The testicular regions of male mice were exposed to x-ray doses ranging from 0 to 400 rads. Forty days after exposure the mice were killed and the testes and cauda epididymal sperm removed surgically. Flow cytometric measurements of acridine orange stained testicular samples indicated a repopulation of testicular cell types following x-ray killing of stem cells. Cauda epididymal sperm were analyzed by the sperm chromatin structure assay (SCSA), a flow cytometric measurement of the susceptibility of the sperm nuclear DNA to in situ acid denaturation. The SCSA detected increased susceptibility to DNA denaturation in situ after 12.5 rads of x-ray exposure, with significant increases following 25 rads. Abnormal sperm head morphology was not significantly increased until the testes were exposed to 60 rads of x-rays. These data suggest that the SCSA is currently the most sensitive, non-invasive method of detecting x-ray damage to testicular stem spermatogonia.

Guinea pig magnocellular neurosecretory cells (MNCs) of the supraoptic nucleus (SON) were studied using the in vitro slice preparation. Intracellular recordings were made with biocytin-fïlled electrodes, permitting immunocytochemical identification of the recorded cells as arginine vasopressin- (AVP) versus oxytocin- (OT) containing. Only AVP cells displaying a depolarizing potential (DP) fired phasically. The DP was associated with a transient inward current measured in voltage clamp, which exhibited a number of properties of the T-type calcium current: activation threshold of –64 mV, time course of up to 250 ms, blockade by nickel and augmentation by barium chloride. This current has not been reported previously in SON neurons. The T-type current (It) was always associated with a damped oscillation of the membrane following the offset from hyperpolarizing steps. In all cells tested, an apamin-sensi-tive afterhyperpolarization (AHP) was observed, similar to the calcium-dependent potassium current (Iĸ, c_a) described in rat SON and other CNS regions. Therefore, as with other CNS regions displaying damped oscillations, guinea pig SON cells possess both an I_T and an I_K, _ca. We have previously described an I_h activating at hyperpolarized potentials in these cells, which depolarizes the membrane to a range in which the It and I_{K, ca} can interactively support oscillations. In summary, the It and associated depolarizing potential appears to be a requisite feature for phasic firing in AVP cells of guinea pig SON.

SUMMARY1. Immunocytochemically identified magnocellular neurosecretory cells (MNCs) in the guinea-pig supraoptic nucleus (SON) were studied using the in vitro intracellular recording technique. Cells were identified as containing arginine vasopressin (AVP) or oxytocin (OT) following recordings made with biocytin-filled electrodes. Both AVP and OT MNCs demonstrated a fusiform or pyramidal shape (15-20 jtm by 26-39,tm), with two to three processes. There were no significant differences in the proportion of AVP and OT cells in the retrochiasmatic (caudal) versus the rostral slices.2. No significant differences in passive membrane properties were observed between AVP and OT cells, except that AVP cells exhibited a significantly broader action potential width (I51+041 ms, n = 11) than did OT cells (IOl +0-08 ms, n = 7).3. Firing patterns were recorded for 100 MNCs, 41 % of which fired in a phasic manner (repeated clustering of action potentials into bursts). Of the seventy-seven cells which were immunocytochemically identified, only AVP-containing MNCs displayed phasic firing. Phasic firing occurred only in MNCs demonstrating a depolarizing potential which followed hyperpolarizing after-potentials (HAPs). The presence of the depolarizing potential was not always associated with phasic firing, however, as both OT cells and non-phasic AVP cells sometimes exhibited a depolarizing potential.4. In 160 MNCs examined for the presence of the time-dependent inward rectification (TDR in current clamp, or Ih in voltage clamp), a significant difference in the proportion of cells expressing the Ih was observed in the two cell types. The was expressed in forty-five of fifty-four AVP MNCs (83 %) and in six of fifteen OT MNCs (40%). No significant association was found with firing pattern.5. The Ih exhibited properties similar to those found in other CNS and peripheral tissues. It appeared on steps to potentials more hyperpolarized than -65 mV. It was augmented by raising the extracellular potassium concentration, blocked by 2 mm CsCl, and insensitive to 100-500 /AM BaCl2. Activation followed a single exponential, and the time constant of activation was voltage dependent.6. The adenylate cyclase activator forskolin increased the Ih and shifted its

Intracellular recordings of magnocellular neurons from the supraoptic nucleus of guinea‐pigs were made with KCI/K citrate‐ and biocytin‐filled electrodes. Fifty of 99 cells exhibited a time‐dependent inward rectification (TDR). The TDR was activated during hyperpolarizing current pulses to membrane potentials more hyperpolarized than −75 mV. In voltage‐clamp recordings, an inward current appeared at voltage steps more hyperpolarized than −75 mV, with properties similar to the slow inward rectifier (Ih) described in other tissues. The Ih was blocked by 2 mM CsCI. BaCI2 (100 to 500 μM) did not block the Ih. Immunocytochemical identification of the recorded cells revealed that both vasopressin (AVP)‐ and oxytocin (OT)‐ containing neurons exhibited an Ih.

No abstract