Cardiovascular and respiratory responses to microinjection of L-glutamate into the caudal pressor area in conscious and anesthetized rats

Abstract

The role of the caudal pressor area (CPA) in the maintenance of vasomotor tonus in anesthetized and decerebrate animals has been clearly established. In conscious animals, however, the participation of CPA in the cardiovascular control remains to be fully elucidated. In the present study, unilateral L-glutamate (L-Glu) (10 and/or 20 nmol/ 70 nl) microinjection into CPA, in conscious male Wistar rats (250-280 g) caused a significant increase in mean arterial blood pressure (MAP; control: 112 ± 1.9 mmHg; after 20 nmol L-Glu: 139 ± 4.5 mmHg, N = 12, P<0.05) and respiratory rate (control: 81 ± 3.5 breaths/ min; after 10 nmol L-Glu: 92 ± 3 breaths/min, P<0.05; after 20 nmol L-Glu: 104 ± 5 breaths/min, N = 6, P<0.05). The subsequent anesthesia with urethane caused a significant increase in basal respiratory frequency (conscious: 81 ± 3.5 breaths/min; under urethane: 107 ± 1.3 breaths/min, N = 6, P<0.05). Anesthesia also significantly attenuated L-Glu-evoked pressor (conscious:, MAP = +27 mmHg; anesthetized:, MAP = +18 mmHg, P<0.05) and respiratory responses. These results suggest that glutamatergic receptors in the CPA are involved in cardiovascular and respiratory modulation in conscious rats.

Maps of cardiovascular and respiratory regions of rat ventral medulla: Focus on the caudal medulla

“…Curiously, Feldberg and Guertzenstein (1986) described a similar anaesthetic sensitivity in their first description of the 'CPA' in cat where a pressor response was only obtained during very deep anaesthesia and further following pretreatment of a ventral surface site with pentobarbitone, leptazol evoked a much larger rise in pressure. Despite intensive investigation considerable confusion still surrounds the location of the so called 'CPA' (Campos et al, 2008;Campos and McAllen, 1999;Gordon and McCann, 1988;Horiuchi and Dampney, 2002;Natarajan and Morrison, 2000;Possas et al, 1994;Silva et al, 2001;Panneton, 2005, 2002;Tolentino-Silva et al, 1997;Yajima et al, 2008;Feldberg and Guertzenstein, 1986;Panneton et al, 2008). We suggest, in light of the present study, this confusion is due to the existence of three caudal pressor regions.…”

“…Such effects may explain differences in criteria that have been used to locate cardiovascular sites. It is also clear that state dependency has been, as yet, insufficiently explored although large pressor responses are clearly evoked from the RVLM, a caudal pressor area and the depressor CVLM also under conscious conditions (Sakima et al, 2000;Silva et al, 2001).…”

“…Furthermore many discrepancies exist in the literature. For example, the anatomical location of the CPA, in the rat can differ by up 1.5 mm rostrocaudally (Campos and McAllen, 1999;Gordon and McCann, 1988;Possas et al, 1994;Silva et al, 2001). Clarity of location has been further clouded as ventral sites are often described with respect to dorsal landmarks or ventral surface landmarks.…”

Brainstem activity, apnea, and death during seizures induced by intrahippocampal kainic acid in anaesthetized rats

“…Time-limited (1-2 minutes) seizures induced by brief (2-second) electrical stimulation of dorsal hippocampus also slow respiration, attributed to alterations in serotonergic neuron activity in the raphe nuclei. 36 We report that status and recurrent seizures substantially increase respiration rate from the baseline established under urethane. Urethane anesthesia raises basal respiratory rate in both mice 35 and rats.…”

Rate-dependent behavioral effects of stimulation of central motoric ?1-adrenoceptors: hypothesized relation to depolarization blockade

“…Some anesthetics used in electrophysiological studies, such as halothane (Ramirez-Munguia et al 2003;Stucke et al 2003;Kirson et al 1998;Miyazaki et al 1997) andurethane (MacIver et al 1996;Hara and Harris 2002;Sun and Reis 1995;Silva et al 2001;Heltovics et al 1995), are known to reduce glutamatergic neurotransmission. The same appears to be true for chloral hydrate (Kreuter et al 2004).…”