous opiates may act as modulators at VMS chemosensitive sites during hypercapnic breathing.

Cutaneous receptive field characteristics of primary afferents and dorsal horn cells in the avian (Gallus domesticus)

Abstract Activity from 118 single dorsal horn cells was recorded extracellularly in the lumbar spinal cord of chickens anesthetized with sodium pentobarbital. Activity in 75 primary afferent fibers was also recorded from lumbar dorsal rootlets. The loci of the dorsal horn cells were histologically verified in frozen, formalin-fixed spinal cord sections in specific regions of the dorsal gray matter. The properties of the cutaneous receptive fields (RFs) of both primary afferent fibers and dorsal horn cells were analyzed. The RFs were categorized into three classes: class 1 encompassed an area equivalent to one digit; class 2 an area equivalent to an entire foot; and class 3 all areas larger than class 2. Seventy-eight percent of class 3,30% of class 2, and 20% of class 1 dorsal horn cells showed gradients of sensitivity. Further, 70% of dorsal horn cell RFs were shown to be class 3, 25% were class 2, and 5% were class 1. There appeared to be a correlation between size of the RF and depth of recording in the dorsal horn, with the majority of class 3 RFs recorded in the deeper laminae. Thirteen percent of the dorsal horn cells that responded in a graded fashion to a wide range of stimulus strengths (dynamic range) were partially surrounded by inhibitory fields. Intense cooling of both feathered and nonfeathered skin was effective in exciting 4% of the dorsal horn cells. On the average, RFs of the primary afferent fibers were smaller than those of the dorsal horn cells. The vast majority of RFs (85%) of the primary afferent fibers were of class 1 and 2 sizes as opposed to 30% of dorsal horn cells. Other characteristics of RFs of the primary afferent fibers (i.e., dynamic range, gradient of sensitivity, etc.) were similar to those of the dorsal horn cells. The present study provides additional observations extending the knowledge of RF properties and of the interaction at the synaptic relay between the primary afferent fibers and the dorsal horn cells of submammalian vertebrates.

Analysis of the sexual dimorphism in the basiocciptal portion of the dog’s skull

Sexual differences in the basioccipital portion of the skull of dogs have been described and an index is presented which reliably predicts the sex of the skull. 92 dolichocephalic skull (44 male, 48 female) from mongrel dogs were used. In the basioccipital region of the male skulls, a triangular area, which extends from the basion to a line joining the medialmost points of the two jugular foramina, appears narrow and elevated. The pharyngeal tubercle is also prominent. In female skulls the rostral angle of this triangle is wider and the triangular area seems smoother and flat. The anterior half of the female basioccipital portion is wider and smoother than in the male skull. In order to quantify the observed differences, four indices were calculated. All of the indices were statistically significant. However, only index IV could be reliably used in predicting the sex of an unknown skull: (formula: see text) was derived from breadth IV (distance between the two temporo-occipital fissures at their lateralmost points) and length II (distance between the basion and a line drawn between the two medialmost points of the jugular foramina in the midline). Values of less than 123 for male and greater than 136 for female placed the skulls in their proper sex group. Skulls that had intermediate values could be placed in correct sex grouping only in conjunction with strong observational criteria. It is suggested that in absence of such strong observational criteria these skulls may belong to immature or castrate animals.

Responses of dorsal horn cells of Gallus domesticus to cutaneous and peroneal nerve stimuli

Abstract Single dorsal horn neurons have been recorded extracellularly in the lumbar spinal cord of chickens anesthetized with sodium pentobarbital and anemically decerebrated. The location of units in the dorsal horn was marked by the electrophoretic deposition of fast green dye from the recording electrode. Seventy percent of 125 units studied were activated by mechanical, thermal, and/or electrical stimulation. Thirty percent were responsive only to electrical stimulation of the ipsilateral peroneal nerve. Some units fired spontaneously with brief bursts of 2 to 4 spikes per burst with varying interburst intervals. Frequently, spontaneously firing units could be inhibited by noxious pinch on the distal region of the comb. Chicken dorsal horn cell responses bear some resemblance to those of mammals, though with certain differences. Some may fire spontaneously in an irregular manner and show properties of convergence. Continuous background activity was uncommon in cells that were excited exclusively by electrical stimulation. Evidence of a prolonged discharge was apparent when the peroneal nerve was stimulated at A-Δ intensity. A progressive increase in frequency and duration of discharge with controlled repetitive C-fiber stimulation, i.e., “windup”, was nerver seen. Several units responded to restricted feather movement. There was no physiological evidence of identifiable zones of concentration of dorsal horn cells in the various laminae (IV to VI) investigated. The present studies provide physiological evidence that supraspinal descending influences are capable of modulating afferent input from chicken dorsal horn cells. The data further suggest that the filtering effect of dorsal horn cells is seen early in phylogeny. The results are described with reference to similarities to and differences from mammalian dorsal horn cell responses.

A survey of receptor mechanisms of the bullfrog. (R. catesbieana).

Abstract The majority of frog skin mechanoreceptors (units) examined responded to light touch. Respectively, fewer units responded to moderate pressure, joint movement, noxious pinch, and electrical stimulation. Most units possessed a wide dynamic range. A few of the units that responded to touch also responded to electrical stimulation. Both tonic and phasic response patterns were observed. A linear relationship between joint flexion and frequency of impulse discharge was revealed. Nociceptive endings adapted slowly and generated no spontaneous activity. Such units were frequently sensitive to temperature changes. The data suggest that, although some receptors may detect more than one type of sensation, a significant degree of receptor specificity exists at this level of phylogenetic development.

Quasi-entrainment and other modal behavior in BVP oscillators interconnected by activity dependent coupling

Abstract Quasi‐entrainment, characterized by a fluctuating latency in the presence of one‐to‐one frequency entrainment, has been elicited in two Bonhoeffer‐Van der Pol type oscillators coupled together on a digital computer via a feedback network that is a function of the average activities of the adjoined units. Such behavior was observed only when specially constructed sigmoidal coupling functions were in place. In contrast, with linear functions in place, the constellation of resulting stable or unstable equilibrium points made the system orbitally stable or unstable depending on initial conditions. Based on the coupling function and system architecture a criterion for predicting ultimate behaviors is developed and tested. Results are contrasted with fluctuating latencies previously observed in loosely coupled heart cell aggregates.