Use of parenteral testosterone prior to hypospadias surgery

Surgical correction of genital defects was formerly proposed when the size of the penis was sufficient to permit easy surgical repair. To enlarge penile size, temporary stimulation with testosterone or dihydrotestosterone cream has been used; however, the results were not only inconsistent, but absorption was also variable. We report our experience with parenteral testosterone as an adjunct to reconstructive genital surgery in 25 patients aged 6-18 months from July 1999 to December 2000, including 8 with penile hypospadias, 15 with penoscrotal hypospadias, and 2 with perineal hypospadias. Each had a penis that was significantly smaller than usual. Testosterone enanthate 25 mg was given i.m. once per month for a total of three doses before surgical repair. Penile length and glans circumference were measured before therapy and at operation. Side effects such as the development of pubic hair and acne were monitored. Bone age was checked 1 year later. An increase in penile length (from 19.8 +/- 2.4 mm to 23.8 +/- 2.0 mm) and glans circumference (from 27.4 +/- 1.4 mm to 37.84 +/- 2.6 mm) was apparent in all except 2 patients (P < 0.001 for both, paired t-test). Four patients had a significant increase in either penile length or glans circumference after the initial dose so that no further injections were required. No definite secondary effects were found. Preoperative parenteral testosterone therapy thus causes a significant increase in penile length and glans circumference without apparent side effects. We suggest that this therapy prior to microphallic hypospadias repair is appropriate.

Synaptic plasticity in the trigeminal principal nucleus during the period of barrelette formation and consolidation

We examined whether the postsynaptic responses of cells in the principal sensory nucleus of the trigeminal nerve (PrV) are subject to long-term changes in synaptic strength, and if such changes were correlated the whisker-specific patterning during and just after the critical period for pattern formation. We used an in vitro brainstem preparation in which the trigeminal ganglion (TG) and PrV remained attached. By electrically activating TG afferents, we evoked large-amplitude extracellular field potentials. These responses were postsynaptic in origin and blocked by the glutamate antagonist, DNQX. At P1, a time when barrelettes are consolidating, high frequency stimulation of their afferents led to an immediate (<1 min) and long-lasting (> or =90 min) reduction (35%) in the amplitude of the evoked response. At P3-7, when the pattern of barrelettes have stabilized, the same form of tetanus led to an immediate and long-lasting increase (40%) in the amplitude of the response. Both forms of synaptic plasticity were mediated by the activation of L-type Ca(2+) channels. Application of the L-type channel blocker, nitrendipine, led to a complete blockade of any the tetanus induced changes. These associative processes may regulate the patterning and maintenance of whisker-specific patterns in the brainstem trigeminal nuclei.

The promoter region of the CTLA4 gene is associated with type 1 diabetes mellitus

The CTLA4 (cytotoxic T lymphocyte associated antigen-4) gene encodes the T cell receptor involved in the control of T cell proliferation and mediates T cell apoptosis. C-T polymorphism is present at position -318 from the ATG start codon in the promoter region of the gene. We report a study on the polymorphism in 347 unrelated children with type 1 diabetes mellitus (DM) (age at diagnosis 7.2+/-3.8 years) and their 260 healthy siblings as controls. Genotype C/C conferred a risk of type 1 DM (RR = 2.02, 95% CI 1.32-3.10, pc = 0.0033). The gene frequency of the C allele was higher in patients (RR = 1.91, 95% CI 1.28-2.84, pc = 0.0026). The gene frequency and phenotype frequency of the T allele were negatively associated with type 1 DM (RR = 0.52, 95% CI 0.35-0.78, pc = 0.0026 and RR = 0.49, 95% CI 0.32-0.76, pc = 0.0022, respectively). The frequency of genotype C/T was lower in patients (RR = 0.50, 95% CI 0.32-0.78, pc = 0.0051). This study demonstrates that nucleotide -318 C-T polymorphism of the CTLA4 gene is associated with type 1 DM. The promoter allele -318 C confers a risk of type 1 DM but allele -318 T confers protection against this disease.

Neonatal deafferentation does not alter membrane properties of trigeminal nucleus principalis neurons

In the brain stem trigeminal complex of rats and mice, presynaptic afferent arbors and postsynaptic target cells form discrete modules ("barrelettes"), the arrangement of which duplicates the patterned distribution of whiskers and sinus hairs on the ipsilateral snout. Within the barrelette region of the nucleus principalis of the trigeminal nerve (PrV), neurons participating in barrelettes and those with dendritic spans covering multiple barrelettes (interbarrelette neurons) can be identified by their morphological and electrophysiological characteristics as early as postnatal day 1. Barrelette cells have focal dendritic processes, are characterized by a transient K(+) conductance (I(A)), whereas interbarrelette cells with larger soma and extensive dendritic fields characteristically exhibit low-threshold T-type Ca(2+) spikes (LTS). In this study, we surveyed membrane properties of barrelette and interbarrelette neurons during and after consolidation of barrelettes in the PrV and effects of peripheral deafferentation on these properties. During postnatal development (PND1-13), there were no changes in the resting potential, composition of active conductances and Na(+) spikes of both barrelette and interbarrelette cells. The only notable changes were a decline in input resistance and a slight increase in the amplitude of LTS. The infraorbital (IO) branch of the trigeminal nerve provides the sole afferent input source to the whisker pad. IO nerve transection at birth abolishes barrelette formation as well as whisker-related neuronal patterns all the way to the neocortex. Surprisingly this procedure had no effect on membrane properties of PrV neurons. The results of the present study demonstrate that distinct membrane properties of barrelette and interbarrelette cells are maintained even in the absence of input from the whiskers during the critical period of pattern formation.

DQA1*Arg52,DQB1*nonAsp57, and DRB1*04 genotypes in Chinese children with insulin-dependent diabetes mellitus

Ethnic comparisons are extremely important and useful for studying the HLA component involved in insulin-dependent diabetes mellitus (IDDM) predisposition. To date there have been only a few reports on the association of HLA loci and IDDM in Chinese. We report here a study on DQA1*Arg52, DQB1*nonAsp57, and DRB1*04 in IDDM children and control adults among Han Chinese living in Taiwan. One hundred and fourteen unrelated children (62 boys) with IDDM were studied. Their ages at diagnosis were between 0.3 and 15.0 years (6.8 +/- 3.6 years). The control population consisted of 120 randomly selected normal adults. DQA1*Arg52(+/+), DQB1*nonAsp57(+/+), and DRB1*04(+/-) were associated with IDDM (RR = 11.50, 2.21, and 2.82; p = 1.11 x 10(-15), 2.84 x 10(-3), and 1.98 x 10(-4), respectively). DQA1*Arg52, DQB1*nonAsp57, and DRB1*04 conferred risks for IDDM (RR = 12.79, 7.11, and 2.83; pc = 8.22 x 10(-4), 5.35 x 10(-3), and 5.68 x 10(-4), respectively). Combinations of DQA1*Arg52 and DRB1*04 conferred the highest risk for IDDM (RR = 19.64, pc = 5.4 x 10(-5)). DQA1*Arg52 was associated with IDDM in subjects with DQB1*nonAsp57+ (RR = 14.87, pc = 2.41 x 10(-4)) and DQB1*nonAsp57 was also associated with IDDM in subjects with DQA1*Arg52+ (RR = 8.41, pc = 1.54 x 10(-3)), suggesting that DQA1*Arg52 and DQB1*nonAsp57 are interacting. This study demonstrates that DQA1*Arg52, DQB1*nonAsp57, and DRB1*04 confer susceptibility for IDDM to Chinese children. A combination of DQA1*Arg52 and DRB1*04 confers the highest risk and it is suggested that a susceptibility gene might be situated between DQA1*Arg52 and DRB1*04 or both are synergistic. There is an interaction between DQA1*Arg52 and DQB1*nonAsp57 and homozygosity for DQA1*Arg52/DQB1*nonAsp57, which encodes four susceptibility DQ heterodimers, confers a high risk.

Polymorphism in the transmembrane region of the MICA gene and type 1 diabetes

Although MHC class II genes have a stronger association with type 1 diabetes than MHC class I genes, studies have shown that MHC class I molecules play an independent role in the etiology of type 1 diabetes, and the existence of susceptibility genes within a segment of MHC between the HLA-B and TNF genes has been predicted, where MHC class I chain-related gene A (MICA) resides. MICA has a triplet repeat polymorphism in the transmembrane region consisting of five alleles. We analyzed this polymorphism in 162 unrelated children (82 boys) with type 1 diabetes (age at diagnosis 7.01 +/- 3.76 yr) and 154 randomly selected unrelated children (87 boys), age 2.81 +/- 2.12 yr. Phenotype frequency of allele A9 in children with type 1 diabetes was significantly higher than in controls (RR = 2.42, 95% CI = 1.52-3.85, p = 0.000162, pc = 0.00081). Gene frequency of allele A9 was also significantly higher in children with type 1 diabetes when compared with control children (RR = 2.73, 95% CI = 1.85-4.03, p = 2.62 x 10(-7), pc = 1.31 x 10(-6)). This study demonstrates that MICA allele A9 confers risk of type 1 diabetes.

Recurrent inhibitory circuitry in the deep layers of the rabbit superior colliculus

1. Local inhibition in the deep layers of the superior colliculus plays a crucial role in sensorimotor integration. Using intracellular and extracellular recording techniques, we studied the organization of inhibitory circuits in the deep layers of the superior colliculus in anaesthetized rabbits. 2. We identified a new cell type in the deep superior colliculus that showed a characteristic burst response to stimulation of both the predorsal bundle and optic chiasm. The response had a jittering latency and failed to follow high frequency stimuli, indicating trans-synaptic (orthodromic) events. Moreover, the predorsal bundle stimulation-evoked orthodromic response could be made to collide with the response to a preceding stimulation of the optic chiasm, suggesting that burst-firing cells received excitatory inputs from the axonal collaterals of predorsal bundle-projecting cells. 3. Stimulation of the predorsal bundle could evoke an IPSP in predorsal bundle-projecting cells. The latency of the IPSP was 0.5-1.0 ms longer than the orthodromic response in burst-firing cells. Simultaneous recordings showed that the IPSP in predorsal bundle-projecting cells was preceded by a burst of extracellular spikes from burst-firing cells with short latency ( approximately 0.9 ms), indicating an inhibitory monosynaptic connection from burst-firing cells to predorsal bundle-projecting cells. 4. Burst-firing cells exhibited a prolonged depression after the predorsal bundle or optic chiasm stimulation due to an inhibitory postsynaptic potential. Latency analysis implies that burst-firing cells may form mutual inhibitory connections. 5. Together our results suggest that burst-firing cells and predorsal bundle-projecting cells form reciprocal excitatory and inhibitory connections and burst-firing cells may function as the recurrent inhibitory interneurons in the deep layers of the rabbit superior colliculus.

Association of CTLA4 gene A-G polymorphism with type 1 diabetes in Chinese children

OBJECTIVE

The CTLA4 (cytotoxic T lymphocyte associated antigen-4) gene encodes the T cell receptor involved in the control of T cell proliferation and mediates T cell apoptosis. Thus it is a strong candidate gene for T cell-mediated autoimmune disease. There is polymorphism at position 49 in exon 1 of the CTLA4 gene, providing a A-G exchange. This polymorphism is reportedly associated with type 1 diabetes in Caucasians but not in a small data set of Chinese. We wished to test this polymorphism in a larger and more homogeneous data set of Chinese children with type 1 diabetes and normal adult controls.

DESIGN

A population-based case-control study of a CTLA4 gene 49 A-G polymorphism was performed to look for an association with type 1 diabetes in Chinese children.

PATIENTS

We analysed this polymorphism in 253 unrelated children (128 boys) with type 1 diabetes (age at diagnosis 7.1 +/- 3.7 years) and 91 randomly selected normal adults. All individuals were Han Chinese.

RESULTS

The genotype and gene frequencies of children with type 1 diabetes differed significantly from those of adult controls (P = 0.0091 and P = 0.0051, respectively). Genotype CTLA4 49 G/G and G allele conferred a risk of type 1 diabetes (RR = 2.13, 95% CI = 1.31-3.46, P = 0.0022; RR = 1.68, 95% CI = 1.17-2.43, P = 0.0051, respectively).

CONCLUSIONS

This study demonstrates that CTLA4 49 A-G polymorphism is associated with type 1 diabetes in Han Chinese children. The CTLA4 49 G allele confers an increased risk of type 1 diabetes.

Synaptic regulation of L-type Ca(2+) channel activity and long-term depression during refinement of the retinocollicular pathway in developing rodent superior colliculus

The retinocollicular pathway undergoes activity-dependent refinement during postnatal development, which results in the precise retinotopic order seen in adults. This process is NMDA- and nitric oxide-dependent. Recent studies have shown that L-type Ca2+ channels may also play a role in synaptic plasticity, but such channel activity has not previously been reported in the developing superior colliculus (SC). Here we report the presence of a postsynaptic plateau potential mediated by L-type Ca2+ channels using whole-cell current clamp of the SC in an isolated brainstem preparation of rats. Seventy percent of SC neurons showed these potentials as early as postnatal day 0 (P0)-P2. The potential was blocked by nitrendipine and/or APV and facilitated by bicuculline, showing that the channel is activated by NMDA receptor-mediated EPSPs and deactivated by GABAA receptor-mediated IPSPs. Blockade of L-type Ca2+ channels also diminished long-term depression, which we could induce in the retinocollicular pathway in neonatal animals. The incidence of plateau potentials decreased to 39% of neurons by P10-P14, suggesting that L-type calcium channels may contribute to retinocollicular pathway refinement in the developing SC.

Electrophysiological properties and synaptic responses of cells in the trigeminal principal sensory nucleus of postnatal rats

In the rodent brain stem trigeminal complex, select sets of neurons form modular arrays or "barrelettes," that replicate the patterned distribution of whiskers and sinus hairs on the ipsilateral snout. These cells detect the patterned input from the trigeminal axons that innervate the whiskers and sinus hairs. Other brain stem trigeminal cells, interbarrelette neurons, do not form patterns and respond to multiple whiskers. We examined the membrane properties and synaptic responses of morphologically identified barrelette and interbarrelette neurons in the principal sensory nucleus (PrV) of the trigeminal nerve in early postnatal rats shortly after whisker-related patterns are established. Barrelette cell dendritic trees are confined to a single barrelette, whereas the dendrites of interbarrelette cells span wider territories. These two cell types are distinct from smaller GABAergic interneurons. Barrelette cells can be distinguished by a prominent transient A-type K(+) current (I(A)) and higher input resistance. On the other hand, interbarrelette cells display a prominent low-threshold T-type Ca(2+) current (I(T)) and lower input resistance. Both classes of neurons respond differently to electrical stimulation of the trigeminal tract. Barrelette cells show either a monosynaptic excitatory postsynaptic potential (EPSP) followed by a large disynaptic inhibitory postsynaptic potential (IPSP) or just simply a disynaptic IPSP. Increasing stimulus intensity produces little change in EPSP amplitude but leads to a stepwise increase in IPSP amplitude, suggesting that barrelette cells receive more inhibitory input than excitatory input. This pattern of excitation and inhibition indicates that barrelette cells receive both feed-forward and lateral inhibition. Interbarrelette cells show a large monosynaptic EPSP followed by a small disynaptic IPSP. Increasing stimulus intensity leads to a stepwise increase in EPSP amplitude and the appearance of polysynaptic EPSPs, suggesting that interbarrelette cells receive excitatory inputs from multiple sources. Taken together, these results indicate that barrelette and interbarrelette neurons can be identified by their morphological and functional attributes soon after whisker-related pattern formation in the PrV.

Three GABA receptor-mediated postsynaptic potentials in interneurons in the rat lateral geniculate nucleus

Inhibition is crucial for the thalamus to relay sensory information from the periphery to the cortex and to participate in thalamocortical oscillations. However, the properties of inhibitory synaptic events in interneurons are poorly defined because in part of the technical difficulty of obtaining stable recording from these small cells. With the whole-cell recording technique, we obtained stable recordings from local interneurons in the lateral geniculate nucleus and studied their inhibitory synaptic properties. We found that interneurons expressed three different types of GABA receptors: bicuculline-sensitive GABA(A) receptors, bicuculline-insensitive GABA(A) receptors, and GABA(B) receptors. The reversal potentials of GABA responses were estimated by polarizing the membrane potential. The GABA(A) receptor-mediated responses had a reversal potential of approximately -82 mV, consistent with mediation via Cl(-) channels. The reversal potential for the GABA(B) response was -97 mV, consistent with it being a K(+) conductance. The roles of these GABA receptors in postsynaptic responses were also examined in interneurons. Optic tract stimulation evoked a disynaptic IPSP that was mediated by all three types of GABA receptors and depended on activation of geniculate interneurons. Stimulation of the thalamic reticular nucleus evoked an IPSP, which appeared to be mediated exclusively by bicuculline-sensitive GABA(A) receptors and depended on the activation of reticular cells. The results indicate that geniculate interneurons form a complex neuronal circuitry with thalamocortical and reticular cells via feed-forward and feedback circuits, suggesting that they play a more important role in thalamic function than thought previously.

Retinal input induces three firing patterns in neurons of the superficial superior colliculus of neonatal rats

By using an in vitro isolated brain stem preparation, we recorded extracellular responses to electrical stimulation of the optic tract (OT) from 71 neurons in the superficial superior colliculus (SC) of neonatal rats (P1-13). At postnatal day 1 (P1), all tested neurons (n = 10) already received excitatory input from the retina. Sixty-nine (97%) superficial SC neurons of neonatal rats showed three response patterns to OT stimulation, which depended on stimulus intensity. A weak stimulus evoked only one spike that was caused by activation of non-N-methyl-D-aspartate (NMDA) glutamate receptors. A moderate stimulus elicited a short train (<250 ms) of spikes, which was induced by activation of both NMDA and non-NMDA receptors. A strong stimulus gave rise to a long train (>300 ms) of spikes, which was associated with additional activation of L-type high-threshold calcium channels. The long train firing pattern could also be induced either by temporal summation of retinal inputs or by blocking gamma-aminobutyric acid-A receptors. Because retinal ganglion cells show synchronous bursting activity before eye opening at P14, the retinotectal inputs appear to be sufficient to activate L-type calcium channels in the absence of pattern vision. Therefore activation of L-type calcium channels is likely to be an important source for calcium influx into SC neurons in neonatal rats.

Control of recurrent inhibition of the lateral posterior-pulvinar complex by afferents from the deep layers of the superior colliculus of the rabbit

We investigated the effect of stimulation of the deep layers of the superior colliculus (SC) on the recurrent inhibition of the lateral posterior-pulvinar complex (LP) in anesthetized rabbits. Intracellular recordings from 23 relay cells in LP showed that they responded to SC stimulation with a long-lasting (140.2 +/- 19.6 ms; mean +/- SD) inhibitory postsynaptic potential (IPSP), which sometimes was followed by a rebound burst of spikes. The same SC stimulation evoked a burst of spikes in extracellular recordings from 31 recurrent inhibitory interneurons in the LP-cortical pathway, which were located in the ventral part of the visual sector of the thalamic reticular nucleus. The mean latency of the burst in reticular cells was 1.6 ms shorter than that of the IPSP in LP relay cells, suggesting that the IPSP in LP cells was mediated by these reticular cells. Intracellular recordings from nine reticular cells showed that the burst of spikes evoked by SC stimulation resulted from an excitatory postsynaptic potential that was always followed by a long-lasting (143.3 +/- 24.0 ms) IPSP. Stimulation of the contralateral predorsal bundle, the main output pathway of deep SC neurons, elicited similar responses in LP cells or reticular neurons with latencies longer than those from SC stimulation. The latency difference between the responses to predorsal bundle and SC stimulation is equal to the antidromic conduction time of predorsal bundle fibers, suggesting that the inhibition in LP originates from the activation of predorsal bundle-projecting neurons. The response characteristics of the inhibitory circuit of LP and of the lateral geniculate nucleus to SC stimulation are strikingly similar, implying that a similar circuit is used by predorsal bundle-projecting neurons to control the recurrent inhibition in both lateral geniculate nucleus and LP. Because the predorsal bundle-projecting neurons are believed to be involved in the initiation of saccadic eye movements, we suggest that the inhibitory circuits may play an important role in modulating ascending visual information during saccadic eye movements.

HLA DQA1 genotyping of Chinese in Taiwan by PCR-RFLP

Population data were established for the HLA DQA1 locus among 147 Chinese in Taiwan by the PCR-RFLP flowchart system. Twelve alleles could be differentiated in this study, although only nine alleles were found among the above samples. There were no discrepancies in the results obtained by PCR-RFLP when compared to the results obtained by the AmpliType HLA DQ alpha typing kit. Using the Chi-square test, significant differences were observed (p < 0.005) between this data and that for Japanese, African Americans and US Caucasians. The observed heterozygosity was 83% with a discrimination power of 0.93.

Physiological properties of neurons in the optic layer of the rat's superior colliculus

We made intracellular recordings from 74 neurons in the optic layer of the rat superior colliculus (SC). Resting membrane potentials were -62.3 +/- 6.2 (SD) mV, and input resistances were 37.9 +/- 10.1 MOmega. Optic layer neurons had large sodium spikes (74.2 +/- 12.3 mV) with an overshoot of 12 mV and a half-amplitude duration of 0.75 +/- 0.2 ms. Each sodium spike was followed by two afterhyperpolarizations (AHPs), one of short duration and one of longer duration, which were mediated by tetraethylammonium (TEA)-sensitive (IC) or apamin-sensitive (IAHP) calcium-activated potassium currents, respectively. Sodium spikes were also followed by an afterdepolarization (ADP), which was only revealed when the AHPs were blocked by TEA or apamin. In response to hyperpolarizing current pulses, optic layer neurons showed an inward rectification mediated by H channels. At the break of the current pulse, there was a rebound low-threshold spike (LTS) with a short duration of <25 ms. The LTS usually induced two sodium spikes (doublet). Most optic layer neurons (84%) behaved as intrinsically bursting cells. They responded to suprathreshold depolarization with an initial burst (or doublet) followed by a train of regular single spikes. The remaining 16% of cells acted as chattering cells with high-frequency gamma (20-80 Hz) rhythmic burst firing within a narrow range of depolarized potentials. The interburst frequency was voltage dependent and also time dependent, i.e., showed frequency adaptation. Unmasking the ADP with either TEA or apamin converted all of the tested intrinsically bursting cells into chattering cells, indicating that the ADP played a crucial role in the generation of rhythmic burst firing. Optic layer neurons receive direct retinal excitation mediated by both N-methyl--aspartate (NMDA) and non-NMDA receptors. Optic tract (OT) stimulation also led to gamma-aminobutyric acid-A (GABAA) receptor-mediated inhibition, the main effect of which was to curtail the excitatory response to retinal inputs by shunting the excitatory postsynaptic current. Intracellular staining with biocytin showed that the optic layer neurons that we recorded from were mostly either wide-field vertical neurons or other cells with predominately superficially projecting dendrites. These cells were similar to calbindin immunoreactive cells seen in the optic layer. The characteristics of these optic layer neurons, such as prominent AHPs, strong shunting effect of inhibition, and short-lasting LTS, suggest that they respond transiently to retinal inputs. This is consistent with a function for these cells as the first relay station in the extrageniculate visual pathway.

Solitary maxillary central incisor and congenital nasal pyriform aperture stenosis

Solitary maxillary central incisor (SMCI) and congenital nasal pyriform aperture stenosis (CNPAS) have been reported as an isolated morphogenic defect or associated with pituitary deficiency, holoprosencephaly, ocular coloboma, or chromosomal abnormalities. We report two cases and analyse 40 cases of SMCI and 24 cases of CNPAS, including 15 cases of combined SMCI and CNPAS, obtained from the literature. Of the patients with SMCI, 69% had short stature, 48% growth hormone deficiency or hypopituitarism, 23% pituitary absence or hypoplasia, and 17% had del (18p-) or r(18). Of the patients with CNPAS, 63% had SMCI, 75% were short, 43% had hypopituitarism or growth hormone deficiency, 36% had pituitary or CNS anomaly, and 33% had del (18p), r(18), or del (13q).

CONCLUSIONS

Solitary maxillary central incisor and congenital nasal pyriform aperture stenosis can be a diagnostic clue to pituitary hypofunction, CNS, ophthalmological and cytogenic anomalies.

Recurrent inhibitory interneurons of the Rabbit's lateral posterior-pulvinar complex

We recorded from 118 neurons in the visual sector of the thalamic reticular nucleus (TRN) in anesthetized rabbits. Cells were identified by their location and characteristic burst responses to stimulation of the primary visual cortex (Cx) and optic chiasm (OX) and were classified into two groups. Type I cells had relatively short latencies from both OX and Cx stimulation, and the latency from OX was always longer than from Cx. In contrast, type II cells had much longer latencies after OX and Cx stimulation, and the latency from OX was always shorter than from Cx. Type I cells were located in the dorsal part of TRN, whereas type II cells were located in the ventral part of TRN. The physiological properties and location of type I TRN cells indicate that they are recurrent inhibitory interneurons of the dorsal lateral geniculate nucleus (LGN). Type II TRN cells most likely function as recurrent inhibitory interneurons for the lateral posterior nucleus-pulvinar complex (LP) because they could be activated antidromically by LP stimulation and orthodromically activated via axonal collaterals of LP cells. Type II TRN cells exhibited a prolonged depression after Cx or OX stimulation. Intracellular recordings showed that a prolonged inhibitory postsynaptic potential was evoked by Cx or OX stimulation. Therefore, these recurrent interneurons of LP, type II cells form mutual inhibitory connections just like those recurrent interneurons of LGN, type I cells. Our data suggest that the geniculocortical and extrageniculate visual pathways have similar recurrent inhibitory circuits.

Lack of visual suppression in the rabbit lateral geniculate nucleus during blink reflex

Stimulation of the supraorbital branch of the trigeminal nerve (SO) elicited eye blinks in the rabbit, but did not decrease the amplitude of visual cortical evoked potential from stimulation of the optic chiasm (OX). In addition, the SO stimulation neither induced an inhibitory postsynaptic potential (IPSP) in LGN cells, nor activated inhibitory interneurons in the thalamic reticular nucleus (TRN), which proved to mediate both recurrent inhibition and saccadic suppression in the dorsal lateral geniculate nucleus (LGN). All these indicate that there is no visual suppression in the rabbit LGN during blink reflex.

Functional connectivity in the rodent trigeminal pathway grown in vitro

In explant cocultures of the rat trigeminal pathway, embryonic trigeminal ganglion cells grow their axons into peripheral cutaneous and central nervous system targets (R.S. Erzurumlu, S. Jhaveri, Target influences on the morphology of trigeminal axons, Exp. Neurol, 135 (1995) 1-16; R.S. Erzurumlu, S. Jhaveri, H. Takahashi, R.D.G. McKay, Target-derived influences on axon growth modes in explant cocultures of trigeminal neurons, Proc. Natl. Acad. Sci. USA 90 (1993) 7235-7239). In heterochronic cocultures, composed of embryonic trigeminal ganglion, embryonic whisker pad and postnatal brainstem slice, trigeminal axons develop arbors and terminal boutons in the brainstem trigeminal nuclei. To determine whether these terminal arbors establish functional connections with the brainstem neurons, we examined the electrophysiological properties of brainstem neurons and their responsiveness to trigeminal ganglion stimulation. Intracellular recordings were done in vitro on cells of the trigeminal subnucleus interpolaris (SPI) in trigeminal pathway cocultures (E15 whisker pad, E15 trigeminal ganglion, and postnatal day (PND) 0-2 brainstem slice) or in the SPI of acutely prepared brainstem slices. Electrophysiological properties of SPI cells in both preparations were virtually identical. The voltage responses of SPI neurons to intracellular current injection were highly linear suggesting they lacked a number of voltage-dependent conductances. Depolarizing current injection produced trains of action potentials with a frequency that varied with stimulus intensity. In explant cocultures, electrical activation of the trigeminal ganglion evoked EPSPs, and EPSPs coupled with IPSPs in SPI cells. Bicuculline blockade of IPSP activity resulted in long lasting EPSPs whose duration increased with membrane depolarization. These results show that brainstem trigeminal neurons can retain their functional properties in culture and establish functional connections with primary sensory afferents.

[Acetylcholine decreases low threshold T-type calcium conductance of relay cells in the cat's lateral geniculate nucleus]

The effect of acetylcholine (ACh) on the low threshold T-type Ca2+ conductance of relay cells in the cat lateral geniculate nucleus (LGN) was studied using in vitro thalamic slices. Results from both current-clamp and voltage-clamp experiments showed that the low threshold Ca2+ conductance was inhibited by ACh in most (82%) of the LGN neurons tested, even when the membrane potential was clamped to the control level. This inhibitory effect was independent of the changes in membrane potential by ACh. Therefore, ACh might exert a direct action on low threshold Ca2+ channels.

An in vitro model of the kitten retinogeniculate pathway

An organotypic explant coculture method is described for the developing retinogeniculate pathway of the cat. Retinal explants and thalamic slices containing the dorsal lateral geniculate nucleus (LGN), derived from early postnatal kittens, can be grown in serum-free culture medium for several days. In such cultures, retinal ganglion cells (RGCs) and LGN neurons retained their age-specific morphological features and developed functional connections. Labeling of RGCs and their processes with DiI showed that all three major classes of RGCs (alpha/Y, beta/X, gamma/W) were present in cocultured retinal explants. Retinal axons readily regenerated into thalamic slices and, over time, developed arbors within the LGN. Retrograde labeling from the LGN traced the origin of these axons almost exclusively to alpha-cells in the retina. In vitro intracellular recordings indicated that LGN cells maintained their basic electrophysiological properties in coculture. Current injection generated action potentials, and, at hyperpolarized levels, it led to low-threshold Ca2+ spiking. Regenerated retinal axons also formed functional connections with LGN neurons. Electrical stimulation of the retinal explant elicited excitatory postsynaptic responses (EPSPs) in LGN cells. Drop application of specific glutamate antagonists indicated that EPSPs had both N-methyl-D-aspartate (NMDA) and non-NMDA receptor components. The morphology of the LGN neurons was examined after intracellular injections of biocytin during recording. Labeled cells were very similar to those of early postnatal kittens. Although, in general, they had relatively small soma and simple dendritic branching patterns, a few could be recognized as X- or Y-cells. Thus the coculture model can be used to assay the regenerative propensity of different types of RGCs during development.

[Passive cable properties of relay cells in dorsal lateral geniculate nucleus of the rabbit]

We measured the passive membrane properties of 24 relay cells in slice preparation of the lateral geniculate nucleus of the rabbit. The resting membrane potential was -62.7 +/- 4.1 mV (mean +/- SD) with an input resistance of 30.4 +/- 11.2 M omega. According to Rall's linear cable model, the electrotonic length (L) of the dendrite was 0.79 +/- 0.13. The voltage attenuation factor (H) was 1.33 +/- 0.11. All these indicated that the relay cells were electrically compact. DC voltage on the distal dendrite could spread to the soma attenuated only by 25%.

Time course of inhibition induced by a putative saccadic suppression circuit in the dorsal lateral geniculate nucleus of the rabbit

Psychological studies have revealed that a visual suppression occurs during the saccadic eye movements to maintain the stable visual image. This visual suppression is named saccadic suppression. A typical saccadic suppression precedes the saccadic eye movements by 30-60 ms, lasts 120-180 ms, and is followed by a 100-150 ms facilitation. Recently, we have revealed an inhibitory circuit connecting the deep layers of the superior colliculus (SC) to the dorsal lateral geniculate nucleus (LGN), via the central lateral nucleus in the thalamus (CL) and thalamic reticular nucleus (TRN). We speculated that this inhibitory circuit might mediate saccadic suppression in the rabbit. In the present study, we used intracellular recording technique to further examine the synaptic and intrinsic responses of CL cells, TRN cells, and LGN cells to the activation of this inhibitory circuit. We found that the stimulation of the deeper layers of the SC induced a fast excitation post-synaptic potential (EPSP) in CL cells, followed by a robust EPSP in TRN cells and a prolonged inhibitory postsynaptic potential (IPSP) in LGN cells. The EPSP in TRN cells was always followed by a small inhibitory postsynaptic potential (IPSP). The IPSP in LGN cells lasted about 133 +/- 27 ms. Sometimes, a rebound bursting occurred after the IPSP in LGN cells. We also examined whether activation of this inhibitory circuit could suppress the retino-geniculo-cortical pathway. We found that the SC stimulation always suppressed the evoked potential in the visual cortex induced by the stimulation of the optic chiasm. Our results of the inhibitory circuit can induce an inhibition in the LGN and a suppression on the retino-geniculo-cortical pathway. The time courses of the inhibition and suppression were compatible with that of saccadic suppression revealed by psychological and physiological studies. These results support the idea that the inhibitory circuit of SC (deeper layers)-CL-TRN-LGN may mediate the saccadic suppression in the rabbit LGN.

Physiological properties of the output neurons in the deep layers of the superior colliculus of the rabbit

Using antidromic and orthodromic stimulation techniques, we studied physiological properties of the output neurons in the deep layers of the superior colliculus (SC) of 34 Now Zealand rabbits. SC cells antidromically activated from the contralateral predorsal bundle (PDB) could also be activated by stimulation of the contralateral SC and ipsilateral central lateral nucleus of the thalamus (CL). The majority of these output neurons responded predominantly to the stimulation of the optic nerve, and only a small proportion of the output neurons were responsive to the stimulation of somatosensory and auditory (and/or vestibular) nerves. These results suggest that the orienting reflex might be elicited mainly by visual afferents in the rabbit. The output SC neurons were subject to a 70 ms inhibition after antidromic stimulation of the PDB and a 40 ms inhibition after transsynaptic (orthodromic) stimulation of the optic chiasm (OX), indicating that the output neurons in the deep layers of the SC might be subject to at least two inhibitory circuits. These results are discussed in the context of a putative saccadic suppression circuitry model.

Feedback inhibition in the cat's lateral geniculate nucleus

Feedback inhibition is generally believed to be a ubiquitous feature of brain circuitry, but few specific instances have been documented. An example in cats is the supposed feedback circuit involving relay cells of the lateral geniculate nucleus and cells of the perigeniculate nucleus (a part of the thalamic reticular nucleus): geniculate relay cells innervate the perigeniculate nucleus, which, in turn, provides an inhibitory, GABAergic projection back to the lateral geniculate nucleus. However, feedback inhibition at the single-cell level requires that a given perigeniculate cell project back onto the same geniculate relay cell that innervates it. We probed for this in an in vitro slice preparation of the cat's lateral geniculate nucleus. We evoked a single action potential in a geniculate cell via a brief, depolarizing pulse delivered through an intracellular recording electrode and looked for any evoked hyperpolarizations. For 6 of the 36 geniculate cells tested, we observed a long-lasting hyperpolarization after the action potential, and much of this was eliminated by application of bicuculline, suggesting synaptically activated inhibitory postsynaptic potentials. We interpreted this to be clear evidence that a given neuron may inhibit itself via circuitry mediating feedback inhibition in the cat's lateral geniculate nucleus.

Intracellular and extracellular in vivo recording of different response modes for relay cells of the cat's lateral geniculate nucleus

Prior studies of thalamic neurons have demonstrated that they exhibit at least two response modes: a relay mode and a burst mode. During the relay mode, sensory information is faithfully relayed to cortex; during the burst mode, which is caused by a voltage-dependent Ca2+ conductance, this relay of sensory information is interrupted. We began in vivo studies of these response modes in neurons from the lateral geniculate nucleus of anesthetized, paralyzed cats. Each of the 9 X and 10 Y cells we recorded intracellularly displayed voltage-dependent, low threshold spikes that were presumably the Ca2+ spikes described from in vitro recording. These spikes were triangular in waveform and typically had 2-7 fast action potentials (interspike intervals of 1.2-4 ms) riding its crest. Furthermore, the cell's membrane had to be hyperpolarized to de-inactivate the low threshold spike before a depolarization could then activate it. We could activate these low threshold spikes in Y cells from EPSPs, whether spontaneous or evoked from activation of the optic chiasm. However, in only one of the X cells could we activate low threshold spikes from chiasm shock; in the remainder, we could activate low threshold spikes only via depolarizing current pulses, possibly because the EPSPs of these X cells were too small to activate these spikes. We also used extracellular recording to study spontaneous activity and responses to chiasm shock from 114 geniculate neurons and, as a control, 57 optic tract axons. We concentrated on periods of bursty responsiveness signifying the burst mode. We define a burst as 2-7 action potentials with interspike intervals less than or equal to 4 ms, and the bursts are separated by greater than 100 ms; from our intracellular recording, we know that such bursts signify low threshold spikes. We found that, during extracellular recording, 20 of the 39 X cells and each of the 75 Y cells displayed evidence of the burst response mode, although burst periods were rare in X cells. Electrical activation of the optic chiasm greatly enhanced the burstiness of Y cells for periods of 500 ms or more. We also electrically stimulated the parabrachial region of the midbrain, which provides a mostly cholinergic innervation to the lateral geniculate nucleus. Although parabrachial activation by itself had no detectable effect on Y cell response modes, prior parabrachial activation prevented the enhanced burstiness caused by chiasm stimulation. This parabrachial effect lasted for roughly 500 ms after stimulation.(ABSTRACT TRUNCATED AT 400 WORDS)

In vivo recording of postsynaptic potentials and low threshold spikes in W cells of the cat's lateral geniculate nucleus

We obtained good intracellular recording from 5 W cells in the C-laminae of the cat's lateral geniculate nucleus. The recordings were made from an anesthetized and paralyzed in vivo preparation. We found a consistent pattern for the postsynaptic potentials evoked from activation of the optic chiasm: first was an IPSP followed by an EPSP. This is very different from the pattern seen in X and Y cells, for which an EPSP always appears first and is then followed by an IPSP. We interpret the pattern for W cells as follows. The initial IPSP is disynaptic; this involves retinogeniculate conduction over very fast Y axons and a relay through an interneuron. The EPSP is monosynaptic, reflecting retinogeniculate conduction over very slow W axons. A possible implication for this is that activity over the Y pathway may generally inhibit geniculate W cells before these W cells can be excited by their retinal afferents. Finally, we elicited from each of these W cells voltage-dependent, low threshold spikes, which are very similar to those displayed by X and Y cells. These spikes can interrupt normal retinogeniculate transmission, and they are prevented by maintaining relatively depolarized membrane potentials.

A study of neuronal circuitry mediating the saccadic suppression in the rabbit

Stimulation of the deep layers of the superior colliculus (SC) evoked an IPSP in the relay cells of the lateral geniculate nucleus (LGN). The latency of the IPSP ranged from 3.3 to 4.7 ms with an average of 3.87 +/- 0.56 ms (S.D.). The IPSP from SC stimulation was proposed to be mediated by the recurrent inhibitory circuit to LGN, since the recurrent inhibitory interneurones in the thalamic reticular nucleus (R) responded to the same stimulation with a latency of 2.14 +/- 0.43 ms, which was 1.73 ms shorter than the latency of the IPSP in LGN relay cells. This was in good agreement with our previous observation that the recurrent interneurones always fired about 1.8 ms prior to the onset of the recurrent IPSP in LGN (Lo and Xie 1987b). The recurrent inhibitory interneurones could also be excited by stimulation of the central lateral nucleus (CL) with a very short latency (0.57 +/- 0.15 ms), suggesting a monosynaptic connection between the central lateral nucleus and the reticular recurrent interneurones. This suggestion was supported by the fact that CL neurones, which projected to the striate cortex (Cx), were antidromically excited by stimulation of the caudal part of R where the recurrent inhibitory interneurones were situated. CL neurone's response to stimulation of the deep layers of SC (SC-CL response) has a latency of 1.68 +/- 0.56 ms, which was comparable with the difference between the latency of SC-R response and that of CL-R response, just as expected from the notion that the saccadic suppression is mediated by a circuit of SC (deep layers) -CL-R-LGN.

Control of recurrent inhibition of the lateral geniculate nucleus by afferents from the superior colliculus of the rabbit: a possible mechanism of saccadic suppression

Stimulation of the ipsilateral superior colliculus elicited a short burst of discharges of the recurrent inhibitory interneurones in the geniculocortical pathway of the rabbit. The most effective stimulating sites for this excitation were located in the deep layers rather than the superficial layers of the superior colliculus. The short latency of the response (2.3 +/- 0.6 ms) implied an oligo-synaptic excitatory pathway from the deep layers of the superior colliculus to the recurrent interneurones located in the caudal reticular nucleus of the thalamus. Following the excitation of the interneurone, there was a prolonged inhibition which started 10-30 ms and ended 150 ms after the collicular stimulation. The maximal inhibition occurred 50-70 ms after the stimulation. The effects of collicular stimulation on the recurrent inhibitory interneurones may be concerned with the inhibition of the visual pathway during saccades and with the disinhibition of "facilitation" during fixation of a new visual target.

Location of interneurones in the recurrent inhibitory circuit of the rabbit lateral geniculate nucleus

Injection of horseradish peroxidase (HRP) into the dorsal lateral geniculate nucleus (LGN) of the rabbit gave rise to retrograde labeling of neurones in the caudal part of the thalamic reticular nucleus. Electrophysiological observations demonstrated that these neurones met all criteria for interneurones in the recurrent inhibitory circuit of the geniculo-cortical pathway. They responded to stimulation of the visual cortex (Cx) or the optic chiasm (OX) with a burst of repetitive discharges, in agreement with the long-lasting IPSP from Cx or OX in relay cells of LGN. Results of collision test showed that the reticular neurones received excitatory input via axonal collaterals of relay cells. The latency of their response to stimulation of Cx or OX is about 1.8 ms shorter than that of the corresponding IPSP in the relay cells. Stimulation of LGN evoked an antidromic spike in reticular neurones with a latency of about 1.1 ms, indicating a monosynaptic projection from the latter to the relay cells. All evidence indicates that interneurones in the recurrent inhibitory circuit are most likely located in the caudal part of the thalamic reticular nucleus of the rabbit.

Interaction between inhibitory pathways to principal cells in the lateral geniculate nucleus of the cat

Inhibitory interactions between interneurones of the lateral geniculate nucleus (LGN) of the cat were studied with an indirect method based on intracellular recordings of synaptic responses in principal cells. Recurrent inhibitory postsynaptic potentials (IPSPs), evoked by antidromic activation of principal cell axons in the visual cortex, were depressed by a preceding stimulation of the optic tract or the visual cortex. Disynaptic feed-forward IPSPs, evoked by optic tract stimulation, were likewise depressed after cortex stimulation. The duration of the depression was in both cases about 100 ms. The effect was not due to conductance changes in the recorded principal cells or to activation of cortico-geniculate fibres. The observations indicate that perigeniculate neurones, the recurrent inhibitory interneurones of the LGN, have mutual inhibitory connexions and that they also project to intrageniculate interneurones, the inhibitory cells in the feed-forward pathway to principal cells. These conclusions were supported by intracellular recordings from a few interneurones. No evidence was found for interaction between feed-forward interneurones activated from separate eyes or for a projection from intrageniculate interneurones to perigeniculate cells. The results point to an unexpected similarity in the organization of the recurrent inhibitory system of principal cells in the LGN and of spinal motoneurones. It is suggested that the recurrent system of the LGN serves as a variable gain regulator in analogy with a recently proposed model for the spinal system.

Inhibition from the brain stem of inhibitory interneurones of the cat's dorsal lateral geniculate nucleus

Brain-stem control of inhibitory circuits in the dorsal lateral geniculate nucleus (d.l.g.n.) of the cat was studied with extracellular recordings from functionally identified interneurones and with intracellular recordings from principal cells. Perigeniculate neurones, the recurrent inhibitory interneurones of the d.l.g.n., were inhibited by low-threshold stimulation within a wide bilateral field of the brainstem reticular formation extending from the rostral mesencephalon to the caudal medulla oblongata. The inhibition had a latency of 10-12 ms for stimulation sites in the mesencephalon and a duration of about 100 ms. The brain-stem stimulation evoked large hyperpolarizing potentials in intracellularly recorded perigeniculate neurones, indicating that the effect was due to post-synaptic inhibition. Intrageniculate interneurones, the feed-forward inhibitory interneurones of the d.l.g.n., were inhibited with a similar time course from the same region of the brain stem. Both feed-forward and recurrent inhibitory post-synaptic potentials (i.p.s.p.s) in principal cells were depressed by a preceding stimulation of brain-stem sites effective for the interneurones. The depression had about the same time course as the inhibition of the interneurones and it occurred without a concomitant change in the membrane potential of the recorded principal cells. A small depolarizing potential, with a latency of 10-20 ms, was observed in some principal cells after brain-stem stimulation. The potential reversed polarity when i.p.s.p.s were reversed by current injection into the recorded cell indicating that it was due to disinhibition of the principal cells. The possible neuronal pathway for the inhibition of the d.l.g.n. in interneurones is considered and it is proposed that the effect is mediated by a group of neurones located in the caudal mesencephalon and the rostral pons close to the fibres of the brachium conjunctivum.

Lack of binocular inhibition in monocular segment of lateral geniculate nucleus of rabbits

In the monocular segment of the rabbit lateral geniculate nucleus, relay cells responded exclusively to the contralateral optic input with an EPSP-IPSP sequence. The ipsilateral optic input could neither evoke PSPs nor facilitate the PSPs from the contralateral eye, indicating the absence of binocular inhibition in the segment.

Both fast and slow relay cells in lateral geniculate nucleus of rabbits receive recurrent inhibition

Intracellular recordings from slow relay cells in the rabbit lateral geniculate nucleus demonstrated that the slow cells, just like the fast ones, receive a monosynaptic EPSP and a trisynaptic IPSP from the optic nerve. The IPSP is most likely mediated by interneurones activated by recurrent collaterals of the relay cell axon. In slow relay cells, both the EPSP and the IPSP from the optic nerve are brought about via the same group of slowly-conducting fibers. No mutual inhibition between the fast and the slow conducting system was observed in the rabbit lateral geniculate nucleus.

Projection of brain stem neurons to the perigeniculate nucleus and the lateral geniculate nucleus in the cat

Small horseradish peroxidase injections in the perigeniculate nucleus (PGN) or the lateral geniculate nucleus (LGN) gave retrograde labeling of many cells in the pontomesencephalic reticular formation (RF), the nuclei raphe dorsalis and centralis linearis, locus coeruleus, nucleus of the optic tract and nucleus parabigeminalis. Antidromic stimulation was used to identify neurons in the RF projecting to the PGN-LGN complex. Threshold mapping through the PGN and the LGN shows separate projection from the reticular formation to the PGN and the LGN.

Functional distinction of perigeniculate and thalamic reticular neurons in the cat

Two types of neurons can be recognized in the region above the lateral geniculate nucleus. One cell type is found in the caudal part of the reticular nucleus of thalamus; these cells are accordingly called reticular neurons. The other cell type is located in the perigeniculate nucleus immediately above lamina A of the lateral geniculate nucleus and in the intermediate zone between the perigeniculate nucleus and the reticular nucleus. These cells are referred to as perigeniculate neurons. Electrical stimulation of the optic tract and the visual cortex typically evokes a short burst of spikes in the perigeniculate neurons, and the excitation has a shorter latency from the cortex (range 1.2-2.5 ms) than from the optic tract (range 1.5-3.1 ms). The perigeniculate neurons are also activated by adequate visual stimuli. In contrast, the reticular neurons are unresponsive to visual stimuli and electrical stimulation of the optic tract but they may respond with a burst of spikes to cortex stimulation with rather long latency (range 2.7-5.5 ms). It is concluded that only perigeniculate neurons qualify as interneurons in the recurrent inhibitory pathway to principal cells in the lateral geniculate nucleus.

Synaptic organization of the lateral geniculate nucleus of the rabbit: lack of feed-forward inhibition

The synaptic organization in the lateral geniculate nucleus of the albino rabbit was studied with an intracellular recording technique. A disynaptic IPSP from the cortex and a trisynaptic IPSP from the optic nerve could be recorded from both fast and slow relay cells. These IPSPs are most likely mediated by a common recurrent inhibitory pathway. No evidence for a feed-forward inhibitory pathway to the relay cells was obtained.

Inhibition of nociceptive discharges of parafascicular neurons by direct electrical stimulation of nucleus centrum medianum

Pain evoked unit discharges in the parafascicular nucleus could be inhibited by direct electrical stimulation of the centromedian nucleus of thalamus, with residual inhibitory effect lasting for several minutes after cessation of stimulation. The optimal frequency of stimulation for production of the inhibitory effect was found to be 4--8 pulses per second. The duration of inhibition following each stimulating pulse lasted for 100--170 msec. Analysis of oscillographic records shows that there exists before the onset of the inhibition of parafascicular discharges a latent period of 10--20 msec which far exceeds the time required for impulse conduction between the two closely related structures, suggesting that a long tortuous neuronal circuit is involved in elaboration and transmission of the inhibitory effect.