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Biomedical subjects

W W Blessing

Publications and source records attributed to W W Blessing.

At least 37 records · Page 2Linked to original sources
PubMed2000

Cutaneous vascular bed is not involved in arterial pressure changes elicited by increasing or decreasing the activity of inhibitory vasomotor neurons in caudal ventrolateral medulla in rabbits.

We determined whether caudal ventrolateral medulla (CVLM) vasodepressor neurons tonically inhibit vasomotor tone in the ear in anesthetized rabbits. Injection of L-glutamate (10 nmol in 100 nl) into the CVLM decreased arterial pressure and increased superior mesenteric conductance. Ear conductance decreased (0.43+/-0.06 to 0. 33+/-0.05 cm s(-1) per mmHg, n=15 injections, 12 rabbits, P<0.01). Conversely, bilateral injection of gamma-aminobutyric acid (100 nmol in 100 nl) increased arterial pressure and decreased superior mesenteric conductance. At the same time ear conductance increased (0.39+/-09 to 0.48+/-0.27 cm s(-1) per mmHg, n=8 injections, eight rabbits, P<0.05). Results suggest that ear vessels are not tonically inhibited by the CVLM vasodepressor neurons. Presympathetic motoneurons regulating cutaneous flow may be excited, rather than inhibited, by the CVLM neurons.

Animals↗
PubMed2000

Regional blood flow and nociceptive stimuli in rabbits: patterning by medullary raphe, not ventrolateral medulla.

1. Regional blood flow was measured with Doppler ultrasonic probes in anaesthetized rabbits. We used focal microinjections of pharmacological agents to investigate medullary pathways mediating ear pinna vasoconstriction elicited by electrical stimulation of the spinal tract of the trigeminal nerve or by pinching the lip, and pathways mediating mesenteric vasoconstriction elicited by electrical stimulation of the afferent abdominal vagus nerve. 2. Bilateral injection of kynurenate into the rostral ventrolateral medulla reduced arterial pressure and prevented the mesenteric vasoconstriction and the rise in arterial pressure elicited by abdominal vagal stimulation. However, kynurenate did not prevent ear pinna vasoconstriction or the fall in pressure elicited by trigeminal tract stimulation. Similar injections of muscimol also failed to prevent the trigeminally elicited cardiovascular changes. 3. Injections of kynurenate into the raphe-parapyramidal area did not diminish trigeminally elicited ear vasoconstriction or the depressor response. However, injections of muscimol substantially reduced or abolished the trigeminally elicited ear vasoconstriction, without affecting the depressor response. Raphe-parapyramidal muscimol injections also entirely abolished ear vasoconstriction elicited by pinching the rabbit's lip. 4. The trigeminal depressor response does not depend on either the rostral ventrolateral medulla or the raphe-parapyramidal region. 5. Mesenteric vasoconstriction elicited by stimulation of the afferent abdominal vagus nerve is mediated via the rostral ventrolateral medulla, but ear vasoconstriction elicited by lip pinch or by stimulation of the trigeminal tract is mediated by the raphe-parapyramidal region. Our study is the first to suggest a brainstem pathway mediating cutaneous vasoconstriction elicited by nociceptive stimulation.

Animals↗
PubMed2000

Carotid and cardiopulmonary chemoreceptor activity increases hippocampal theta rhythm in conscious rabbits.

We have examined whether activation of carotid artery chemoreceptors causes alerting in conscious rabbits. Injection of phenylbiguanide (a 5-hydroxytryptamine(3)-receptor agonist) into the common carotid artery of conscious rabbits increased the proportion of theta rhythm in the hippocampal EEG, commencing in the first 5-s epoch after the injection. Intravenous injection of phenylbiguanide also increased the proportion of theta rhythm in the hippocampal electroencephalogram (EEG), but the onset of the change was not until the second 5-s epoch following injection. Injection of Ringer solution, either into the common carotid artery or into the marginal ear vein, did not affect the hippocampal EEG. Results suggest that phenylbiguanide-mediated activation of carotid and cardiopulmonary chemoreceptor afferents alerts the animal, as assessed by induction of theta rhythm in the hippocampal EEG. This alerting response presumably reflects the action of neural inputs that enter the brain with the carotid sinus nerve at the level of the medulla oblongata.

Anesthesia↗
PubMed2000

Herpes simplex replication and dissemination is not increased by corticosteroid treatment in a rat model of focal Herpes encephalitis.

Neurological damage in Herpes simplex type 1 encephalitis results from neuronal cell death secondary to viral invasion, and from inflammatory changes and cerebral oedema secondary to the immune response to the virus. Corticosteroids could have an important role in the management of Herpes simplex encephalitis because their anti-inflammatory action reduces cerebral oedema. However their use has been limited by concerns that their immunosuppressive actions could increase viral replication and spread. The present study examined this issue in a rat model in which injection of HSV-1 into the cervical vagus nerve produced a well-defined focal encephalitis, characterised by an orderly progression of the virus through central neural pathways connected with vagal afferent termination sites in the medulla oblongata. After injection of HSV-1, rats were treated twice a day, either with vehicle (saline, 400 microl i.p.), with acyclovir (30 mg/kg i.p.), with dexamethasone (5 mg/kg i.p.), or with both acyclovir and dexamethasone. Animals were sacrificed after 72 h, and viral load in different brain regions was quantified by computer-assisted measurement of the area occupied by immunohistochemical reaction product. Treatment with acyclovir reduced viral load to 17 +/- 5% of the saline value (P < 0.01). After dexamethasone treatment, the viral load (63 +/- 13% of the saline value) was also reduced (P < 0.05). Treatment with both acyclovir and dexamethasone reduced viral load to 26 +/- 8% of the saline value (P < 0.01 compared with saline, and P > 0.05 compared to acyclovir alone). Our results confirm the effectiveness of acyclovir in a new model of HSV-1 infection, and provide evidence that corticosteroids do not inhibit the antiviral action of acyclovir. In addition corticosteroids may decrease the extent of infection in their own right. The acute time course studied in our model parallels the time course of acute Herpes simplex encephalitis in humans. Our data suggests that corticosteroids are not detrimental when combined with acyclovir in the management of this condition.

Acyclovir↗
PubMed1999

Synchronous changes in ear and tail blood flow following salient and noxious stimuli in rabbits.

Simultaneous recordings were made of ear and tail blood flow during alerting responses to salient environmental stimuli in conscious rabbits, and during electrical stimulation of the spinal trigeminal tract and raphe pallidus in anesthetized rabbits. Blood flow fell in a highly correlated manner (Pearson coefficient ranging from 0.52 to 0.95) in these experimental situations. Salient stimuli in conscious rabbits, and noxious stimuli in anesthetized rabbits appear to cause a generalized vasoconstriction in cutaneous beds.

Animals↗
PubMed1999

Subpopulations of sympathetic neurons project to specific vascular targets in the pinna of the rabbit ear.

We have characterised sympathetic neurons projecting to a range of cutaneous and striated muscle vascular targets in the pinna of the rabbit ear by examining neurotransmitter-related enzymes and peptides in perivascular axons and in somata identified by retrograde axonal tracing. Fast Blue was injected into one of seven sites in each pinna (n = 21 pinnae). The soma cross-sectional area and immunoreactivity (IR) for tyrosine hydroxylase (TH) and neuropeptide Y (NPY) were determined for each of 2,041 retrogradely labelled neurons in the ipsilateral superior cervical ganglion (SCG) or stellate ganglion (StG). Larger neurons in the SCG with TH-IR but not NPY-IR projected predominantly to veins along the medial edge of the pinna. Larger neurons in the StG with TH-IR but not NPY-IR projected predominantly to arteries and veins in the tip and lateral edge of the pinna. Smaller neurons in the SCG with IR to both TH and NPY projected predominantly to arteries in the striated muscles at the base of the ear. The smallest retrogradely labelled neurons in the SCG or StG lacked TH-IR but contained NPY-IR and projected almost exclusively to arterial vessels in the lateral muscle at the base of the ear. Thus, somata of sympathetic neurons projecting to cutaneous versus striated muscle vessels or to different regions of the cutaneous bed could be distinguished by a combination of location, size, and immunohistochemical profile. Consequently, regulation of blood flow within the rabbit ear is likely to involve coordination between neuronal pathways containing neurochemically and morphologically distinct populations of sympathetic neurons.

Animals↗
PubMed1999

Raphe pallidus and parapyramidal neurons regulate ear pinna vascular conductance in the rabbit.

We have determined whether alteration of neuronal function in raphe pallidus and the parapyramidal region alters ear blood flow, measured by an implanted Doppler ultrasonic probe, in anesthetized rabbits. Injection of GABA (5 nmol in 50 nl) increased ear flow from 6.0 +/- 1.0 to 31 +/- 10 kHz, without changing arterial pressure or heart rate. Focal electrical stimulation of raphe pallidus at low current amplitude caused ear pinna blood flow to fall from 41 +/- 6 to 9 +/- 3 kHz, again with little or no change in arterial pressure. These excitatory and inhibitory stimuli did not affect superior mesenteric blood flow. The fall in ear flow in response to electrical stimulation of raphe pallidus was not prevented by tetrodotoxin-mediated inhibition of the rostral ventrolateral medulla. Thus raphe pallidus and parapyramidal region may regulate ear pinna vascular conductance via a direct spinal projection.

Animals↗
PubMed1999

Medullary projections of rabbit carotid sinus nerve.

In New Zealand white rabbits, cholera-toxin HRP was injected into the carotid sinus nerve just proximal to the carotid sinus. After survival periods of 3-5 days the rabbits were anesthetized and the brain fixed with aldehyde solution. Transverse sections were cut on a sledge microtome and the sections reacted with the tetramethylbenzidine procedure. HRP-positive fibers entered the ipsilateral dorsolateral medulla at the level of the acoustic tubercle, joining the tractus solitarius. Positive fibres were found principally ipsilaterally in four regions of the medulla: in the caudal two thirds of the nucleus tractus solitarius, in its dorsolateral regions and, more caudally, in its commissural subdivision; in the dorsolateral aspect of the spinal nucleus of the trigeminal nerve; in the region ventral and ventrolateral to the tractus solitarius (extending beyond the nucleus tractus solitarius); and in the ventrolateral medulla oblongata.

Animals↗
PubMed1999

Amygdala co-ordinates sudden falls in ear pinna blood flow in response to unconditioned salient stimuli in conscious rabbits.

Tetrodotoxin (10 pmol in 300 nl of Ringer), injected bilaterally into the region of the amygdala in conscious rabbits, virtually abolished the sudden falls in ear pinna blood flow that normally occur in response to salient environmental stimuli (touching the animal's fur, slightly moving its cage, or applying or removing a drape covering the cage). Time spent at 0-20% of maximum flow values during a 10 min observation period, commencing 15 min after injection of tetrodotoxin, significantly decreased compared with the pre-injection control period (30+/-14 s compared with 286+/-24 s, P<0.01, n=8 rabbits) and the time spent at 70-100% of maximum flow values significantly increased (521+/-36 s compared with 127+/-29 s, P<0.01). Vehicle was injected on the day before tetrodotoxin injections in four of eight rabbits and on the day after tetrodotoxin injections in the other four rabbits, in a counterbalanced design. Rabbits fully recovered from the effects of tetrodotoxin in one day. Vehicle did not significantly affect the time spent at different flow percentage values. Falls in ear blood flow elicited by noxious stimuli (ear pinch, inhalation of formaldehyde vapor) occurred in a normal pattern after tetrodotoxin. Amygdaloid circuitry is thus necessary for the production of falls in ear pinna blood flow that occur in response to unconditioned non-noxious stimuli, but not for the falls that occur in response to unconditioned noxious stimuli in rabbits. In humans, the amygdaloid region may also be involved in co-ordinating falls in cutaneous blood flow occurring in response to salient or anxiety-evoking stimuli. Thus, discovery of the neural pathways by which amygdaloid circuitry alters ear pinna blood flow in rabbits may elucidate the manner in which similar cardiovascular changes occur in humans during anxiety reactions.

Amygdala↗
PubMed1998

Constriction of the ear pinna vascular bed accompanies the trigeminal depressor response in rabbits.

Electrical stimulation of the spinal tract of the trigeminal nerve at 5 Hz to elicit the trigeminal depressor response in anesthetized rabbits also causes an acute fall in ear pinna blood flow to near zero levels (from 31+/-8 to 2+/-2 kHz, n = 5, P < 0.01). This active vasoconstriction in the ear artery contrasts with the active vasodilation in femoral, renal and mesenteric arteries known to be part of the trigeminal depressor response. The selective vasoconstriction observed in the ear bed in response to noxious stimulation in anesthetized rabbits is similar to the vigorous acute vasoconstriction occurring in this cutaneous bed in conscious rabbits responding to salient environmental stimuli.

Animals↗
PubMed1998

Destruction of locus coeruleus neuronal perikarya after injection of anti-dopamine-B-hydroxylase immunotoxin into the olfactory bulb of the rat.

Saporin, a ribosome-inactivating protein, was coupled to a monoclonal antibody to dopamine-B-hydroxylase (DBH) and injected unilaterally into the olfactory bulb of rats. After 4-13 days survival, the rat brain was processed histologically and the locus coerulei (LC) examined with Nissl and anti-DBH staining. There were degenerating dendrites in surviving LC neurons on the side ipsilateral to the immunotoxin-injected olfactory bulb. The number of Nissl-positive LC neurons in a transverse section through the caudal one third of the LC was reduced from 116+/-10 to 50+/-8 neurons (P < 0.01, n = 7) and the number of DBH-positive neurons in the more rostral LC sections was reduced from 13+/-2 to 5+/-1 (P < 0.05, n = 4). Our results indicate that it is possible to lesion LC neurons via retrograde intraaxonal transport of saporin-anti-DBH immunotoxin from the olfactory bulb.

Animals↗
PubMed1998

Cutaneous vasoconstriction with alerting stimuli in rabbits reflects a patterned redistribution of cardiac output.

1. In conscious rabbits, when alerting stimuli elicit vasoconstriction in the ear vascular bed, there is little or no associated change in cardiac output (CO), as measured by chronically implanted Doppler ultrasonic probes. 2. Local anaesthetic injected around the base of the ear substantially diminished the degree of the vasoconstriction elicited during responses. 3. Our results emphasize that selective cutaneous vasoconstriction, an integral part of the response to alerting stimuli in conscious animals, is part of a patterned redistribution of the CO, organized by the brain.

Anesthesia, Local↗
PubMed1997

Parasympathetic innervation of cephalic arteries in rabbits: comparison with sympathetic and sensory innervation.

We investigated the distribution of parasympathetic, sympathetic, and sensory perivascular nerve fibers in rabbit cephalic arteries supplying the brain, exocrine glands, nasal mucosa, masseter muscles, tongue, and skin in the face and also examined cranial autonomic and sensory ganglia. NADPH diaphorase (NADPHd)-positive and vasoactive intestinal peptide-like immunoreactive (VIP-LI) neurons were located in the cranial parasympathetic ganglia. Neuropeptide Y (NPY)-LI neurons occurred mainly, and dopamine beta-hydroxylase (DBH)-LI neurons occurred exclusively, in the superior cervical (sympathetic) ganglion. Substance P (SP)-LI and calcitonin gene-related peptide (CGRP)-LI neurons occurred only in the trigeminal (sensory) ganglion. Therefore, it was assumed that NADPHd-positive and VIP-LI perivascular nerve fibers in cephalic arteries were parasympathetic, all DBH-LI and most NPY-LI fibers were sympathetic, and SP-LI and CGRP-LI fibers were sensory in nature. In the cerebral arteries, NADPHd-positive and VIP-LI varicose fibers were more numerous in the rostral than in the caudal half of the Circle of Willis. In the extracranial arteries, NADPHd-positive and VIP-LI fibers were most abundant in the lingual, lacrimal, and supraorbital arteries; sparse in the parotid and submandibular arteries; and absent in the ear artery. There was an obvious proximal-to-distal density gradient along individual cephalic arterial trees. In contrast, DBH-LI, NPY-LI, SP-LI, and CGRP-LI varicose nerve fibers were similar in density in all cephalic arteries and their branches. These neuroanatomical findings suggest that differential parasympathetic innervation in cephalic arteries may play a role in the partitioning of blood flow between different cephalic tissues.

Animals↗
PubMed1997

Cerebral blood flow in rabbits during the nasopharyngeal reflex elicited by inhalation of noxious vapor.

We used chronically implanted Doppler ultrasonic flow probes to measure internal carotid and vertebral blood flow during the nasopharyngeal reflex elicited by inhalation of formaldehyde vapor in conscious rabbits. Internal carotid flow gradually increased to 157 +/- 5% of baseline and vertebral artery increased to 123 +/- 9% of baseline, with maximum values reached approximately 20-40 s after administration of vapor, at a time when arterial pO2 had decreased from 80 +/- 3 to 53 +/- 4 mmHg. Increases in flow were associated with increases in vascular conductance. The delayed increases in cerebral blood flow contrasted with rapid decreases in ear and distal aortic flows, measured at the same time. Our results indicate that forebrain vascular conductance increases in response to inhalation of noxious vapor, possibly reflecting cerebrovascular events associated with hypoxemia.

Administration, Inhalation↗
PubMed1997

Preganglionic parasympathetic neurons projecting to the sphenopalatine ganglion contain nitric oxide synthase in the rabbit.

We have investigated the possible presence of nitric oxide synthase (NOS) and choline acetyltransferase (ChAT) in brainstem preganglionic parasympathetic neurons projecting to the sphenopalatine ganglion in rabbits, using combined retrograde axonal tracing and immunohistochemistry. Retrogradely labeled neurons were observed in the ipsilateral rostral medulla and caudal pons, in a region laterodorsal to the facial motor nucleus. Double-labeling experiments demonstrated that 75 +/- 5% of retrogradely labeled neurons contained NOS immunoreactivity, while all of retrogradely labeled neurons contained ChAT immunoreactivity. These observations suggest that nitric oxide could influence cholinergic transmission from preganglionic endings in the sphenopalatine ganglion.

Animals↗
PubMed1997

Acute increases in forebrain blood flow during altering responses in conscious rabbits.

We have previously shown that alerting responses (documented by appearance of theta rhythm in the hippocampal EEG) are associated with a characteristically timed acute vasoconstriction in the ear artery bed of the conscious rabbit. We have now determined what happens to forebrain blood flow (Doppler probe chronically implanted around the internal carotid artery) during similar alerting responses in conscious rabbits, comparing forebrain flow to simultaneously measured ear flow. During an alerting response, forebrain flow increased by 31 +/- 8% of baseline (n = 6, P < 0.01), with the increase commencing within 1 s of the stimulus, at approximately the same time as the decrease in ear flow. Arterial pressure increased from 77 +/- 3 to 81 +/- 3 mmHg (P < 0.01), so that internal carotid conductance increased from 0.17 +/- 0.02 to 0.20 +/- 0.02 kHz/mmHg (P < 0.01). During a 1 h continuous recording period in the laboratory there was a negative correlation between forebrain and skin flow, with the Pearson coefficient in individual rabbits ranging from -0.18 to -0.62 (n = 6, all correlations P < 0.01). During this period, forebrain blood flow was just as variable, from second to second, as distal aortic flow, but not as variable as ear blood flow. Our study thus demonstrates that alerting responses in rabbits are associated with rapid increases in cerebral vascular conductance. We believe that this is the first demonstration of this phenomenon in the conscious experimental animal.

Acoustic Stimulation↗