Robin A. Barraco

An atlas of the rat subpostremal nucleus tractus solitarius

The nucleus tractus solitarius (NTS) in the dorsal medulla is the principal visceral sensory relay nucleus in the brain. In the rat, numerous lines of evidence indicate that the caudal NTS at the level of the area postrema serves as a major integrating site for coordinating cardiorespiratory reflexes and viscerobehavioral responses. This region of the caudal NTS not only exhibits high densities of binding sites for an impressive array of transmitters and modulators but microinjections of many of these same neuroactive substances into the rat subpostremal NTS elicit pronounced cardiorespiratory and visceral response patterns. This report provides an abbreviated atlas of the rat subpostremal NTS consisting of a series of transverse, sagittal, and horizontal plates. Photomicrographs, together with their corresponding schematic drawings, are provided for the serial sections generated from each reference plane.

Central effects of adenosine analogs on locomotor activity in mice and antagonism of caffeine

Mice implanted with chronic indwelling cannulas were injected in the lateral cerebral ventricle with a series of adenosine analogs and the effects on spontaneous locomotor activity were recorded. All analogs produced dose-related decreases in locomotor activity. The relative order of potency for locomotor depression was: NECA much greater than L-PIA greater than CADO greater than D-PIA. Caffeine at the lowest dose produced a significant decrease in locomotor activity. At higher doses caffeine had no effect on locomotor activity but it did antagonize the depressant effects of NECA, a finding consistent with the notion that the central stimulant action of methylxanthines is due to their antagonism of central adenosine receptors.

Autopsy of an Egyptian mummy

The mummy studied by multidisciplinary approach, was Pum II, belonging to the Philadelphia Art Museum. Radiographic studies had indicated that it was in good condition. The extensive wrapping is described, and parasites and insects found are noted. Protein and lipid material were extracted and analyzed by various biochemical methods; the blood group was determined. Carbon-14 dating of the linen from the wrappings indicate a Ptolemaic date, 170±70 B.C. Amino acid racemization reaction can be used to estimate the age of organic material; this method is being investigated. The mummy wrappings are linen, with some cotton; this is an unusually early occurrence of the latter. Metals in the bone were analyzed by neutron activation analysis, which was not practicable because of the large amount of calcium present, and atomic absorption, which showed the lead content to be less than that of modern man, and mercury content to be about the same. -- AATA

Cardiovascular effects of microinjection of adenosine into the nucleus tractus solitarius

Rats were anesthetized with urethane and limited occipital craniotomy was conducted to expose the caudal medulla in the region of the obex. Microinjections of adenosine were made into the nucleus tractus solitarius and heart rate and blood pressure responses recorded. Adenosine produced dose-related decreases in blood pressure and heart rate. The data indicate that adenosine may play a neuromodulatory role in central cardiovascular control areas.

Cardiorespiratory response patterns elicited by microinjections of neuropeptide Y in the nucleus tractus solitarius

A limited occipital craniotomy was conducted on anesthetized, spontaneously breathing rats to expose the caudal medulla in the region of the obex. Microinjections of neuropeptide Y (NPY), a putative neuromodulator associated with catecholaminergic (CA) synapses, were made into the medial region of the caudal nucleus tractus solitarius (NTS) at the level of the posterior portion of the area postrema, an area of the NTS in which there is known to be a functional coexistence of cardiovascular and respiratory-related neuronal elements. This region of the caudal NTS in the rat is not only the principal site of termination of baro- and chemoreceptor afferents, but it also has profuse reciprocal connections with NPY-containing cardiorespiratory control regions in the hypothalamus and with other brainstem regulatory nuclei. Moreover, this same region of the rat NTS also shows very high densities of NPY binding sites. Cardiorespiratory responses were subsequently recorded for a 60-min test period following NPY administration. Microinjections of NPY, in the dose range of 10-100 pmol/rat, into the caudal NTS of intact rats produced significant dose-related reductions in mean arterial blood pressure, pulse pressure and minute volume. To a lesser extent, NPY microinjections also produced significant reductions in heart rate, respiratory rate and tidal volume. In a series of separate experiments, in an effort to ascertain the modulatory influences of rostral brain regions on these NPY-evoked, NTS-mediated cardiorespiratory response patterns, microinjections of NPY were made under identical anesthetic and experimental conditions in a group of rats wherein reciprocal connections between the NTS and rostral brain regions had been disrupted via supracollicular decerebration. In addition, since NPY microinjections were made into specific loci wherein afferent inputs from cardiopulmonary receptors are known to converge in the rat NTS, the effects of bilateral vagotomy on NPY-evoked, NTS-mediated cardiorespiratory response patterns were also examined in otherwise intact rats and under the same experimental conditions. The effects of NPY microinjections at the same dosage on NTS-mediated cardiorespiratory response patterns were subsequently compared among the intact, decerebrate and vagotomized rats. The results showed that whereas the hypotensive actions of NPY were not affected by decerebration, vagotomy significantly increased the magnitude of the hypotension elicited by NPY microinjections in comparison to the intact and decerebrate groups of rats. On the other hand, vagotomy abolished the NPY-evoked bradycardia which had a similar magnitude in both intact and decerebrate rats.(ABSTRACT TRUNCATED AT 400 WORDS)

SUBTYPES OF ADENOSINE RECEPTORS IN THE BRAINSTEM MEDIATE OPPOSITE BLOOD PRESSURE RESPONSES

Microinjections of selective agonists for adenosine receptor subtypes were made into the caudal NTS of rats. CGS 21680, a selective A2 receptor agonist, elicited pronounced, dose-related decreases in mean arterial blood pressure (ED50 = .021 nmols/rat). Conversely, CPA, a selective A1 receptor agonist, elicited potent dose-related increases in mean arterial blood pressure (ED50 = 0.185 nmols/rat). Additionally, the depressor responses elicited by the A2 agonist and the pressor responses elicited by the A1 agonist were completely and selectively blocked, respectively, by the selective A2 antagonist, CGS 15943A, and the selective A1 antagonist, DPCPX. These data indicate that selective activation of brainstem adenosine receptors in vivo may elicit distinct and opposing response patterns.

N6-cyclopentyladenosine impairs passive avoidance retention by selective action at A1 receptors

The effects of N6-cyclopentyladenosine (CPA), a highly selective agonist for adenosine A1 receptors, on retention of one-trial inhibitory avoidance behavior were examined in mice. Water-deprived animals were trained to avoid drinking by pairing foot-shock with licks from a water spout. Retention was measured as the suppression of drinking (latency to drink) 48 h following training. Administration of CPA (0.15-2.25 mumol/kg) 30 min prior to training produced a dose-dependent impairment in memory of the original avoidance task. The CPA-elicited deficits in retention performance were blocked by pretreatment with 8-cyclopentyl-1,3-dipropylxanthine (DPCPX), a selective A1 receptor antagonist; DPCPX (15 mumol/kg) administration alone had no effect on retention performance. These findings suggest that selective activation of a presumably central population of A1 receptors may impair retention performance and influence information processing.

Activation of P2-purinoceptors in the nucleus tractus solitarius mediate depressor responses

The purpose of the study was to examine the role of P2 purinergic receptors in mechanisms of cardiovascular control mediated by the nucleus tractus solitarius (NTS), a major integrative site in the brainstem involved in the reflex coordination of cardiorespiratory and visceral response patterns. Microinjections of ATP and its analogues were made into the subpostremal NTS of anesthetized, spontaneously breathing rats. ATP, alpha,beta-methylene ATP (alpha beta-meATP) and 2-methylthio-ATP (2-meSATP) produced significant dose-related reductions in arterial blood pressure. alpha beta-meATP was slightly more potent than ATP and 2-meSATP. Pretreatment with the P2 receptor antagonist, suramin (0.5 nmol/rat), into the same NTS site 10 min prior to agonist administration completely blocked pronounced depressor response pattern elicited by the highest dose of alpha beta-meATP (0.1 nmol/rat). The present findings suggest that endogenous ATP may serve as a fast transmitter substance in NTS-mediated mechanisms of cardiovascular control.

Activation of P2x-purinoceptors in the nucleus tractus solitarius elicits differential inhibition of lumbar and renal sympathetic nerve activity

Activation of P2x-purinoceptors in the nucleus tractus solitarius (NTS) via microinjection of alpha,beta-methylene ATP (alpha,beta-MeATP) elicits large dose-dependent decreases in mean arterial pressure (MAP) and heart rate (HR) and preferential dilation of the iliac vascular bed in comparison to renal and mesenteric vascular beds. We investigated whether sympathoinhibition contributes to the depressor responses and whether differential changes in regional sympathetic output occur. In 43 chloralose/urethane anesthetized male Sprague-Dawley rats, MAP, HR, renal (RSNA) and lumbar sympathetic nerve activity (LSNA) were recorded. Data were analyzed as both the maximum decrease and the integral of the decrease over the duration of the depressor response. Microinjection of alpha,beta-MeATP (25 and 100 pmol in 50 nl volume) into the subpostremal NTS caused significant and dose-dependent decreases in MAP, HR, RSNA and LSNA. However, the changes in RSNA were significantly greater than those observed in LSNA for both doses and both methods of analysis of data (maximum responses in delta %: 84 +/- 3 vs 62 +/- 4, and 93 +/- 3 vs 74 +/- 4 for low and high dose of alpha,beta-MeATP, respectively; integral responses in delta % x min: 32 +/- 4 vs 18 +/- 3 and 179 +/- 7 vs 134 +/- 14 for low and high dose of alpha,beta-MeATP, respectively). Blockade of P2-purinoceptors in the NTS by the specific P2-receptor antagonist suramin abolished responses to 100 pmol alpha,beta-MeATP and microinjections of vehicle did not alter neural nor hemodynamic parameters. We conclude that activation of P2x-purinoceptors in the NTS inhibits sympathetic nerve activity and evokes differential regional sympathetic responses. However, differential sympathoinhibition does not explain differential vascular responses to the activation of P2x-purinoceptors in the NTS.

Evidence for presynaptic adenosine A2a receptors associated with norepinephrine release and their desensitization in the rat nucleus tractus solitarius

Abstract: Rat medullary brain segments containing primarily nucleus tractus solitarius (NTS) were used for superfusion studies of evoked transmitter release and for isotherm receptor binding assays. Isotherm binding assays with [3H]CGS‐21680 on membranes prepared from NTS tissue blocks indicated a single high‐affinity binding site with a KD of 5.1 ± 1.4 nM and a Bmax of 20.6 ± 2.4 fmol/mg of protein. The binding density for [3H]CGS‐21680 on NTS membranes was 23 times less than comparable binding on membranes from striatal tissue. Electrically stimulated (1 min at 25 mA, 2 ms, 3 Hz) release of [3H]norepinephrine ([3H]NE) from 400‐µm‐thick NTS tissue slices resulted in an S2/S1 ratio of 0.96 ± 0.02. Superfusion of single tissue slices with 0.1–100 nM CGS‐21680, a selective adenosine A2a receptor agonist, for 5 min before the S2 stimulus produced a significant concentration‐dependent increase in the S2/S1 fractional release ratio that was maximal (31.3% increase) at 1.0 nM. However, superfusion of tissue slices with CGS‐21680 over the same concentration range for 20 min before the S2 stimulus did not alter the S2/S1 ratio significantly from control release ratios. The augmented release of [3H]NE mediated by 1.0 nM CGS‐21680 with a 5‐min tissue exposure was abolished by 1.0 and 10 nM CGS‐15943 as well as by 100 nM 8‐(3‐chlorostyryl)caffeine, both A2a receptor antagonists, but not by 1.0 nM 8‐cyclopentyl‐1,3‐dipropylxanthine, the A1 receptor antagonist. Taken together, these results suggest that CGS‐21680 augmented the evoked release of [3H]NE in the NTS via activation of presynaptic A2a receptors within the same concentration range as the binding affinity observed for [3H]CGS‐21680. It was also apparent that this population of presynaptic adenosine A2a receptors in the NTS desensitized within 20 min because the augmenting action of CGS‐21680 on evoked transmitter release was not evident at the longer interval.