Effects of somatosensory and parallel-fiber stimulation on neurons in dorsal cochlear nucleus

1. Single units and evoked potentials were recorded in the dorsal cochlear nucleus (DCN) of paralyzed decerebrate cats in response to electrical stimulation at two sites: 1) in the somatosensory dorsal column nuclei (together called MSN below for medullary somatosensory nuclei), which activates mossy-fiber inputs to granule cells in superficial DCN, and 2) on the free surface of the DCN, which activates granule cell axons (parallel fibers) directly. The goal was to evaluate hypotheses about synaptic interactions in the cerebellum-like circuitry of the superficial DCN. A four-pulse facilitation paradigm was used (50-ms interpulse interval); this allows identification of three components of the responses of DCN principal cells (type IV units) to these stimuli. The latencies of the response components were compared with the latency of the evoked potential in DCN, which signals the arrival of the parallel fiber volley at the recording site. 2. The first component is a short-latency inhibitory response; this component is seen only with MSN stimulation and is seen almost exclusively in units also showing the second component, the transient excitatory response. The short-latency inhibitory component precedes the evoked potential. No satisfactory explanation for the short-latency component can be given at present; it most likely reflects a fast-conducting inhibitory input that arrives at the type IV unit before the slowly conducting parallel fibers. 3. The second component is a transient excitatory response; this component is seen with both MSN and parallel fiber stimulation; it is weak and appears to be masked easily by the inhibitory response components. The excitatory component occurs at the same latency as the evoked potential and probably reflects direct excitation of principal cells by granule cell axons. The excitatory component is seen in about half the type IV units for both stimulating sites. With MSN stimulation, the lack of excitation in some units suggests a heterogeneity of cochlear granule cells, with some carrying somatosensory information and some not carrying this information; with parallel fiber stimulation, excitation probably requires the stimulating and recording electrodes to be lined up on the same "beam" of parallel fibers. 4. The third component is a long-lasting inhibitory response that is observed in virtually all type IV units with both MSN and parallel-fiber stimulation; its latency is longer than the evoked potential. Evidence suggests that it is produced by inhibitory input from cartwheel cells. The appearance of this inhibitory component in almost all type IV units can be accounted for by the considerable spread of cartwheel-cell axons in the direction perpendicular to the parallel fibers. 5. The evoked potential and all three components of the unit response vary systematically in size over the four pulses of the electrical stimulus. These results can be accounted for by two phenomena: 1) a facilitation of the granule cell synapses on all cell types that produces a steadily growing response through the four pulses, resembles presynaptic facilitation, and is seen with both MSN and parallel-fiber stimulation; and 2) a strong reduction in the granule cell response between the first and second pulse for MSN stimulation only. This reduction probably occurs presynaptically in the glomerulus or in the granule cell itself and could reflect inhibitory inputs. 6. The response components described above are seen in type IV units recorded in both the fusiform-cell and deep layers of the DCN; this suggests that both pyramidal and giant cells are activated similarly. The simplest interpretation is that both principal cell types are activated by the cerebellum-like circuitry in superficial DCN. Alternatively, because giant cells appear to make limited contact with the granule-cell circuits of superficial DCN, this finding may suggest the existence of currently undescribed granule cell circuits in deep DCN that are si     

Selective stimulation of jugular ganglion afferent neurons in guinea pig airways by hypertonic saline

We evaluated the ability of hyperosmolar stimuli to activate afferent nerves in the guinea pig trachea and main bronchi and investigated the neural pathways involved. By using electrophysiological techniques, studies in vitro examined the effect of hyperosmolar solutions of sodium chloride (hypertonic saline) on guinea pig airway afferent nerve endings arising from either vagal nodose or jugular ganglia. The data reveal a differential sensitivity of airway afferent neurons to activation with hypertonic saline. Afferent fibers (both A delta and C fibers) with cell bodies located in jugular ganglia were much more sensitive to stimulation with hypertonic saline, compared with afferent neurons with cell bodies located in nodose ganglia. Additional studies in vivo demonstrated that inhalation of aerosols of hypertonic saline induced plasma extravasation in guinea pig trachea that was mediated via tachykinin NK1 receptors. Identification of a differential sensitivity of guinea pig airway afferent nerves to hypertonic saline leads to the speculation that airway responses to hyperosmolar stimuli may result from activation of afferent neurons originating predominantly from the jugular ganglion.     

Effects of electrical stimulation of the superior cervical ganglion on cochlear blood flow in guinea pig

A twenty-four-hour blood pressure (BP) monitoring was performed in 20 normotensive and 20 hypertensive subjects, matched by sex and age. Blood pressure and heart rate (HR) variability were evaluated both as absolute and percent standard deviation. In agreement with the literature no significant difference in HR and BP variability was observed between the two groups. The linear regression between HR and BP values was evaluated in both groups. The authors observed a significant difference in the relationship between these two cardiovascular variables between the two groups. In the hypertensive group the cardiovascular control of HR and BP showed a different relationship than in normotensive subjects, suggesting a different neurovegetative modulation.     

Distinct contributions of high- and low-voltage-activated calcium currents to afterhyperpolarizations in cholinergic nucleus basalis neurons of the guinea pig

The contributions made by low- (LVA) and high-voltage-activated (HVA) calcium currents to afterhyperpolarizations (AHPs) of nucleus basalis (NB) cholinergic neurons were investigated in dissociated cells. Neurons with somata >25 microM were studied because 80% of them stained positively for choline acetyltransferase and had electrophysiological characteristics identical to those of cholinergic NB neurons previously recorded in basal forebrain slices. Calcium currents of cholinergic NB neurons first were dissected pharmacologically into an amiloride-sensitive LVA and at least five subtypes of HVA currents. Approximately 17% of the total HVA current was sensitive to nifedipine (3 microM), 35% to omega-conotoxin-GVIA (200-400 nM), 10% to omega-Agatoxin-IVA (100 nM), and 20% to omega-Agatoxin-IVA (300-500 nM), suggesting the presence of L-, N-, P-, and Q-type channels, respectively. A remaining current (R-type) resistant to these antagonists was blocked by cadmium (100-200 microM). We then assessed pharmacologically the role that LVA and HVA currents had in activating the apamin-insensitive AHP elicited by a long train of action potentials (sAHP) and the AHP evoked either by a short burst of action potentials or by a single action potential (mAHP) that is known to be apamin-sensitive. During sAHPs, approximately 60% of the hyperpolarization was activated by calcium flowing through N-type channels and approximately 20% through P-type channels, whereas T-, L-, and Q-type channels were not involved significantly. In contrast, during mAHPs, N- and T-type channels played key roles (approximately 60 and 30%, respectively), whereas L-, P-, and Q-type channels were not implicated significantly. It is concluded that in cholinergic NB neurons various subtypes of calcium channels can differentially activate the apamin-sensitive mAHP and the apamin-insensitive sAHP.     

Effect of electrical stimulation of red nucleus on acupuncture analgesia

The function of red nucleus (RN) was important in motor control. This work was to study whether the RN influenced the effect of EA and the somatosensory afferent system. C-responses of spinal dorsal horn neurons (SDHN) were recorded as nociceptive responses. Electrical stimulation of RN could intensify the inhibitory effect of EA and inhibit nociptive response of SDHN. Naloxone (NX) could completely block that inhibition of RN. The result inferred that the RN can modulate both of somatomotion and somatosense. The endogenous opiate system is involved in the somatosensory modulation of RN.     

Induction of long-term receptive field plasticity in the auditory cortex of the waking guinea pig by stimulation of the nucleus basalis.

Learning induces neuronal receptive field (RF) plasticity in primary auditory cortex. This plasticity constitutes physiological memory as it is associative, highly specific, discriminative, develops rapidly, and is retained indefinitely. This study examined whether pairing a tone with activation of the nucleus basalis (NB) could induce RF plasticity in the waking guinea pig and, if so, whether it could be retained for 24 hrs. Subjects received 40 trials of a single frequency paired with electrical stimulation of the NB at tone offset. The physiological effectiveness of NB stimulation was assessed later while subjects were anesthetized with urethane by noting whether stimulation produced cortical desynchronization. Subjects in which NB stimulation was effective did develop RF plasticity and this was retained for 24 hrs. Thus, activation of the NB during normal learning may be sufficient to induce enduring physiological memory in auditory cortex. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of gastric distension and electrical stimulation of dorsomedial medulla on neurons in parabrachial nucleus of rats

The effects of gastric distension and electrical stimulation of the dorsomedial medulla on neurons within the parabrachial nucleus (PB) were investigated electrophysiologically in urethane-chloralose anesthetized rats. Among 74 neurons tested, electrical stimulation of the nucleus of the solitary tract (NTS) excited 30 neurons (excitatory neurons) and inhibited 14 neurons (inhibitory neurons). Fourteen neurons increased and 12 neurons decreased their discharge rates in response to gastric distension. Twenty-two neurons responded to both electrical stimulation of the NTS and gastric distension. Both excitatory and inhibitory neurons showed either an increase or a decrease in discharge rate responding to gastric distension. Furthermore, three neurons that decreased their discharge rates and two neurons that increased their discharge rates during gastric distension also responded to intravenous administration of metaraminol indicating some effect of baroreceptor activation on the neural activity. The responses of another 49 neurons in the PB to electrical stimulation of area postrema and gastric distension were analyzed. Electrical stimulation of the AP excited 14 neurons and inhibited only one neuron. Five neurons increased and seven neurons decreased their discharge rates in response to gastric distension. Only one inhibitory neuron responded to gastric distension. These observations suggested that the PB neurons received gastric mechanoreceptive inputs from the NTS.     

Effects of airway inflammation on cough response in the guinea pig

We have developed a guinea pig model for cough related to allergic airway inflammation. Unanesthetized animals were exposed to capsaicin aerosols for 10 min, and cough frequency was counted during this period. The cough evaluation was performed by the following three methods: visual observation, acoustic analysis, and monitoring of pressure changes in the body chamber. These analyses clearly differentiated a cough from a sneeze. To elucidate the relationship between cough response and airway inflammation, animals were immunosensitized and multiple challenged. Sensitized guinea pigs presented no specific changes microscopically, but multiple-challenged animals showed an increased infiltration of inflammatory cells into the airway. Cough number in response to capsaicin increased significantly from 4.7 +/- 1.4 coughs/10 min in normal animals to 10.6 +/- 2.0 coughs/10 min in sensitized animals and further to 22.8 +/- 1.3 coughs/10 min in multiple-challenged animals. This augmented cough frequency was significantly inhibited by the inhalation of tachykinin-receptor antagonists and by oral ingestion, but not inhalation, of codeine phosphate. The results suggest that airway inflammation potentiates an elevation of cough sensitivity in this model.     

Acoustic frequency tuning of neurons in the basal forebrain of the waking guinea pig

The acoustic responses of cells in the basal forebrain were studied in the adult waking guinea pig. Frequency receptive fields were obtained across wide frequency (0.094-45.0 kHz) and intensity (0-90 dB) ranges. A total of 326 recordings were obtained in 26 electrode penetrations from five subjects; 205 from the globus pallidus (GP), 98 from the caudate-putamen (CPu) and 23 from the central nucleus of the amygdala (ACE). Twenty-nine recordings exhibited acoustic responses (GP=20 (9.8%); CPu=9 (9.2%); ACE=0). Cells in the regions of the GP that project to the primary auditory cortex (ACx) exhibited frequency tuning that was dominantly suppressive. Responses in the CPu were excitatory, but poorly tuned. The spontaneous rate of discharge of GP cells that yielded complete tuning data was positively correlated with power in the beta bands (12-25 and 25-50 Hz) and negatively correlated with power in the delta band (1-4 Hz) of the EEG of the ACx. These findings suggest that acoustically tuned neurons in the GP that are inhibited by tones are involved in the regulation of auditory cortical state, possibly promoting deactivation to unimportant sounds, and may be cholinergic in nature.     

Projections of submucous neurons to the myenteric plexus in the guinea pig small intestine

Coronary venous hypertension induced by partial coronary sinus obstruction (CSO) in the dog, prevents or delays the predictable ventricular fibrillation (VF) of the early phase of acute ischemia. Also, CSO acting presumably through enhanced myocardial hydration, normalizes the inhomogenous extracellular potassium ([K+]o) accumulation, a major factor in producing the electrophysiological disparities, characteristic of arrhythmogenic substrate. To further clarify the mechanism of early ischemic VF prevention in dogs, radioactive microspheres were used to evaluate regional perfusion changes, resulting from CSO sufficient to raise the coronary sinus pressure to 40 mmHg, before and during ischemia induced by double coronary artery occlusion (CAO) (n=5). Also, global or regional unipolar electrogram mapping was used to assess changes of epicardial ventricular activation times (AT) and sequence and activation recovery intervals (ARI) during CSO, CAO and combined CSO and CAO, induced in random order (n=8). CSO did not affect regional perfusion nor improved collateral blood flow during ischemia. With CSO, AT shortened modestly over time (0.41+/-1.1 ms/min, r=0.85, P<0. 05) and ARI transiently decreased by up to 5.5%. With CAO, AT became variably delayed and isochrone map distortions were indicative of localized conduction delays or blocks, consistent with elevated [K+]o. In contrast, when CAO was preceded by CSO, AT delays were homogenous and normal activation sequence was preserved. Also, whereas with CAO, ARI shortened unequally over the ischemic region by as much as 43% at individual sites (average of 38.3+/-6.8 ms, P<0. 001), with combined CSO and CAO, ARI shortening was less pronounced and more homogenous (26.1+/-5.6 ms, P<0.05), not exceeding 29% at any site. Thus, in accordance with previous findings of enhanced [K+]o homogeneity, coronary venous hypertension reduces the disparities of activation and refractoriness of ischemia attributable, at least in part, to disparate [K+]o accumulation. Since no collateral blood flow improvement could be identified, the salutary electrophysiological effects of CSO may reflect a more homogenous extracellular environment, due to preservation of normal microvascular pressure (Pmv) and sustained filtration and lymph flow.     

Muscarine receptor activation in the substantia gelatinosa of the spinal trigeminal nucleus of the guinea pig

1. Intracellular recordings were made from slices of guinea pig spinal trigeminal nucleus pars caudalis (SG). 2. Muscarine [0.3-30 microM; half maximally effective concentration (EC50) = 2.9 microM] hyperpolarized 61% of SG neurons. The effect was mimicked by carbachol (0.3-30 microM; EC50 = 3.9 microM) and antagonized by pirenzepine (1 microM). Thirty-four percent of the neurons were depolarized by muscarine and carbachol (1-30 microM: EC50 = 5.7 microM), and the effect was antagonized by pirenzepine (100 nM). 3. In approximately 80% of recordings, muscarine (10-30 microM) evoked repetitive spontaneous inhibitory postsynaptic potentials (IPSPs) that were sensitive to bicuculline (10 microM). 4. Muscarine (1-30 microM; EC50 = 3 microM) decreased the amplitude of the majority of evoked excitatory postsynaptic potentials (EPSPs), and the effect was mimicked by carbachol and antagonized by pirenzepine (100 nM). 5. These results indicate that there are at least three mechanisms by which muscarine inhibits SG neurons: 1) hyperpolarization through activation of non-M1 receptors; 2) activation of gamma-amino-butyric acid-containing interneurons that mediate IPSPs in a subset of neurons; and 3) a decrease in evoked EPSP amplitude. Muscarine can also activate SG neurons via interaction with an M1-type receptor.     

Effects of acute brainstem compression on auditory brainstem response in the guinea pig

BACKGROUND: The purpose of this study was to establish the norm for parameters of auditory brainstem response (ABR) in the guinea pig and to investigate if acute brainstem compression results in significant changes to these parameters. METHODS: Thirty-six guinea pigs with positive Preyer's reflex were anesthetized. A craniectomy was performed to remove the right occipital bone and the dura mater was opened to expose the brain, cerebellum and cerebellopontine angle (CPA). A small inflatable balloon was placed into the CPA precisely and slowly. ABR was recorded before incision of the skin as a baseline value, after placement and after inflation of the balloon with water at 0.1-ml intervals. RESULTS: Five stable peaks were recorded in 27 experimental animals. When the balloon was inflated with 0.1 ml water, the absolute latency (AL) of peaks IV and V and the interpeak latency (IPL) of peaks III and IV, and IV and V were prolonged. The amplitude ratios (AR) of peaks II, III, IV and V to peak I decreased. Inflation of the balloon with 0.2 ml of water caused further elongation of ALs of peaks IV and V and decreases in each AR. When the balloon volume increased to 0.3 ml, peak V became unrecognizable and peaks III and IV showed significant elongation of AL; peaks I and II did not show significant change in ALs. Further increase of the balloon volume to 0.4 ml resulted in disappearance of peaks III, IV and V; AL of peak II was also elongated. However, the amplitude and AL of peak I remained unchanged. Similar changes were observed in IPLs. CONCLUSIONS: This study establishes the norm of parameters of ABR in guinea pigs and demonstrates that acute brainstem compression causes elongation of ALs and IPLs of peaks II, III, IV and V. This suggests that peaks II, III, IV and V come from the brainstem and that peak I is not generated from the brainstem in the guinea pig.     

Effects of K(+)-channel blockers on cochlear potentials in the guinea pig

The effects of different K+ channel blockers, 4-aminopyridine (4-AP), tetraethylammonium (TEA) and quinine, on the various cochlear potentials were observed by the means of perilymph infusion. Each of the three blockers depressed the compound action potential. However, they exerted quite different effects on other cochlear potentials, especially comparing 4-AP, a fast K(+)-channel blocker, with two other blockers. 4-AP induced a significant increase in the magnitude of summating potential, while TEA and quinine decreased it; 4-AP showed no effect on the general endocochlear potential (G-EP, the EP value recorded directly from the scala media, SM) and the negative EP component (N-EP), while TEA and Quinine increased G-EP and decreased the absolute value of N-EP. They also exerted different effects on the EP changes induced by exposure to intense noise. The results indicate the different roles of different K(+)-channels in the generation of cochlear potentials. The relationship of the two components of EP (positive and negative) and the G-EP was discussed.     

Spatial organization of facial vibrissae and cortical barrels in the guinea pig and golden hamster

The arrangements of vibrissae in guinea pigs and golden hamsters were previously reported to be different from those in mice and rats. Whereas the mystacial pads in mice and rats include four straddlers and five rows of vibrissae, guinea pigs were described to possess six rows of irregularly aligned mystacial vibrissae and no straddlers, and golden hamsters to include seven vibrissal rows and also no straddlers. We found that all of these four species possess similar vibrissal arrangements within the mystacial pad. To demonstrate this similarity, we developed a new method of sinus hair visualization in flattened and cleared preparations of the mystacial pad. Intrinsic muscles of the mystacial pad that were revealed in thick histological preparations showed clearly the structural and functional relationships between straddlers and vibrissal rows. To verify this finding, and to extend the knowledge of vibrissal cortical representations in guinea pigs and golden hamsters, we have investigated the spatial organization and the functional vibrissal representations of barrels in the posteromedial barrel subfield (PMBSF) of these rodents. The barrel morphology was clearly preserved in Nissl-stained sections and sections processed for cytochrome oxidase of flattened cerebral cortices. We demonstrate that the vibrissal arrangement in the mystacial pad is replicated in the PMBSF of guinea pigs and golden hamsters and that this arrangement is similar to that found in mice and rats. To facilitate comparative studies, these findings strongly recommend the use, in guinea pigs and golden hamsters, of the same classifications and nomenclatures that are used in mice and rats to describe mystacial vibrissae and cortical barrels.     

Electrophysiological properties and their modulation by norepinephrine in the ambiguus neurons of the guinea pig

Electrophysiological properties of guinea pig ambiguus (AMB) neurons were studied in a brainstem slice preparation. During subthreshold depolarization AMB neurons displayed an early slow depolarization and a late outward rectification both of which were blocked by replacing Ca2+ with Co2+ in the extracellular solution. AMB neurons showed hyperpolarizing inward rectification which was blocked by extracellular Cs+ and is likely caused by the activation of Ih: In 58% (n = 49) of AMB neurons spike firing was restricted to the early phase of a long-lasting depolarizing current injection (phasic firing). The remaining AMB neurons showed repetitive firing throughout the depolarization (tonic firing). A Ca(2+)-mediated K+ current (IK(Ca)) caused an afterhyperpolarization that followed both single and repetitive spike firing. IK(Ca) also controlled the firing pattern in both types of firing, especially in the phasic firing. Norepinephrine (NE) blocked both the hyperpolarizing inward rectification and the Ca(2+)-dependent AHP. These effects of NE were antagonized by propranolol. It is proposed that the blockade of IK(Ca) and Ih contribute to the improvement of the 'signal-to-noise ratio' by NE in AMB neurons.     

Effects of saccades on the activity of neurons in the cat lateral geniculate nucleus

Effects of saccades on individual neurons in the cat lateral geniculate nucleus (LGN) were examined under two conditions: during spontaneous saccades in the dark and during stimulation by large, uniform flashes delivered at various times during and after rewarded saccades made to small visual targets. In the dark condition, a suppression of activity began 200-300 ms before saccade start, peaked approximately 100 ms before saccade start, and smoothly reversed to a facilitation of activity by saccade end. The facilitation peaked 70-130 ms after saccade end and decayed during the next several hundred milliseconds. The latency of the facilitation was related inversely to saccade velocity, reaching a minimum for saccades with peak velocity >70-80 degrees /s. Effects of saccades on visually evoked activity were remarkably similar: a facilitation began at saccade end and peaked 50-100 ms later. When matched for saccade velocity, the time courses and magnitudes of postsaccadic facilitation for activity in the dark and during visual stimulation were identical. The presaccadic suppression observed in the dark condition was similar for X and Y cells, whereas the postsaccadic facilitation was substantially stronger for X cells, both in the dark and for visually evoked responses. This saccade-related regulation of geniculate transmission appears to be independent of the conditions under which the saccade is evoked or the state of retinal input to the LGN. The change in activity from presaccadic suppression to postsaccadic facilitation amounted to an increase in gain of geniculate transmission of approximately 30%. This may promote rapid central registration of visual inputs by increasing the temporal contrast between activity evoked by an image near the end of a fixation and that evoked by the image immediately after a saccade.     

The topographical organization of descending projections from the central nucleus of the inferior colliculus in guinea pig

We describe the descending projections from the central nucleus of the inferior colliculus (CNIC) in guinea pig. Focal injections of the tracer biocytin, made in physiologically defined frequency regions of the CNIC, labelled laminated axonal terminal fields in the ipsilateral dorsal nucleus of the lateral lemniscus, and bilaterally in the ventral nucleus of the trapezoid body and the dorsal cochlear nucleus. Labelling was also present in the rostral periolivary nucleus, but we could not distinguish a clear border between the terminal fields in this nucleus and those in the ventral nucleus of the trapezoid body. Labelling observed in the ventral nucleus of the lateral lemniscus, and to a lesser extent in the dorsal nucleus of the lateral lemniscus, was accompanied by retrogradely labelled somata and therefore we cannot conclude unequivocally that the CNIC projects to these lemniscal nuclei. Where the labelling was ordered topographically, its position varied as a function of the best frequency at the injection site. High-frequency regions in the CNIC project to the medial parts of the ventral nucleus of the trapezoid body and dorsal cochlear nucleus, while low-frequency regions in the CNIC project to the lateral parts of the ventral nucleus of the trapezoid body and dorsal cochlear nucleus. Additional axonal labelling with terminal boutons, but with no apparent topographical arrangement, was present in the ipsilateral horizontal cell group, sagulum, and also bilaterally in the superficial granule cell layer of the ventral cochlear nucleus and layer 2 of the dorsal cochlear nucleus. Our findings are consistent with the existence of tonotopically organised feedback projections from the CNIC to the brainstem nuclei that project to it.     

Effects of raloxifene in a guinea pig model for leiomyomas

OBJECTIVE: Chronic exposure of oophorectomized guinea pigs to 17beta-estradiol causes leiomyoma formation. Our aims were to determine whether these leiomyomas can become estradiol independent after exposure to estradiol and if raloxifene inhibits leiomyoma growth when given concomitantly with estradiol. STUDY DESIGN: To induce leiomyoma development, 6 oophorectomized animals received two estradiol implants for 140 days. Next, the estradiol implants were replaced with empty implants in 3 animals, whereas the other 3 received 2 new estradiol implants and raloxifene given per os 10 mg/kg per day for 60 days. Tumor size was monitored biweekly by ultrasonography. RESULTS: On estradiol removal, abdominal wall leiomyomas regressed within 15 to 30 days; when estradiol implants were reintroduced, leiomyomas redeveloped. Within 30 days on raloxifene, all abdominal leiomyomas (n = 9) regressed as determined by ultrasonography and verified at laparotomy. Serum raloxifene and estradiol levels were 432 +/- 46 pg/mL and 78 +/- 13 pg/mL (mean +/- SEM, n = 3), respectively, after 60 days of treatment. CONCLUSIONS: Leiomyomas did not become estradiol independent, even after long exposure to estradiol; ultrasonography allowed frequent, noninvasive assessment of leiomyoma size, and raloxifene rapidly regressed leiomyomas in this animal model.