Stereotaxic Apparatus Research Articles

Experimental Models of Partial Lesion of Rat Spinal Cord to Investigate Neurodegeneration, Glial Activation, and Behavior Impairments

The article demonstrates two experimental models of spinal cord partial injury in rats: a contuse model promoted by the NYU impactor system and a partial hemitransection model achieved by a stereotaxic-posi-tioned adjustable wire knife. By means of a defined impact weight (10 g) and a digital optical potentiometer linked to a computer, the impactor transferred and registered a moderate or a severe contusion to the rat spinal cord at a low thoracic level after dropping the weight from distances of 25 mm and 50 mm, respectively, to the dorsal surface of the exposed dura spinal cord. Impact curve was calculated and the parameters of the trauma, like impact velocity, cord compression distance and cord compression rates were obtained in order to demonstrate trauma severity. To promote partial hemitransection, rats were positioned in a spinal cord unit of a stereotaxic apparatus and lesion was made with the adjustable wire knife spatially oriented. By means of a computerized infrared motion sensor-home cage activity monitor and a noncomputerized evaluation of motor behavior using the inclined plane and the motor score of Tarlov tests, behavior was analyzed in an acute period postlesion. Rats were sacrificed and spinal cords were processed for routine staining to show neurons and for GFAP and OX42 immunohistochemistry to demonstrate glial cells. The tissue labelings were quantified using computer assisted stereology by means of an optical disector and microden-sitometric image analysis by means of quantification of gray values of discriminated profiles. While partial hemitransection model favored a more accurate control of the lesion location, the contuse model allowed us to perform different degrees of lesion severity. A close correlation between behavioral impairment and severity of trauma was seen in the rats submitted to spinal cord contusion. The stereologic lesion index showed a correlation between severity of trauma and tissue damage by 7 days and demonstrated a time-dependent secondary degeneration after moderate but not after severe spinal cord contusion from 7 to 30 days after injury. Long-lasting activations of astrocytes and microglia seen by persisted increases in the specific mean gray values of immu-noreactivities were also found in all levels of the white and gray matters of the partial hemitransected spinal cord until 3 months postinjury which can he related to wound/repair events and paracrine trophic support to spinal cord remaining neurons. The results showed that controlled partial lesions may provide an important toll to study trophism and plasticity in the spinal cord.

INCREASES IN INTRACAVERNOUS PENILE PRESSURE FOLLOWING INJECTIONS OF EXCITATORY AMINO ACID RECEPTOR AGONISTS IN THE HYPOTHALAMIC PARAVENTRICULAR NUCLEUS OF ANESTHETIZED RATS

We examined whether N-methyl-D-aspartate (NMDA), amino-3-hydroxy-5-methyl-isoxazole-4-propionic acid (AMPA) or trans-1-amino-1,3-cyclo-pentadicarboxylic acid (ACPD) increase intracavernous pressures when injected in the paraventricular nucleus of the hypothalamus. Sprague-Dawley rats weighing 250 to 300 gm. were anesthetized with pentobarbital and placed in a stereotaxic apparatus after catheterization of the carotid artery and insertion of a 25 gauge needle in the corpus cavernosum. Both catheters were coupled to pressure transducer systems. Electrical stimulations with glass tungsten microelectrodes and chemical injections with a 0.5 microl. syringe were done in the paraventricular nucleus. At the end of each experiment rats were perfused with saline and 10% formalin solutions. Brains slices 16 microm. thick were mounted and stained with cresyl violet to identify chemical and electrical stimulation sites. Electrical stimulations of the paraventricular nucleus increased intracavernous pressure from 15.5 +/- 5.7 to 50.02 +/- 20.4 cm. H2O in 10 rats (p <0.001) and decreased central pressure in 10 (p <0. 001). Intracavernous pressure increased from 17.2 +/- 5.26 to 60.6 +/- 14.36 cm. H2O with NMDA, 26.0 +/- 8.9 to 49.6 +/- 12.2 cm. H2O with AMPA and 18.0 +/- 2.3 to 41.0 +/- 22.68 cm. H2O with ACPD when injected in the paraventricular nucleus of 5 rats (analysis of variance 12.18, df 3, p <0.007). Mean delays and durations varied between 3.6 to 4.0 and 5.6 to 7.0, respectively, and were similar for all agonists (analysis of variance not significant). Glutamate receptor subtypes NMDA, ACPD and AMPA cause an increase in intracavernous pressure when injected in the paraventricular nucleus. Therefore, increases in intracavernous pressure following injection of glutamate must be initiated by the synergistic or additive effects of all of these receptor subtypes.

Changes in expression of N-methyl- d-aspartate receptor subunits in the rat neostriatum after a single dose of antisense oligonucleotide specific for N-methyl- d-aspartate receptor 1 subunit

In order to investigate the process of gene expression of N-methyl- d-aspartate glutamate receptor (NMDAR) subunits in the rat neostriatum and how this relates to motor behaviors, a single dose of antisense phosphodiester oligodeoxynucleotide specific for NMDAR1 was unilaterally applied in the neostriatum in a stereotaxic apparatus. After one day of antisense treatment, ipsilateral rotation behaviors that were induced by apomorphine were found in the treated animals. Reductions in the levels of expression of NMDAR1 and NMDAR2A messenger RNAs (NMDAR1: 20.6%; NMDAR2A: 19.7%) were found in the antisense-treated striatal tissues by reverse transcriptase–polymerase chain reaction. There was no change in the levels of NMDAR2B, NMDAR2C and NMDAR2D messenger RNAs. After two days, western blotting experiments showed that there were decreases in the levels of expression of NMDAR1 (decreased 27.6%) and NMDAR2A (decreased 19.2%) proteins in the NMDAR1 antisense-treated striatal tissues. In addition, NMDAR1 immunoreactivity was found to decrease in intensity in the NMDAR1 antisense-treated neostriatum. At the cellular level, the intensity of NMDAR1 immunoreactivity in perikarya of presumed medium spiny neurons was found to decrease. These results indicate that a single dose of NMDAR1 antisense modifies the expression of NMDAR1 messenger RNA and protein in neurons in the neostriatum. The modification in the expression of NMDAR1 has differential effects in the expression of NMDAR2 subunits. Gene expression of the native NMDAR subunits is likely to be a dynamic process. The change in gene expression of the NMDAR subunits in the neostriatum may have a profound effect on the motor behaviors of rats.

Sampling extracellular aspartate, glutamate and γ-aminobutyric acid in striate cortex of awake cat by in vivo microdialysis: surgical and methodological aspects

A method which permits repeated microdialysis in the cortical layers of area 17 of the awake cat is described. Under visual control through a surgical microscope and using a stereotactic instrument, four probe guides are permanently implanted in area 17 of one hemisphere of the anesthetized animal and two fixation bars are mounted on the skull to allow fixation of the cat in a stereotactic frame. The implantation of four probe guides in the same hemisphere allows simultaneous sampling from different cortical regions serving different parts of the visual field. A removable transparent cover protects the probe guides. After recovery from surgery the awake cats are trained to adapt to a fixation of 5 h in a stereotaxic apparatus. Once adapted to that situation, the cats are ready for microdialysis experiments without anesthesia. The day of the experiment, the awake animal was fixed in the stereotactic frame and the probes inserted into the guides. To test the validity of the method, the basal efflux and the depolarization efflux, triggered by the addition of 65 mM K + to the artificial cerebrospinal fluid, of the amino acids aspartate, glutamate and γ-aminobutyric acid are measured by two HPLC–electrochemical detection methods. The exact localization of the probes and the reaction of the surrounding tissue is studied using immunocytochemistry for glutamate and glial fibrilary acidic protein. Our neurochemical and morphological results suggest the feasibility of multiple and repeated probe insertions for microdialysis experiments in the cerebral cortex of awake and behaving cat. This method provides a new tool to investigate the cortical plasticity.

Cocaine-induced changes in extracellular dopamine determined by microdialysis in awake squirrel monkeys.

The behavioral effects of cocaine have been linked to brain dopamine systems. Extending the findings to neurochemical studies in the squirrel monkey would enhance our understanding of the behavioral pharmacology of cocaine in nonhuman primates. The present studies characterized the effects of cocaine and the selective dopamine uptake inhibitor GBR 12909 on extracellular dopamine in the caudate nucleus of awake squirrel monkeys through microdialysis experiments. Guide cannulae were implanted in the caudate nucleus of four monkeys using a stereotaxic apparatus and coordinates obtained from a standard squirrel monkey brain atlas. Accurate probe placement was confirmed in all subjects with magnetic resonance imaging. Collectively, the results support the feasibility of a repeated-measures design. Stability of tissue integrity after repeated probe insertion was supported by measurement of consistent basal levels of dopamine and its metabolites across several experiments, observation of potassium-induced dopamine release and absence of significant glial proliferation as assessed by GFAP (glial fibrillary acidic protein) immunochemistry. Moreover, peak drug effects and time-course of action were similar when multiple probes were positioned in the same anatomical site over several experiments. Cocaine (1.0 mg/kg i.m.) and GBR 12909 (3.0 mg/kg i.m.) elevated extracellular dopamine to approximately 300% of basal levels, but GBR 12909 produced a slower, more sustained elevation than cocaine. The results validate the use of microdialysis in awake primates using repeated sampling of the same anatomical site and demonstrate orderly changes in extracellular dopamine following administration of dopamine uptake inhibitors.

Simultaneous depletion of neurokinin A, substance P and calcitonin gene-related peptide from the caudal trigeminal nucleus of the rat during electrical stimulation of the trigeminal ganglion

The central terminals of the primary sensory trigeminal ganglion (TG) neurons projecting into the caudal trigeminal nucleus (CTN) of the rat exhibit neurokinin A (NKA)-, substance P (SP)-, and calcitonin gene-related peptide (CGRP)-immunoreactivities (IRs). We stimulated the TG in the rat to induce some of the alterations which might occur during migraine (neurogenic inflammation). Under a stereotaxic apparatus and by means of a bipolar electrode, one-side TG of the animals were electrically stimulated (7.5 Hz, 5 ms, 0.8–1.4 mA) with square pulses for 5 min. Then, using immunohistochemical methods, the lower medulla of each rat was studied for NKA-, SP- and CGRP-IRs. Light microscopic examination of brain-stem sequencial sections revealed a simultaneous decrease in the immunoreactivities of all neuropeptides (NKA, SP and CGRP) in the CTN ipsilateral to TG stimulation in comparison with the other (not stimulated) side CTN. It is suggested that this decrease in immunoreactivity would be due to the co-release of neuropeptides following noxious stimuli and that NKA, SP and CGRP might therefore act as co-transmitters or co-modulators at the first central synapses of the trigeminal sensory pathway.

Acute Phase Histopathological Study of Spinally Administered Midazolam in Cats

Acute Phase Histopathological Study of Spinally Administered Midazolam in Cats

The influence of nimodipine, nicardipine and amlodipine on the brain free fatty acid level in rats with penicillin-induced seizures

1. 1. The aim of this study was to investigate the effects of the calcium channel blockers, nimodipine, nicardipine and amlodipine, on the brain free fatty acid (FFA) level in rats with chemically-induced seizures. 2. 2. The study was carried out on Hannover-Wistar rats. Animals were anesthetized and placed in a stereotaxic apparatus. Each of them received an injection of penicillin (5000 IU/5 μl) into the left lateral ventricle (i.c.v.). Various doses (1,3,10 or 30 mg/kg) of niniodipine, nicardipine or amlodipine had been injected i.p, 30 min before the penicillin application. The rats were decapitated 5 min after the occurrence of epileptic seizures. FFAs were quantified by gas chromatography using the internal standard method. 3. 3. The results demonstrate that i.c.v. injection of penicillin was associated with significant increase in the brain FFA concentration. Tested doses of nicardipine and amlodipine did not influence the increase of the brain free palmitic, stearic, oleic and arachidonic acid level while nimodipine prevented the accumulation of free palmitic, oleic and arachidonic acid in rats with penicillin-induced seizures. Statistically insignificant decrease of steric acid was observed in animals pretreated with nimodipine. 4. 4. It maybe assumed that the brain FFA accumulation caused by i.c.v. penicillin administration is not predominantly associated with a disturbance in calcium homeostasis via L-type voltage-sensitive calcium channels, but by some other membrane and/or intracellular mechanisms .

Amphetamine microinfusion in the dorso-ventral axis of the prefrontal cortex differentially modulates dopamine neurotransmission in the shell-core subterritories of the nucleus accumbens.

The two main subdivisions of the nucleus accumbens (NAC), the dorsolateral core and the ventromedial shell, can be distinguished by a distinct connectivity pattern originating mainly from the prefrontal cortex (PFC).1,2 More specifically, the core of the NAC receives major projections from the anterior cingulate and dorsocaudal prelimbic cortices, which are referred to as the dorsal PFC.3,4 In contrast to the core, the shell of the NAC receives main afferents from the ventral prelimbic and rostral infralimbic cortices, which are termed the ventral PFC.3,4 The present study sought to evaluate the contributions of the ventral prelimbic/infralimbic cortices and shell subterritory of the NAC as well as the dorsal prelimbic/anterior cingulate cortices and core subregion of the NAC to the microinfusion of amphetamine (AMPHE) on dialysate DA levels using a dual-probe microdialysis design. Male Wistar rats were anesthetized with sodium pentobarbital (60 mg/kg, i.p.) and mounted on a stereotaxic apparatus. The skull was exposed and two holes were drilled for unilateral placement of microdialysis probes into (1) the core of the NAC and the dorsal PFC, and (2) the shell of the NAC and the ventral PFC. One-hourly dose of chloral hydrate (100 mg/kg, i.p.) was administered to maintain a constant level of anesthesia throughout the experiment. Following the determination of basal DA levels, 5 increasing concentrations of AMPHE (1, 10, 100, 500, 1000 μM) were substituted for the dialysis perfusate in the PFC for 60 min each. Both microdialysis procedures and chromatographic analyses of brain microdialysates were the same as described previously.5 Basal DA levels were significantly higher in the ventral PFC compared with the dorsal PFC and higher concentrations of DA were also observed in the core of the NAC compared with its shell counterpart (FIG. 1A). Reverse microdialysis of AMPHE in the ventral PFC produced a significant dose-dependent decrease in dialysate DA levels. In contrast, no significant alterations in DA levels were observed following AMPHE microinfusion in the dorsal PFC (FIG. 2A). Furthermore, the

Stereotaxic atlas of the pig brain

A stereotaxic atlas of the pig brain has been established. It consists of 60 frontal and 18 sagittal drawings illustrating Nissl stained sections. A stereotaxic apparatus adapted for the Pig was used to determine the brain coordinates. Radiographic techniques were applied to verify the correct position of the central nervous structures in the apparatus. The zero horizontal plane contains the line joining the recessus preopticus and the posterior commissure (PC) images. These two landmarks were identified by ventriculography. The anterior limit of the PC is used as zero on the stereotaxic atlas. Vertical electrode trajectories implanted at a fixed depth in the brain and at different anterior and lateral levels were used to determine the lateral, vertical and height coordinates in the different planes. Then the brains were perfused and embedded to avoid major displacement of the cerebral structures. Frontal and sagittal serial sections of 100 μm were performed in two different animals. Magnified diagrams of brain sections representing the cellular architecture of the brain structures were produced, some of which are illustrated with photomicrographs. For certain areas, the limits of the nuclei were difficult to determine even when complementary electrophysiological studies were carried out. Each plate is accompanied by a list of abbreviations used to label structures on the plate, together with the terms which they represent. This work should provide a useful anatomical guide for research on the pig brain.

GDNF improves dopamine function in the substantia nigra but not the putamen of unilateral MPTP-lesioned rhesus monkeys

Microdialysis measurements of dopamine (DA) and DA metabolites were carried out in the putamen and substantia nigra of unilateral 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned rhesus monkeys that received intraventricular injections of vehicle or glial-derived neurotrophic factor (GDNF, 300 μg) 3 weeks prior to the microdialysis studies. Following behavioral measures in the MPTP-lesioned monkeys, they were anesthetized with isoflurane and placed in a stereotaxic apparatus. Magnetic resonance imaging (MRI)-guided sterile stereotaxic procedures were used for implantations of the microdialysis probes. Basal extracellular levels of DA and the DA metabolites, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), were found to be decreased by >95% in the right putamen of the MPTP-lesioned monkeys as compared to normal animals. In contrast, basal DA levels were not significantly decreased, and DOPAC and HVA levels were decreased by only 65% and 30%, respectively, in the MPTP-lesioned substantia nigra. Significant reductions in d-amphetamine-evoked DA release were also observed in the MPTP-lesioned substantia nigra and putamen of the monkeys as compared to normal animals. A single intraventricular administration of GDNF into one group of MPTP-lesioned monkeys elicited improvements in the parkinsonian symptoms in these animals at 2–3 weeks post-administration. In addition, d-amphetamine-evoked overflow of DA was significantly increased in the substantia nigra but not the putamen of MPTP-lesioned monkeys that had received GDNF. Moreover, post-mortem brain tissue studies showed increases in whole tissue levels of DA and DA metabolite levels primarily within the substantia nigra in MPTP-lesioned monkeys that had received GDNF. Taken together, these data support that single ventricular infusions of GDNF produce improvements in motoric behavior in MPTP-lesioned monkeys that correlate with increases in DA neuronal function that are localized to the substantia nigra and not the putamen.

The inhibition by central bombesin of peripheral stimulation of gastric secretion involves the release of nitric oxide in the dorsal motor nucleus of the vagus

Background: The neuropeptide bombesin inhibits gastric acid secretion (GAS) when administered centrally (1). Pentagastrin stimulates GAS acting on parietal cells of the stomach mucosa. Previous studies have shown that nitric oxide (NO) synthetised in the dorsal motor nucleus of the vagus (DMN) has an inhibitoy role on GAS stimulated by centrally acting agents such as distension or insulin (2). Aim: To analyse the implication of NO in the DMN in the inhibitory effects of bombesin on peripherallly stimulated GAS. Method: GAS was evaluated in rats perfused intragastrically with saline (0.9 ml min-l). Animals were placed in a stereotaxic apparatus and thereafter they received a bolus of pentagastrin (100 pg kg-l). Prior to this injection, L-NAME (80 pg kg -1) was administered locally in the DMN or in the nucleus of the tractus solitarius (NTS), and animals received an intracisternal (i.e.) administration of bombesin (40 ng kg-l). A bilateral vagotomy was performed in some experiments. Control animals were treated with vehicle (PBS) Results: (A~tEqH + 30 min -1 100 g-l; mean -+ s.e.m.; n > 6 per group)

Inhibition by bombesin of centrally-mediated gastric acid secretion implicates the synthesis of nitric oxide in the dorsal motor nucleus of the vagus

Background: Cerebral administration of the endogenous neuropeptide bombesin inhibits gastric acid secretion (GAS). We have previously shown that synthesis of neuronal nitric oxide (NO) in the dorsal motor nucleus of the vagus (DMN) is implicated in the inhibition of GAS (2). Aim: To analyse the role of NO in the acid inhibitory effect of bombesin on two different stimulants of centrally mediated GAS. Methods: Gastric acid secretion was evaluated in urethane (1.5 mg kg -1) anaesthetized rats perfused intragastrically with saline (0.9 ml min-1). Once secretion had remained constant for 60 minutes, rats were placed in a stereotaxic apparatus and L-NAME (80 lag kg -1) or vehicle (PBS) were administered in the DMN. Animals received either an intracistemal (i.c.) microinjection of TRH (300 ng kg 1) or an i.p. bolus of insulin (0.75 u.i. kg-l). Previously bombesin was administered i.e.(40 ng kg-l). In the TRH stimulated group, some animals received a co-administration of L-NAME (80 lag kg q) and L-arginine (400 lag kgd). Results: Expressed as AlaEqH + 100 g-l during the appropriate experimental time in each experimental model (mean ± s.e.m., n>5):

V-6-87 - Three-dimensional image synthesis of MRI and CT angiography on an image-guided neurosurgical simulation system

This chapter reviews the historical background of stereotaxy, beginning with the stereotaxic apparatus of Horsley and Clarke, acknowledging some of the earlier nineteenth-century methodology, and including the early work associated with the Horsley–Clarke frame. The development of a human stereotactic frame by Spiegel and Wycis is then reviewed, followed by discussion of the many subsequent systems, including those of Leksell, Reichert, Mundinger, Talairach, Narabayashi, and others. The development of stereotactic systems not requiring a frame—so-called “frameless stereotaxy,” “neuronavigation,” and “image-guidance”—resulted from the availability of computational resources. The multiple technologies available to accomplish fundamental component tasks of stereotaxy are then reviewed: for definition of intraoperative coordinate spaces: articulated arms, sonic digitizers, optical digitizers, electromagnetic digitizers; for accomplishment of co-registration: paired-pair methodology, contour matching, mutual information algorithms; for stereotactic effectors: probes, radiation beams, graphic displays, heads-up displays, and robotics.

A method for improving the accuracy of stereotaxic procedures in monkeys using implanted fiducial markers in CT scans that also serve as anchor points in a stereotaxic frame

We developed a relatively inexpensive method for stereotaxic placement of electrodes or needles in the brains of monkeys. Steel balls were affixed to the skulls of monkeys. These balls served as fiducial markers and were also used as points at which the monkey's skull was held in a modified stereotaxic apparatus. Computed tomography (CT) was used to establish the location of an injection target with respect to the fiducial markers. A computer program related the CT coordinates to stereotaxic coordinates. These were used to direct an electrode marker toward a target in the hypothalamus. With the marker left in place, the monkey was removed from the stereotaxic frame and a second CT scan was performed. Corrections for errors in marker placement were made and retrograde tracers were injected. This procedure was found to be more accurate and reliable than conventional stereotaxic procedures. The accuracy and repeatability of the technique were also established using a phantom model of a monkey's skull. Two important advantages of this method are that animals can be repeatedly placed into the stereotaxic frame in precisely the same position and that there are many opportunities during the procedure to check for and correct errors.

歯髄の電気刺激に応答するネコ三叉神経中脳路核一次ニューロンの性質

The existence of primary afferent neurons innervating the tooth pulp (TP) has been demonstrated by the HRP tracing method in the mesencephalic trigeminal nucleus (MTN) of the cat, dog and monkey by Amano et al. (1987) and Yoshino et al. (1989), (1993). The intention of the present study was to confirm electrophysiologically that the neurons in the feline MTN that respond to electrical stimulation of the TP are cell bodies of primary afferent fibers and to examine their functional properties. Adult cats of either sex were anesthetized with urethane-chloralose and mounted on a stereotaxic apparatus. For electrical stimulation and whole nerve recordings, the right inferior alveolar nerve (IAN) was exposed and a pair of Ag-AgCl wire electrodes were placed in contact with the intact nerve. For bipolar EMG recording, a pair of copper wire electrodes were sutured into the ipsilateral anterior digastric muscle (DIG). The right maxillary and mandibular canine teeth were used for electrical stimulation of the TP. To activate as many pulpal afferent fibers as possible with constant low current stimulation, two Ag-AgCl wire electrodes were implanted into deep dentin cavities prepared in the canine root portions corresponding to the apical one- and two-fourths. Single-unit recordings were made with glass-coated elgiloy microelectrodes in the region of P2.5 and L2.5, corresponding to the caudal part of the MTN. During recordings in the MTN, unitary spindle and periodontal activities were detected with occasional manual force to the mandible or to the canine teeth. The only unitary activity related to the electrical TP stimulation was investigated. The recording sites were histologically verified with the aid of electrode tip marking. A total of 25 single neurons were recorded from the MTN of 20 cats. These neurons followed faithfully double pulse stimuli separated by 2 msec (i.e., 500 Hz) delivered to the canine TP, responded with a consistent short latency ranging 1.2-2.0 msec (1.6±0.2 msec, mean±SD) and were histologically confirmed to locate in the MTN. Their conduction velocities were 38.0-63.3 m/sec (48.9±6.4 m/sec, mean±SD) and agreed well with the aβ range of 35-70 m/sec. Prior to paralyzation, recordings were carried out simultaneously from an ipsilateral MTN primary pulpal neuron, whole IAN and DIG. The responses to gradually increasing intensity of single pulse stimuli (20 μsec duration) to the mandibular canine TP were graded and the thresholds were carefully determined. The fastest component of the IAN compound action potential due to the largest pulpal afferent fibers apperared at 2.7 mA. Stimulus intensity had to be increased to 1.4 times threshold to cause firing of the MTN pulpal neuron and short-latency digastric reflex activity (7.0 msec latency). This MTN pulpal neuron with the same threshold for the digastric reflex was histologically confirmed to locate in the mesencephalic trigeminal tract a little away from other primary afferent neurons with relatively large soma aggregating in clusters. The main finding of the present study is that the feline MTN primary neurons supply the TP with Aβ afferent fibers. These MTN pulpal neurons might play a role of mechanoreception, as indicated by Dong et al. (1985) in the feline intradental afferents with soma in the TG.

Antisense Knockdown of Brain Dopamine Receptors

Publisher Summary Antisense knockdown refers to the ability of specifically designed short sequences of antisense oligodeoxynucleotides (AON) to bind to their complementary mRNA and stop translation, thereby preventing the production of the protein that the mRNA codes for. Because it is so highly specific, it can be used to probe the functions of receptor subtypes for which specific and selective agonists or antagonists do not exist. This chapter describes the electrophysiological consequences following antisense knockdown of dopamine D2 and/or D3 receptors in DA substantia nigra (SN) neurons. In this purpose male Sprague-Dawley rats were anesthetized with ketamine-xylazine, placed in a stereotaxic apparatus, and implanted with a 28-g stainless steel guide cannula at a 20-degree angle. Three to 7 days after the start of the infusion, rats were anesthetized with urethane, the left femoral vein or a lateral tail vein was cannulated, and each rat was placed into a stereotaxic frame. A bipolar stimulating electrode was inserted into the ipsilateral neostriatum, and extracellular recordings of antidromically identified SN DA neurons were obtained. Studies show that although there were clear effects of both D2 and D3 AON treatment on the apomorphine dose-response relation, on the terminal excitability and on the proportion of antidromic responses consisting of the initial segment and somadendritic components, there was no effect of any AON treatment on the baseline spontaneous firing rate or pattern. The data presented in the chapter shows that DA neurons possess functional D2 and D3 autoreceptors at both their axon terminal and somatodendritic regions. Both types of terminal autoreceptors modulate terminal excitability and presumably the release of DA from the nerve terminals and/or its synthesis.

Neuronal responses to iontophoretically applied angiotensin II, losartan and aldosterone, as well as gustatory stimuli, in non-anesthetized control and desoxycorticosterone acetate-pretreated rats

The neuronal mechanism of the sodium appetite initiated in rats by priming with a mineralocorticoid (desoxycorticosterone acetate (DOCA)) treatment and subsequent central angiotensin II (Ang II) was investigated using electrophysiological-iontophoretic techniques and sapid salt stimulation of the tongue in non-anesthetized restrained, DOCA-pretreated (0.5 mg/day s.c. for 3 days) or non-pretreated male Wistar rats. The rats were trained to drink water and a 1.6% NaCl solution while their heads were painlessly held in a stereotaxic apparatus with an attachment fixed to the skull. A total of 634 neurons (375 in non-pretreated and 259 in DOCA-pretreated rats) were recorded in the medial septum and median preoptic area during iontophoretic application of Ang II, aldosterone or losartan, or tongue application of the salty solution or water. Of the 151 neurons recorded in control rats during the application of the solutions on the tongue, one (0.7%) was found specifically excited and 16 (10.6%) inhibited by the sapid sodium. Similarly, of the 110 neurons tested in the DOCA-pretreated rats, 5 (4.5%) were found specifically excited and 8 (7.3%) inhibited by the sapid sodium. The number of neurons responding to the iontophoretically applied agents was not significantly changed by the DOCA pretreatment. Thus, the DOCA pretreatment significantly increased the number of preoptic neurons that were specifically excited by a salty solution applied on the tongue. These results suggest that hormonally induced changes in the gustatory responsiveness of ventral forebrain neurons may be part of the sequence that alters the hedonic valence of NaCl during sodium appetite.

Neuronal responses to iontophoretically applied angiotensin II, losartan and aldosterone, as well as gustatory stimuli, in non-anesthetized control and desoxycorticosterone acetate-pretreated rats

The neuronal mechanism of the sodium appetite initiated in rats by priming with a mineralocorticoid (desoxycorticosterone acetate (DOCA)) treatment and subsequent central angiotensin II (Ang II) was investigated using electrophysiological-iontophoretic techniques and sapid salt stimulation of the tongue in non-anesthetized restrained, DOCA-pretreated (0.5 mg/day s.c. for 3 days) or non-pretreated male Wistar rats. The rats were trained to drink water and a 1.6% NaCl solution while their heads were painlessly held in a stereotaxic apparatus with an attachment fixed to the skull. A total of 634 neurons (375 in non-pretreated and 259 in DOCA-pretreated rats) were recorded in the medial septum and median preoptic area during iontophoretic application of Ang II, aldosterone or losartan, or tongue application of the salty solution or water. Of the 151 neurons recorded in control rats during the application of the solutions on the tongue, one (0.7%) was found specifically excited and 16 (10.6%) inhibited by the sapid sodium. Similarly, of the 110 neurons tested in the DOCA-pretreated rats, 5 (4.5%) were found specifically excited and 8 (7.3%) inhibited by the sapid sodium. The number of neurons responding to the iontophoretically applied agents was not significantly changed by the DOCA pretreatment. Thus, the DOCA pretreatment significantly increased the number of preoptic neurons that were specifically excited by a salty solution applied on the tongue. These results suggest that hormonally induced changes in the gustatory responsiveness of ventral forebrain neurons may be part of the sequence that alters the hedonic valence of NaCl during sodium appetite.

In vivo electrochemical studies of dopamine overflow and clearance in the striatum of normal and MPTP-treated rhesus monkeys.

Rapid chronoamperometric recordings, using Nafion-coated carbon-fiber electrodes (30-90 microns o.d.), were used to investigate overflow and uptake of dopamine (DA) in the striatum of normal and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated rhesus monkeys. The monkeys were anesthetized with isoflurane and placed in a stereotaxic apparatus. Magnetic resonance imaging-guided sterile stereotaxic procedures were used for implantations of the electrochemical electrodes coupled with single-barrel micropipettes that were used to apply potassium or DA locally. Potassium evoked a robust overflow of DA-like electrochemical signals into the brain extracellular space in the unlesioned or normal putamen and caudate nucleus of the rhesus monkeys. In contrast, potassium did not produce any detectable changes (> 97% depletion) of DA in the MPTP-lesioned striatum. In addition, the diffusion/clearance of locally applied DA was markedly altered in the lesioned caudate nucleus and putamen compared with unlesioned striatum. Cell counts of the number of residual tyrosine hydroxylase-positive neurons in MPTP-treated monkeys, in conjunction with whole-tissue levels of DA and its metabolites, showed that the MPTP lesions produced extensive damage of the nigrostriatal DA system. These data indicate that residual dopaminergic fibers remaining after MPTP lesions are dysfunctional and have a greatly diminished capacity for high-affinity DA uptake.