Anabolic Steroids Activate the NF-κB Pathway in Porcine Ovarian Putative Stem Cells Independently of the ZIP-9 Receptor

Boldenone (Bdn) and nandrolone (Ndn) are anabolic androgenic steroids (AASs) that, as our previous studies have shown, may increase the risk of neoplastic transformation of porcine ovarian putative stem cells (poPSCs). The NF-κB pathway may be important in the processes of carcinogenesis and tumour progression. Therefore, in this work, we decided to test the hypothesis of whether Bdn and Ndn can activate the NF-κB pathway by acting through the membrane androgen receptor ZIP-9. For this purpose, the expression profiles of both genes involved in the NF-κB pathway and the gene coding for the ZIP-9 receptor were checked. The expression and localization of proteins of this pathway in poPSCs were also examined. Additionally, the expression of the ZIP-9 receptor and the concentration of the NF-κB1 and 2 protein complex were determined. Activation of the NF-κB pathway was primarily confirmed by an increase in the relative abundances of phosphorylated forms of RelA protein and IκBα inhibitor. Reduced quantitative profiles pinpointed not only for genes representing this pathway but also for unphosphorylated proteins, and, simultaneously, decreased concentration of the NF-κB1 and 2 complex may indicate post-activation silencing by negative feedback. However, the remarkably and sustainably diminished expression levels noticed for the SLC39A9 gene and ZIP-9 protein suggest that this receptor does not play an important role in the regulation of the NF-κB pathway.

The Relative Abundances of Human Leukocyte Antigen-E, α-Galactosidase A and α-Gal Antigenic Determinants Are Biased by Trichostatin A-Dependent Epigenetic Transformation of Triple-Transgenic Pig-Derived Dermal Fibroblast Cells

The present study sought to establish the mitotically stable adult cutaneous fibroblast cell (ACFC) lines stemming from hFUT2×hGLA×HLA-E triple-transgenic pigs followed by trichostatin A (TSA)-assisted epigenetically modulating the reprogrammability of the transgenes permanently incorporated into the host genome and subsequent comprehensive analysis of molecular signatures related to proteomically profiling the generated ACFC lines. The results of Western blot and immunofluorescence analyses have proved that the profiles of relative abundance (RA) noticed for both recombinant human α-galactosidase A (rhα-Gal A) and human leukocyte antigen-E (HLA-E) underwent significant upregulations in tri-transgenic (3×TG) ACFCs subjected to TSA-mediated epigenetic transformation as compared to not only their TSA-unexposed counterparts but also TSA-treated and untreated non-transgenic (nTG) cells. The RT-qPCR-based analysis of porcine tri-genetically engineered ACFCs revealed stable expression of mRNA fractions transcribed from hFUT2, hGLA and HLA-E transgenes as compared to a lack of such transcriptional activities in non-transgenic ACFC variants. Furthermore, although TSA-based epigenomic modulation has given rise to a remarkable increase in the expression levels of Galα1→3Gal (α-Gal) epitopes that have been determined by lectin blotting analysis, their semi-quantitative profiles have dwindled profoundly in both TSA-exposed and unexposed 3×TG ACFCs as compared to their nTG counterparts. In conclusion, thoroughly exploring proteomic signatures in such epigenetically modulated ex vivo models devised on hFUT2×hGLA×HLA-E triple-transgenic ACFCs that display augmented reprogrammability of translational activities of two mRNA transcripts coding for rhα-Gal A and HLA-E proteins might provide a completely novel and powerful research tool for the panel of further studies. The objective of these future studies should be to multiply the tri-transgenic pigs with the aid of somatic cell nuclear transfer (SCNT)-based cloning for the purposes of both xenografting the porcine cutaneous bioprostheses and dermoplasty-mediated surgical treatments in human patients.

Quality parameters and fertility of ram semen cryopreserved in egg yolk and soybean lecithin supplemented extenders

The aim of the study was to investigate the effect of soybean lecithin as a substitute for egg yolk in milk and tris based extenders in ram semen cryopreservation. Twenty ejaculates were col- lected from four healthy, mature Wrzosówka rams (2-3 years of age). Each ejaculate was divided into four equal aliquots and diluted with four different extenders: 1) milk extender containing 5% egg yolk, 2) milk extender containing 1.5% soybean lecithin, 3) tris extender containing 20% egg yolk, 4) tris extender containing 1.5% soybean lecithin. Extended semen was loaded into 0.25 ml French straws, cooled and frozen in liquid nitrogen vapor. Total motility, curvilinear velocity, plasma membrane integrity and fertilizing ability of sperm were assessed after thawing. Total mo- tility was lower (p⟨0.05) in tris-soybean lecithin extender when compared to other extenders. Curvilinear velocity was higher (p⟨0.05) for spermatozoa cryopreserved in milk-soybean lecithin extender compared to other extenders tested. For the percentage of live sperm no significant difference was observed between extenders. The lambing rate were higher (not statistically signifi- cant) in ewes inseminated with semen doses frozen in milk-soybean lecithin extender (42.9%) than in the tris-egg yolk extender (16.7%). In conclusion, replacing the egg yolk with soybean lecithin was effective in milk but not in tris extender.

The use of butylated hydroxytoluene in cryopreservation of boar semen

The objective of the study was to determine the effect of butylated hydroxytoluene (BHT) on the quality and fertilizing capacity of frozen-thawed (FT) boar semen. Semen from five boars (36 ejaculates) was resuspended in lactose-egg yolk-glycerol extender supplemented with 0 (control), 1.0 (R1), 1.5 (R2) or 2.0 mM BHT (R3). Sperm quality was assessed based on motility (CASA; TM: total motility; PM: progressive motility), phosphatidylserine (PS) translocation across the plasma membrane (Annexin-V-FLuos Staining Kit) and DNA fragmentation (TUNEL Assay). The FT semen was also used for intrauterine artificial insemination (AI) of synchronized gilts. The fertilizing capacity of the FT semen was assessed on the basis of the gilt insemination rate and the number of morphologically normal embryos. The quality of the preimplantation embryos was determined by observing a TUNEL-positive reaction. The highest percentage of progressive motile and viable spermatozoa was noted in extender R3 (74.8 ±4.4% and 63.7 ±5.8%), as compared with the control (38.3 ±2.8% and 36.1 ±2.6%). The addition of BHT to the extender did not increase early apoptotic changes in the frozen-thawed spermatozoa with respect to the control. Irrespective of the variant of the extender, cryopreservation and thawing did not induce fragmentation in the boar spermatozoa. The highest number of morphologically normal embryos from inseminated gilts was observed in the case of semen cryopreserved in extender supplemented with 1.5 mM BHT. No significant differences were observed in DNA fragmentation in the expanded blastocysts from gilts inseminated with FT semen cryopreserved in the extenders analysed.

Apoptotic-like changes of boar spermatozoa in freezing media supplemented with different antioxidants

This study evaluated the effect of supplementing the freezing extender with exogenous anti-oxidants on apoptotic-like changes in post-thaw boar spermatozoa. A total of 36 ejaculates were resuspended in standard lactose-egg yolk-glycerol extender supplemented with antioxidant to final concentrations of 0 (as control), 2.5mM GSH (group I), 5.0 mM GSH (group II), 150 IU/mL SOD (group III), 300 IU/mL SOD (group IV), 200 IU/mL CAT (group V), 400 IU/mL CAT (group VI), 150 IU/mL SOD+200 IU/mL CAT (group VII), 300 IU/mL SOD+400 IU/mL CAT (group VIII). Sperm motility and apoptotic-like changes were determined before and after freeze-thawing. The various markers of apoptotic-like changes were measured: plasma membrane permeability by YO-PRO-1/PI assay, phosphatidylserine (PS) translocation across the plasma membrane using fluorescein-labeled Annexin-V, mitochondrial transmembrane potential detected by JC-1, and DNA fragmentation evaluated by TUNEL assay. The highest percentage of progressive motile sperm was noticed in group II (PM% 64.2±15.4) compared with control (PM% 36.8±5.5). The supplementation of 400 IU/mL CAT (group VI) revealed significant (P<0.01) reduction of apoptotic-like changes (YO-PRO-1+/PI-: 13.1±7.5%, AnV+/PI-: 9.9±4.1%) in frozen-thawed spermatozoa compared with extender supplemented with 200 IU/mL CAT (group V). Irrespective of the concentration used, SOD and CAT in combination (group VII and group VIII) significantly (P<0.01) improved post-thaw sperm survival compared with the control. Evaluation by TUNEL assay revealed that cryopreservation and thawing did not induce DNA fragmentation in boar spermatozoa.

Quality and fertilizing capacity of boar spermatozoa during liquid storage in extender supplemented with different antibiotics

The aim of the study was to determine the effect of antibiotics on quality parameters and fertilizing capacity of boar sperm during liquid preservation. In the first experiment, semen was diluted in an extender containing 200 μg/mL of gentamicin as a control and diluted in a modified extenders: Ext I (contained 200 μg/mL florfenicol), Ext II (contained 200 μg/mL polymyxin B), Ext III (contained 100 μg/mL gentamicin and 100 μg/mL florfenicol) and Ext IV (contained 100 μg/mL gentamicin and 100 μg/mL polymyxin B). The semen was stored for ten days. Sperm quality was evaluated based on the motility (CASA; TM: total motility; PM: progressive motility), membrane integrity (YO-PRO-1/PI assay), mitochondrial activity (JC-1) and DNA integrity (TUNEL). The highest PM% (62.5 ± 9.6) was observed in Ext III at Day 6 of storage. The highest sperm viability and mitochondrial transmembrane potential was noticed at the end of the storage period in Ext III. Long-term storage did not induce DNA fragmentation in the extenders analyzed. In the second experiment, semen diluted in the control extender and in the extender providing the highest quality spermatozoa on Day 10 (Ext III) was used for artificial insemination (AI) of synchronized gilts. Our studies showed that the highest reproductive performance of inseminated gilts (pregnant gilts: 97.0%, litter size: 11.4 ± 1.2) occurred with Ext III semen dilution. The combination of 100 μg/mL gentamicin and 100 μg/mL florfenicol in the extender maintained sperm motility, membrane integrity and mitochondrial activity and enhanced the higher reproduction success.

Fertility of boar semen cryopreserved in extender supplemented with butylated hydroxytoluene

The present study was to determine the effect of butylated hydroxytoluene (BHT) on quality and fertilizing ability of frozen-thawed boar semen. In the first experiment, five crossbreds of Polish Landrace and Large White boars (five ejaculates per boar) were frozen in 0.5 mL straws after dilution with lactose-egg yolk-glycerol extender supplemented with 0 (control), 0.5, 1.0, and 2.0 mM BHT. The sperm quality was verified based on the motility (computer-assisted sperm analysis; total motility, %; progressive motility, %), membrane integrity (YO-PRO-1/propidium iodide [PI] assay), acrosome integrity (fluorescein isothiocyanate-conjugated with peanut agglutinin/PI), and lipid peroxidation (chemiluminescence method) at 15 minutes postthaw. In the second experiment, the semen cryopreserved in extender supplemented with 1.0 and 2.0 mM BHT were selected for intrauterine artificial insemination of synchronized gilts. An intrauterine artificial insemination with low numbers of spermatozoa (500 × 10(6)) was surgically infused into each uterine horn. The highest (P < 0.001) progressive motility (%), membrane integrity, and acrosomal integrity were noted by the addition of 1.0 and 2.0 mM BHT to the freezing extender. Moreover, the various concentrations (0.5-2.0 mM) of BHT caused a considerable decrease in lipid peroxidation in relation to the control extender (P < 0.001). The highest reproductive performance of inseminated gilts (farrowing rate, 86.7%; litter size, 10.8 ± 1.6) was observed when semen was cryopreserved in extender supplemented with 1.0 mM BHT. These findings demonstrate that the addition of 1.0 mM BHT to the freezing extender efficiently improves the fertilizing ability of postthaw boar spermatozoa.

Studies on chityn level in vegetative mycelium of some mycorrhizal fungi

Chitin content was investigated in vegetative mycelium of the <i>Basidiomycetes</i> and <i>Ascomycetes</i> mycorrbizal fungi grown in vitro. It was demonstrated that the content varies between species and even between strains of a given species, and it changes with the age of mycelium. The chitin content increased with age in the mycelium of fungi of <i>Basidiomycetes</i> while it decreased in fungi of <i>Ascomycetes</i>. Essential effect was found of nitrogen source on chitin content in the mycelium. Less chitin was determined in the mycelium grown on nitrate than in that grown on urea or ammonia salts.

Effect of semen quality in transgenic boars on the developmental competence of preimplantation embryos

The aim of this study was to compare the fertilising capacity of sperm from 6 transgenic (TG) and 6 non-transgenic (NTG) boars based on analyses of embryos resulting from insemination with sperm from these particular boars. Expanded blastocysts were collected from five groups of synchronised gilts (six gilts per group) inseminated by TG boars bearing a gene construct containing the human alpha1,2-fucosyltransferase gene and by NTG boars. The ejaculates used for insemination were analysed to detect apoptotic changes using two fluorescence methods: an assay to assess early changes in the membrane integrity of the sperm using the YO-PRO-1 fluorophore and an assay for phosphatidylserine (PS) translocation across the plasma membranes using fluorescein-labelled Annexin-V. Our results, using a combination of YO-PRO-1 and PI fluorophores, revealed no significant differences in the percentage of sperm subpopulations between non-transgenic and transgenic boars (P<0.01). Moreover, the second fluorescent probe also revealed no significant differences between the average values of live (Ann-V(-)/PI(-)), early apoptotic (Ann-V(+)/PI(-)), and late apoptotic/early necrotic sperm (Ann-V(+)/PI(+)) as calculated for TG and NTG boars. Only the percentage of necrotic sperm (Ann-V(-)/PI(+)) was significantly different (P<0.05) between transgenic and non-transgenic boars (3.4%+/-2.7; 7.2%+/-2.1, respectively). The quality of the preimplantation embryos at the blastocyst stage was determined by counting the number of cells, observing a TUNEL-positive reaction and by caspase-3 labelling. We found that expanded blastocysts that were derived from gilts inseminated with TG and NTG boar semen showed almost no DNA fragmentation (80%) and 70% caspase-3 activity. The expanded blastocysts that were derived from gilts inseminated with TG and NTG boar semen did not differ significantly in their DNA fragmentation, and there were no differences in caspase-3 activity. These results revealed a positive correlation between the percentage of blastocysts with TUNEL-positive nuclei and the percentage of blastocysts with caspase-3 activity (r=0.9787; P<0.0001).

Assessment of plasma membrane and chromatin structure of sperm from transgenic and non-transgenic boars

The aim of this study was to determine the apoptotic changes and chromatin damage in non-transgenic and transgenic boars carrying the human alpha1,2-fucosyltransferase gene. Five ejaculates were collected from six transgenic (TG) and six non-transgenic (NTG) boars. Five ejaculates were collected from six transgenic (TG) and six non-transgenic (NTG) boars both crossbreds of Polish Landrace and Large White. Two fluorescence methods were employed to measure apoptosis: an assay to assess the early changes in sperm membrane integrity using fluorophore YO-PRO-1 and an assay for phosphatidylserine (PS) translocation across the plasma membrane using fluorescein-labeled Annexin-V. The chromatin damage was assessed based on the sperm chromatin structure assay method. No significant differences in the proportion of all detected subpopulations of spermatozoa were found between TG and NTG boars. Similarly, the analysis of the chromatin structure revealed no statistical differences in the sperm chromatin damage between TG and NTG boars. In conclusion, the presence of the human alpha1,2-fucosyltransferase gene in the genome of TG boars did not cause any spermatogenesis process disturbances leading to the increased production of apoptotic spermatozoa. Moreover, the low level of sperm with damaged chromatin in TG boars confirms the high stability of the spermatogenesis process in the TG boars analyzed.

Social stress does not alter the expression of sensitization to cocaine

The effects of chronic social stress on behavioral sensitization to cocaine were investigated in the Syrian hamster. Adolescent animals received either 15 mg/kg i.p. of cocaine or saline twice per day for 7 consecutive days. Two weeks following the last injection (young adulthood), they were given a challenge dose of 5 mg/kg i.p. of cocaine and scored for locomotion. Motor activity was significantly greater in cocaine-treated animals, demonstrating sensitization to this psychostimulant. Following the results of the first study, another group of adolescent animals was exposed to either a novel clean cage (control) or an aggressive resident male hamster (social stress) for 15 min following an injection of cocaine (20 mg/kg i.p. once daily) or saline for 7 consecutive days. The groups were as follows: Social Stress/Cocaine (SSC), No Social Stress/Cocaine (NSSC), Social Stress/Saline (SSS) and No Social Stress/Saline (NSSS). Two weeks following the last injection (Day 21), all animals were given a challenge dose of cocaine (5 mg/kg i.p.) and were rescored for locomotion. At that time, the suppressive effect of stress on locomotion was no longer detectable, as the expression of sensitization was observed in the NSSC but not in the SSC group. These results suggest that chronic social stress administered during adolescence does not cross-sensitize with cocaine in young adult hamsters.

CGP 44532, a GABAB receptor agonist, is hedonically neutral and reduces cocaine-induced enhancement of reward

Drugs that alter the function of gamma-aminobutyric acid (GABA) neurotransmission seem to reduce cocaine reinforcement, and as such may be useful in pharmacologically treating cocaine addiction. In the present experiment, the anti-cocaine effects of CGP 44532, a phosphinic acid analogue of GABA, and a highly selective GABA(B) receptor agonist were examined in male Sprague-Dawley rats using brain stimulation reward (BSR) paradigm. In this method, the relationship between the rate of bar pressing and the frequency of stimulation pulses was analyzed in two measures: the maximum rate of responding (MAX) and the frequency necessary to sustain half maximal rate of responding known as the locus of rise (LOR). CGP 44532 was found to be hedonically neutral without producing any measurable effects on performance (MAX). It also dose-dependently reduced cocaine-induced BSR enhancement, in the order of 15-31%, as shown by progressive shifts in LOR towards baseline. Thus, in theory, administration of CGP 44532 might reduce cocaine's hedonic effects, while also maintaining patient compliance. Whether this agent would also be effective at curbing craving, a long-term consequence of drug abuse, remains to be determined.

Effects of repeated GBR 12909 administration on brain stimulation reward

Male rats were trained at three separate currents to bar press for intracranial self-stimulation. On days 1 and 15, all subjects were given 1-(2-bis(4-fluorophenyl)-methoxy)-ethyl-4-(3-phenylpropyl) piperazine, also known as GBR 12909 (10 mg/kg, i.p.), prior to test session. Between these days, the paired Chronic-before group was injected (every other day) with GBR 12909 prior to intracranial self-stimulation, while unpaired, Chronic-after group was given the drug just after the end of the session. A third group (Control) received saline injections (i.p.) 20 min following the session. Although GBR 12909 was found to be reward enhancing, neither sensitization nor tolerance developed to the rewarding and performance/motor effects regardless of the injection regimen. In addition, the rewarding effects of intracranial self-stimulation were found to be independent of both current and environment-specific pairing. The present data obtained for GBR 12909 agree with previous observations of the effects of repeated administration of drugs of abuse on intracranial self-stimulation.

Novel monoamine transporter ligands reduce cocaine-induced enhancement of brain stimulation reward

Six novel monoamine reuptake inhibitors were screened for their intrinsic effects on brain stimulation reward (BSR), as well as for their potential to reduce cocaine-induced reward-enhancement in that paradigm. Two of the compounds, nocaine-3B and 5-ara-74A (disubstituted piperidines) significantly reduced locus of rise (LOR), threshold measure of reward, at some doses. One compound, 1-RV-96A (a hybrid of the GBR and WIN-like agents) significantly reduced reward (increased LOR), but only at the highest dose tested. No effect of dose was found for MC9-20 (a GBR-like acyclic analogue of the N-bisarylmethoxyethyl-N'-phenylpropyl piperazine), nocaine-250B or 4-ara-42C (disubstituted piperidines). When cocaine (10 mg/kg, ip) and selected, hedonically neutral doses of novel compounds were combined, the following findings were obtained: MC9-20 (2.5 mg/kg, ip) showed a significant increase in cocaine-induced reward enhancement (0.2 log units or 53%). In contrast, nocaine-250B and 1-RV-96A (both at 10 mg/kg, ip) demonstrated a significant reduction (0.13 log units or 41%) in cocaine-induced reward enhancement (P<.01 and P<.05, respectively), as measured by changes in LOR. There were no differences in the maximum behavioral output (MAX) at either dose of each of the six drugs, or when selected doses were combined with cocaine. These results indicate that nocaine-250B and 1-RV-96A constitute two potential anticocaine compounds worthy of further behavioral and biochemical evaluation.

Prenatally protein-malnourished rats are less sensitive to the amnestic effects of medial septal infusions of chlordiazepoxide

Evidence is mounting that prenatal protein malnutrition affects the physiological properties of the GABAergic neurotransmitter system in rats. To investigate the functional behavioral consequences of these changes, chlordiazepoxide (CDP, a positive modulator of the GABA(A) receptor) was applied directly to the medial septum and the amnestic response appraised. In adulthood, male offspring of rats provided with a protein-deficient diet (6% casein) for 5 weeks prior to mating and throughout pregnancy underwent stereotaxic surgery to implant steel cannulae aimed at the medial septum. After recovery, spatial learning performance in the submerged platform version of the Morris water maze task was assessed immediately following a 1 microl infusion of either artificial cerebrospinal fluid (aCSF), or one of three doses of CDP (15, 30 and 60 nmol). Well-nourished control rats demonstrated a robust amnestic response to intraseptal CDP. During task acquisition, well-nourished rats administered each of the doses exhibited significantly longer escape latencies than those given aCSF. On the probe trial (platform removed) a lower proportion of time was spent in the target quadrant (all three doses) at a greater average distance from the former platform location (30 and 60 nmol doses). In contrast, prenatally malnourished rats exhibited a muted sensitivity to CDP, most notable at the 30 nmol dose. These findings provide further support for functional changes within the GABAergic system consequent to malnutrition.

Functional connections between medial prefrontal cortex and caudate-putamen in brain-stimulation reward of rats

Rats were trained to self-stimulate for trains of cathodal pulses delivered via electrodes placed in the medial prefrontal cortex (MPFC) and caudate-putamen (CPu). When the pulses were delivered via 9 ipsilateral MPFC and CPu sites alternately, summation varied from 13% to 40%. However, the overall summation for 2 contralateral MPFC-CPu pairs was 5%, thus indicating a greater integration of ipsilateral than contralateral reward signals. When the interval between alternate pulses decreased in 4 of the 9 ipsilateral pairs, the summation also decreased, an outcome consistent with collision of action potentials passing between the MPFC and CPu sites. The size of the collision effect ranged from 15% to 33%. Estimates of conduction velocity varied between 0.4 to 5.4 m/s, with a 1.7 m/s average. According to these values, the neurons connecting the MPFC and CPu self-stimulation sites appear to be slower than the ones that have been shown to link reward fibers that course between posterior brain regions.

Prenatal malnutrition-induced changes in blood pressure: dissociation of stress and nonstress responses using radiotelemetry

A link between prenatal malnutrition and hypertension in human populations has recently been proposed. Rat models of prenatal malnutrition have provided major support for this theory on the basis of tail-cuff measurements. However, this technique requires restraint and elevated temperature, both potential sources of stress. To determine the effect of prenatal protein malnutrition on blood pressure under nonstress conditions, 24-hour radiotelemetric measurements were taken in the home cage. Male rats born to dams fed a 6% casein diet for 5 weeks before mating and throughout pregnancy were studied in early adulthood (from 96 days of age). During the waking phase of their cycle but not the sleep phase, prenatal malnutrition gave rise to small but significant elevations of diastolic blood pressure and heart rate compared with well-nourished controls. Direct effects of stress on blood pressure responses were determined in a second experiment using an olfactory stressor. Prenatally malnourished rats showed a greater increase in both systolic and diastolic pressures compared with well-nourished controls during the first exposure to ammonia. A different pattern of change of cardiovascular responses was also observed during subsequent presentations of the stressor. These findings of a small baseline increase in diastolic pressure consequent to prenatal malnutrition, but an augmented elevation of both systolic and diastolic pressures after first exposure to stress, suggest the need to reevaluate interpretation of the large elevations in blood pressure previously observed in malnourished animals using the stressful tail-cuff procedure.

Activation of reward-relevant neurons in the caudate-putamen influences the development of medial prefrontal cortex self-stimulation: a moveable electrode mapping study

Two hundred fifty five medial prefrontal cortical (MPFC) and 187 caudate-putamen (CPu) sites were evaluated for intracranial self-stimulation in 67 animals using moveable electrodes and collecting trade-off functions between current and frequency. Eleven percent of the examined areas, located predominantly in the ventromedial aspects of MPFC and CPu, showed reliable self-stimulation and the average charge of 1.12 and 1.11 microC respectively, values that are in line with those reported for the Medial forebrain bundle. The distribution of charge, however, was greater than reported for the latter region, and ranged between 0.68 to 1.63 microC across sites. Some subjects were implanted with two electrodes, one aimed at the MPFC, and the other at the CPu, ventral tegmental area, or lateral hypothalamus. Only animals with CPu placements showed transference of self-stimulation to the MPFC, suggesting that these two regions might form part of the same reward substrate, a view that has anatomical, electrophysiological and recently behavioral support.

Characteristics of stimulation-induced feeding sites in the sulcal prefrontal cortex

Double pulse tests were used to infer the refractory periods of the substrate underlying stimulation-induced feeding in the sulcal prefrontal cortex of the rat. Eleven sites were examined, of which five supported the behaviour at currents of 250 to 400 microA; pulse duration was 100 microseconds. The average profile indicates a recovery function that begins at 0.5 ms and ends at 3.0 ms, with no apparent contribution from local potential summations. The mean effectiveness value corresponding to the asymptotic portion of the curves was 91%. These results suggest that there is substantial overlap in the excitability of neurons underlying stimulation-induced feeding in the sulcal prefrontal cortex and that reported for the medial forebrain bundle, but unlike the latter structure, there is no evidence of self-stimulation from the same sulcal prefrontal cortex placements. Response rates were collected for a maximum of 21 days from each of the cortical sites at which feeding was recorded and at the same currents used to evaluate the refractory periods underlying stimulation-induced feeding. The rates averaged between 0 and 3 responses per minute whether the current was available or not. These data represent the first demonstration of a site that supports stimulation-induced feeding in the absence of brain stimulation reward, at least at these specific placements and stimulation parameters.

Behaviourally derived estimates of excitability in striatal and medial prefrontal cortical self-stimulation sites

The refractory periods of the substrate underlying brain-stimulation reward were investigated in three rats with moveable electrodes implanted in the rostral caudate-putamen and the medial prefrontal cortex. Acquisition of caudate-putamen self-stimulation occurred within the first session, while self-stimulation for medial prefrontal cortex was observed only after three sessions of caudate-putamen stimulation. The currents required for self-stimulation ranged from 300 to 800 microA (0.1 ms pulse duration) across animals; the maximum response rates averaged roughly 40 bar presses per minute for both structures. Refractory period estimates were obtained from ten caudate-putamen and four medial prefrontal cortex sites. The time course of recovery had the following profile: the curves began to rise at 0.65 ms and 0.95 ms for caudate-putamen and medial prefrontal cortex stimulation, respectively, thereafter increasing to approach an asymptote at 6.00 ms for the caudate-putamen and 6.25 ms for the medial prefrontal cortex. The mean effectiveness value corresponding to the asymptotic portion of the curves was 73% for the caudate-putamen and 69% for the medial prefrontal cortex. Like other forebrain structures, the behaviourally derived refractory periods underlying caudate-putamen and medial prefrontal cortex stimulation, at least at these particular sites, are significantly longer than those observed in most medial forebrain bundle areas, both beginning and ending later. One interpretation for the similarity in their refractory period profiles and the apparent facilitating effect of caudate-putamen stimulation on acquisition of medial prefrontal cortex self-stimulation is that these two regions form part of the same reward substrate.