Biomedical subjects

D F Cechetto

Publications and source records attributed to D F Cechetto.

61 records · Page 4Linked to original sources

PubMed1984

Units in the amygdala responding to activation of carotid baro- and chemoreceptors.

The distribution of units in the amygdala responding to selective activation of baro- and chemoreceptors was investigated in 12 cats under alpha-chloralose anesthesia. Changes in the firing frequency of spontaneously discharging units were monitored during baroreceptor activation (BA) (phenylephrine hydrochloride, 2 micrograms/kg iv) and chemoreceptor activation (CA) (sodium cyanide, 25 micrograms in 0.1 ml saline into the medial thyroid artery). CA altered the firing frequency of 23% (35/154) of the units; 37% (13/35) were excited, and 63% (22/35) were inhibited. BA altered the firing frequency of 16% (24/154) of the units; 71% (17/24) were excited, while 29% (7/24) were inhibited. The units responsive to CA were located primarily in the dorsomedial amygdala, while those responsive to BA were located primarily in the ventrolateral amygdala. The anatomic separation of units within the amygdala responding to activation of baroreceptors or chemoreceptors suggests that the specificity of function of different parts of the amygdala is related to the different kinds of inputs received by these components of the amygdala from cardiovascular receptors.

Amygdala↗

PubMed1983

Afferent connections to cardiovascular sites in the amygdala: a horseradish peroxidase study in the cat.

To investigate afferent connections to nuclei of the amygdala that have been shown electrophysiologically to receive inputs from baro- and chemoreceptors, small discrete deposits of horseradish peroxidase (HRP) were placed in the region of the central and lateral nuclei of the amygdala in cats. HRP deposits localized to the medial central nucleus of the amygdala labeled neurons in the ipsilateral hypothalamus, primarily in the paraventricular and ventromedial nuclei. In addition, the parabrachial nuclei and the locus coeruleus were observed to project to the region of the central nucleus. After HRP deposits in the medial portion of the lateral nucleus of the amygdala only a few labeled neurons were found scattered throughout the ipsilateral hypothalamus. In addition thalamic and cortical projections shown by previous investigators were confirmed. This study has demonstrated that in the cat several areas in the hypothalamus and brain stem project to the medial portions of the central and lateral nuclei of the amygdala suggesting that these areas may be relay stations for baro- and chemoreceptor information projecting to the amygdala.

Afferent Pathways↗

PubMed1983

Response of single units in the amygdala to stimulation of buffer nerves in cat.

Electrical activity of spontaneously active units in the amygdala of 19 chloralose-anesthetized cats was monitored for changes in firing frequency during electrical stimulation of the carotid sinus (CSN) and aortic depressor (ADN) nerves. Stimulation of the CSN altered the firing frequency of 30% (73/241) of the units on both sides of the amygdala. Of these units, 47% were excited and 53% were inhibited. Stimulation of the ADN elicited a change in firing frequency of 20% (50/251) of ipsi- and contralateral units. Of these, 68% were excited and the remainder were inhibited. The average latency for all CSN responses (53 +/- 4.0 ms) was significantly longer than the average latency for ADN responses (35 +/- 3.3 ms). The majority of the responsive units were located in the central and lateral nuclei of the amygdala. Spontaneously firing units responding to both CSN and ADN stimulation were found infrequently (7%, 14/188). These results indicate that the two buffer nerves project to specific regions within the amygdala, but the CSN and the ADN follow separate pathways probably involved in reflex arcs mediating different physiological responses.

Amygdala↗

PubMed1983

Parabrachial units responding to stimulation of buffer nerves and forebrain in the cat.

Spontaneously firing units in the region of parabrachial nuclei (PB) and Kölliker-Fuse nuclei (KF) of 19 chloralose-anesthetized cats were monitored for changes in firing frequency during electrical stimulation of carotid sinus (CSN) and aortic depressor (ADN) nerves, of central nucleus of the amygdala (ACE), and of paraventricular nuclei of the hypothalamus (PVH). In the ipsilateral PB 64 of 189 and in the contralateral PB 9 of 103 units responded to CSN stimulation; 18 of 185 ipsilaterally and 7 of 97 contralaterally responded to ADN stimulation. Responses were primarily excitatory, and units were located primarily in the ventrolateral portion of the PB. Only 9 of 267 units responded to stimulation of both CSN and ADN. Stimulation of the ACE and PVH antidromically activated 9 and 7 units, respectively, in PB and approximately half of these also responded to buffer nerve stimulation. In the ipsilateral PB 56 of 207 and in the contralateral PB 11 of 103 units responded orthodromically to ACE stimulation, and 23 of 177 ipsilaterally and 2 of 103 contralaterally responded orthodromically to PVH stimulation with primarily excitatory responses and were located primarily in the ventrolateral portion of the PB and KF. Of these units approximately half also responded to buffer nerve stimulation. These results suggest an important role for PB-KF in mediating ascending and descending cardiovascular and respiratory control signals.

Afferent Pathways↗

PubMedDate not supplied

Identification of a cortical site for stress-induced cardiovascular dysfunction.

The evidence indicating that the insular cortex is a likely candidate to mediate stress-induced cardiovascular responses is reviewed. Both neuroanatomical and electrophysiological investigations demonstrate that the insular cortex receives an organized representation of visceral information. In addition, the insular cortex also receives highly processed association cortex information. The insular cortex is also highly interconnected with many subcortical limbic and autonomic regions. This combination of sensory input and limbic/autonomic connectivity would be necessary to permit the insular cortex to be a critical site for the integration of emotional and autonomic responses. Stimulation of the insular cortex elicits specific cardiovascular and autonomic responses from discrete sites. Phasic stimulation entrained to the cardiac cycle is even capable of causing severe arrhythmias. The efferent pathways and some of the neurotransmitter mechanisms have determined. It appears that the lateral hypothalamic area is the primary site of synapse for responses originating in the insular cortex and this information is relayed by NMDA glutamatergic receptors and modulated by neuropeptides including neuropeptide Y, neurotensin, leu-enkephalin and dynorphin. Finally, a rat stroke model, which includes the insular cortex in the infarct region indicates that disruption of the insula can produce substantial cardiac and autonomic abnormalities, which might be similar to those produced by stress. Some of the chronic neurochemical changes, including increases in opioids, neuropeptide Y and neurotensin in the central nucleus of the amygdala, which might be mediating these cardiovascular disturbances, have been determined.

Animals↗

PubMedDate not supplied

Inhibition of the firing of vasopressin neurons by atriopeptin.

Atriopeptin, the atrial natriuretic peptide, is a circulating hormone that is released from the atria of mammalian hearts in response to volume expansion and acts upon the kidneys, adrenal glands and vasculature to regulate fluid and electrolyte homeostasis. Atriopeptin is also present in the brain of the rat. Atriopeptin immunoreactive cell bodies and fibres are found in many areas known to be involved in the central regulation of the cardiovascular system, suggesting that it may be a neuromediator in the central control of fluid and electrolyte balance. The paraventricular nucleus of the hypothalamus, which contains the cell bodies of neurons that secrete vasopressin from the posterior pituitary gland, receives a dense innervation from atriopeptin-like immunoreactive fibres. We have studied the effect of atriopeptin on the electrical activity of single neurons in the paraventricular nucleus of anaesthetized rats and found that atriopeptin is a potent inhibitor of putative vasopressin neurons. Atriopeptin, which has systemic actions that oppose those of vasopressin, may act as a neuromodulator in the brain to prevent vasopressin secretion.

Action Potentials↗

PubMedDate not supplied

Neurotransmission in the medulla mediating insular cortical and lateral hypothalamic sympathetic responses.

Previous evidence has shown sympathetic nerve responses to insular cortical (IC) stimulation are mediated by synapses within the lateral hypothalamic area (LHA) and ventrolateral medulla (VLM). The present study was aimed at determining the neurotransmitter(s) and receptor(s) involved at the synapse in the VLM. Twenty male Wistar rats were instrumented for renal nerve, arterial pressure, and heart rate recording. The IC or the LHA was stimulated with a bipolar electrode (200-1000 microA; 2 ms; 0.8 Hz) to elicit sympathetic nerve responses. Antagonists were then pressure-injected into the VLM (300 nL). Bilateral and unilateral kynurenate (25 mM) resulted in 100% block of IC-and LHA-stimulated sympathetic nerve responses. Bilateral injection of the non-NMDA (N-methyl-D-aspartate) receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX; 200 microM) also resulted in up to 100% block of IC and LHA sympathetic responses. In addition, unilateral injections of CNQX were made in two animals, resulting in 100 and 83% block of LHA sympathetic responses. Bilateral injection of the NMDA receptor antagonist DL-2-amino-5-phosphonopentanoic acid (AP5; 200 microM) did not affect the response to IC or LHA stimulation. Kynurenate, CNQX, and AP5 all resulted in an elevation of baseline sympathetic nerve activity and a pressor response. Kynurenate resulted in a 263+/-79% increase in baseline activity, while CNQX and AP5 resulted in 83+/-19% and 91+/-21% increases. respectively. Bilateral injections of antagonists for GABA(A) (bicuculline; 0.1 microM), acetylcholine (atropine; 0.1 microM) and catecholaminergic alpha and beta receptors (phentolamine and propranolol: 0.1 microM) had no effect on LHA sympathetic responses. Thus, sympathetic responses originating in the IC and LHA are mediated by a non-NMDA receptors in the VLM, which are likely AMPA receptors.

Action Potentials↗