Alloanti-c in a c-positive, JAL-positive patient

BACKGROUND AND OBJECTIVES

In the Rh blood group system, partial D, C, and e antigens are well-known, but a partial c antigen resulting in the production of alloanti-c in a c+ individual is rare. One example of an alloanti-c in a c+ person was an anti-Rh26, which can appear as anti-c, and another was an alloanti-c in a c+ person with a presumed R(1)r phenotype. The finding of an apparent alloanti-c in a transfused c+ patient initiated this investigation.

MATERIALS AND METHODS

Haemagglutination tests, DNA extraction, polymerase chain reaction (PCR)-based assays (PCR-restriction fragment length polymorphism, allele-specific PCR), reticulocyte mRNA extraction, reverse transcriptase (RT)-PCR and sequencing were performed by standard procedures.

RESULTS

Plasma from a 64-year-old African American woman with a wound infection following a mastectomy contained anti-E, anti-S, anti-K, anti-Fy(a) and anti-Jk(b), reacting by the indirect antiglobulin test. In addition, the patient's plasma gave reactions that were consistent with an anti-c, while her pre-transfusion red blood cells typed c+ with some anti-c reagents. These results are consistent with a partial c antigen. The patient's red blood cells also typed V+(W)VS- and JAL+. Analyses of DNA and Rh-transcripts from this patient showed the presence of the following genes: RHD*D, RHD*DAU0, RHCE*Ce and RHCE*ce(S)(340).

CONCLUSION

The nucleotide 340C>T change in RHCE exon 3 (predicted to encode 114Trp) of the RHCE*ce(S)(340) allele is associated with a JAL+ phenotype and the altered expression of the c, V and VS antigens. This alteration in the c antigen allowed the patient to make an alloanti-c. This case reveals that the RHCE*ce(S)(340) allele encodes a partial c antigen.

Perianal mucinous adenocarcinoma arising from chronic anorectal fistulae: a review from a single institution

BACKGROUND

Mucinous adenocarcinoma arising from a chronic anorectal fistula is rare, with few reports in the literature. Such lesions present in an innocuous manner and can be mistaken for the more common clinical condition of a benign perianal abscess or fistula.

METHODS

From our prospectively collected database, we identified 4 patients with chronic perianal inflammatory conditions who were subsequently found to have developed perianal mucinous adenocarcinoma on biopsy. We received the symptomatology, subsequent management and further follow-up of each patient. These patients were treated with radical surgery, with or without adjuvant therapy.

RESULTS AND CONCLUSIONS

A high index of clinical suspicion is required to make the diagnosis of perianal tumours while assessing patients presenting with perianal inflammatory conditions. Wide excision of the tumour with abdominoperineal resection is the surgical treatment of choice and can provide good long-term results in patients with localized disease.

A low temperature method of isolating normal human articular chondrocytes

OBJECTIVE

Numerous methods for isolation of human chondrocytes are reported in the literature, most based on isolation from animal cartilage. Normal human articular cartilage (NHAC) poses particular problems for isolating chondrocytes when compared to animal or other types of human cartilage: a hardy matrix, combined with few and friable chondrocytes makes isolation difficult. Our objective was to develop an efficient method of isolating chondrocytes from NHAC without jeopardising the viability of these cells.

DESIGN

In this study we demonstrate that lowering the enzymatic digestion temperature to 27 degrees C increases cell yield and chondrocyte viability. We then optimised this low temperature isolation of chondrocytes from NHAC by comparing the relative efficacies of trypsin and protease and hyaluronidase in combination with different types of collagenase (I, II and XI) at releasing chondrocytes from their surrounding cartilaginous matrix. Enzymes were tested at different concentrations and for differing times. Outcome measures included determining the amount of cartilage digested, the number of viable chondrocytes isolated per gram of cartilage and cell adherence rates.

CONCLUSIONS

From these set of experiments, the method that maximised cell yield without jeopardising cell viability proved to be a two stage process: pre-digestion step using trypsin for 15 min; followed by overnight digestion with a combination of two types of collagenase (types I and II) and at a lower temperature of 27 degrees C. This has resulted in an efficient and robust method of releasing chondrocytes from cartilage, without jeopardising the viability of these cells.

Subventricular Zone Proliferation after α-Amino-3-Hydroxy-5-Methyl-4-Isoxazolepropionic Acid Receptor-Mediated Neonatal Brain Injury

The mammalian forebrain subventricular zone (SVZ) contains stem cells capable of generating new neurons and glia. Recent studies indicate that acute brain injury is a potent stimulus for SVZ stem cell proliferation. To better understand mechanisms of the SVZ response to neonatal brain injury, we used a model that focuses on a unique mechanism of vulnerability of the immature CNS, alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor-mediated excitotoxicity. We previously demonstrated that intracerebroventricular injection of the glutamate analog AMPA in rats at postnatal day 7 (P7) caused bilateral periventricular gray and white matter injury. We hypothesized that excitotoxic injury would stimulate cellular proliferation in the SVZ; we used the AMPA intracerebroventricular injection model to test this hypothesis. P7 rat pups received either left or right intracerebroventricular injections of S-AMPA (2.5 nmol). Normal and PBS-injected littermates were included as controls. On P8 or P14, serial coronal sections through the SVZ were collected; an immunohistochemical assay was performed with an antibody to the cell proliferation marker Ki-67. Bilateral Ki-67+ cells/SVZ were quantitated stereologically using the optical disector method. The median number of Ki-67+ cells/SVZ was increased in the SVZ of AMPA-injected rats relative to normal controls on both P8 and P14. To evaluate neurogenesis, we assayed the expression of doublecortin, a microtubular protein expressed only by immature neurons. From P8 to P14, there was a marked increase in doublecortin immunoreactive cells in the AMPA-injected SVZ. Many Ki-67+ nuclei were immediately surrounded by doublecortin staining. This study indicates that there is a proliferative response in the immature SVZ after an excitotoxic stimulus. Our findings suggest that some of these newly generated cells differentiate as immature neurons. This model may provide information about the mechanisms that regulate SVZ responses to neonatal brain injury.

Long-term follow-up of Anglian Germ Cell Cancer Group surveillance versus patients with Stage 1 nonseminoma treated with adjuvant chemotherapy

OBJECTIVES

To study survival and late events after adjuvant chemotherapy in Stage 1 nonseminoma.

METHODS

From 1978 to 1986, all patients had surveillance. From 1986, adjuvant chemotherapy (initially a 3-day regimen of etoposide, bleomycin, and cisplatin, but, more recently, bleomycin, Oncovin, and cisplatin) was offered to patients at a high risk of relapse (greater than 30%).

RESULTS

A total of 382 patients with Stage 1 nonseminoma treated between 1978 and 2000 were reviewed. Of the 234 patients treated by surveillance, 71 (30%) had relapses (5 after 2 years), 6 died (2.6%) of germ cell cancer, and 3 developed second primary testicular cancer. Of the 148 men treated with adjuvant chemotherapy, 6 (4%) had relapses and 2 (1.4%) died of chemoresistant cancer. After one course of etoposide, bleomycin, and cisplatin, 3 (6.5%) of 46 developed a relapse; after two courses, 1 (3.6%) of 28 did so; and after bleomycin, Oncovin, and cisplatin every 10 days x2, 2 (2.7%) of 74 patients did so. Of the high-risk patients who were offered adjuvant treatment, 24% declined. As a consequence, the relapse rate of the surveillance patients only fell from 36% to 27% after the introduction of adjuvant therapy, although for the total cohort treated in the adjuvant era, the relapse rate was 16%.

CONCLUSIONS

Adjuvant chemotherapy is more effective than retroperitoneal lymph node dissection for reducing the relapse risk in high-risk Stage 1 nonseminoma. However, given the uncertainty about the incidence of postchemotherapy late events, surveillance and retroperitoneal lymph node dissection remain justified alternatives. With positron emission tomography and laparoscopy showing increasing promise in these cases, quality-of-life studies and greater patient involvement in treatment selection are needed.

Outcome of patients with HIV-related germ cell tumours: a case-control study

Testicular germ cell tumour (GCT) is not an AIDS-defining illness despite an increased incidence in men with HIV infection. We performed a matched case-control study comparing outcomes in HIV-positive men and the general population with GCT, using three age and stage matched controls for each case. There was no difference in the 5-year GCT-free survival between cases and controls. However, overall survival was significantly decreased in the cases (log rank P=0.03). HIV was responsible for 70% of this mortality. The relapse-free survival for stage I patients treated with orchidectomy and surveillance was not affected by HIV status (log rank P=0.68). There was no difference in disease free survival in patients with metastatic disease (log rank P=0.78). The overall survival has not improved since the introduction of highly active antiretroviral therapy (log rank P=0.4). Thus, HIV-related GCT is not more aggressive than GCT in the general population.

Testis conserving chemotherapy in germ cell cancer: its potential to increase understanding of the biology and treatment of carcinoma-in-situ

Prompted by recognition of the potential of chemotherapy to increase the success of testis conserving surgery in patients with germ cell cancer, background and outcome data are reviewed and their contribution to the ongoing debate about how germ cell cancer develops discussed. The review is based on three previous studies of: a) time trends in tumour size in 578 personal series of all stages of testis cancer treated since 1978; b) impact of chemotherapy on actuarial risk of tumours in contralateral testis examined on 1221 patients treated in trials through the Anglian Germ Cell Cancer Consortium; and c) testes conservation attempted using chemotherapy in 78 patients. Since 1978 tumour size has decreased from 4.8 to 3.0 cms while cure has gone from 77 to 97%. There was no overall long term reduction in second cancers beyond 10 years in stage 1 patients after orchidectomy alone compared to stage 1 or metastatic disease patients receiving chemotherapy though the incidence was non significantly lower up to 10 years particularly in those patients receiving etoposide based combination. Testis conservation was initially successful in 28 of 78 (36%). An additional 25 (32%) had no viable cancer in orchidectomy specimen. In the 28 primary tumours cured by chemotherapy there was a 26% late relapse rate between 5 and 10 years (all cured by orchidectomy) compared to less than 5% in those cured with established metastases. In conclusion, testis conservation with chemotherapy is safe and feasible, though relapse is too frequent for routine service use. Confirmation of the high frequency of late relapse by others has raised the question whether these recurrences are due to post pubertal events reinducing CIS in intrauterine oestrogen primed germ cells and highlights the potential of testes conservation studies to better understand germ cell cancer development.

Attenuation of morphine withdrawal signs by the GABA(B) receptor agonist baclofen

The present study examined the effect of the gamma-aminobutyric acidB (GABA(B)) receptor agonist, baclofen on naloxone-induced withdrawal signs in morphine-dependent rats and modification by the antagonist, 3-aminopropyl-cyclohexylmethylphosphinic acid (CGP 46381). Morphine was administered via mini-osmotic pumps for 7 days to induce physical dependence. Baclofen (20 mg kg(-1)) decreased stereotyped head movements, chewing, chatter, ptosis and body weight loss, induced by naloxone (10 mg kg(-1)) in morphine-dependent rats. CGP 46381 (20 mg kg(-1)) reversed the effects exerted by baclofen on stereotyped head movements, ptosis, and weight loss and partially reversed the effect of baclofen on chewing. It can be concluded that baclofen has some potential in the treatment of opioid withdrawal and that GABA(B) receptors may be implicated in such a withdrawal.

Cryptogenic cirrhosis and posttransplantation nonalcoholic fatty liver disease

Some patients diagnosed with cryptogenic cirrhosis may have "burned-out" nonalcoholic fatty liver disease (NAFL). To test this hypothesis, we used our liver transplant database (November 1984 to November 1998) to assess the incidence of NAFL in patients with cryptogenic cirrhosis after orthotopic liver transplantation (OLT). We also examined the clinicodemographic features associated with post-OLT NAFL, obtained by chart review and telephone interviews. When available, post-OLT liver biopsy specimens were reviewed blindly by a hepatopathologist according to the NAFL pathology protocol. We identified 51 patients with cryptogenic cirrhosis (mean age, 51 +/- 12 years); 60% were women, 94% were white, and 34% had type 2 diabetes mellitus (DM). Mean pre-OLT body mass index (BMI) was 27.33 +/- 5.54 kg/m(2). Twenty-five patients underwent at least 1 post-OLT liver biopsy. Post-OLT NAFL was identified in 13 patients (25.4%), whereas post-OLT nonalcoholic steatohepatitis (NASH) was seen in 8 patients (15.7%). Features associated with post-OLT NASH were pre- and post-OLT type 2 DM (P < or =.05) and an elevated fasting triglyceride level (P <.05). BMI tended to be greater in patients with post-OLT NAFL or NASH. Those who did not develop post-OLT NAFL showed a decrease in BMI. Patients with cryptogenic cirrhosis undergoing OLT resemble patients with NAFL. Post-OLT NAFL and NASH can be seen in a number of patients with cryptogenic cirrhosis. This supports the notion that some cases of cryptogenic cirrhosis represent burned-out NAFL.

Carboplatin AUC8 in combination with etoposide and bleomycin in the treatment of intermediate and poor-risk metastatic germ cell tumours: a phase II study

PURPOSE

Carboplatin has demonstrated significantly poorer response rates in non-seminomatous germ cell tumours. A phase II study of higher than standard doses of carboplatin was conducted because of suspicion that the poorer response might have been due to suboptimal dosing.

PATIENTS AND METHODS

A group of 19 patients with advanced germ cell tumours (International Germ Cell Cancer Collaborative Group intermediate and poor prognosis) were treated with carboplatin at an AUC of 8 mg/ml.min (using Calvert's formula) on day 1, etoposide 120 mg/m2 days 1-3 and bleomycin 60,000 U over 2 days (EBCa). Treatment was repeated every 3 weeks and a maximum of four courses was given.

RESULTS

Of the 19 patients, 7 (37%) achieved complete remission, of whom 6 (32%) remained long-term progression-free. Post-chemotherapy surgery and further chemotherapy salvaged an additional 26%, leading to an overall disease-free survival rate of 58%. No relationship between outcome and degree of myelosuppression could be established.

CONCLUSION

Dose-escalated carboplatin in combination, although feasible, did not improve the results and led to poorer results than those expected with cisplatin-based therapy. There is no evidence that the patients relapsing following this were easier to salvage. Further investigation of this regimen cannot be recommended.

CGP 36216 is a selective antagonist at GABA(B) presynaptic receptors in rat brain

In rat neocortical preparations maintained in Mg(2+)-free Krebs medium, baclofen depressed the frequency of spontaneous discharges in a concentration-dependent manner (EC(50) = 6 microM), sensitive to (3-aminopropyl)ethylphosphinic acid (CGP 36216) (100, 300 and 500 microM) (pA(2) = 3.9 +/- 0.1). By contrast, CGP 36216, up to 1 mM, was ineffective in antagonising baclofen-induced hyperpolarisations, mediated through gamma-aminobutyric acid(B) (GABA(B)) postsynaptic receptors. In electrically stimulated brain slices preloaded with [3H]GABA, CGP 36216 increased [3H]GABA release (IC(50) = 43 microM), which was reversed by baclofen (20 microM). While CGP 36216 is ineffective at GABA(B) postsynaptic receptors, it is appreciably more active at presynaptic receptors.

Comparative activities of the enantiomeric GABA(B) receptor agonists CGP 44532 and 44533 in central and peripheral tissues

In neocortical slices maintained in Mg(2+)-free Krebs medium, the gamma-aminobutyric acid (GABA(B)) receptor agonists baclofen, (3-amino-2(S)-hydroxypropyl)methylphosphinic acid (CGP 44532), and its (R)-enantiomer CGP 44533 depressed the frequency of spontaneous discharges in a concentration-dependent manner (EC(50)=10, 6.5, and 50 microM, respectively). These effects were reversibly antagonised by the GABA(B) receptor antagonist (+)-(S)-5,5 dimethylmorpholinyl-2-acetic acid (Sch 50911) (3, 10, and 30 microM) (average pA(2) value=6.0+/-0.2). In neocortical wedges, baclofen, CGP 44532 and CGP 44533 elicited concentration-dependent hyperpolarisations (the EC(50)s were 14, 7.5 and 16 microM, respectively) sensitive to Sch 50911 (1, 5, 10 microM) (average pA(2) value=6.0+/-0.1), whilst they also depressed ileal electrically elicited cholinergic twitch contractions (EC(50)=11, 7, and 50 microM) that were antagonised by Sch 50911 (average pA(2) value=6.0+/-0.1). In electrically stimulated brain slices preloaded with [3H]GABA, baclofen, CGP 44532 and CGP 44533 decreased [3H]GABA release (IC(50)=5, 0.45, and 10 microM); this effect was reversed by Sch 50911 (50 microM). It is concluded that CGP 44532 is a far more potent agonist at GABA(B) autoreceptors than at central or peripheral heteroreceptors.

Modification of d-amphetamine-induced responses by baclofen in rats

RATIONALE

d-Amphetamine is known to have effects on heart rate, body temperature and locomotor activity. However, it is not known if GABAB receptor stimulation modifies these actions of d-amphetamine.

OBJECTIVES

Using telemetry recordings, this study examined the interactions between the GABAB receptor agonist baclofen and d-amphetamine, on heart rate responses, body temperature and locomotor activity, and whether these effects could be blocked by the GABAB receptor antagonist SCH 50911.

METHODS

Rats were prepared with telemetry implants, which allowed continuous monitoring of heart rate, core temperature and spontaneous locomotor activity. Drugs were subsequently administered subcutaneously to the animals for simultaneous recording over a period of 180 min.

RESULTS

d-Amphetamine alone (0.3, 1.0 and 3.0 mg/kg) produced a dose-related increase in heart rate, but was without any effect on body temperature, whilst at 1.0 mg/kg, it significantly increased locomotor activity. Baclofen increased heart rate without affecting locomotor activity, and, at the highest dose of 10.0 mg/kg, it induced a significant reduction in body temperature. Graded doses of baclofen (3.0-10.0 mg/kg), when co-administered with d-amphetamine (1.0 mg/kg), did not modify the d-amphetamine-induced increase in heart rate, but the combination produced significant reductions of body temperature. The latter was only partially reversed by the GABAB receptor antagonist SCH 50911 (10.0 mg/kg). By contrast, the increase in locomotor activity by d-amphetamine was markedly blocked by baclofen in a dose-related manner, and this effect was abolished by SCH 50911 (10.0 mg/kg). SCH 50911 alone at doses of 3.0, 6.0 and 10.0 mg/kg had no effect on temperature or locomotor activity. Heart rate was increased significantly, but the magnitude of change was small.

CONCLUSIONS

The results of the present study suggest that stimulation of GABAB receptors by baclofen completely blocks the locomotor stimulatory effects of d-amphetamine. Baclofen did not significantly modify the increase in heart rate produced by d-amphetamine and decreased body temperature, both alone and in combination with d-amphetamine. GABAB receptor ligands may well have potential as pharmacotherapies in the treatment of amphetamine abuse and dependence.

Liver transplantation in patients with transjugular intrahepatic portosystemic shunts

BACKGROUND

In patients with intractable oesophageal variceal bleeding, transjugular intrahepatic portosystemic shunts (TIPSS) are being used increasingly as a bridge to orthotopic liver transplantation (OLTx). There is little information in the literature concerning variations in the operative techniques of OLTx required because of the presence of TIPSS.

METHODS

A retrospective review of patients treated by TIPSS prior to OLTx was undertaken. The aims were to assess the effectiveness of TIPSS in bridging patients to OLTx and to examine whether TIPSS influence the operative management of OLTx.

RESULTS

Over a 4-year period eight adult patients underwent TIPSS insertion prior to OLTx in the Australian National Liver Transplant Unit (ANLTU). Transplantation was performed at a mean of 14.6 (0.3-53.8) months after TIPSS insertion. Prevention of major recurrent variceal haemorrhage prior to transplantation was achieved in six cases. In two patients the stents were predominantly intrahepatic and they did not interfere with OLTx. In five patients the stents extended into the portal vein, requiring removal during OLTx either by division of the stent with the recipient portal vein, followed by removal of the fractured stent wires from the portal veins (n = 3), or by 'endarterectomy' of the recipient portal vein, allowing removal of the intact stent (n = 2). In one case where the stent extended into the suprahepatic inferior vena cava, removal was achieved by traction without difficulty. All patients are alive at a mean of 24 (7-53) months post-transplant and none has portal vein abnormalities. When compared to 178 adult patients who had no TIPSS and underwent primary OLTx during the same study period, there was no difference in the length of operating time or the usage of blood products during OLTx.

CONCLUSION

Transjugular intrahepatic portosystemic shunts offer a bridge to OLTx by providing effective control of variceal haemorrhage. In the present series TIPSS did not increase surgical morbidity or mortality, but emphasis is placed upon the need for optimal TIPSS placement within the liver to facilitate subsequent OLTx.

Effects of Ca2+ concentration on GABA(B) receptor function in rat neocortical slices

In rat neocortical slices maintained in Mg2+-free Kreb's medium, the effects of Ca2+ concentration on repetitive spontaneous discharges and on GABA(B) receptor-mediated responses were investigated. Over a concentration range of 0.3-2.4 mM Ca2+, there was a reduction of discharge amplitude, with a 50 +/- 6.5% reduction in 0.3 mM Ca2+, whilst the burst frequency remained unaffected. Baclofen, the GABA(B) receptor agonist, produced a concentration-dependent depression of discharge frequency, reversibly antagonised by the antagonist (+)-(S)-5,5-dimethylmorpholinyl-2-acetic acid (Sch 50911). The EC50 value for baclofen in 2.4 mM Ca2+ was 11 microM, while the EC50 values in 0.3, 0.6, 1.2, and 1.8 mM Ca2+ were 1.3, 2.5, 3.6, and 10 microM, respectively, resulting in 8.5, 4.4, 3.1, and 1.1-fold leftward shifts. This enhanced action of baclofen in low extracellular Ca2+ concentrations in the neocortex may be the result of a lower concentration gradient which reinforces the action of baclofen.

Effects of Ca2+ concentration on GABAB receptor function in rat neocortical slices

In rat neocortical slices maintained in Mg2+-free Kreb's medium, the effects of Ca2+ concentration on repetitive spontaneous discharges and on GABAB receptor-mediated responses were investigated. Over a concentration range of 0.3-2.4 mM Ca2+, there was a reduction of discharge amplitude, with a 50 ± 6.5% reduction in 0.3 mM Ca2+, whilst the burst frequency remained unaffected. Baclofen, the GABAB receptor agonist, produced a concentration-dependent depression of discharge frequency, reversibly antagonised by the antagonist (+)-(S)-5,5-dimethylmorpholinyl-2-acetic acid (Sch 50911). The EC50 value for baclofen in 2.4 mM Ca2+ was 11 µM, while the EC50 values in 0.3, 0.6, 1.2, and 1.8 mM Ca2+ were 1.3, 2.5, 3.6, and 10 µM, respectively, resulting in 8.5, 4.4, 3.1, and 1.1-fold leftward shifts. This enhanced action of baclofen in low extracellular Ca2+ concentrations in the neocortex may be the result of a lower concentration gradient which reinforces the action of baclofen.Key words: baclofen, GABAB receptors, rat neocortical slices, spontaneous discharges, Ca2+ ions, neurotransmitter release.

Role of OCA-B in 3'-IgH enhancer function

OCA-B (alternately called Bob1 and OBF-1) is a B cell-specific coactivator that interacts with the ubiquitously expressed Oct-1 and the B cell-restricted Oct-2 to activate transcription via the octamer site (5'-ATGCAAAT-3'). OCA-B-/- mice appear to undergo normal Ag-independent B cell maturation. However, Ag-dependent B cell differentiation, including germinal center formation, production of secondary Ig isotypes, and proliferation in response to surface Ig cross-linking, is greatly affected. We demonstrate that the observed reductions in expression of class-switched isotypes in OCA-B-/- mice may be due in part to deficiencies in the function of the 3'-IgH enhancer elements. Furthermore, we find that surface Ig cross-linking represses all the Ig enhancers and that this repression is absent in OCA-B-/- B cells. These results suggest an important role for OCA-B in Ig enhancer function in vivo.

Recent advances in GABAB receptors: from pharmacology to molecular biology

Bicuculline-insensitive receptors for the inhibitory neurotransmitter gamma-aminobutyric acid (GABA), GABAB receptors, are a distinct subclass of receptors that mediate depression of synaptic transmission and contribute to neuronal inhibition. When activated, these receptors reduce transmission at excitatory and inhibitory synapses, as a result of an increase in K+ conductance, or a decrease in voltage-dependent Ca2+ currents. They are also linked to G-proteins, or intracellular effector systems in a very complex manner. The recent development of highly specific and potent agonists and antagonists for these receptors has led to a much better understanding of their physiology and pharmacology, including their heterogeneity, as well as their molecular biology. Over the past year, expression and cloning studies have contributed to major advances in characterizing GABAB receptor structure, with the discovery of the amino acid sequences of GABABR1a/R1b splice variants and GABABR2 receptors. These isoforms are widely distributed throughout the nervous system, and can be functionally expressed. Importantly, GABABR2 receptors can form a heteromeric assembly with GABABR1 proteins to operate as a heterodimer that displays robust coupling to inward-rectifying K+ channels, as well as inhibition of forskolin-stimulated adenylate cyclase activity. Further insights underlying the mechanisms of GABAB receptor functions can now be gained, leading ultimately to the therapeutic potential of drugs acting at these sites. It is increasingly clear that new information on GABAB receptor molecular structure will provide a plethora of targets for pharmaceutical intervention in areas such as drug addiction, nociception and absence seizures. This review summarizes the renewed efforts, and highlights the recent advances emerging in this field.