Adaptation of an osmotically pumped continuous in situ water sampler for application in riverine environments.

We present the design of an osmotic water sampler that is adapted to and validated in freshwater. The sample is drawn into and stored in a continuous narrow bore tube. This geometry and slow pump rate (which is temperature dependent: 0.8 mL/d at 4 °C to 2.0 mL/d at 28 °C) minimizes sample dispersion. We have implemented in situ time-stamping which enables accurate study of pump rates and sample time defining procedures in field deployments and comparison with laboratory measurements. Temperature variations are common in rivers, and without an accurate time-stamping, or other defining procedure, time of sampling is ambiguous. The sampler was deployed for one month in a river, and its performance was evaluated by comparison with manually collected samples. Samples were analyzed for major ions using Ion Chromatography and collision reaction Inductively Couple Mass Spectrometry. Despite the differences of the two sampling methods (osmotic sampler averages, while manual samples provide snapshots), the two data sets show good agreement (average R(2) ≈ 0.7), indicating the reliability of the sampler and at the same time highlighting the advantages of high frequency sampling in dynamic environments.

Identifying migrations in marine fishes through stable-isotope analysis.

The isotopic composition of many elements varies across both land and ocean surfaces in a predictable fashion. These stable-isotope ratios are transferred into animal tissues, potentially providing a powerful natural geospatial tag. To date, most studies using stable isotopes as geolocators in marine settings have focussed on mammals and seabirds conducting large ocean-basin scale migrations. An increasing understanding of isotopic variation in the marine environment, and improved sampling and analytical techniques, however, means that stable isotopes now hold genuine promise as a natural geolocation tag in marine fishes. Here, the theoretical background underpinning the use of stable isotopes of C, N and O in otolith, scale and muscle tissues as geolocation tools in the marine environment is reviewed, and examples of their applications are provided.

[Quantification of changes in the external morphology of the back by means of surface topography based on structured light in idiopathic scoliosis in adolescents after a year of treatment with orthopedic corse]. / Cuantificación de cambios en la morfología externa de la espalda mediante topografía de superficie basada en luz estructurada en la escoliosis idiopática del adolescente tras un año de tratamiento con corsé ortopédico.

BACKGROUND: To quantify the morphological changes in the surface of the back of adolescents with idiopathic scoliosis as a result of treatment with braces and to correlate them with radiographic changes. MATERIAL AND METHODS: An analytical, cohort, prospective study on a sample of 31 adolescents with idiopathic scoliosis. We divided them into two groups: eleven treated with braces and twenty without them. Quantification of the deformity was performed on two separate occasions with an interval of one year using three systems: 1) angle of trunk rotation (scoliometer); 2) surface topography; 3) full spine X-rays. RESULTS: No statistically significant differences were detected between the initial and final assessment of the topographic and radiographic variables in the group with braces. In the untreated group, only in measures with the scoliometer significant differences were registered. A positive correlation was found between the Cobb angle difference of the main curve with two topographic variables that quantify the asymmetry in the axial and coronal plane, respectively. DISCUSSION: In following patients with scoliosis treated with braces, we should consider and evaluate not only radiographic parameters such as the Cobb angle, but also clinical and topographic parameters that quantify the external deformity of the back, as there is a clinical-radiographic discrepancy amply demonstrated in the literature. The improvement of the external shape of the back is a very important factor for the patient, and can influence a better completion of the orthopedic treatment. In our study, the scoliotic curve and external deformity of the back remained stable during the follow-up period in both treated and untreated patients.

ANTECEDENTES: Cuantificar los cambios morfológicos producidos en la superficie de la espalda de adolescentes con escoliosis idiopática como resultado del tratamiento mediante corsé y correlacionarlos con las variaciones radiográficas. MATERIAL Y MÉTODOS: Estudio analítico, de cohortes, prospectivo, sobre una muestra de 31 adolescentes con escoliosis idiopática divididos en dos grupos: 11 con tratamiento mediante corsé y 20 sin corsé. Se realizó una cuantificación de la deformidad en dos ocasiones separadas entre sí por un intervalo de un año mediante tres sistemas: 1) ángulo de rotación del tronco (escoliómetro); 2) topografía de superficie; 3) radiografía simple de raquis completo. RESULTADOS: No se detectaron diferencias estadísticamente significativas entre la valoración inicial y final de las variables topográficas y radiográficas en el grupo con corsé. En el grupo no tratado, sólo hubo diferencias significativas para las medidas del escoliómetro. Se encontró una correlación positiva entre la diferencia del ángulo de Cobb de la curva principal con la de dos variables topográficas que cuantifican la asimetría en el plano axial y en el coronal, respectivamente. DISCUSIÓN: En el seguimiento de pacientes con escoliosis tratados con corsé, se deben tener en cuenta y valorar no sólo parámetros radiográficos como el ángulo de Cobb, sino también parámetros clínicos y topográficos que cuantifiquen la deformidad externa de la espalda, ya que existe una discrepancia clínico-radiográfica demostrada de manera amplia en la literatura. La mejoría de la forma externa de la espalda es un factor muy importante para el paciente y es lo que va a percibir fundamentalmente, lo que puede influir en una mejor cumplimentación del tratamiento ortopédico. En nuestro estudio, la curva escoliótica, así como la deformidad externa de la espalda, se mantuvo estable en el período de seguimiento tanto en los pacientes tratados con corsé como en los no tratados.

Initial studies of embryonic transplants of human hippocampus and cerebral cortex derived from schizophrenic women.

Human fetal brain tissue was obtained from first-trimester elective abortions of two women who also had schizophrenia. Portions of the embryonic hippocampus or cerebral cortex were transplanted into the anterior eye chamber of immunologically compromised athymic nude rats. In this environment, embryonic brain tissue derived from normal women generally continues organotypic growth and development for many months. Although initial survival after transplantation was normal, the tissue derived from schizophrenic women manifested less robust growth. However, cells in the transplants showed typical neuronal differentiation, with development of different neuronal types, such as pyramidal cells, granule cells, and gamma-aminobutyric acid (GABA)-containing interneurons. Rhythmic electrical activity was also observed, indicative of some local synaptic organization. The presence of messenger RNA (mRNA) for brain-derived neuronotrophic factor (BDNF) was observed using in situ hybridization. The reason for the decreased rate of growth of these transplants remains unknown and the significance of the finding cannot be assessed from only two fetuses. However, these preliminary findings suggest that fetal transplants may be a useful model system for the detection of developmental pathogenic processes in the expression and transmission of schizophrenia.

Age-induced changes in single locus coeruleus brain transplants grown in oculo: an in vivo electrochemical study.

Brain stem tissue from fetal Sprague-Dawley rats containing the nucleus locus coeruleus (LC) was transplanted into the anterior chamber of the eye of young adult host rats and was studied at 4-6 months (young control) or 24-28 months after grafting (old). High-speed in vivo electrochemical measurements were used to characterize the potassium-evoked synaptic overflow of norepinephrine (NE) in both young and aged LC brain grafts. The amplitudes of potassium-evoked NE overflow were attenuated in the aged grafts as compared to the young LC grafts. In addition, the rise times of potassium-evoked responses were longer in the old LC grafts than in the young transplants. In contrast, the NE content of aged LC grafts, as determined by high-performance liquid chromatography coupled with electrochemical detection (HPLC-EC), was only slightly diminished and not significantly different from the NE levels seen in young LC grafts. However, light microscopical evaluation using tyrosine-hydroxylase immunocytochemistry revealed pyknotic cell bodies and fluorescent accumulations in aged locus coeruleus transplants which were indicative of degeneration in these grafts. The present data demonstrate a significant age-related decline in the presynaptic function of NE-containing neurons in intraocular locus coeruleus transplants of Sprague-Dawley rats.

Systemic lymphoblastoid interferon therapy in chronic progressive multiple sclerosis. I. Clinical and MRI evaluation.

A randomized, double-blind, placebo-controlled, noncrossover trial determined the efficacy of lymphoblastoid interferon (IFN) in chronic progressive multiple sclerosis (CP MS). Fifty patients received 5 X 10(6) IU IFN subcutaneously daily for 6 months while 50 received placebo. After 2 years, there were no significant differences between the 2 groups based on clinical evaluations and quantitative MRI analysis of the brain, although a trend was observed in the IFN group. Clinically, the IFN group was worse at 1 and 3 months and improved at 6 to 18 months, when compared with the placebo group. Results of MRI evaluations of the brain at 6 months support this trend. This trend likely resulted from a subpopulation of 10 IFN-treated patients, characterized by a higher women:men ratio and a lower EDSS score at entry into the trial. We cannot recommend lymphoblastoid IFN as treatment for CP MS at this time.

Effects of dopamine on spontaneous and evoked activity of caudate neurons.

This study examined the effects of dopamine (DA), pressure ejected from multi-barrelled micropipettes, on the spontaneous and evoked activity of caudate neurons, recorded extracellularly in rats anesthetized with urethane. Neurons were categorized according to their discharge latencies in response to supramaximal cortical stimulation: neurons which fired with latencies less than 13 msec were classified "short-latency-discharge neurons", while neurons with latencies greater than or equal to 13 msec were classified "long-latency-discharge neurons". This procedure also allowed the detection of neurons with low levels of spontaneous activity. The predominant effect of DA on both neuronal types was inhibition of spontaneous activity. However, DA exerted a modulatory effect in that spontaneous activity was inhibited at "doses" which did not affect activity evoked by cortical stimulation. Although DA-induced excitation was infrequent, it was significantly more prevalent among long-latency neurons than among short-latency-discharge neurons. Long-latency-discharge neurons were also significantly more spontaneously active than were short-latency neurons. In rats depleted of endogenous DA by treatment with reserpine, caudate neurons had significantly increased rates of spontaneous and evoked activity, shorter duration of stimulus-evoked inhibition, and longer latency for evoked discharges than in control rats. These results suggest that DA exerts modulatory effects on caudate neuronal activity. Furthermore, these results suggest that short- and long-latency-discharge neuronal groups may consist of pharmacologically, as well as physiologically, distinct neuronal types.

Electrophysiological interactions between haloperidol and reduced haloperidol, and dopamine, norepinephrine and phencyclidine in rat brain.

Haloperidol and its metabolite, reduced haloperidol, were compared as antagonists of catecholaminergic neurotransmission in central nervous system of the rat. Agonists and antagonists were applied from multibarrelled micropipettes, which were also used to record extracellularly the effects of these substances on neuronal discharge. Haloperidol antagonized dopaminergic inhibition of caudate neurons and inhibition of cerebellar Purkinje neurons induced by noradrenaline, whereas reduced haloperidol was an ineffective antagonist. Phencyclidine, which is an indirect dopaminergic agonist in the caudate, caused inhibition of the discharges of caudate neurons resembling that induced by dopamine itself. These indirect effects of phencyclidine were also antagonized by haloperidol but not by reduced haloperidol. The data suggest that the metabolite, reduced haloperidol, is not an effective neuroleptic drug in the central nervous system.

Interactions between phencyclidine and cholinergic excitation of hippocampal pyramidal neurons.

The interaction between phencyclidine and acetylcholine-evoked responses of hippocampal pyramidal neurons was investigated in normal and catecholamine-depleted rats. Phencyclidine antagonized the acetylcholine-induced excitations in both preparations. However, in the majority of cases, this effect was observed only at doses of phencyclidine which also manifested nonspecific membrane stabilization. In contrast, phencyclidine-induced decreases in firing rate, which have been shown to be mediated by catecholamines, occurred at doses of phencyclidine which do not cause local anesthesia. Taken together, these data suggest that the catecholaminergically-mediated effects of phencyclidine may be more important in the hippocampus.

Survival and growth of neurons with enkephalin-like immunoreactivity in fetal brain areas grafted to the anterior chamber of the eye.

Areas of fetal rat brain and spinal cord known to contain enkephalin-like immunoreactive cell bodies and/or terminal fields were transplanted to the anterior chamber of the eye of adult rats. Enkephalin-like immunoreactive neurons survive and produce an enkephalin-like immunoreactive fiber network within grafts of spinal cord, ventral medulla oblongata, ventrolateral pons, tectum, locus coeruleus, substantia nigra and the areas containing columna fornicis and globus pallidus. Although single intraocular grafts of neocortex do not apparently contain enkephalin-like immunoreactive fibers, such grafts contain a variable amount of sparsely distributed enkephalin-like fibers when sequentially grafted in oculo with either locus coeruleus or spinal cord. Combinations of locus coeruleus and globus pallidus contained a rich enkephalin fiber network in the locus coeruleus part and a sparse innervation of the globus pallidus part. We conclude that enkephalin-like immunoreactive neurons in small areas of fetal rat brain can be successfully transplanted to the anterior chamber of the eye. They are able to survive and develop to maturity in complete isolation from the rest of the brain. In general, the enkephalin-like immunoreactive fiber density in the various single grafts approximated that of their brain counterparts in situ. Fiber formation can be reinitiated in mature enkephalin-like immunoreactive neurons by addition of new brain target areas. Thus, the technique permits establishment of isolated, defined enkephalin systems and pathways accessible to functional analysis.

Stereoselectivity of opiate antagonists in rat hippocampus and neocortex: responses to (+) and (-) isomers of naloxone.

The relative potencies of the (+) and (-) isomers of naloxone in antagonizing electrophysiological responses to D-alanine2-methionine enkephalinamide were compared in rat frontal cortex and hippocampus. In the in vitro hippocampus, the (-) isomer was found to be at least a 100 times more potent than the (+) isomer in antagonizing opiate-induced changes in field potentials. Similar stereoselectivity was observed in vivo in both frontal cortex and hippocampus in terms of the antagonism of enkephalin-induced changes in spontaneous cell firing. The direct effects of (+) and (-)-naloxone were examined as well. In hippocampus both in vivo and in vitro, no differential effect was observed, whereas in the neocortex (-)-naloxone was considerably more potent than the (+) isomer in eliciting depressions of spontaneous activity. These direct effects of naloxone in the cortex do not appear to be due to an antagonism of the effects of endogenously released opioids. These results demonstrate that the stereoselectivity of naloxone isomers in antagonizing electrophysiological responses to opiates in the cortex and hippocampus parallels that previously observed in other brain regions and in other tissues. In addition, they suggest that naloxone may have interactions with other unknown opiate (or possibly non-opiate) receptors which are of physiological significance.

Toxic effects of lead in the developing nervous system: in oculo experimental models.

Modern man is chronically exposed to lead in the biosphere at levels several orders of magnitude higher than the natural level that once existed. There is much concern about the possible adverse effects of this population-wide, low-level lead exposure, particularly on the developing organism, wherein the central nervous system may be one primary target. We have developed in oculo test systems, which permit temporal and spatial discrimination of possible effects of lead and other potential neurotoxic agents in the environment on the developing central nervous system as well as on different types of peripheral nerves in the adult. In one experimental protocol, defined areas of the fetal rat brain are grafted to the anterior chamber of the eye of adult rat recipients that are exposed to lead. Such grafts will become vascularized from the host iris and continue developing in oculo. Thus, grafted brain tissue and host brain will share circulation and therefore be exposed to similar amounts of lead. Studies of cerebellar grafts revealed that, although there was a normal gross cytological development in the presence of lead, there was a marked and permanent impairment of spontaneous discharge rates of the grafted Purkinje neurons as observed with electrophysiological techniques long after cessation of lead treatment. The host Purkinje neurons were not affected. A similar, although less dramatic, impairment of cerebellar function could be subsequently demonstrated in intact animals when newborn rats were given lead during the first 20 days of life and studied as adults.(ABSTRACT TRUNCATED AT 250 WORDS)

Interactions of a neuroleptic drug (fluphenazine) with catecholamines in hippocampus.

The interactions of fluphenazine with the electrophysiological responses to catecholamines were studied in the rat hippocampus and parietal cortex. In the in vitro hippocampal slice, changes in synaptically evoked responses induced by norepinephrine, isoproterenol and dopamine were not altered by superfusion of fluphenazine. Both alpha- and beta- components of adrenergic responses were unaffected by neuroleptic administration in this preparation. Similarly, alterations in the spontaneous firing of single hippocampal pyramidal neurons in situ to adrenergic agonists or dopamine were not affected by local fluphenazine and administration using pressure ejection through multibarreled micropipettes. In contrast, norepinephrine- or isoproterenol-induced inhibitions of parietal cortical neurons in situ were potently antagonized by fluphenazine. A similar interaction was observed from a hippocampal basket neuron. It is concluded that while fluphenazine can antagonize well-defined noradrenergic effects in some brain regions (e. g., cerebellum, cortex), this property is not generalized to all brain regions receiving noradrenergic input.

A pharmacokinetic model for the concentration of 10B in blood after boronophenylalanine-fructose administration in humans.

An open two-compartment model has been developed for predicting (10)B concentrations in blood after intravenous infusion of the l-p-boronophenylalanine-fructose complex (BPA-F) in humans and derived from studies of pharmacokinetics in 24 patients in the Harvard-MIT Phase I clinical trials of BNCT. The (10)B concentration profile in blood exhibits a characteristic rise during the infusion to a peak of approximately 32 microg/g (for infusion of 350 mg/kg over 90 min) followed by a biphasic exponential clearance profile with half-lives of 0.34 +/- 0.12 and 9.0 +/- 2.7 h, due to redistribution and primarily renal elimination, respectively. The model rate constants k(1), k(2) and k(3) are 0.0227 +/- 0.0064, 0.0099 +/- 0.0027 and 0.0052 +/- 0.0016 min(-1), respectively, and the central compartment volume of distribution, V(1), is 0.235 +/- 0.042 kg/kg. The validity of this model was demonstrated by successfully predicting the average pharmacokinetic response for a cohort of patients who were administered BPA-F using an infusion schedule different from those used to derive the parameters of the model. Furthermore, the mean parameters of the model do not differ for cohorts of patients infused using different schedules.

Biological dosimetry for epithermal neutron beams.

The radiobiological effectiveness of an epithermal neutron beam is described using cell survival as the end point. The M67 epithermal neutron beam at the Nuclear Reactor Laboratory, Massachusetts Institute of Technology, that was used for clinical trials of boron neutron capture therapy was used to irradiate Chinese hamster ovary cells at seven depths in a water-filled phantom that simulated healthy tissue. No boron was added to the samples. Therefore, this experiment evaluates the biological effectiveness of the neutron and photon components, which comprise 80-95% of the dose to healthy tissue. Cell survival was dependent upon the depth in the phantom, as a result of moderation and attenuation of the epithermal neutron beam components by the overlying water. The results were compared with 250 kVp X irradiations to determine relative biological effectiveness values. Cell survival as a function of the dose delivered was lowest at the most shallow depth of 0.5 cm, and increased at depths of 1.5, 3, 4, 5.6, 6.6 and 8.1 cm. The gradual increase in cell survival with increasing depth in the phantom is due to the exponential drop of the fast-neutron intensity of the beam. These results are applicable to clinical boron neutron capture therapy Phase I/II trials in which healthy tissue toxicity was an end point.

Characterization of the techniques of pressure ejection and microiontophoresis using in vivo electrochemistry.

Catecholamine levels in frontal cortex were determined in vivo by electrochemical detection after the local application of dopamine (DA) from multibarrel micropipettes by pressure ejection or microiontophoresis. Tissue DA levels were linearly related to microapplication doses with either technique and reached steady state with longer application times. Furthermore, the plateau DA tissue concentrations were clearly related to ejection pressure or iontophoretic current. Using either microapplication technique, the tissue DA levels decreased as distance between the recording electrode and the tip of the drug pipette increased. However, pressure ejected and iontophoretically applied drug differed in their concentration versus time dynamics. Thus, although similar tissue concentrations of drug can be generated by the two techniques, the time dynamics of the drug effects may not be comparable. The quantitative use of these drug application techniques requires a minimal amount of variance in release between pipettes in order to effectively measure small sensitivity differences. Although the 10-fold variance with microiontophoresis does not appear resolvable at present, improved pipette construction techniques permit the variability in dosage to be limited to a maximum of 3-fold with pressure ejection. In addition, the present data also suggest that this variance can be further minimized by holding either ejection duration or ejection pressure constant when establishing dose-response relationships.

Electrophysiological effects of norepinephrine on Purkinje neurons in intraocular cerebellar grafts: alpha- vs beta-specificity.

The present study investigates the receptor specificity of the electrophysiological effects of norepinephrine (NE) on cerebellar Purkinje neurons. Intraocular cerebellar grafts were utilized to allow both superfusion and local administration of selective adrenergic agonists and antagonists. Fetal cerebellar anlagen (E13-15) were homologously transplanted to the anterior chamber of the eye of adult recipient rats and allowed to mature in the eye for at least 5 weeks. Spontaneous activity of Purkinje neurons was recorded extracellularly in the intraocular grafts. Superfusion of 5 microM NE caused elevations of the spontaneous firing rate. Superfusion of 30 microM NE caused depressions, which were occasionally preceded by an excitation. Iontophoretic application of NE to grafted Purkinje neurons primarily caused depressions of the spontaneous discharge rate. Thus, the NE-induced excitations previously reported from in vitro slices are not anomalies of the in vitro slice preparation, but can be observed with superfusion of NE in our in vivo preparation as well. In general, the excitations caused by low doses of superfused NE were blocked by timolol, a specific beta-adrenergic antagonist, while the depressions caused by 30 microM superfused NE or iontophoretically applied NE were blocked by the specific alpha-adrenergic antagonist phentolamine. Large doses of sotalol were found to block both excitatory and depressant responses while lower doses only antagonized the NE-induced excitations. Taken together, these results suggest that the inhibitory effects of NE on PUrkinje neuron firing rate in intraocular cerebellar grafts in vivo are mediated via an alpha-adrenergic receptor mechanism, while the excitations caused by NE may be beta-mediated.

Evidence for functional contact between cografted locus coeruleus and spinal cord in oculo: electrophysiological studies.

The functional consequences of the locus coeruleus innervation of the spinal cord are not yet clearly understood. In a recent histological study it was shown that intraocular spinal cord grafts will become innervated by tyrosine hydroxylase-positive nerve fibers from a cografted locus coeruleus. In the present study we use this intraocular model of the descending coeruleo-spinal pathway to investigate functional contact between locus coeruleus and the spinal cord. We have pharmacologically characterized the receptor mediation of norepinephrine-induced, as well as locus coeruleus-mediated depressions of spinal cord neurons grafted in oculo. We found that electrical stimulation of the locus coeruleus part of the double grafts predominantly caused an inhibition of cografted spinal cord neurons. Norepinephrine-induced inhibition of the firing rate of single grafted spinal cord neurons was antagonized by phentolamine, an alpha-adrenergic antagonist, but was unaffected by timolol, a beta-adrenergic antagonist. Similarly, inhibition of the firing rate of grafted spinal cord neurons by stimulation of cografted locus coeruleus was antagonized by phentolamine but not by timolol. Interestingly, single spinal cord grafts were more sensitive to the depressant effects of perfused norepinephrine than was the spinal cord cografted with locus coeruleus. We conclude that spinal cord grafts can be functionally innervated by cografted locus coeruleus and that the noradrenergic inputs to spinal cord from cografted locus coeruleus are alpha-adrenergically mediated. Furthermore, the postsynaptic receptors in single spinal cord grafts appear to be supersensitive to norepinephrine application.

Spinal cord-skeletal muscle cografts: trophic and functional interactions.

Skeletal muscle from embryonic day 20 (E20) was combined with E15 rat spinal cord in the anterior chamber of the eye of adult albino rats. The two grafts were either transplanted concomitantly or sequentially, in which case muscle tissue was added 4 months after the spinal cord. Control groups received a single graft of either spinal cord or skeletal muscle. Survival and intraocular growth were observed through the cornea. After maturation in oculo, the double grafts were examined immunohistologically utilizing antisera to neurofilament (NF) and acetylcholinesterase (AChE). The grafts were also evaluated using electrical stimulation to determine functional connectivity. The spinal cord and skeletal muscle grafts were found to exert reciprocal trophic effects on each other, evidenced as a larger muscle mass in skeletal muscle grafts allowed to develop in the presence of spinal cord tissue, and a larger volume of spinal cord grafts allowed to develop together with a skeletal muscle graft, respectively. Immunohistochemistry revealed NF-positive nerve fibers leaving the spinal cord graft and entering the muscle tissue. AChE-positive endplates developed in the muscle grafts. Electrical stimulation of the spinal cord part of double-graft combinations generally elicited contractile responses in specific areas of the muscle cograft. These results demonstrate both structural and functional connections between grafts of spinal cord and skeletal muscle tissue in vivo. The fact that such connections were also established between a mature (adult) spinal cord graft and fetal skeletal muscle tissue suggests that some alpha-motoneurons are able to survive for many months in the intraocular grafts without an appropriate target, and that they are able to subsequently innervate skeletal muscle targets.

Multiple single-unit recordings in the striatum of freely moving animals: effects of apomorphine and D-amphetamine in normal and unilateral 6-hydroxydopamine-lesioned rats.

Ensembles of striatal neurons were recorded in freely moving normal and unilateral 6-hydroxydopamine (6-OHDA)-lesioned rats using chronically implanted electrode arrays. Animals received bilateral striatal implants of two 16-microwire arrays 1 week before recordings. Identified striatal neurons were categorized as medium spiny-like and large aspiny-like based on a combination of their activity autocorrelations and firing rates. Baseline firing rates of medium spiny-like neurons in the 6-OHDA-lesioned striata were significantly faster than were firing rates of the same neurons in the intact hemispheres of 6-OHDA-lesioned rats or normal animals. However, firing rates of large aspiny-like neurons were faster in both hemispheres of the 6-OHDA-lesioned rats as compared to normal animals. Interestingly, firing rates of neurons in all groups decreased by fivefold or greater under urethane anesthesia, although the relative firing rates between hemispheres were unchanged. d-Amphetamine (5.0 mg/kg, s.c.) increased the firing rates of both types of striatal neurons by twofold or greater in normal rats and in the intact hemispheres of 6-OHDA-lesioned animals. By contrast, this treatment did not alter neuron firing in the 6-OHDA-lesioned striata. Apomorphine (0.05 mg/kg, s.c.) did not affect neuronal firing rates either in normal rat striatum or in the unlesioned hemispheres of 6-OHDA-lesioned animals. However, it did significantly increase the firing rate of the medium spiny-like neurons in 6-OHDA-lesioned striata. These results demonstrate that the dopaminergic innervation of the striatum differentially influences two electrophysiologically distinct sets of striatal neurons in freely moving rats.