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PubMed1990

Nicotine-induced conditioned taste aversions are enhanced in rats with lesions of the area postrema.

Lesions, which destroy the area postrema and damage the adjacent nucleus of the solitary tract, attenuate or abolish conditioned taste aversions (CTA) induced by a variety of pharmacological agents. In the present experiment 2 groups of male rats received lesions of the area postrema and 2 groups were given sham lesions. One lesioned group and one sham-lesioned group were twice conditioned with 30-min access to a novel 0.15% saccharin solution followed by injection of nicotine (1 mg/kg, IP). The other 2 groups were similarly conditioned with saccharin followed by saline injections. In subsequent two-bottle choice tests (saccharin vs. water), the saline-injected rats exhibited strong preferences for saccharin, the sham-lesioned rats injected with nicotine showed a weak but significant (p less than 0.05) aversion to saccharin, and the area postrema-lesioned rats injected with nicotine displayed a significantly (p less than 0.05) stronger CTA than the drug-injected sham-lesioned animals. In Phase 2 all rats were given novel chocolate metrecal (30 min) followed by injection of scopolamine HCl (1 mg/kg, IP). The area postrema-lesioned rats showed significant (p less than 0.01) preference for the chocolate taste relative to the aversions shown by the sham-lesioned animals. Thus, area postrema lesions attenuated a scopolamine-induced CTA, but enhanced a nicotine-induced aversion. These results suggest that nicotine and scopolamine act at different neural sites in producing CTAs.

Animals↗
PubMed1984

Amines and other transmitter-like compounds in the bovine area postrema.

The bovine area postrema (AP) was examined for the presence of monoamines and other neuroactive substances which might act as neurotransmitters in the nucleus. High performance liquid chromatography indicated the occurrence of noradrenaline, adrenaline, dopamine and serotonin within the AP. Thin layer chromatography of dansylated derivatives of the AP revealed the presence of gamma amino butyric acid (GABA), glycine, glutamate and aspartate. Finally, direct immunofluorescence histochemistry localised substance P-like and serotonin-like immunoreactivity within neuronal fibres and varicosities in the AP and in the subjacent nucleus tractus solitarius. Dopamine-beta-hydroxylase-like immunoreactivity was found in neuronal perikarya throughout the AP, nucleus tractus solitarius and dorsal motor nucleus of the vagus. These studies provide evidence that dopamine, serotonin, noradrenaline and GABA may all act as neurotransmitters in the bovine AP.

Animals↗
PubMed1981

Detection of dopamine receptors in the area postrema.

[3H]Spiroperidol labeled dog area postrema membranes with high affinity (KD, 0.1 nM) and stereospecificity. The displacement of the radioligand by different dopamine agonists and antagonists indicated that the labeled sites were dopaminergic in nature. Guanine nucleotides decreased agonist affinity for the labeled sites without affecting the affinity for antagonists. Adenylate cyclase in the area postrema was stimulated by guanine nucleotides and sodium fluoride but not by dopamine. The results suggest that the dopamine receptor in the area postrema can be classified as D2-type receptors.

Adenylyl Cyclases↗
PubMed2003

17 beta-Estradiol inhibits angiotensin II activation of area postrema neurons.

It is well established that the area postrema, as a circumventricular organ, is susceptible to modulation by circulating hormones and peptides. Furthermore, activation of the area postrema has been shown to modulate central neurons involved in the regulation of cardiovascular function and blood pressure. In particular, the vasoactive peptide angiotensin II (ANG II) has been shown to inhibit baroreflex regulation of heart rate and increase sympathetic outflow and blood pressure via activation of area postrema neurons. Estrogen is thought to protect against hypertension in both humans and animal models and has been shown in a number of systems to alter the effects of ANG II. The purpose of the present study was to determine the effects of estrogen on ANG II activation of area postrema neurons. In this study, the effects of ANG II and KCl on fura 2-measured cytosolic Ca2+ concentration ([Ca2+]i) responses in cultured area postrema neurons in the presence and absence of 12-h exposure to 100 nM 17 beta-estradiol (E2) were evaluated. In neurons incubated in control vehicle media, 50 nM ANG II increased [Ca2+]i by 92 +/- 12%. In neurons preincubated with 100 nM E2, ANG II increased [Ca2+]i by only 68 +/- 11%, for a total inhibition of the ANG II-evoked response of 24%. Coapplication of the estrogen receptor antagonist ICI-182,780 did not inhibit the effects of E2. In the same cells in which the effects of E2 on ANG II-evoked responses were tested, the effects of incubation in E on the depolarization-induced increased [Ca2+2]i due to 60 mM KCl were also tested. Incubation of the cells with 100 nM E increased the KCl-evoked [Ca2+2]i response, and this response was blocked by ICI-182,780. These results suggest that in the area postrema, estrogen may utilize multiple pathways to modulate neural activity and responses to ANG II.

Angiotensin II↗
PubMed1981

Taste aversions conditioned with intravenous copper sulfate: attenuation by ablation of the area postrema.

Borison and Wang identified the area postrema as the locus of chemoreceptors that mediate emetic reflexes elicited by blood-borne toxins. In the present experiments we have extended a systematic investigation of the afferent pathways mediating taste aversions by examining the effects of area postrema lesions on the aversions that follow either intravenous or intragastric administration of copper sulfate. Intrajugular cannulas were implanted in rats after ablation of the area postrema (Group AP-L) and in operated controls (Group AP-C). Every third day rats were offered a saccharin solution and immediately afterward were injected intravenously with 0.05 ml isotonic CuSO4. A group of pseudo-conditioned rats (Group SAC-C) was injected with CuSO4 approximately 24 h after ingestion of saccharin. Compared to controls animals, rats with area postrema damage acquired significantly weaker aversions to saccharin when it was paired repeatedly with intravenous CuSO4. After three conditioning trials, the rats in Group AP-L that were most resistant to acquisition of a taste aversion (Group AP-L) were again offered saccharin, but ingestion in this case was followed immediately by intragastric injection of CuSO4. After a single conditioning trial rats in Group AP-L demonstrated a robust aversion. The results are discussed in terms of the parallels in afferent systems between emetic physiology and some instances of taste aversion conditioning.

Afferent Pathways↗
PubMed1994

Circulating vasopressin influences area postrema neurons.

Extracellular single-unit recordings were obtained from 107 area postrema and 74 nucleus tractus solitarius neurons in sodium pentobarbital anaesthetized rats. Systemic administration of vasopressin (1-10 ng) decreased the firing frequency of 45.8% of area postrema neurons and 58.1% of nucleus tractus solitarius neurons tested while the firing frequency of 38.3% of area postrema neurons and 21.6% of nucleus tractus solitarius neurons was increased by this peptide. To determine whether these neurons were specifically influenced by vasopressin or the accompanying pressor response, the effects of alpha-adrenergic agonists on neuronal activity were also determined. Cells that responded similarly to vasopressin and the change in blood pressure elicited by alpha-adrenergic agonists were classified as "blood pressure-sensitive", whereas those neurons that responded differently to both agents were classified as "vasopressin-sensitive" neurons. The majority (85.2%) of area postrema cells that decreased firing frequency in response to vasopressin were determined to be "vasopressin-sensitive", while 68.8% of area postrema neurons responding to vasopressin with increases in firing frequency were classified as "blood pressure-sensitive". In contrast, 78.6% of nucleus tractus solitarius neurons that decreased firing frequency in response to vasopressin and 55.5% of those that increased firing frequency were classified as "blood pressure-sensitive" neurons. To determine whether the actions of vasopressin in the area postrema were mediated by V1 receptors the effect of vasopressin after V1 receptor blockade was examined in seven "vasopressin-sensitive" area postrema neurons. All seven neurons tested showed no response to vasopressin after such V1 receptor blockade. These data suggest that there exists a population of area postrema neurons specifically responsive to circulating vasopressin as a result of actions of this peptide at V1 receptors. They also implicate these neurons in the physiological mechanisms through which circulating vasopressin acts in the area postrema to influence baroreceptor reflex sensitivity.

Animals↗
PubMed1983

Taste aversions conditioned with gamma radiation: attenuation by area postrema lesions in rats.

The role of the area postrema in radiation induced taste aversions in rats was examined. One group of rats received lesions of the area postrema, another group was given sham lesions and a third group received no surgery. These three groups of rats were then given one pairing of 1 h access to a novel 0.15% sodium saccharin solution followed immediately with exposure to 200 rad gamma radiation. A fourth group of rats with area postrema lesions was given 1 h access to saccharin followed by a sham irradiation procedure. Four days later all groups were given daily two bottle preference tests (saccharin vs water) on 5 consecutive days. The groups with sham lesions or no surgery displayed a strong aversion to saccharin on all 5 test days. The two area postrema lesioned groups displayed a moderate and increasing preference for saccharin over the 5 day test period. The lesioned group given radiation treatment showed a weak but significant aversion (P less than 0.05) to saccharin on the first test day, when compared to the lesioned rats not given radiation treatment. Thus, lesions of the area postrema strongly attenuated the radiation induced taste aversions, but did not completely abolish them.

Animals↗
PubMed1987

Area postrema of the goldfish, Carassius auratus: ultrastructure, fiber connections, and immunocytochemistry.

The area postrema in goldfish is a dorsal midline structure in the caudal medulla spanning the level of the obex. As in other vertebrates, the sinus capillaries of the area postrema in goldfish are fenestrated. In goldfish, however, the area postrema is organized in a unique laminar fashion; from superficial to deep: meninx, vasculature, palisade layer, cell body layer, and ventral neuropil layer. Virtually all of the neurons of the area postrema exhibit tyrosine hydroxylase-like immunoreactivity. Each immunoreactive neuron is essentially bipolar, with a short apical dendrite extending dorsally to reach the external basal lamina of the capillaries and a basal dendrite reaching into the subjacent layer of neuropil. The apical dendrites have no synaptic specializations and probably function as interoceptors detecting blood-borne chemicals that leak out of the fenestrated capillaries. The basal dendrites receive synaptic input both within the neuropil of the area postrema and in the commissural nucleus of Cajal into which they extend. Primary afferent fibers of the subdiaphragmatic branches of the vagus nerve terminate within the area postrema and commissural nucleus. Thus the neurons of the area postrema may serve not only as direct chemoreceptive interoceptors but may also receive input from other visceral afferent systems.

Animals↗
PubMed2000

17-beta-estradiol modulation of area postrema potassium currents.

The purpose of this study was to determine the effects of 17-beta-estradiol on area postrema neuronal activity in vivo and on area postrema potassium currents (IK) in vitro. In anesthetized rats, intravenous injection of 17-beta-estradiol (10 ng/kg bw) -inhibited area postrema neuronal activity in 8/8 neurons tested. The averaged firing rate decreased from 2.9 +/- 1.1 to 1.1 +/- 0.3 Hz. The inhibitory effects of 17-beta-estradiol on area postrema neuronal activity were rapid in onset (within 1 min) and long-lasting (>8 min). To study the cellular mechanisms involved in this response, the effects of 17-beta-estradiol were examined in dissociated area postrema neurons. In these cells, 17-beta-estradiol (0.5 nM) increased the averaged peak IK 27 +/- 8%. The time course for the potentiation was observed within approximately 0.5-1 min after the application of 17-beta-estradiol. Full recovery from the potentiation usually occurred within approximately 3-4 min after the washout of 17-beta-estradiol. The biologically inactive 17-alpha-estradiol had no effect on area postrema IK and the 17-beta-estradiol antagonist, ICI 182,780 blocked the effects of 17-beta-estradiol on area postrema IK. Finally, big conductance calcium-activated potassium current (MaxiK(+)) was identified in area postrema neurons (n = 12/12). Blockade of MaxiK(+) with 100 nM iberiotoxin blocked the effects of 17-beta-estradiol on IK. These results suggested 17-beta-estradiol might modulate area postrema neuronal activity by increasing MaxiK(+) current.

Animals↗
PubMed1987

Inhibition of renal sympathetic nervous activity by area postrema stimulation in rabbits.

This study investigated the effect of chemical and electrical stimulation of the area postrema on renal sympathetic nerve activity (RSNA), arterial pressure, and heart rate in urethan-anesthetized rabbits. Electrical stimulation of the area postrema at 2, 5, 10, 20, 40, and 80 Hz using constant currents of 7.5, 15, and 30 microA (pulse duration = 0.3 ms, train duration = 5 s) produced progressive decreases in RSNA and heart rate, with no consistent change in arterial pressure. To control for electrical activation of fibers of passage in or near the area postrema, L-glutamate was injected into the area postrema using glass micropipettes. Micropressure injection of L-glutamate (10 mM) in volumes of 5-10 nl produced rapid decreases in RSNA averaging 27 +/- 5% (P less than 0.05) accompanied by a small bradycardia. The effects of electrical stimulation of the area postrema, but not the adjacent nucleus tractus solitarius, were totally eliminated by micropressure injection of kainic acid (40 ng in 40 nl) into the area postrema. During continuous electrical stimulation of the area postrema using parameters that produced small decrements in RSNA and heart rate, the slope of the line relating baroreflex inhibition of RSNA to increases in arterial pressure during graded infusions of phenylephrine was significantly enhanced (-6.77 +/- 1.30 vs. -3.81 +/- 0.66% RSNA/mmHg). These data are consistent with the hypothesis that activation of neurons in the area postrema results in an inhibition of RSNA. Furthermore, stimulation of the area postrema augments baroreflex inhibition of RSNA during increases in arterial pressure with phenylephrine.

Animals↗
PubMed1981

Immunocytochemical localization of catecholamine synthesizing enzymes and neuropeptides in area postrema and medial nucleus tractus solitarius of rat brain.

The catecholaminergic and peptidergic neurons in the area postrema and adjacent portion of the medial nucleus tractus solitarii (mNTS) were characterized by the immunocytochemical localization of the catecholamine synthesizing enzymes tyrosine hydroxylase (TH), dopamine-beta-hydroxylase (DBH) and phenylethanolamine-N-methyltransferase (PNMT) and two neuropeptides, substance P and (Leu5)-enkephalin. The catecholamine synthesizing enzymes TH and DBH, found jointly only in noradrenergic and adrenergic neurons, were localized in cells having a similar morphology and topographical distribution. These cells were located throughout the rostrocaudal and dorsoventral extent of the area postrema, as well as in neurons within the mNTS. The processes showing TH and DBH immunoreactivity appear to form reciprocal connections between the area postrema and mNTS. Phenylethanolamine-N-methyltransferase, the enzymatic marker found only in adrenergic neurons, was detected immunocytochemically in terminals distributed throughout the area postrema and in neuronal perikarya and varicosities within the adjacent mNTS. Like the catecholamine synthesizing enzymes TH and DBH, enkephalin-like immunoreactivity was localized to perikarya, proximal processes and varicose axon terminals within the area postrema and the adjacent mNTS. However, in contrast to the widespread distribution of the enzymes, the enkephalin-like immunoreactivity was localized predominantly along the dorsal and ventrolateral margins of the area postrema. The distribution of substance P immunoreactivity, which was detected only in varicose processes, paralleled the distribution of enkephalin-like immunoreactivity, being predominantly located along the dorsal and ventrolateral margins of the area postrema. Within the mNTS adjacent to the area postrema, substance P immunoreactivity was localized to neuronal perikarya, proximal processes and varicose axon terminals. Based upon the presence of appropriate biosynthetic enzyme markers and neuropeptide localization, these findings suggest that neurons within the area postrema contain noradrenalin and enkephalin and that the afferent axons contain substance P, adrenalin and, probably, noradrenalin.

Animals↗
PubMed1993

Area postrema and aortic or vagal afferents converge to excite cells in nucleus tractus solitarius.

Area postrema neurons enhance baroreflex function, perhaps by augmenting baroreceptor afferent processing in the nucleus tractus solitarius (NTS). If so, NTS neurons should receive convergent excitatory inputs from area postrema neurons and baroreceptors. The aims of this study were to record extracellular activity of NTS neurons to determine whether 1) area postrema and aortic baroreceptor afferents converged in NTS, 2) area postrema and vagal afferents converged in NTS, and 3) the convergent inputs were facilitative. Studies were performed in pentobarbital sodium- or alpha-chloralose-anesthetized rabbits. Forty-six of 194 NTS neurons received inputs from the area postrema and aortic depressor nerve. Twelve of the 23 inputs showed facilitative summation; unit response rate evoked by paired inputs (79%) doubled the predicted (calculated) response rate for simple addition (37%). Fifty-eight of 114 NTS neurons received excitatory inputs from the area postrema and vagus. Eleven of the 13 inputs showed facilitative summation; unit response to paired inputs (87%) doubled the predicted response (44%). Area postrema neurons may augment the processing of aortic and vagal inputs by NTS neurons and, hence, enhance the reflex output of these afferent pathways.

Animals↗
PubMed1980

Characterization of the sympatho-facilitative area postrema pathway.

1. The mechanism by which the area postrema augments central sympathetic drive during electrical stimulation is presently unknown. This pathway may involve either direct facilitation of brain-stem vasomotor neurons or inhibition of the sympatho-inhibitory baroreceptor relay in the nucleus tractus solitarii. 2. The present study employed selective lesions within the solitary tract nucleus to assess the participation of the primary baroreceptor relay in the pressor response during electrical stimulation of the area postrema. 3. The magnitude of the pressor response was unchanged after destruction of the solitary tract and lateral solitary nucleus which centrally interrupted the baroreceptor reflex. However, microknife cuts through the medial solitary nucleus, which spared the carotid sinus reflex, significantly reduced the magnitude of the area postrema pressor response. 4. Previous anatomical studies support these results and confirm that, although the area postrema pressor pathway traverses the most medial portion of the solitary complex, it does not produce augmented sympathetic outflow by inhibition of the primary baroreflex relay.

Animals↗
PubMed1996

Area postrema voltage-activated calcium currents.

1. Calcium currents in rabbit area postrema neurons were studied with the perforated patch-clamp technique. Experimental conditions eliminated Na+ and K+ currents and identified both low- and high-threshold voltage-activated calcium currents. 2. Low-threshold, T-type calcium currents were observed in 64% of the area postrema neurons recorded. This current activated near -60 mV and had an average peak amplitude of -36.2 +/- 5 pA (mean +/- SE) at -40 mV. This current began rapid inactivation near -95 mV, reached half-maximal inactivation at -71 mV and was totally inactivated by -40 mV. 3. A high-threshold transient current was recorded in all area postrema neurons, which consisted of both a transient and sustained component. This current was present at voltages greater than -40 mV and the transient component of this current was responsible for the majority of the total Ca2+ current. 4. Nickel ions (10 microM) effectively reduced both the T-type current and the high-threshold current. Cadmium ions (100 microM) effectively reduced the high-threshold current while having insignificant effects on the low-threshold current. 5. Application of the dihydropyridine antagonist nimodipine (1-10 microM) had no effect on either the low- or high-threshold voltage-activated calcium Ca2+ in area postrema neurons. In addition, application of omega-conotoxin-GVIA (2-10 microM) was also without effect on either the low- or high-threshold voltage-activated Ca2+ current, suggesting that area postrema neurons possess neither L- or N-type voltage-activated Ca2+ currents. 6. Application of omega-conotoxin MVIIC (10 microM) significantly inhibited the peak high-threshold Ca2+ current by 65.4% suggesting that area postrema neurons do possess a omega-conotoxin MVIIC-sensitive high-threshold Ca2+ channel. 7. Arg-vasopressin (150 nM) significantly increased the transient component of the high-threshold Ca2+ current but had little effect on either the low-threshold or the high-threshold sustained component.

Angiotensin II↗
PubMed1985

Cholecystokinin-octapeptide like immunoreactivity in the area postrema of the rat and cat.

The distribution of cholecystokinin-8 (CCK-8)-like immunoreactivity in the area postrema of the rat and cat was visualized using the peroxidase, antiperoxidase technique. In the rat the greatest amount of immunostaining occurred in peripheral regions of the area postrema at intermediate and rostral levels. Caudally, scattered immunoreactivity predominated. After colchicine treatment, numerous immunoreactive somata were observed throughout the area postrema. The cat area postrema had a different and more complex pattern of immunostaining than the rat. Moderate to dense accumulations of immunostaining occurred in the ventromedial region of the area postrema bordering the solitary tract and dorsal vagal nuclei. The central region of the area postrema possessed scattered amounts of immunoreactivity at rostral levels. Following colchicine treatment, no visible CCK-8-like immunoreactive cell bodies were observed in the cat area postrema. Results of the present investigation provide morphological evidence for the role of CCK-8 in cardiovascular regulation and satiety. The difference in the distribution of CCK-8 in the rat and cat suggest a possible role in the emetic reflex.

Animals↗
PubMed1995

Membrane properties of area postrema neurons.

Intrinsic membrane properties, voltage-dependent sodium and voltage-dependent potassium currents of area postrema neurons in culture have been characterized with respect to their voltage dependence, time dependence and sensitivity to specific blocking agents. The area postrema is a hindbrain circumventricular organ which is known to have an important role in the central regulation of cardiovascular function. This study is the first to describe the biophysical properties of ion channels present in rat area postrema neurons. Recordings in current-clamp mode revealed a mean resting membrane potential of -55.0 +/- 1.6 (n = 24) mV and an input resistance of 213.6 +/- 23 M omega. For the 24 neurons tested, the evoked action potential had a mean threshold of 38.8 +/- 2 mV and a mean amplitude of 107.3 +/- 15 mV. Our results show that the area postrema possesses only one principle sodium current which is completely abolished by 5 microM tetrodotoxin (TTX) (n = 28). This current activated near -50 mV and reached peak amplitude at -30 mV. The area postrema does not possess a TTX insensitive sodium current. The area postrema has at least two types of potassium currents. All area postrema neurons studied with tetraethylamonium (TEA) (n = 40) showed the presence of a slowly activating outward current which was present at voltages greater than -40 mV and was blocked by 10 mM TEA. In addition, 75% of the neurons studied (n = 30/40) also showed a rapidly inactivating, 4-AP sensitive IA type current which activated near -30 mV. Angiotensin II attenuated both the peak and the steady-state potassium currents, suggesting that angiotensin II may modulate area postrema activity by inhibiting voltage-gated potassium channels.

4-Aminopyridine↗
PubMed1987

The area postrema in deoxycorticosterone-salt hypertension in rats.

Ablation of the area postrema in rats prevents sustained hypertension during angiotensin II infusion and after unilateral renal artery constriction (two-kidney, one clip hypertension). The current experiment was performed to determine whether an intact area postrema is required for hypertension development in a low renin model of experimental hypertension in rats. In 11 rats, the area postrema was destroyed using electrical current; the extent and specificity of each lesion was confirmed later by blind histological analysis. In 12 rats, sham operations were performed. All rats were uninephrectomized and drank saline. During once-weekly injections of deoxycorticosterone pivalate (5 mg/wk) for 4 weeks, sham-operated rats (n = 10) showed a significant increase in mean arterial pressure (Days 6-28) and saline intake (Days 12-28), but no significant increase in sodium or water retention. Deoxycorticosterone-treated rats with area postrema ablation (n = 9) exhibited no change in arterial pressure, sodium retention, or water retention, but a significant increase in saline intake (Days 17-28). Plasma renin activity was equally suppressed in both groups of rats. The depressor response to ganglion blockade with hexamethonium (20 mg/kg i.v.) was significantly increased during the 2nd, 3rd, and 4th weeks of steroid treatment in sham-operated, but not area postrema-ablated, rats. Four rats (2 sham-operated; 2 ablated) showed no change in any variable over 28 days in the absence of steroid treatment. It is concluded that the area postrema may be important in some non-angiotensin-dependent forms of experimental hypertension, possibly by affecting neurogenic control mechanisms.

Animals↗
PubMed1985

The distribution of substance P, enkephalin, and serotonin immunoreactivities in the area postrema of the rat and cat.

With the use of the peroxidase-antiperoxidase technique the distribution of substance P (SP), enkephalin (ENK), and serotonin (5HT) immunoreactivities were described in the area postrema of the rat and cat. In both species, immunoreactivity in the area postrema was differentially distributed as either fibers only, or cell bodies and fibers. In the rat and cat, ENK had the greatest accumulation of immunoreactive fibers, followed by 5HT and SP. In the area postrema of the rat the majority of SP-, ENK-, and 5HT-immunoreactive fibers were along the ventral and ventrolateral borders, with fewer immunostained fibers at the dorsal surface. The area postrema of the cat had the majority of SP-, ENK-, and 5HT-immunoreactive fibers at the ventral and lateral borders, with fewer immunostained fibers at the dorsal and medial borders. In both species, the area postrema's central region contained the fewest immunostained fibers. In general, for each putative neurotransmitter examined, immunostained fibers in both species progressively decreased in number rostrocaudally. Serotonin- and ENK-immunoreactive cell bodies were found in the rat area postrema; in the cat area postrema only ENK-immunoreactive cell bodies were present. The area postrema of both species lacked SP-immunoreactive cell bodies. The heterogeneous distribution of immunoreactive fibers and cell bodies within the area postrema of the rat and cat may reflect the different functions of the area postrema in both species.

Animals↗